Fibrillar force generation by fibroblasts depends on formin

Fibroblasts in the extra-cellular matrix (ECM) often adopt a predominantly one-dimensional fibrillar geometry by virtue of their adhesion to the fibrils in the ECM. How much forces such fibrillar fibroblasts exert and how they respond to the extended stiffness of their micro-environment comprising of other ECM components and cells are not clear. We use fibroblasts adherent on fibronectin lines micropatterned onto soft polyacrylamide gels as an in vitro experimental model that maintains fibrillar cell morphology while still letting the cell mechanically interact with a continuous micro-environment of specified stiffness. We find that the exerted traction, quantified as the strain energy or the maximum exerted traction stress, is not a function of cell length. Both the strain energy and the maximum traction stress exerted by fibrillar cells are similar for low (13 kPa) or high (45 kPa) micro-environmental stiffness. Furthermore, we find that fibrillar fibroblasts exhibit prominent linear actin structures. Accordingly, inhibition of the formin family of nucleators strongly decreases the exerted traction forces. Interestingly, fibrillar cell migration is, however, not affected under formin inhibition. Our results suggest that fibrillar cell migration in such soft microenvironments is not dependent on high cellular force exertion in the absence of other topological constraints.

ALCAM a novel biomarker in patients with type 2 diabetes mellitus complicated with diabetic nephropathy

BACKGROUND & AIM

Activated leukocyte cell adhesion molecule (ALCAM/CD166) functions analogue to the receptor of advanced glycation end products, which has been implicated in the development of diabetic nephropathy (DN). We investigated the expression of ALCAM and its ligand S100B in patients with DN.

METHODS

A total of 34 non-diabetic patients, 29 patients with type 2 diabetes and normal albuminuria and 107 patients with type 2 diabetes complicated with DN were assessed for serum concentration of soluble ALCAM (sALCAM) by ELISA. Expression of ALCAM and S100B in kidney histology from patients with DN was determined by immunohistochemistry. Cell expression of ALCAM and S100B was analyzed through confocal immunofluorescence microscopy.

RESULTS

Serum concentration of sALCAM was increased in diabetic patients with DN compared to non-diabetic (59.85±14.99ng/ml vs. 126.88±66.45ng/ml, P<0.0001). Moreover sALCAM correlated positively with HbA1c (R=0.31, P<0.0001), as well as with the stages of chronic kidney disease and negatively correlated with eGFR (R=-0.20, P<0.05). In diabetic patients with normal albuminuria sALCAM was increased compared to patients with DN (126.88±66.45ng/ml vs. 197.50±37.17ng/ml, P<0.0001). In diabetic patients, ALCAM expression was significantly upregulated in both the glomeruli and tubules (P<0.001). ALCAM expression in the glomeruli correlated with presence of sclerosis (R=0.25, P<0.001) and localized mainly in the podocytes supporting the hypothesis that membrane bound ALCAM drives diabetic nephropathy and thus explaining sALCAM decrease in diabetic patients with DN. The expression of S100B was increased significantly in the glomeruli of diabetic patients (P<0.001), but not in the tubules. S100B was as well localized in the podocytes.

CONCLUSIONS

This study identifies for the first time ALCAM as a potential mediator in the late complications of diabetes in the kidney.

Formin 1 Regulates Ectoplasmic Specialization in the Rat Testis Through Its Actin Nucleation and Bundling Activity

During spermatogenesis, developing spermatids and preleptotene spermatocytes are transported across the adluminal compartment and the blood-testis barrier (BTB), respectively, so that spermatids line up near the luminal edge to prepare for spermiation, whereas preleptotene spermatocytes enter the adluminal compartment to differentiate into late spermatocytes to prepare for meiosis I/II. These cellular events involve actin microfilament reorganization at the testis-specific, actin-rich Sertoli-spermatid and Sertoli-Sertoli cell junction called apical and basal ectoplasmic specialization (ES). Formin 1, an actin nucleation protein known to promote actin microfilament elongation and bundling, was expressed at the apical ES but limited to stage VII of the epithelial cycle, whereas its expression at the basal ES/BTB stretched from stage III to stage VI, diminished in stage VII, and was undetectable in stage VIII tubules. Using an in vitro model of studying Sertoli cell BTB function by RNA interference and biochemical assays to monitor actin bundling and polymerization activity, a knockdown of formin 1 in Sertoli cells by approximately 70% impeded the tight junction-permeability function. This disruptive effect on the tight junction barrier was mediated by a loss of actin microfilament bundling and actin polymerization capability mediated by changes in the localization of branched actin-inducing protein Arp3 (actin-related protein 3), and actin bundling proteins Eps8 (epidermal growth factor receptor pathway substrate 8) and palladin, thereby disrupting cell adhesion. Formin 1 knockdown in vivo was found to impede spermatid adhesion, transport, and polarity, causing defects in spermiation in which elongated spermatids remained embedded into the epithelium in stage IX tubules, mediated by changes in the spatiotemporal expression of Arp3, Eps8, and palladin. In summary, formin 1 is a regulator of ES dynamics.

An intact brachyury function is necessary to prevent spurious axial development in Xenopus laevis

We have previously shown that the member of the HES family hairy2 induces the ectopic expression of dorsal markers when it is overexpressed in the ventral side of Xenopus embryos. Intriguingly, hairy2 represses the mesoderm transcription factor brachyury (bra) throughout its domain in the marginal zone. Here we show that in early gastrula, bra and hairy2 are expressed in complementary domains. Overexpression of bra repressed hairy2. Interference of bra function with a dominant-negative construct expanded the hairy2 domain and, like hairy2 overexpression, promoted ectopic expression of dorsal axial markers in the ventral side and induced secondary axes without head and notochord. Hairy2 depletion rescued the ectopic dorsal development induced by interference of bra function. We concluded that an intact bra function is necessary to exclude hairy2 expression from the non-organiser field, to impede the ectopic specification of dorsal axial fates and the appearance of incomplete secondary axes. This evidence supports a previously unrecognised role for bra in maintaining the dorsal fates inhibited in the ventral marginal zone, preventing the appearance of trunk duplications.

An integrated functional genomics approach identifies the regulatory network directed by brachyury (T) in chordoma

Chordoma is a rare malignant tumour of bone, the molecular marker of which is the expression of the transcription factor, brachyury. Having recently demonstrated that silencing brachyury induces growth arrest in a chordoma cell line, we now seek to identify its downstream target genes. Here we use an integrated functional genomics approach involving shRNA-mediated brachyury knockdown, gene expression microarray, ChIP-seq experiments, and bioinformatics analysis to achieve this goal. We confirm that the T-box binding motif of human brachyury is identical to that found in mouse, Xenopus, and zebrafish development, and that brachyury acts primarily as an activator of transcription. Using human chordoma samples for validation purposes, we show that brachyury binds 99 direct targets and indirectly influences the expression of 64 other genes, thereby acting as a master regulator of an elaborate oncogenic transcriptional network encompassing diverse signalling pathways including components of the cell cycle, and extracellular matrix components. Given the wide repertoire of its active binding and the relative specific localization of brachyury to the tumour cells, we propose that an RNA interference-based gene therapy approach is a plausible therapeutic avenue worthy of investigation.

Galectins: guardians of eutherian pregnancy at the maternal-fetal interface

Galectins are multifunctional regulators of fundamental cellular processes. They are also involved in innate and adaptive immune responses, and play a functional role in immune-endocrine crosstalk. Some galectins have attracted attention in the reproductive sciences because they are highly expressed at the maternal-fetal interface, their functional significance in eutherian pregnancies has been documented, and their dysregulated expression is observed in the 'great obstetrical syndromes'. The evolution of these galectins has been linked to the emergence of eutherian mammals. Based on published evidence, galectins expressed at the maternal-fetal interface may serve as important proteins involved in maternal-fetal interactions, and the study of these galectins may facilitate the prediction, prevention, diagnosis, and treatment of pregnancy complications.

Concerted action of two formins in gliding motility and host cell invasion by Toxoplasma gondii

The invasive forms of apicomplexan parasites share a conserved form of gliding motility that powers parasite migration across biological barriers, host cell invasion and egress from infected cells. Previous studies have established that the duration and direction of gliding motility are determined by actin polymerization; however, regulators of actin dynamics in apicomplexans remain poorly characterized. In the absence of a complete ARP2/3 complex, the formin homology 2 domain containing proteins and the accessory protein profilin are presumed to orchestrate actin polymerization during host cell invasion. Here, we have undertaken the biochemical and functional characterization of two Toxoplasma gondii formins and established that they act in concert as actin nucleators during invasion. The importance of TgFRM1 for parasite motility has been assessed by conditional gene disruption. The contribution of each formin individually and jointly was revealed by an approach based upon the expression of dominant mutants with modified FH2 domains impaired in actin binding but still able to dimerize with their respective endogenous formin. These mutated FH2 domains were fused to the ligand-controlled destabilization domain (DD-FKBP) to achieve conditional expression. This strategy proved unique in identifying the non-redundant and critical roles of both formins in invasion. These findings provide new insights into how controlled actin polymerization drives the directional movement required for productive penetration of parasites into host cells.

Gliding motility is a unique property of the Apicomplexa. Members of this phylum include important human and animal pathogens. An actomyosin-based machine powers parasite motility and is crucial for parasite migration across biological barriers, host cell invasion and egress from infected cells. The timing, duration and orientation of the gliding motility are tightly regulated to insure successful establishment of infection. Controlled polymerization of actin filaments is a key feature of motility, and we demonstrate here the implication of two formins that catalyse actin nucleation and fast assembly of filaments. Both proteins are essential and act in concert during productive penetration of the parasite into host cells.

Tnk1/Kos1: a novel tumor suppressor

Tnk1/Kos1 is a non-receptor protein tyrosine kinase implicated in negative regulation of cell growth by a mechanism involving inhibition of Ras activation and requiring Tnk1/Kos1's intrinsic catalytic activity. Tnk1/Kos1 null mice were created by homologous recombination by deleting the catalytic domain. Upon aging, both Tnk1+/- and Tnk1-/- mice develop spontaneous tumors, including lymphomas and carcinomas at high rates (i.e. 27%, and 43%, respectively), indicating that Tnk1/Kos1 is a tumor suppressor. Tissues from Tnk1/Kos1-null mice exhibit proportionally higher levels of basal and growth factor-stimulated Ras activation. Mechanistically, Tnk1/Kos1 requires either or both Y277 and Y287 sites to be intact for enzymatic activity and phosphorylation of its substrate, growth factor receptor binding protein 2 (Grb2). Data indicate that following tyrosine phosphorylation of Grb2 by Tnk1/Kos1, the Grb2-Sos1 guanine exchange factor (GEF) complex that mediates growth factor stimulated Ras activation becomes disrupted, resulting in the reversal of Ras activation. Conversely, the loss of Tnk1/Kos1 activity results in constitutive activation of Ras due to prolonged stabilization/activation of the Grb2-Sos1 GEF activity. Tnk1/Kos1 is the first tyrosine kinase discovered to have tumor suppressor activity, and the mechanism of spontaneous tumor formation involves constitutive, indirect activation of Ras. Thus, Ras may display "oncogenic activity" without undergoing "oncogenic" mutation. We now find that a cohort of patients with diffuse large B-cell lymphoma (DLBCL) display downregulation of Tnk1/Kos1 that may account for tumorigenesis in humans.

Six2 activity is required for the formation of the mammalian pyloric sphincter

The functional activity of Six2, a member of the so/Six family of homeodomain-containing transcription factors, is required during mammalian kidney organogenesis. We have now determined that Six2 activity is also necessary for the formation of the pyloric sphincter, the functional gate at the stomach-duodenum junction that inhibits duodenogastric reflux. Our data reveal that several genes known to be important for pyloric sphincter formation in the chick (e.g., Bmp4, Bmpr1b, Nkx2.5, Sox9, and Gremlin) also appear to be required for the formation of this structure in mammals. Thus, we propose that Six2 activity regulates this gene network during the genesis of the pyloric sphincter in the mouse.

Dazap2 is required for FGF-mediated posterior neural patterning, independent of Wnt and Cdx function

The organization of the embryonic neural plate requires coordination of multiple signal transduction pathways, including fibroblast growth factors (FGFs), bone morphogenetic proteins (BMPs), and WNTs. Many studies have suggested that a critical component of this process is the patterning of posterior neural tissues by an FGF-caudal signaling cascade. Here, we have identified a novel player, Dazap2, and show that it is required in vivo for posterior neural fate. Loss of Dazap2 in embryos resulted in diminished expression of hoxb9 with a concurrent increase in the anterior marker otx2. Furthermore, we found that Dazap2 is required for FGF dependent posterior patterning; surprisingly, this is independent of Cdx activity. Furthermore, in contrast to FGF activity, Dazap2 induction of hoxb9 is not blocked by loss of canonical Wnt signaling. Functionally, we found that increasing Dazap2 levels alters neural patterning and induces posterior neural markers. This activity overcomes the anteriorizing effects of noggin, and is downstream of FGF receptor activation. Our results strongly suggest that Dazap2 is a novel and essential branch of FGF-induced neural patterning.

Teasing out T-box targets in early mesoderm

T-box transcription factor genes are widely conserved in metazoan development and widely involved in developmental processes. With the phase of T-box gene discovery winding down, the phase of transcriptional target discovery for T-box transcription factors is finally taking off and yielding rich rewards. Mutant phenotypes in mouse and zebrafish as well as morpholino studies in zebrafish have helped to link the T-box genes to a variety of signaling pathways through diverse target genes and feedback loops. Particularly in early mesoderm development, it is emerging that a network of T-box genes interacts with Wnt/beta-catenin and Notch/Delta signaling pathways, among others, to control the important processes of mesoderm specification, somite segmentation, and left/right body axis determination.

Maternally administered melatonin differentially regulates lipopolysaccharide-induced proinflammatory and anti-inflammatory cytokines in maternal serum, amniotic fluid, fetal liver, and fetal brain

Lipopolysaccharide (LPS) has been associated with adverse developmental outcome, including intra-uterine fetal death and intra-uterine growth retardation. In the LPS model, tumor necrosis factor alpha (TNF-alpha) is the major mediator leading to intra-uterine fetal death and intra-uterine growth retardation. Interleukin (IL)-10 protects rodents against LPS-induced intra-uterine fetal death and intra-uterine growth retardation. Melatonin is an immunomodulator. In the present study, we investigated the effect of maternally administered melatonin on LPS-induced proinflammatory and anti-inflammatory cytokines in maternal serum, amniotic fluid, fetal liver and fetal brain. The time pregnant mice were injected with melatonin [5.0 mg/kg, intraperitoneal (i.p.)] 30 min before LPS (500 microg/kg, i.p.) on gestational day 17. As expected, TNF-alpha, IL-1beta, IL-6 and IL-10 were obviously increased in maternal serum and amniotic fluid in response to LPS. In addition, maternal LPS exposure significantly increased the levels of TNF-alpha, IL-1beta, IL-6 and IL-10 in fetal liver, and TNF-alpha and IL-10 in fetal brain. Melatonin pretreatment significantly attenuated LPS-evoked elevation of TNF-alpha in maternal serum. On the contrary, melatonin aggravated LPS-induced increase in IL-10 in maternal serum. Melatonin had no effect on LPS-evoked IL-1beta and IL-6 in maternal serum and amniotic fluid. Interestingly, maternally administered melatonin also significantly attenuated LPS-evoked elevation of TNF-alpha in fetal brain, whereas the indole aggravated LPS-induced increase in IL-10 in fetal liver. Taken together, these results indicate that maternally administered melatonin differentially regulates LPS-induced proinflammatory and anti-inflammatory cytokines in maternal serum, amniotic fluid, fetal liver, and fetal brain.

Role of tumor endothelium in CD4+ CD25+ regulatory T cell infiltration of human pancreatic carcinoma

BACKGROUND

Regulatory T (Treg) cells have been detected in human carcinomas and may play a role in preventing the rejection of malignant cells.

METHODS

We quantified Treg cells and the expression of the addressins and the respective ligands that attract them in blood and in human pancreatic tumors and adjacent nonmalignant tissues from 47 patients. The capacity of Treg cells to adhere to and transmigrate through autologous endothelial cells was tested in vitro using spheroid adhesion assays and in vivo using a xenotransplant NOD/SCID model and in the presence and absence of antibodies to addressins. All statistical tests were two-sided.

RESULTS

More Treg cells infiltrated pancreatic carcinomas than adjacent nonmalignant pancreatic tissues (120 cells per mm2 versus 80 cells per mm2, difference = 40 cells per mm2, 95% confidence interval [CI] = 21.2 cells per mm2 to 52.1 cells per mm2; P<.001). In contrast to conventional CD4+ T cells, more blood-derived Treg cells adhered to (1.0% versus 5.2%, difference = 4.2%, 95% CI = 2.7% to 5.6%; P<.001) and transmigrated through (3332 cells versus 4976 cells, difference = 1644 cells, 95% CI = 708 cells to 2580 cells; P = .008) autologous tumor-derived endothelial cells in vitro and in vivo (458 cells versus 605 cells, difference = 147 cells, 95% CI = 50.8 to 237.2 cells; P = .04). Tumor-derived endothelial cells expressed higher levels of addressins--including mucosal adressin cell adhesion molecule-1 (MAdCAM-1), vascular cell adhesion molecule-1 (VCAM-1), CD62-E, and CD166--than endothelial cells from normal tissue. Experiments using antibodies to addressins showed that transmigration was mediated by interactions of addressins, including MAdCAM-1, VCAM-1, CD62-E, and CD166 with their respective ligands, beta7 integrin, CD62L, and CD166, which were expressed specifically on Treg cells.

CONCLUSIONS

Tumor-induced expression of addressins on the surface of endothelial cells allows a selective transmigration of Treg cells from peripheral blood to tumor tissues.

Lineage-independent mosaic expression and regulation of theCiona multidomgene in the ancestral notochord

The transcription factor Ciona Brachyury (Ci-Bra) plays an essential role in notochord development in the ascidian Ciona intestinalis. We characterized a putative Ci-Bra target gene, which we named Ci-multidom, and analyzed in detail its expression pattern in normal embryos and in embryos where Ci-Bra was misexpressed. Ci-multidom encodes a novel protein, which contains eight CCP domains and a partial VWFA domain. We show that an EGFP-multidom fusion protein localizes preferentially to the endoplasmic reticulum (ER), and is excluded from the nucleus. In situ hybridization experiments demonstrate that Ci-multidom is expressed in the notochord and in the anterior neural boundary (ANB). We found that the expression in the ANB is fully recapitulated by an enhancer element located upstream of Ci-multidom. By means of misexpression experiments, we provide evidence that Ci-Bra controls transcription of Ci-multidom in the notochord; however, while Ci-Bra is homogeneously expressed throughout this structure, Ci-multidom is transcribed at detectable levels only in a random subset of notochord cells. The number of notochord cells expressing Ci-multidom varies among different embryos and is independent of developmental stage, lineage, and position along the anterior-posterior axis. These results suggest that despite its morphological simplicity and invariant cell-lineage, the ancestral notochord is a mosaic of cells in which the gene cascade downstream of Brachyury is differentially modulated.

TACC3 depletion sensitizes to paclitaxel-induced cell death and overrides p21WAF-mediated cell cycle arrest

Regulators of the mitotic spindle apparatus are attractive cellular targets for antitumor therapy. The centrosomal protein transforming acidic coiled coil (TACC) 3 is required for spindle assembly and proper chromosome segregation. In this study, we employed an inducible RNA interference approach to downregulate TACC3 expression. We show that TACC3 knock-down in NIH3T3 fibroblasts caused aneuploidy, but failed to overtly impair mitotic progression. TACC3 depletion rather triggered a postmitotic p53-p21(WAF) pathway and led to a reversible cell cycle arrest. Similar effects were induced by low concentrations of paclitaxel, a spindle poison used in antitumor therapy. Interestingly, however, and unlike in TACC3-proficient cells, paclitaxel was able to induce strong polyploidy and subsequent apoptosis in TACC3-depleted cells. Even though paclitaxel treatment was associated with the activation of the survival kinase Akt and an antiapoptotic expression of cytoplasmic p21(WAF) and cyclin D1, this inhibition of cell death was abrogated by depletion of TACC3. Thus, our data identify TACC3 as a potential target to overcome p21(WAF)-associated protection of transformed cells against paclitaxel-induced cell death.

Tropomyosin regulates elongation by formin at the fast-growing end of the actin filament

The balance between dynamic and stable actin filaments is essential for the regulation of cellular functions including the determination of cell shape and polarity, cell migration, and cytokinesis. Proteins that regulate polymerization at the filament ends and filament stability confer specificity to actin filament structure and cellular function. The dynamics of the barbed, fast-growing end of the filament are controlled in space and time by both positive and negative regulators of actin polymerization. Capping proteins inhibit the addition and loss of subunits, whereas other proteins, including formins, bind at the barbed end and allow filament growth. In this work, we show that tropomyosin regulates dynamics at the barbed end. Tropomyosin binds to constructs of FRL1 and mDia2 that contain the FH2 domain and modulates formin-dependent capping of the barbed end by relieving inhibition of elongation by FRL1-FH1FH2, mDia1-FH2, and mDia2-FH2 in an isoform-dependent fashion. In this role, tropomyosin functions as an activator of formin. Tropomyosin also inhibits the binding of FRL1-FH1FH2 to the sides of actin filaments independent of the isoform. In contrast, tropomyosin does not affect the ability of capping protein to block the barbed end. We suggest that tropomyosin and formin act together to ensure the formation of unbranched actin filaments, protected from severing, that could be capped in stable cellular structures. This role, in addition to its cooperative control of myosin function, establishes tropomyosin as a universal regulator of the multifaceted actin cytoskeleton.

Thirty-eight-negative kinase 1 (TNK1) facilitates TNFα-induced apoptosis by blocking NF-κB activation

Thirty-eight-negative kinase 1 (TNK1) is a member of the ACK-family of nonreceptor tyrosine kinases and was originally cloned from CD34+/Lin-/CD38-hematopoietic stem/progenitor cells. The signaling pathways induced by TNK1 are largely unknown. Here, we report that expression and consequent activation of TNK1 enables tumor necrosis factor alpha (TNFalpha)-induced apoptosis by selectively inhibiting TNFalpha-induced activation of nuclear factor-kappaB (NF-kappaB). TNK1 has no effect on NF-kappaB DNA binding or the composition of the NF-kappaB complex; however, the kinase markedly prevents TNFalpha-induced NF-kappaB transactivation. TNK1 therefore acts as a novel molecular switch that can determine the properties of TNFalpha signaling and therefore cell death.

Direct activation by Ets and Zic is required for initial expression of the Brachyury gene in the ascidian notochord

Extrinsic fibroblast growth factor (FGF) signal and intrinsic factors that determine the response of the signal-receiving blastomeres to FGF regulate mesoderm patterning in embryos of the ascidian Halocynthia roretzi. To investigate how cells integrate information from extrinsic and intrinsic inputs, we examined Brachyury (Hr-Bra) promoter activity in the early embryo. Hr-Bra, which encodes a key transcription factor for notochord development, is expressed exclusively in notochord precursors in a manner dependent on the FGF-MEK-MAPK-Ets signaling pathway and on the intrinsic factors Zic and FoxA. Reporter gene expression driven by the 900-bp upstream region of the Hr-Bra promoter was detected as early as the 110-cell stage in notochord precursors by in situ hybridization with a LacZ probe. Deletion analysis combined with MEK inhibitor treatment demonstrated that the -598/-499 region carries FGF-responsiveness. Electrophoretic mobility shift assay identified three Ets-binding sites in this region that were required for promoter activity. Further deletion analysis conducted by injecting eggs with reporter constructs at higher concentration suggested that the -398/-289 region also has enhancer activity, although ectopic reporter expression was detected in nerve cord and endoderm precursors. The -398/-289 region has a Zic-binding site that was also essential for the enhancer activity. These results indicate that Ets- and Zic-binding sites are critical for the initiation of Hr-Bra expression. In conclusion, information from both extrinsic and intrinsic factors is integrated at the level of enhancer of the target gene by direct binding of the transcription factors to the enhancer region.

TACC3 is required for the proper mitosis of sclerotome mesenchymal cells during formation of the axial skeleton

Transforming acidic coiled-coil-containing (TACC) family members regulate mitotic spindles and have essential roles in embryogenesis. However, the functions of TACC3 in mitosis during mammalian development are not known. We have generated and characterized three mutant alleles of mouse Tacc3 including a conditional allele. Homozygous mutants of a hypomorphic allele exhibited malformations of the axial skeleton. The primary cause of this defect was the failure of mitosis in mesenchymal sclerotome cells. In vitro, 36% of primary mouse embryo fibroblasts (MEF) obtained from mutants homozygous for the hypomorphic allele and 67% of MEF from Tacc3 null mutants failed mitosis. In cloned immortalized MEF, Tacc3 depletion destabilized spindles and prevented chromosomes from aligning properly. Furthermore, chromosome separation and cytokinesis were also severely impaired. Chromosomes were moved randomly and cytokinesis initiated but the cleavage furrow eventually regressed, resulting in binucleate cells that then yielded aneuploid cells in the next cell division. Thus, in addition to spindle assembly, Tacc3 has critical roles in chromosome separation and cytokinesis, and is essential for the mitosis of sclerotome mesenchymal cells during axial formation in mammals.

Nodal activity around Kupffer's vesicle depends on the T-box transcription factors notail and spadetail and on notch signaling

The node, or its zebrafish equivalent, Kupffers Vesicle (KV), is thought to generate laterality cues through cilia-dependent signaling. An interaction between Nodal ligands and Nodal antagonists around the node/KV is also required. Here we investigate whether loss of Brachyury/Notail or Tbx16/Spadetail disrupts the balance of Nodal ligands (Southpaw) and antagonists (Charon) around Kupffers Vesicle. Reduction of Spadetail or Notail disrupts expression of southpaw in the perinodal domains flanking Kupffers Vesicle. Similar to what was published for Notail, we find Spadetail is also required for expression of charon. We present evidence for the model that Notail has a direct role in regulating the charon promoter. In particular, a flanking genomic region with putative Notail binding sites can drive KV expression of a reporter in a Notail-dependent fashion. This region also contains motifs for CSL/RBP-J/Su(H). Consistent with this, we find charon expression is strongly Notch-dependent whereas perinodal southpaw expression is not.

Brachyury is required for elongation and vasculogenesis in the murine allantois

Mouse conceptuses homozygous for mutations in brachyury (T) exhibit a short, misshapen allantois that fails to fuse with the chorion. Ultimately, mutant embryos die during mid-gestation. In the 60 years since this discovery, the role of T in allantoic development has remained obscure. T protein was recently identified in several new sites during mouse gastrulation, including the core of the allantois, where its function is not known. Here, using molecular, genetic and classical techniques of embryology, we have investigated the role of T in allantoic development. Conceptuses homozygous for the T(Curtailed) (T(C)) mutation (T(C)/T(C)) exhibited allantoic dysmorphogenesis shortly after the allantoic bud formed. Diminution in allantoic cell number and proliferation was followed by cell death within the core. Fetal liver kinase (Flk1)-positive angioblasts were significantly decreased in T(C)/T(C) allantoises and did not coalesce into endothelial tubules, possibly as a result of the absence of platelet endothelial cell adhesion molecule 1 (Pecam1), whose spatiotemporal relationship to Flk1 suggested a role in patterning the umbilical vasculature. Remarkably, microsurgical perturbation of the wild-type allantoic core phenocopied the T(C)/T(C) vascularization defect, providing further support that an intact core is essential for vascularization. Last, abnormalities were observed in the T(C)/T(C) heart and yolk sac, recently reported sites of T localization. Our findings reveal that T is required to maintain the allantoic core, which is essential for allantoic elongation and vascular patterning. In addition, morphological defects in other extraembryonic and embryonic vascular organs suggest a global role for T in vascularization of the conceptus.

Activated Leukocyte Cell Adhesion Molecule (ALCAM) is associated with suppression of breast cancer cells invasion

BACKGROUND

Activated Leukocyte Cell Adhesion Molecule (ALCAM) is expressed in different kinds of normal and neoplastic tissues. Data on the tissue distribution of ALCAM suggest that this protein is involved in tumor progression and metastasis. The lack of available data on ALCAM protein expression in breast cancer prompted us to undertake a study on the involvement of this adhesion molecule in tumor development.

MATERIAL/METHODS

The expressions of ALCAM and reference biomarkers were examined in 56 breast cancer specimens by laser scanning cytometry and confocal microscopy. The results were related to clinical and pathological parameters, i.e. histological grade, tumor diameter, lymph node involvement, NPI, steroid receptor (estrogen, ER, and progesterone, PgR) expression, and HER2/neu over-expression.

RESULTS

High levels of ALCAM significantly correlated with small tumor diameter (p=0.009), low tumor grade (p=0.001), and the presence of progesterone (p=0.009) and estrogen (p=0.006) receptors. Declining ALCAM concentrations correlated with HER2/neu gene amplification, inasmuch as the obtained p value, 0.065, was very close to the established statistical significance level of p=0.05. The ALCAM/MMP-2 ratio was significantly higher in cancer cases characterized by small tumor size (p=0.04) and low tumor grade (p=0.022).

CONCLUSIONS

Analysis of ALCAM expression in relation to other molecular biomarkers revealed that ALCAM expression and the ALCAM/MMP-2 ratio are more promising indicators of breast cancer progression than MMP-2, E-cadherin, and alpha-catenin. Low ALCAM concentration correlated with an aggressive tumor phenotype, which supports the view that this adhesion molecule is a tumor suppressor marker with prognostic significance.

RhoA regulates initiation of invagination, but not convergent extension, during sea urchin gastrulation

During gastrulation, the archenteron is formed using cell shape changes, cell rearrangements, filopodial extensions, and convergent extension movements to elongate and shape the nascent gut tube. How these events are coordinated remains unknown, although much has been learned from careful morphological examinations and molecular perturbations. This study reports that RhoA is necessary to trigger archenteron invagination in the sea urchin embryo. Inhibition of RhoA results in a failure to initiate invagination movements, while constitutively active RhoA induces precocious invagination of the archenteron, complete with the actin rearrangements and extracellular matrix secretions that normally accompany the onset of invagination. Although RhoA activity has been reported to control convergent extension movements in vertebrate embryos, experiments herein show that RhoA activity does not regulate convergent extension movements during sea urchin gastrulation. Instead, the results support the hypothesis that RhoA serves as a trigger to initiate invagination, and once initiation occurs, RhoA activity is no longer involved in subsequent gastrulation movements.

Biochemical Characterization of the Diaphanous Autoregulatory Interaction in the Formin Homology Protein FHOD1

Diaphanous related formins (DRFs) are cytoskeleton remodeling proteins that mediate specific upstream GTPase signals to regulate cellular processes such as cytokinesis, cell polarity, and organelle motility. Previous work on the Rho-interacting DRF mDia has established that the biological activity of DRFs is regulated by an autoinhibitory interaction of a C-terminal diaphanous autoregulatory domain (DAD) with the DRF N terminus. This autoinhibition is released upon competitive binding of an activated GTPase to the N terminus of the DRF. Analyzing autoregulation of the Rac1-interacting DRF FHOD1, we utilized in vitro binding studies to identify a 60-amino acid DAD at the protein C terminus that recognizes an N-terminal formin homology (FH) 3 domain. Importantly, the FH3 domain of FHOD1 does not overlap with the proposed Rac1-binding domain. The FHOD1 DAD was found to contain one functional hydrophobic autoregulatory motif, while a previously uncharacterized basic cluster that is conserved in all DRF family DADs also contributed to the FH3-DAD interaction. Simultaneous mutation of both motifs efficiently released autoinhibition of FHOD1 in NIH3T3 cells resulting in the formation of actin stress fibers and increased serum response element transcription. A second putative hydrophobic autoregulatory motif N-terminal of the DAD belongs to a unique FHOD subdomain of yet undefined function. NMR structural analysis and size exclusion chromatography experiments revealed that the FHOD1 DAD is intrinsically unstructured with a tendency for a helical conformation in the hydrophobic autoregulation motif. Together, these data suggest that in FHOD1, DAD acts as signal sequence for binding to the well folded and monomeric FH3 domain and imply an activation mechanism that differs from competitive binding of Rac1 and DAD to one interaction site.

Cooperative non-cell and cell autonomous regulation of Nodal gene expression and signaling by Lefty/Antivin and Brachyury in Xenopus

Dynamic spatiotemporal expression of the nodal gene and its orthologs is involved in the dose-dependent induction and patterning of mesendoderm during early vertebrate embryogenesis. We report loss-of-function studies that define a high degree of synergistic negative regulation on the Xenopus nodal-related genes (Xnrs) by extracellular Xenopus antivin/lefty (Xatv/Xlefty)-mediated functional antagonism and Brachyury-mediated transcriptional suppression. A strong knockdown of Xlefty/Xatv function was achieved by mixing translation- and splicing-blocking morpholino oligonucleotides that target both the A and B alloalleles of Xatv. Secreted and cell-autonomous inhibitors of Xnr signaling were used to provide evidence that Xnr-mediated induction was inherently long-range in this situation in the large amphibian embryo, essentially being capable of spreading over the entire animal hemisphere. There was a greater expansion of the Organizer and mesendoderm tissues associated with dorsal specification than noted in previous Xatv knockdown experiments in Xenopus, with consequent exogastrulation and long-term maintenance of expanded axial tissues. Xatv deficiency caused a modest animal-ward expansion of the marginal zone expression territory of the Xnr1 and Xnr2 genes. In contrast, introducing inhibitory Xbra-En(R) fusion constructs into Xatv-deficient embryos caused a much larger increase in the level and spatial extent of Xnr expression. However, in both cases (Xatv/Xlefty-deficiency alone, or combined with Xbra interference), Xnr2 expression was constrained to the superficial cell layer, suggesting a fundamental tissue-specific competence in the ability to express Xnrs, an observation with direct implications regarding the induction of endodermal vs. mesodermal fates. Our experiments reveal a two-level suppressive mechanism for restricting the level, range, and duration of Xnr signaling via extracellular inhibition by Xatv/Xlefty coupled with potent indirect transcriptional repression by Xbra.

Primitive streak formation in mice is preceded by localized activation of Brachyury and Wnt3

The prevalent model for the generation of axial polarity in mouse embryos proposes that a radial to a linear transition in the expression of primitive streak markers precedes the formation of the primitive streak on one side of the epiblast. This model contrasts with the models of mesoderm formation in other vertebrates as it suggests that the primitive streak is initially established in a radial pattern rather than a localized region of the epiblast. Here, we examine the proposed correlation between the expression of Brachyury and Wnt3, two genes reported as expressed radially in the proximal epiblast, with the movements of proximal anterior epiblast cells at stages leading to the formation of the primitive streak. Our results reveal that neither Brachyury nor Wnt3 forms a ring of expression in the proximal epiblast as previously thought. In embryos dissected between 5.5 and 6.5 dpc, Brachyury is first expressed in the distal extra-embryonic ectoderm and subsequently on one side of the epiblast. Wnt3 expression is evident first in the posterior visceral endoderm of 5.5 dpc embryos and later in the posterior epiblast. Lineage analysis shows that the movements of the proximal epiblast do not restrict Brachyury expression to the posterior epiblast. Our data suggest a model whereby the localized expression of these genes in the posterior epiblast, and hence the formation of the primitive streak, is the result of local cell-cell interactions in the future posterior portion of the egg cylinder rather than regionalization of a radial pattern of expression in proximal epiblast cells.

Activated Leukocyte Cell Adhesion Molecule (ALCAM/CD166/MEMD), a Novel Actor in Invasive Growth, Controls Matrix Metalloproteinase Activity

Activated leukocyte cell adhesion molecule (ALCAM/CD166/MEMD) could function as a cell surface sensor for cell density, controlling the transition between local cell proliferation and tissue invasion in melanoma progression. We have tested the hypothesis that progressive cell clustering controls the proteolytic cascade for activation of gelatinase A/matrix metalloproteinase-2 (MMP-2), which involves formation of an intermediate ternary complex of membrane type 1 MMP (MT1-MMP/MMP-14), tissue inhibitor of metalloproteinase-2 (TIMP-2), and pro-MMP-2 at the cell surface. Surprisingly, truncation of ALCAM severely impaired MMP-2 activation in a nude mouse xenograft model, in which we previously observed diminished primary tumor growth and enhanced melanoma metastasis. Comparative studies of two-dimensional monolayer and three-dimensional collagen-gel cultures revealed that extensive cell-to-cell contacts, wild-type ALCAM, and cell-to-matrix interactions were all indispensable for efficient conversion of pro-MMP-2 to its active form in metastatic melanoma cells. Truncated, dominant-negative ALCAM diminished MMP-2 activation via reduced transcript levels and decreased processing of MT1-MMP. Failure of the proteolytic cascade after selective ALCAM depletion by RNA interference was mainly due to incomplete MT1-MMP processing, which was otherwise promoted by extensive cell-to-cell contacts. These data attribute a novel signaling role to ALCAM in regulation of proteolysis and support its previously postulated sensor function in invasive growth.

Collaboration of PSD-Zip70 with its binding partner, SPAR, in dendritic spine maturity

Recent studies have reported on the molecular mechanisms underlying dendritic spine (spine) dynamics. Because most of these studies investigated spine dynamics by overexpressing constitutively active or dominant-negative PSD (postsynaptic density) proteins in cultured mature neurons, the results represent the enlargement of mature spines or their return to an immature state. Here, we developed the technique of in utero electroporation to investigate spine dynamics. Using this technique, we demonstrated the suppression of spine maturation by the C-terminal variants of PSD-Zip70 in vitro and in vivo. Transient overexpression of the C terminus of PSD-Zip70 and knock-down of PSD-Zip70 also displayed the destabilization of mature spines. We further found the PSD-Zip70 and SPAR (spine-associated RapGAP) interaction via the short C-terminal region of PSD-Zip70 and the GK-binding domain of SPAR. In association with immature spines induced by overexpression of the PSD-Zip70 C terminus or knock-down of PSD-Zip70, SPAR lost its spine localization. Overexpression of the GK-binding domain of SPAR also induced to form immature spines without affecting the localization of PSD-Zip70 in the small heads of filopodial spines. Our results suggest that PSD-Zip70 in collaboration with SPAR is critically involved in spine maturity, especially in the mature spine formation and the maintenance of spine maturity.

FHOD1 coordinates actin filament and microtubule alignment to mediate cell elongation

Diaphanous-related formins (DRFs) are actin nucleators that mediate rearrangements of the actin cytoskeleton downstream of specific Rho GTPases. The DRF Formin Homology 2 Domain containing 1 (FHOD1) interacts with the Rac1 GTPase and induces the formation of and associates with bundled actin stress fibers. Here we report that active FHOD1 also coordinates microtubules with these actin stress fibers. Expression of a constitutive active FHOD1 variant in HeLa cells not only resulted in pronounced formation of FHOD1-actin fibers but also caused marked cell elongation and parallel alignment of microtubules without affecting cytokinesis of these cells. The analysis of deletions in the FH1 and FH2 functional regions revealed that the integrity of both domains was strictly required for FHOD1's effects on the cytoskeleton. Dominant-negative approaches demonstrated that filament coordination and cell elongation depended on the activity of the Rho-ROCK cascade, but did not involve Rac or Cdc42 activity. Experimental depolymerization of actin filaments or microtubules revealed that the formation of FHOD1-actin fibers was a prerequisite for the polarization of microtubules. However, only simultaneous disruption of both filament systems reversed the cell elongation induced by activated FHOD1. Thus, sustained cell elongation was a consequence of FHOD1-mediated actin-microtubule coordination. These results suggest filament coordination as a conserved function of mammalian DRFs.

Increased angiogenesis and expression of vascular endothelial growth factor during scarless repair

Vascular endothelial growth factor (VEGF) is a dimeric heparin-binding glycoprotein that is a potent endothelial cell-specific mitogen with increased expression during adult cutaneous wound healing. VEGF activity is mediated by two receptors, VEGFR-1 (Flt-1) and VEGFR-2 (Flk-1/KDR), which are expressed primarily in vascular endothelial cells. Initiation of profibrotic cytokine expression likely coordinates the transition from scarless healing to scar formation in fetal wounds. Angiogenesis is an important component of the scarring repair process, but the function of VEGF and degree of angiogenesis during scarless repair has not been investigated. We hypothesize that VEGF and its receptors are differentially expressed in scarless compared with scarring fetal wounds because VEGF is implicated in angiogenesis during skin development and adult wound healing. Excisional wounds were created on fetal rats at gestational ages 16.5 days (E16) and 18.5 days (E18) (term = 21.5 days). Wounds were harvested at 24 and 72 hours (n = 12 wounds per time point). Nonwounded fetal skin (E17, E19, and E21) was used as control. Reduced-cycle, specific-primer, reverse-transcriptase polymerase chain reaction was performed to determine the expression of VEGF and its receptors, VEGFR-1 and VEGFR-2. Wounds at 72 hours and fetal skin controls were examined under high-power microscopy for blood vessel counts. Unpaired two-tailed t test was used (p < 0.05 was considered significant). VEGF expression increased 2.4-fold (p < 0.001) during normal skin development from E17 to E19. In scarless wounds (E16), VEGF expression increased 2.8-fold (p < 0.02) at 72 hours. No increased expression occurred in the scarring wounds (E18). VEGFR-1 and VEGFR-2 expression increased over 2-fold during normal skin development from E17 to E21. However, each was down-regulated 30 to 50 percent in scarless (E16) and scarring (E18) wounds. There is a 2-fold increase in mean vessel counts per high-power field in scarless (E16) wounds at 72 hours compared with age-matched control skin (p < 0.02) and a 1.7-fold increase in mean vessel count in scarring fetal wounds (E18) compared with age-matched control skin (p < 0.05). There is no difference in the total number of vessels found in scarless versus scarring wounds or between 19.5-day versus 21.5-day fetal skin. VEGF and its receptors, VEGFR-1 and VEGFR-2, increase expression during skin development and dermal differentiation. VEGF expression quickly elevates during scarless compared with scarring repair, which likely contributes to the more rapid scarless fetal repair rate. Similar numbers of new ves-sels are formed during scarless and scarring fetal repair.

T-box genes in the ascidianCiona intestinalis: Characterization of cDNAs and spatial expression

Members of the T-box family of transcription factors share an evolutionarily conserved DNA-binding domain and play significant roles in various processes of embryonic development. Vertebrate T-box genes are categorized into the following five major subfamilies (eight groups), depending on sequence similarities: Brachyury, Tbx1 (Tbx1/10, Tbx15/18/22, Tbx20), Tbx2/3/4/5 (Tbx2/3 and Tbx4/5), Tbx6, and Tbr/Eomes/TBX21. Ascidians are primitive chordates, and their tadpole larva are considered to represent the simplified and basic body plan of vertebrates. In addition, it has been revealed that the ascidian genome contains the basic ancestral complement of genes involved in development. The present characterization of cDNAs and survey of the Ciona intestinalis draft genome demonstrated that the Ciona genome contains a single copy gene for each of the Brachyury, Tbx1/10, Tbx15/18/22, Tbx20, Tbx2/3, and Tbr/Eomes/TBX21 groups, and at least three copies of the Tbx6 subfamily. Each of the Ciona T-box genes shows a characteristic expression pattern, although that of Tbx20 was not determined in the present study. These results provide basic information that will be useful for future studies of the function of each gene, genetic cascades of different T-box genes, and genome-wide surveys of evolutionary changes in the T-box gene structure and organization in this primitive chordate.

Screening of FGF target genes inXenopusby microarray: temporal dissection of the signalling pathway using a chemical inhibitor

Microarray is a powerful tool for analysing gene expression patterns in genome-wide view and has greatly contributed to our understanding of spatiotemporal embryonic development at the molecular level. Members of FGF (fibroblast growth factor) family play important roles in embryogenesis, e.g. in organogenesis, proliferation, differentiation, cell migration, angiogenesis, and wound healing. To dissect spatiotemporally the versatile roles of FGF during embryogenesis, we profiled gene expression in Xenopus embryo explants treated with SU5402, a chemical inhibitor specific to FGF receptor 1 (FGFR1), by microarray. We identified 38 genes that were down-regulated and 5 that were up-regulated in response to SU5402 treatment from stage 10.5-11.5 and confirmed their FGF-dependent transcription with RT-PCR analysis and whole-mount in situ hybridization (WISH). Among the 43 genes, we identified 26 as encoding novel proteins and investigated their spatial expression pattern by WISH. Genes whose expression patterns were similar to FGFR1 were further analysed to test whether any of them represented functional FGF target molecules. Here, we report two interesting genes: one is a component of the canonical Ras-MAPK pathway, similar to mammalian mig6 (mitogen-inducible gene 6) acting in muscle differentiation; the other, similar to GPCR4 (G-protein coupled receptor 4), is a promising candidate for a gastrulation movement regulator. These results demonstrate that our approach is a promising strategy for scanning the genes that are essential for the regulation of a diverse array of developmental processes.

Defective Lung Vascular Development and Fatal Respiratory Distress in Endothelial NO Synthase-Deficient Mice

Endothelium-derived NO plays a critical role in the regulation of cardiovascular function and structure, as well as acting as a downstream mediator of the angiogenic response to numerous vascular growth factors. Although endothelial NO synthase (eNOS)-deficient mice are viable, minor congenital cardiac abnormalities have been reported and homozygous offspring exhibit high neonatal mortality out of proportion to the severity of these defects. The aim of the present report was to determine whether abnormalities of the pulmonary vascular development could contribute to high neonatal loss in eNOS-deficient animals. We now report that eNOS-deficient mice display major defects in lung morphogenesis, resulting in respiratory distress and death within the first hours of life in the majority of animals. Histological and molecular examination of preterm and newborn mutant lungs demonstrated marked thickening of saccular septae, with evidence of reduced surfactant material. Lungs of eNOS-deficient mice also exhibited a striking paucity of distal arteriolar branches and extensive regions of capillary hypoperfusion, together with misalignment of pulmonary veins, which represent the characteristic features of alveolar capillary dysplasia. We conclude that eNOS plays a previously unrecognized role in lung development, which may have relevance for clinical syndromes of neonatal respiratory distress.

[Ephrins, neuronal development and plasticity]

AIMS

In this work we review the main characteristics of ephrins and their Eph receptors (ER), as well as descriptions that have been published to date of the different functions the ephrin/Eph system (EES) performs in neuronal development.

DEVELOPMENT

ER constitute the largest group of tyrosine kinase receptors and are found in many different types of cells during development and in mature tissues. Their ligands, the ephrins, are membrane anchored proteins that are divided into class A ephrins, with a glycosylphosphatidylinositol bond, and class B ephrins, with a hydrophobic transmembrane region and a cytoplasmic domain. The EES is the only one that involves bidirectional signalling. Thus, the ephrin Eph interaction both activates the tyrosine kinase domain of the ER, with the resulting signal transduction in the cell that expresses Eph, and produces a reverse signal in the cells that contain the ligands. Over the last decade a number of studies have been conducted that establish the involvement of the EES in neuronal development. Although the classic function of this system is that of establishing patterns of both cellular and axonal organisation, recent reports describe how the ER and their ephrin ligands regulate synaptogenesis and the maturation of terminals during development, as well as the plasticity of the adult brain.

CONCLUSIONS

Recent findings open up new expectations regarding the possible functions carried out by the interaction of ephrin and Eph. They also confirm the crucial role played by this system in all the processes involved in allowing neuronal development to take place in a correct fashion.

The initiation of Hox gene expression in Xenopus laevis is controlled by Brachyury and BMP-4

Hox genes encode a family of transcription factors that specify positional identities along the anterior-posterior (AP) axis during the development of vertebrate embryos. The earliest Hox expression in vertebrates is during gastrulation, at a position distant from the organiser or its equivalent. However, the mechanism that initiates this early expression is still not clear. Guided by the expression pattern, we identified upstream regulators in Xenopus laevis. The mesodermal transcription factor brachyury (Xbra) controls the early Hox expression domain in the animal-vegetal direction and the secreted growth factor BMP-4 limits it in the organiser/non-organiser direction. The overlap of these two signals, indicated by a Cartesian coordinate system, defines the initial Hox expression domain. We postulate that this system is a general mechanism for the activation of all Hox genes expressed during gastrulation.

Formin homology domain protein (FHOD1) is a cyclic GMP-dependent protein kinase I-binding protein and substrate in vascular smooth muscle cells

Cyclic GMP-dependent protein kinase I (PKGI) mediates vascular relaxation by nitric oxide and related nitrovasodilators and inhibits vascular smooth muscle cell (VSMC) migration. To identify VSMC proteins that interact with PKGI, the N-terminal protein interaction domain of PKGIalpha was used to screen a yeast two-hybrid human aortic cDNA library. The formin homology (FH) domain-containing protein, FHOD1, was found to interact with PKGIalpha in this screen. FH domain-containing proteins bind Rho-family GTPases and regulate actin cytoskeletal dynamics, cell migration, and gene expression. Antisera to FHOD1 were raised and used to characterize FHOD1 expression and distribution in vascular cells. FHOD1 is highly expressed in human coronary artery, aortic smooth muscle cells, and in human arterial and venous endothelial cells. In glutathione S-transferase pull-down experiments, the FHOD1 C terminus (amino acids 964-1165) binds full-length PKGI. Both in vitro and intact cell studies demonstrate that the interaction between FHOD1 and PKGI is decreased 3- to 5-fold in the presence of the PKG activator, 8Br-cGMP. Immunofluorescence studies of human VSMC show that FHOD1 is cytoplasmic and is concentrated in the perinuclear region. PKGI also directly phosphorylates FHOD1, and studies with wild-type and mutant FHOD1-derived peptides identify Ser-1131 in the FHOD1 C terminus as the unique PKGI phosphorylation site in FHOD1. These studies demonstrate that FHOD1 is a PKGI-interacting protein and substrate in VSMCs and show that cyclic GMP negatively regulates the FHOD1-PKGI interaction. Based on the known functions of FHOD1, the data are consistent with a role for FHOD1 in cyclic GMP-dependent inhibition of VSMC stress fiber formation and/or migration.

A Southpaw Joins the Roster: The Role of the Zebrafish nodal-related Gene Southpaw in Cardiac LR Asymmetry

The establishment of the left-right (LR) asymmetry of the zebrafish heart involves at least two discrete events: cardiac jogging and cardiac looping. The nodal-related gene southpaw is required for both aspects of heart LR asymmetry as well as for LR patterning of other visceral organs. Reductions in southpaw activity abolish the normal LR biases of jogging and looping and uncouple the normal correlation between jogging and looping polarities. These loss-of-function experiments also reveal that southpaw is required for organizing at least the initial phase of diencephalic LR asymmetry and suggest that heart and brain LR patterning may be coordinated by southpaw signaling originating within the anterior, left lateral plate mesoderm.

The formin-homology-domain-containing protein FHOD1 enhances cell migration

Formin-homology-domain-containing proteins interact with Rho-family GTPases and regulate actin cytoskeleton organization and gene transcription. FHOD1 is a member of this family, interacts with Rac1 and induces transcription from the serum response element. In this study, we examined the effects of FHOD1 expression on cytoskeletal organization and function in mammalian cells. FHOD1 proteins were stably expressed in WM35 melanoma cells and NIH-3T3 fibroblasts. Cells expressing full-length FHOD1 demonstrated an elongated phenotype compared with vector-transfected cells and cells expressing a truncated FHOD1 (1-421) that lacks the conserved FH1 and FH2 domains. Full-length FHOD1 co-localized with filamentous actin at cell peripheries. Cells transiently expressing a C-terminal FHOD1 truncation mutant (DeltaC, residues 1-1010), which lacks an autoinhibitory protein-protein interaction domain, displayed prominent stress fibers. FHOD1 (1-421) did not induce stress fibers but localized to membrane ruffles in a manner similar to the full-length protein, indicating that the FH1 and FH2 domains are required for stress fiber appearance. FHOD1 DeltaC (1-1010)-dependent stress fibers were sensitive to dominant-negative RacN17 and the RhoA and ROCK inhibitors, C3 transferase and Y-27632. Stable overexpression of full-length FHOD1 enhanced the migration of WM35 and NIH-3T3 cells to type-I collagen and fibronectin, respectively. Cells expressing FHOD1 (1-421) migrated similar to control cells. Integrin expression and activation were not affected by FHOD1 expression. Moreover, FHOD1 overexpression did not alter integrin usage during adhesion or migration. These data demonstrate that FHOD1 interacts with and regulates the structure of the cytoskeleton and stimulates cell migration in an integrin-independent manner.

Notochord anomalies in the adriamycin rat model: A morphologic and molecular basis for the VACTERL association

BACKGROUND/PURPOSE

The Adriamycin rat model (ARM) is a reliable model of the VACTERL association. The notochord is structurally abnormal in the region of the foregut, midgut, and hindgut in the ARM. The authors hypothesised that notochord anomalies allow ectopic expression of molecular signals in the developing embryo and thus lead to VACTERL malformations. This study was designed to investigate this hypothesis.

METHODS

Adriamycin (1.75 mg/kg) was administered intraperitoneally to pregnant rats on days 7, 8, and 9 of gestation. Control animals were given saline. Embryos were recovered on gestational days 10.5 to 14 at (1/2)-day intervals and at full term. The first group of embryos were embedded in resin, and sagittal sections stained with Toluidine blue were studied for morphologic abnormalities. The second group of embryos were examined using in situ hybridization for the expression of Sonic Hedgehog (Shh), a patterning gene implicated in the etiology of the VACTERL association.

RESULTS

Twenty-seven of the 28 (96.4%) full-term embryos showed VACTERL anomalies. Forty-five of the 50 (90%) experimental embryos (gestational days 10.5 to 14) showed notochord abnormalities. Abnormal ventral branches from the notochord toward the gut were a commonly observed abnormality. These were seen to impinge on the developing foregut, midgut, dorsal aorta, and kidney. In situ hybridization for Shh showed that these branches from the notochord expressed Shh in 66.6% of experimental embryos. This abnormal Shh expression was not seen in the control embryos.

CONCLUSIONS

Adriamycin diffusely induces altered notochord morphology in the rat embryo. The abnormal notochord morphology may allow ectopic expression of Sonic Hedgehog, and, thus, contribute to the malformations found in the VACTERL association.

Fibroblast growth factor signaling in the developing tracheoesophageal fistula

BACKGROUND/PURPOSE

The Adriamycin-induced rat model of esophageal atresia and tracheoesophageal fistula (EA/TEF) provides a reliable system for the study of EA/TEF pathogenesis. The authors previously hypothesized that faulty branching lung morphogenesis pathways were a critical component of its pathogenesis. The authors have found evidence for faulty fibroblast growth factor (FGF) signaling related to epithelial-mesenchymal interactions in the fistula tract. To better define FGF signaling, the differential expression of FGF ligands and their receptors between lung, fistula tract, and esophagus are described.

METHODS

Time-dated pregnant, Sprague-Dawley rats were injected with Adriamycin (2 mg/kg intraperitoneally) on days 6 through 9 of gestation. Tissues were processed for histology and reverse transcriptase polymerase chain reaction. FGF-1, -7 and -10 were measured from whole lung, fistula tract, and esophagus of TEF or normal embryos. Expression of FGF2RIIIb and FGF2RIIIc receptors was measured in isolated epithelium and mesenchyme of lung and fistula tract of TEF embryos as well as lung and esophagus from normal controls.

RESULTS

FGF-1 mRNA was present in the fistula tract and normal and Adriamycin-exposed lung but absent from whole esophagus. Interestingly, FGF-7 mRNA was present only in normal lung. FGF-10 was present in all tissues examined. FGF2RIIIb mRNA was absent in fistula mesenchyme but present in all other tissues examined. However, the splice variant FGF2RIIIc mRNA was present in all tissues examined.

CONCLUSIONS

These findings support defective FGF signaling in the rat model of EA/TEF. Absence of FGF-7 mRNA in Adriamycin-exposed tissues suggests the primary effect of Adriamycin may be to inhibit FGF-7 expression. Moreover, absence of FGF2RIIIb in fistula mesenchyme may be caused by loss of positive feedback from FGF-7, its normal obligate ligand. Understanding these specific defects in FGF signaling may provide insight into faulty mechanisms of EA/TEF.

Development of the cardiac pacemaking and conduction system

The heartbeat is initiated and coordinated by a heterogeneous set of tissues, collectively referred to as the pacemaking and conduction system (PCS). While the structural and physiological properties of these specialized tissues has been studied for more than a century, distinct new insights have emerged in recent years. The tools of molecular biology and the lessons of modern embryology are beginning to uncover the mechanisms governing induction, patterning and developmental integration of the PCS. In particular, significant advances have been made in understanding the developmental biology of the fast conduction network in the ventricles--the His-Purkinje system. Although this progress has largely been made by using animal models such as the chick and mouse, the insights gained may help explain cardiac disease in humans, as well as lead to new treatment strategies.

Neural crest and cardiovascular development: a 20-year perspective

BACKGROUND

Twenty years ago this year was the first publication describing a region of neural crest cells necessary for normal cardiovascular development. Ablation of this region in chick resulted in persistent truncus arteriosus, mispatterning of the great vessels, outflow malalignments, and hypoplasia or aplasia of the pharyngeal glands.

METHODS

We begin with a historical perspective and then review the progress that has been made in the ensuing 20 years in determining the direct and indirect contributions of the neural crest cells, now termed cardiac neural crest cells, in cardiovascular and pharyngeal arch development. Many of the molecular pathways that are now known to influence the specification, migration, patterning and final targeting of the cardiac neural crest cells are also reviewed.

RESULTS

Although much knowledge has been gained by using many genetic manipulations to understand the cardiac neural crest cells' role in cardiovascular development, most models fail to explain the phenotypes seen in syndromic and non-syndromic human congenital heart defects, such as the DiGeorge syndrome.

CONCLUSIONS

We propose that the cardiac neural crest exists as part of a larger cardiocraniofacial morphogenetic field and describe several human syndromes that result from abnormal development of this field.

Regulation of heart morphology: current molecular and cellular perspectives on the coordinated emergence of cardiac form and function

BACKGROUND

During early heart development, in addition to cells being induced to differentiate into cardiomyocytes, pathways are activated that lead to cardiac morphogenesis or the development of form.

METHODS

Orchestration of organogenesis involves the incremental activation of regulatory pathways that lead to pivotal transition points, such as cardiac compartment delineation and looping. Each embryonic stage sets up the correct patterning of morphoregulatory molecules that will regulate the next process, until an organ is formed from the mesoderm layer after gastrulation. The current review provides an understanding of the morphoregulatory, cell adhesion and extracellular matrix-mediated, processes that coordinate development of heart form with that of function. The period reviewed encompasses the formation of a definitive cardiac compartment from the lateral plate mesoderm to the time-point in which the single, beating heart tube loops directionally to the right. Looping results in the correct spatial orientation for subsequent modeling of the four-chambered heart. Even subtle alterations in looping can form the basis upon which malformations of the inlet or the outlet regions of the heart, or both, are superimposed.

RESULTS

In the future, DNA microarray data sets may allow modeling the specific sequence of gene regulatory dynamics leading to these transition points to discover the regulatory "modes" that the cells adopt during heart organogenesis. The regulatory genes, however, can only specify the proteins that will be present.

CONCLUSIONS

To fully understand the timing and mechanisms underlying heart development, it is necessary to define the sequential synthesis, patterning, and interaction of the proteins, and of still other receptors, which eventually drive cells to organize into functioning organs.

Early events in valvulogenesis: a signaling perspective

The proper formation and function of the vertebrate heart requires a multitude of specific cell and tissue interactions. These interactions drive the early specification and assembly of components of the cardiovascular system that lead to a functioning system before the attainment of the definitive cardiac and vascular structures seen in the adult. Many of these adult structures are hypothesized to require both proper molecular and physical cues to form correctly. Unlike any other organ system in the embryo, the cardiovascular system requires concurrent function and formation for the embryo to survive. An example of this complex interaction between molecular and physical cues is the formation of the valves of the heart. Both molecular cues that regulate cell transformation, migration, and extracellular matrix deposition, and physical cues emanating from the beating heart, as well as hemodynamic forces, are required for valvulogenesis. This review will focus on molecules and emerging pathways that guide early events in valvulogenesis.

Hox genes and spinal cord development

The spinal cord is differentiated along the rostrocaudal axis into large domains with regional distinctions reflected in the position and projection of specific cell types. Spinal cord patterning is likely to be mediated by the local expression and activity of transcription factors. This review will examine the expression of one class of transcription factors, encoded by the Hox genes, that are active in spinal cord patterning. Hox genes encode homeodomain-containing proteins with overlapping rostrocaudal domains of expression in the developing spinal cord. Rostrally expressed Ant-p/Ubx/Abd-D-related Hox genes may function in patterning the cervical spinal cord, while Abd-D-related, caudally expressed Hox genes may pattern the lumbar spinal cord. Changes in spinal cord patterning are apparent following Hox gene inactivation, supporting a role for these genes in defining or establishing this pattern.

EphA4 constitutes a population-specific guidance cue for motor neurons

Motor neurons in the ventral neural tube project axons specifically to their target muscles in the periphery. Although many of the transcription factors that specify motor neuron cell fates have been characterized, less is understood about the mechanisms that guide motor axons to their correct targets. We show that ectopic expression of EphA4 receptor tyrosine kinase alters the trajectories of a specific population of motor axons in the avian hindlimb. Most motor neurons in the medial portion of the lateral motor column (LMC) extend their axons aberrantly in the dorsal nerve trunk at the level of the crural plexus, in the presence of ectopic EphA4. This misrouting of motor axons is not accompanied by alterations in motor neuron identity, settling patterns in the neural tube, or the fasciculation of spinal nerves. However, ectopic EphA4 axons do make errors in pathway selection during sorting in the plexus at the base of the hindlimb. These results suggest that EphA4 in motor neurons acts as a population-specific guidance cue to control the dorsal trajectory of their axons in the hindlimb.

Ephrins are not only unattractive

The ephrins and their Eph receptors have emerged as repulsive cues for growing axons during the past decade. Since then, great effort has been made to understand the significance and mechanisms of Eph-mediated repulsion. More recently, it has become clear that ephrins perform in many more developmental processes than the repulsion-dependent establishment of topography in the nervous system. As numerous studies suggest functions more akin to adhesion or attraction than to repulsion, increasing attention is now being paid to the intracellular mechanisms that might explain this duality.

EphA4 is not required for Purkinje cell compartmentation

The Purkinje cells of both the adult and the developing cerebellar cortex are organized into parasagittal stripes or 'segments' expressing a variety of biochemical markers. We show that in the developing mouse cerebellar cortex, members of the Eph receptor gene family are expressed in mediolaterally alternating Purkinje cell segments. Since members of the Eph receptors family have been shown to play a role in hindbrain segmentation and boundary formation (Philos. Trans. R. Soc. Lond. B: Biol. Sci. 355 (2000) 993), we analyzed the effect of a null mutation of the EphA4 gene on Purkinje cell compartmentation. Using well characterized markers of Purkinje cell compartmentation in both the developing and the adult cerebellum, we observed no significant alteration in the banding pattern of these markers between the EphA4 knockout mice and their wild type controls. The ribboned pattern of migrating granule cells in the developing cerebellum also appears unaltered. The expression of other members of this gene family, including ephrin-B2, EphA2, and ephrin-A1, in a compartmentalized pattern within the Purkinje cell layer suggests a possible redundancy and/or a compensation of EphA4 function in the segmental patterning of cerebellar Purkinje cells.

Wnt-1 and Wnt-4 regulate thymic cellularity

Thymic primordium, formed by cells derived from the endoderm, the ectoderm and the neural crest-derived mesenchyme, receive fetal liver derived lymphoid precursors. Reciprocal cell-cell interactions between thymic stromal cells and lymphoid precursors are critical in the expansion and maturation of thymocytes. Transcription factor TCF-1 is critical for the expansion of thymocytes because deletion of TCF-1 results in a significant decrease in the number of thymocytes without affecting the developmental pattern. In this report we show that Wnt-1 and Wnt-4 are expressed in the thymus and the deletion of Wnt-1 or Wnt-4 result in a substantial decrease in the number of thymocytes without affecting the pattern of maturation. Wnt-1 and Wnt-4 both regulate developing thymocytes because a double deficiency results in a significantly greater decrease of immature and mature thymocytes compared to deficiency in either Wnt-1 or Wnt-4.