Msx2 and p21(CIP1/WAF1) mediate the proapoptotic effects of bone morphogenetic protein-4 on ventricular zone progenitor cells

Acute upregulation of bone morphogenetic protein-4 regulates endogenous cell response and promotes cell death in spinal cord injury

Traumatic spinal cord injury (SCI) elicits a cascade of secondary injury mechanisms that induce profound changes in glia and neurons resulting in their activation, injury or cell death. The resultant imbalanced microenvironment of acute SCI also negatively impacts regenerative processes in the injured spinal cord. Thus, it is imperative to uncover endogenous mechanisms that drive these acute injury events. Here, we demonstrate that the active form of bone morphogenetic protein-4 (BMP4) is robustly and transiently upregulated in acute SCI in rats. BMP4 is a key morphogen in neurodevelopment; however, its role in SCI is not fully defined. Thus, we elucidated the ramification of BMP4 upregulation in a preclinical model of compressive/contusive SCI in the rat by employing noggin, an endogenous antagonist of BMP ligands, and LDN193189, an intracellular inhibitor of BMP signaling. In parallel, we studied cell-specific effects of BMP4 on neural precursor cells (NPCs), oligodendrocyte precursor cells (OPCs), neurons and astrocytes in vitro. We demonstrate that activation of BMP4 inhibits differentiation of spinal cord NPCs and OPCs into mature myelin-expressing oligodendrocytes, and acute blockade of BMPs promotes oligodendrogenesis, oligodendrocyte preservation and remyelination after SCI. Importantly, we report for the first time that BMP4 directly induces caspase-3 mediated apoptosis in neurons and oligodendrocytes in vitro, and noggin and LDN193189 remarkably attenuate caspase-3 activation and lipid peroxidation in acute SCI. BMP4 also enhances the production of inhibitory chondroitin sulfate proteoglycans (CSPGs) in activated astrocytes in vitro and after SCI. Interestingly, our work reveals that despite the beneficial effects of BMP inhibition in acute SCI, neither noggin nor LDN193189 treatment resulted in long-term functional recovery. Collectively, our findings suggest a role for BMP4 in regulating acute secondary injury mechanisms following SCI, and a potential target for combinatorial approaches to improve endogenous cell response and remyelination.

Protection by nitrite against the ischemic effects induced by acute myocardial infarction in mice

OBJECTIVE

This research was aimed to investigate the correct dose of nitrite that would act as a protection against the ischemic effects induced by acute myocardial infarction (AMI).

METHODS

Mice were randomly divided into a sham-operation group (sham), an AMI operation group (AMI), and a nitrite pretreatment+AMI operation group (N+AMI). Seven days before the AMI operation, mice in the N+AMI group were pretreated with sodium nitrite in drinking water.

RESULTS

One week after the AMI operation, serum lactate dehydrogenase (LDH) and creatine kinase (CK) activities in both AMI and N+AMI group were significantly higher than those in the sham group, but there were no significant differences between AMI and N+AMI mice. Contents of inducible nitric oxide synthase (iNOS) in the noninfarct area of the left ventricle in the N+AMI mice were significantly higher than those in the AMI mice, with no difference in the infarct area. Coagulation necrosis in the cardiomyocytes was observed in both AMI and N+AMI mice; however, it was less severe in the N+AMI mice. Western blot analyses showed that nitrite pretreatment resulted in up-regulation of antiapoptotic factors Bcl-2 and p21waf1/cip1 signal proteins, but down-regulation of the proapoptotic factor Bax signal protein. Furthermore, nitrite pretreatment also showed significant alleviation of AMI-induced signal protein expressions of inflammatory factors of NF-K B and oxidative factors of Hsp 70 and HO-1.

CONCLUSION

These results suggest that nitrite show certain protective effects against the ischemic effects induced by AMI in mice, which might be attributed to the synthesis of NO induced by iNOS through up-regulation of antiapoptotic factors and down-regulation of proapoptotic and inflammatory factors.

MSX2 and BCL2 expressions in the development of anorectal malformations in ethylenethiourea-induced rat embryos

BACKGROUND

This study aimed to determine Msh homeobox 2 (MSX2) and B cell lymphoma-2 (BCL2) expression patterns during anorectal development in anorectal malformations (ARM) and normal rat embryos, with the goals of determining the role of MSX2 and BCL2 in ARM pathogenesis.

METHODS

ARM was induced in rat embryos with ethylenethiourea administered to dams on gestational day 10 (GD10). Embryos were harvested by cesarean deliveries from GD14 to GD16. MSX2 and BCL2 expression was evaluated via immunohistochemical staining, immunofluorescence, western blotting and quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

Immunohistochemical staining of ARM embryos revealed that MSX2 was mainly expressed in the epithelium of the hindgut and urorectal septum (URS) on GD14. On GD15 and GD16, MSX2-immunolabeled cells were noted in the epithelium of the rectum, fistula and URS. However, in normal embryos, faint immunopositivity for MSX2 was demonstrated in the epithelium of the rectum and URS from GD14 to GD16. As for BCL2, in normal embryos, BCL2-immunopositive cells were extensively expressed in the epithelium of the hindgut and URS on GD14 and GD15. In ARM embryos, weak immunopositivity for BCL2 was detected in the epithelium of hindgut and URS on GD14 and GD15. Immunofluorescence revealed that MSX2 and BCL2 colocalized in the hindgut. In ARM embryos, we observed more MSX2-positive than BCL2-positive cells on GD14; the normal embryos had the opposite pattern. Analyses by western blot and qRT-PCR showed that MSX2 protein and mRNA expression was significantly increased in ARM embryos compared with the normal embryos on GD15 and GD16 (p < 0.05). However, BCL2 protein and mRNA expression was significantly decreased in ARM embryos compared with the normal embryos on GD14 (p < 0.05). The MSX2/BCL2 ratio of protein and mRNA expression level in the ARM group was the highest on GD15.

CONCLUSION

These results indicate that upregulation of MSX2 and downregulation of BCL2 during cloacal development into the rectum and urethra might be related to the ARM development, and MSX2 promoted apoptosis through reduction of BCL2 expression during the development of anorectal development in ARM.

Homeobox genes and tooth development: Understanding the biological pathways and applications in regenerative dental science

OBJECTIVES

Homeobox genes are a group of conserved class of transcription factors that function as key regulators during the embryonic developmental processes. They act as master regulator for developmental genes, which involves coordinated actions of various auto and cross-regulatory mechanisms. In this review, we summarize the expression pattern of homeobox genes in relation to the tooth development and various signaling pathways or molecules contributing to the specific actions of these genes in the regulation of odontogenesis.

MATERIALS AND METHODS

An electronic search was undertaken using combination of keywords e.g. Homeobox genes, tooth development, dental diseases, stem cells, induced pluripotent stem cells, gene control region was used as search terms in PubMed and Web of Science and relevant full text articles and abstract were retrieved that were written in English. A manual hand search in text books were also carried out. Articles related to homeobox genes in dentistry and tissue engineering and regenerative medicine of odontogenesis were selected.

RESULTS

The possible perspective of stem cells technology in odontogenesis and subsequent analysis of gene correction pertaining to dental disorders through the possibility of induced pluripotent stem cells technology is also inferred.

CONCLUSIONS

We demonstrate the promising role of tissue engineering and regenerative medicine on odontogenesis, which can generate a new ray of hope in the field of dental science.

TGF-β Family Signaling in Neural and Neuronal Differentiation, Development, and Function

Signaling by the transforming growth factor β (TGF-β) family is necessary for proper neural development and function throughout life. Sequential waves of activation, inhibition, and reactivation of TGF-β family members regulate numerous elements of the nervous system from the earliest stages of embryogenesis through adulthood. This review discusses the expression, regulation, and function of TGF-β family members in the central nervous system at various developmental stages, beginning with induction and patterning of the nervous system to their importance in the adult as modulators of inflammatory response and involvement in degenerative diseases.

MSX2 in ameloblast cell fate and activity

While many effectors have been identified in enamel matrix and cells via genetic studies, physiological networks underlying their expression levels and thus the natural spectrum of enamel thickness and degree of mineralization are now just emerging. Several transcription factors are candidates for enamel gene expression regulation and thus the control of enamel quality. Some of these factors, such as MSX2, are mainly confined to the dental epithelium. MSX2 homeoprotein controls several stages of the ameloblast life cycle. This chapter introduces MSX2 and its target genes in the ameloblast and provides an overview of knowledge regarding its effects in vivo in transgenic mouse models. Currently available in vitro data on the role of MSX2 as a transcription factor and its links to other players in ameloblast gene regulation are considered. MSX2 modulations are relevant to the interplay between developmental, hormonal and environmental pathways and in vivo investigations, notably in the rodent incisor, have provided insight into dental physiology. Indeed, in vivo models are particularly promising for investigating enamel formation and MSX2 function in ameloblast cell fate. MSX2 may be central to the temporal-spatial restriction of enamel protein production by the dental epithelium and thus regulation of enamel quality (thickness and mineralization level) under physiological and pathological conditions. Studies on MSX2 show that amelogenesis is not an isolated process but is part of the more general physiology of coordinated dental-bone complex growth.

Induction of p53-dependent p21 limits proliferative activity of rat hepatocytes in the presence of hepatocyte growth factor

Background

Hepatocyte growth factor (HGF), a potent mitogen for hepatocytes, enhances hepatocyte function without stimulating proliferation, depending on the physiological conditions. p53, a transcription factor, suppresses the cell proliferation by expressing p21^WAF1/CIP1 in various tissues.

Aim

To investigate the mechanism through which the hepatocytes maintain mitotically quiescent even in the presence of HGF.

Methods

We studied the relationship between p53 and p21 expression and the effect of p53-p21 axis on hepatocyte proliferation in primary cultured rat hepatocytes stimulated by HGF. Hepatic p21 levels are determined serially after partial hepatectomy or sham operation in rats.

Results

DNA synthesis was markedly increased by HGF addition in rat hepatocytes cultured at low density but not at high density. Cellular p53 levels increased in the hepatocytes cultured at both the densities. p21 levels were increased and correlated with cellular p53 levels in hepatocytes cultured at high density but not at low density. When the activity of p53 was suppressed by a chemical inhibitor for p53, cellular p21 levels were reduced, and DNA synthesis was increased. Similarly, p21 antisense oligonucleotide increased the DNA synthesis. In rats after partial hepatectomy, transient elevation of hepatic p21 levels was observed. In contrast, in sham-operated rats, hepatic p21 levels were increased on sustained time scales.

Conclusion

p53-related induction of p21 may suppress hepatocyte proliferation in the presence of HGF in the setting that mitogenic activity of HGF is not elicitable.

Functional and prognostic relevance of the homeobox protein MSX2 in malignant melanoma

Background:

The homeobox containing transcription factor MSX2 is a key regulator of embryonic development and has been implicated to have a role in breast and pancreatic cancer.

Methods:

Using a selection of two- and three-dimensional in vitro assays and tissue microarrays (TMAs), the clinical and functional relevance of MSX2 in malignant melanoma was explored. A doxycyline-inducible over-expression system was applied to study the relevance of MSX2 in vitro. For TMA construction, tumour material from 218 melanoma patients was used.

Results:

Ectopic expression of MSX2 resulted in the induction of apoptosis and reduced the invasive capacity of melanoma cells in three-dimensional culture. MSX2 over-expression was shown to affect several signalling pathways associated with cell invasion and survival. Downregulation of N-Cadherin, induction of p21 and inhibition of both BCL2 and Survivin were observed. Cytoplasmic MSX2 expression was found to correlate significantly with increased recurrence-free survival (P=0.008). Nuclear expression of MSX2 did not result in significant survival correlations, suggesting that the beneficial effect of MSX2 may be independent of its DNA binding activity.

Conclusions:

MSX2 may be an important regulator of melanoma cell invasion and survival. Cytoplasmic expression of the protein was identified as biomarker for good prognosis in malignant melanoma patients.

BMP signaling in the human fetal ovary is developmentally regulated and promotes primordial germ cell apoptosis

Primordial germ cells (PGCs) are the embryonic precursors of gametes in the adult organism, and their development, differentiation, and survival are regulated by a combination of growth factors collectively known as the germ cell niche. Although many candidate niche components have been identified through studies on mouse PGCs, the growth factor composition of the human PGC niche has not been studied extensively. Here we report a detailed analysis of the expression of components of the bone morphogenetic protein (BMP) signaling apparatus in the human fetal ovary, from postmigratory PGC proliferation to the onset of primordial follicle formation. We find developmentally regulated and reciprocal patterns of expression of BMP2 and BMP4 and identify germ cells to be the exclusive targets of ovarian BMP signaling. By establishing long-term cultures of human fetal ovaries in which PGCs are retained within their physiological niche, we find that BMP4 negatively regulates postmigratory PGC numbers in the human fetal ovary by promoting PGC apoptosis. Finally, we report expression of both muscle segment homeobox (MSX)1 and MSX2 in the human fetal ovary and reveal a selective upregulation of MSX2 expression in human fetal ovary in response to BMP4, suggesting this gene may act as a downstream effector of BMP-induced apoptosis in the ovary, as in other systems. These data reveal for the first time growth factor regulation of human PGC development in a physiologically relevant context and have significant implications for the development of cultures systems for the in vitro maturation of germ cells, and their derivation from pluripotent stem cells.

Homeobox transcription factor muscle segment homeobox 2 (Msx2) correlates with good prognosis in breast cancer patients and induces apoptosis in vitro

Introduction

The homeobox-containing transcription factor muscle segment homeobox 2 (Msx2) plays an important role in mammary gland development. However, the clinical implications of Msx2 expression in breast cancer are unclear. The aims of this study were to investigate the potential clinical value of Msx2 as a breast cancer biomarker and to clarify its functional role in vitro.

Methods

Msx2 gene expression was first examined in a well-validated breast cancer transcriptomic dataset of 295 patients. Msx2 protein expression was then evaluated by immunohistochemistry in a tissue microarray (TMA) containing 281 invasive breast tumours. Finally, to assess the functional role of Msx2 in vitro, Msx2 was ectopically expressed in a highly invasive breast tumour cell line (MDA-MB-231) and an immortalised breast cell line (MCF10a), and these cell lines were examined for changes in growth rate, cell death and cell signalling.

Results

Examination of Msx2 mRNA expression in a breast cancer transcriptomic dataset demonstrated that increased levels of Msx2 were associated with good prognosis (P = 0.011). Evaluation of Msx2 protein expression on a TMA revealed that Msx2 was detectable in both tumour cell nuclei and cytoplasm. Cytoplasmic Msx2 expression was associated with low grade tumours (P = 0.012) and Ki67 negativity (P = 0.018). Nuclear Msx2 correlated with low-grade tumours (P = 0.015), estrogen receptor positivity (P = 0.038), low Ki67 (P = 0.005) and high cyclin D1 expression (P = 0.037). Increased cytoplasmic Msx2 expression was associated with a prolonged breast cancer-specific survival (P = 0.049), recurrence-free survival (P = 0.029) and overall survival (P = 0.019). Ectopic expression of Msx2 in breast cell lines resulted in radically decreased cell viability mediated by induction of cell death via apoptosis. Further analysis of Msx2-expressing cells revealed increased levels of p21 and phosphorylated extracellular signal-regulated kinase (ERK) and decreased levels of Survivin and the 'split ends' (SPEN) protein family member RBM15.

Conclusions

We conclude that increased Msx2 expression results in improved outcome for breast cancer patients, possibly by increasing the likelihood of tumour cell death by apoptosis.

Msx and dlx homeogene expression in epithelial odontogenic tumors

Epithelial odontogenic tumors are rare jaw pathologies that raise clinical diagnosis and prognosis dilemmas notably between ameloblastomas and clear cell odontogenic carcinomas (CCOCs). In line with previous studies, the molecular determinants of tooth development-amelogenin, Msx1, Msx2, Dlx2, Dlx3, Bmp2, and Bmp4-were analyzed by RT-PCR, ISH, and immunolabeling in 12 recurrent ameloblastomas and in one case of CCOC. Although Msx1 expression imitates normal cell differentiation in these tumors, other genes showed a distinct pattern depending on the type of tumor and the tissue involved. In benign ameloblastomas, ISH localized Dlx3 transcripts and inconstantly detected Msx2 transcripts in epithelial cells. In the CCOC, ISH established a lack of both Dlx3 and Msx2 transcripts but allowed identification of the antisense transcript of Msx1, which imitates the same scheme of distribution between mesenchyme and epithelium as in the cup stage of tooth development. Furthermore, while exploring the expression pattern of signal molecules by RT-PCR, Bmp2 was shown to be completely inactivated in the CCOC and irregularly noticeable in ameloblastomas. Bmp4 was always expressed in all the tumors. Based on the established roles of Msx and Dlx transcription factors in dental cell fates, these data suggest that their altered expression is a proposed trail to explain the genesis and/or the progression of odontogenic tumors.

Apoptosis in the medaka embryo in the early developmental stage

Apoptosis is an important event of the development of various organs. In this study, we used in situ terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) to visualize the temporal and spatial distribution of apoptosis in the developing medaka embryo, which is a useful model for developmental biology and genetics. Most of the apoptotic cells were distributed in the central nervous system and tailbud. In the brain and retina, most of the apoptosis occurred in the restricted period. In situ hybridization against caspase 3A and caspase 3B showed that these were distributed in the tailbud and the head, respectively. These results suggested that two types of caspase 3 were involved in apoptosis in different areas.

Bone morphogenetic proteins promote gliosis in demyelinating spinal cord lesions

OBJECTIVE

To determine the role of bone morphogenetic proteins (BMPs) in stimulating glial scar formation in demyelinating lesions of the adult spinal cord.

METHODS

The dorsal columns of adult rats were injected with lysolecithin to induce a local demyelinating lesion. Levels of BMP4 and BMP7 proteins were assayed and compared with glial fibrillary acidic protein expression in the injury area. BMP-responsive cells were identified by expression of phosphorylated Smad1/5/8. Cultures of mature spinal cord astrocytes were treated with BMP4, and levels of chondroitin sulphate proteoglycans (CSPGs) were measured. The effect of BMP4 on CSPG gene regulation was determined by real-time polymerase chain reaction for CSPG core proteins.

RESULTS

BMP4 and BMP7 increase rapidly at the site of demyelination, and astrocytes surrounding the lesion increase expression of phosphorylated Smad1/5/8. Cultured mature astrocytes respond directly to BMPs with Smad1 translocation to the nucleus, increased phosphorylated Smad1/5/8, and increases in glial fibrillary acidic protein and CSPG expression. BMP treatment also increased CSPG messenger RNA for CSPG core proteins, including aggrecan and neurocan. Increases in CSPG expression in astrocytes by BMPs were blocked by the inhibitor noggin. Injections of BMP4 or BMP7 into the dorsal columns in the absence of demyelination led to increases in CSPG expression.

INTERPRETATION

Local increases in BMPs at the site of a demyelinating lesion causes upregulation of gliosis, glial scar formation, and heightened expression of CSPGs such as neurocan and aggrecan that may inhibit remyelination.

High glucose alters the expression of genes involved in proliferation and cell-fate specification of embryonic neural stem cells

AIMS/HYPOTHESIS

Maternal diabetes induces neural tube defects during embryogenesis. Since the neural tube is derived from neural stem cells (NSCs), it is hypothesised that in diabetic pregnancy neural tube defects result from altered expression of developmental control genes, leading to abnormal proliferation and cell-fate choice of NSCs.

MATERIALS AND METHODS

Cell viability, proliferation index and apoptosis of NSCs and differentiated cells from mice exposed to physiological or high glucose concentration medium were examined by a tetrazolium salt assay, 5-bromo-2'-deoxyuridine incorporation, terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling and immunocytochemistry. Expression of developmental genes, including sonic hedgehog (Shh), bone morphogenetic protein 4 (Bmp4), neurogenin 1/2 (Neurog1/2), achaete-scute complex-like 1 (Ascl1), oligodendrocyte transcription factor 1 (Olig1), oligodendrocyte lineage transcription factor 2 (Olig2), hairy and enhancer of split 1/5 (Hes1/5) and delta-like 1 (Dll1), was analysed by real-time RT-PCR. Proliferation index and neuronal specification in the forebrain of embryos at embryonic day 11.5 were examined histologically.

RESULTS

High glucose decreased the proliferation of NSCs and differentiated cells. The incidence of apoptosis was increased in NSCs treated with high glucose, but not in the differentiated cells. High glucose also accelerated neuronal and glial differentiation from NSCs. The decreased proliferation index and early differentiation of neurons were evident in the telencephalon of embryos derived from diabetic mice. Exposure to high glucose altered the mRNA expression levels of Shh, Bmp4, Neurog1/2, Ascl1, Hes1, Dll1 and Olig1 in NSCs and Shh, Dll1, Neurog1/2 and Hes5 in differentiated cells.

CONCLUSIONS/INTERPRETATION

The changes in proliferation and differentiation of NSCs exposed to high glucose are associated with altered expression of genes that are involved in cell-cycle progression and cell-fate specification during neurulation. These changes may form the basis for the defective neural tube patterning observed in embryos of diabetic pregnancies.

BMP-signaling regulates the generation of hair-cells

Bone morphogenetic proteins (BMPs) are diffusible molecules involved in a variety of cellular interactions during development. Bmp4 expression accompanies the development of the ear sensory organs during patterning and specification of sensory cell fates, yet there is no understanding of the role of BMP4 in this process. The present work was aimed at exploring the effects of BMP-signaling on the development of hair-cells. For this purpose, we studied gene expression, cell proliferation and cell death in isolated chick otic vesicles that were grown in vitro in the presence of recombinant BMP4 or the BMP-inhibitor Noggin. Cath1 was used as a marker for hair-cell specification. BMP4 reduced the number of Cath1-cells and, conversely, Noggin increased the size of the sensory patches and the number of Cath1-positive cells. The effect of BMP4 was irreversible and occurred before hair-cell specification. Lfng and Fgf10 were expressed in the prosensory domain before Cath1, and their expression was expanded by Noggin. At these stages, modifications of BMP activity did not respecify non-sensory epithelium of the otic vesicle. The expression of Bmp4 at sensory patches was suppressed by BMP4 and induced by Noggin suggesting an autoregulatory loop. Analysis of BrdU incorporation during 6 and 18 h indicated that the effects of BMP4 were due to its ability to reduce the number of actively proliferating progenitors and inhibit cell fate specification. BMP4 induced cell death within the prosensory domain of the otic vesicle, along with the expression of Msx1, but not Msx2. On the contrary, BMP-inhibition with Noggin favored hair-cell specification without changes in the overall cell proliferation. We propose that about the stage of terminal division, the balance between BMP and BMP-inhibitory signals regulates survival and specification of hair-cell precursors, the final number of sensory hair-cells being limited by excess levels of BMPs. The final size of sensory patches would hence depend on the balance between BMP4 and opposing signals.

BMP-4 induces a Smad-dependent apoptotic cell death of mouse embryonic stem cell-derived neural precursors

Embryonic ectoderm is fated to become either neural or epidermal, depending on patterning processes that occur before and during gastrulation. It has been stated that epidermal commitment proceeds from a bone morphogenetic protein-4 (BMP-4)-dependent inhibition of dorsal ectoderm neuralization. We recently demonstrated that murine embryonic stem (ES) cells treated with BMP-4 undergo effective keratinocyte commitment and epidermogenesis. Focusing on the precise role of BMP-4 in the early choice between neural and epidermal commitment, we show here that BMP-4 treatment of ES cells leads to a dramatic apoptotic death of Sox-1+ neural precursors with concomitant epidermal engagement. In addition, neutralization of the Smad pathway prevents both the BMP-4 apoptotic process and the inhibition of neural differentiation. Our results suggest that, in mammals, BMP-4, as an active inducer of epidermal commitment, interferes with the survival of neural precursors through induction of their apoptotic cell death.

msh/Msx gene family in neural development

The involvement of Msx homeobox genes in skull and tooth formation has received a great deal of attention. Recent studies also indicate a role for the msh/Msx gene family in development of the nervous system. In this article, we discuss the functions of these transcription factors in neural-tissue organogenesis. We will deal mainly with the interactions of the Drosophila muscle segment homeobox (msh) gene with other homeobox genes and the repressive cascade that leads to neuroectoderm patterning; the role of Msx genes in neural-crest induction, focusing especially on the differences between lower and higher vertebrates; their implication in patterning of the vertebrate neural tube, particularly in diencephalon midline formation. Finally, we will examine the distinct activities of Msx1, Msx2 and Msx3 genes during neurogenesis, taking into account their relationships with signalling molecules such as BMP.

Perp is required for tissue-specific cell survival during zebrafish development

The tumor suppressor p53 has two alternative effects, causing either cell cycle arrest or apoptosis. These different effects are supposed to be mediated by the transcriptional activation of different target genes. perp, encoding a transmembrane protein of the Pmp22 family, is a transcriptional p53 target exclusively upregulated in apoptotic cells. However, its role during normal development had remained largely unclear. Here, we report the isolation and characterization of a zebrafish perp homolog. Upon overexpression in early zebrafish embryos, perp induces apoptosis. In addition, it contributes to p53-dependent and UV-induced cell death. However, during normal zebrafish development, perp displays a p53-independent and spatially restricted expression in specific cell types and tissues. Antisense-mediated loss of Perp function leads to increased apoptosis in perp-expressing cells of the developing skin and notochord. We conclude that, in contrast to its proapoptotic function in stressed cells, Perp plays an antiapoptotic role during normal zebrafish development to regulate tissue-specific cell survival.

Adaptation of the endothelium to fluid flow: in vitro analyses of gene expression and in vivo implications

Biomechanical forces generated by blood flow play an important role in the pathogenesis of vascular disease. For example, regions exposed to non-uniform shear stresses develop early atherosclerotic lesions while areas exposed to uniform shear stresses are protected. A variety of in vitro flow apparatuses have been created to apply well-characterized flow patterns to endothelial cells in an effort to dissect the cellular and molecular pathways involved in these distinct processes. Recent advances in biotechnology have permitted large-scale transcriptional profiling techniques to replace candidate gene screens and have allowed the genome-wide examination of biomechanical force-induced endothelial gene expression profiles. This review provides an overview of biomechanical force-induced modulation of endothelial phenotype. It examines the effect of sustained laminar shear stress (LSS), a type of uniform shear stress, on in vitro endothelial gene expression by synthesizing data from the early candidate gene and differential display polymerase chain reaction (PCR) approaches to the numerous, recent, high throughput functional genomic analyses. These studies demonstrate that prolonged LSS regulates the expression of only a small percentage (approximately 1-5%) of endothelial genes, and this transcriptional profile produces an endothelial phenotype that is quiescent, being protected from apoptosis, inflammation and oxidative stress. These observations provide a possible molecular mechanism for the strong correlation between patterns of blood flow and the occurrence of vascular pathologies, such as atherosclerosis, in vivo.

BMP signaling initiates a neural crest differentiation program in embryonic rat CNS stem cells

Bone morphogenetic proteins (BMPs) have an important role in neuronal and astrocytic differentiation of embryonic and adult neural stem cells (NSCs). Here, we show that BMP6, BMP7, GDF5, and GDF6 instructively differentiate E12, E14, and E17 rat cortical NSCs into a variety of neural crest lineages. Clonal analysis shows that BMP7-treated NSCs develop mostly into smooth muscle and peripheral glia. We observed a rapid induction of premigratory neural crest markers like p75NTR, and AP-2 alpha followed by Msx1, Msx2, and Slug, transcription factors that participate in neural crest development. These results suggest that NSCs cultured in vitro in the presence of FGF2 display expanded developmental potential.

Necdin interacts with the Msx2 homeodomain protein via MAGE-D1 to promote myogenic differentiation of C2C12 cells

Necdin is a potent growth suppressor that is expressed predominantly in postmitotic cells such as neurons and skeletal muscle cells. Necdin shows a significant homology to MAGE (melanoma antigen) family proteins, all of which contain a large homology domain. MAGE-D1 (NRAGE, Dlxin-1) interacts with the Dlx/Msx family homeodomain proteins via an interspersed hexapeptide repeat domain distinct from the homology domain. Here we report that necdin associates with the Msx homeodomain proteins via MAGE-D1 to modulate their function. In vitro binding and co-immunoprecipitation analyses revealed that MAGE-D1 directly interacted with necdin via the homology domain and Msx1 (or Msx2) via the repeat domain. A ternary complex of necdin, MAGE-D1, and Msx2 was formed in vitro, and an endogenous complex containing these three proteins was detected in differentiating embryonal carcinoma cells. Co-expression of necdin and MAGE-D1 released Msx-dependent transcriptional repression. C2C12 myoblast cells that were stably transfected with Msx2 cDNA showed a marked reduction in myogenic differentiation, and co-expression of necdin and MAGE-D1 canceled the Msx2-dependent repression. These results suggest that necdin and MAGE-D1 cooperate to modulate the function of Dlx/Msx homeodomain proteins in cellular differentiation.

Elevated expression of a regulator of the G2/M phase of the cell cycle, neuronal CIP-1-associated regulator of cyclin B, in Alzheimer's disease

Adult neurons are generally accepted to be in a quiescent, nonproliferative state. However, it is becoming increasingly apparent that, in Alzheimer's disease (AD), alterations in cell cycle machinery, suggesting an attempt to reenter cell cycle, relate temporally and topographically to degenerating neurons. These findings, together with the fact that neurons lack the necessary components for completion of mitosis, have led to the notion that an ill-regulated attempt to reenter the cell cycle is associated with disease pathogenesis and, ultimately, neuronal degeneration. To understand better the role of such cell cycle abnormalities in AD, we undertook a study of CIP-1-associated regulator of cyclin B (CARB), a protein that associates with two key proteins, p21 and cyclin B, involved in cellular checkpoints in the cell cycle. Our results show that there are increases in CARB localized to intraneuronal neurofibrillary tangles and granulovacuolar degeneration in susceptible hippocampal and cortical neurons in AD. By marked contrast, CARB is found only at background levels in these neuronal populations in nondiseased age-matched controls. Our data not only provide another line of evidence indicative of cell cycle abnormalities in neurons in AD but also lend further credence to the hypothesis that susceptible neurons may be arrested at the G2/M phase of the cell cycle before they die. Therefore, therapeutics targeted toward initiators of the cell cycle are likely to prove of great efficacy for the treatment of AD.

Analysis of differentially expressed genes in keloids and normal skin with cDNA microarray

BACKGROUND

Microarray analysis is a popular tool to investigate the function of genes that are responsible for the phenotype of diseases. Keloid is an intricate lesion that is probably modulated by interplay of many genes. We ventured to study the differences of gene expressions between keloids and normal skin with the aid of a cDNA microarray to explore the molecular mechanism underlying keloid formation.

MATERIALS AND METHODS

The polymerase chain reaction products of 8400 human genes were spotted on a chip in array. The DNAs were then fixed on the glass plate by a series of treatments. Total RNAs were isolated from freshly excised human keloids and normal skins and then were purified to mRNAs by Oligotex. Both the mRNAs from keloids and normal skins were reversely transcribed to cDNAs with the incorporation of fluorescent dUTP for preparing the hybridization probes. The mixed probes were then hybridized to the cDNA microarray. After highly stringent washing, the cDNA microarray was scanned for the fluorescent signals to display the differences between two kinds of tissues.

RESULTS

Among 8400 human genes, there were 402 genes (4.79%) with different expression levels between the keloids and normal skins in all cases, 250 genes, including TGF-beta1 and NGF, were upregulated (2.98%) and 152 downregulated (1.81%). Analyses of collagen, fibronectin, proteoglycan, growth factors, and apoptosis-related molecule gene expression confirmed that our molecular data obtained by cDNA microarray were consistent with the published biochemical and clinical observations of keloids. Higher expression of TGF-beta(1) and NGF in keloids versus normal skins was also testified with reverse transcription polymerase chain reaction method.

CONCLUSIONS

DNA microarray technology is an effective technique in screening for differences in gene expression between keloid and normal skin. Many genes are involved in the formation of keloids. Further analysis of the obtained genes will help to understand the molecular mechanism of keloid formation.

Induction and patterning of neuronal development, and its connection to cell cycle control

Nervous tissue is derived from early embryonic ectoderm, which also gives rise to epidermal derivatives such as skin. The progression from naive ectoderm to differentiated postmitotic neurons involves multiple steps, two of which are crucial in shaping the final neurogenesis pattern. First, is the identification of the neural plate by the process of neural induction. Second, is the selection of a restricted number of sites within the neural plate where neurogenesis, the process leading to final differentiation of neural precursors, is initiated. Recent findings point to the existence of positive inducers of the neural state, whereas, neurogenesis initiation sites appear to be largely defined by inhibition. However, both neural induction and the initiation of neurogenesis appear to be connected to cell cycle control systems that govern whether stem cell maintenance and cell proliferation, or cell specification and differentiation, take place.

Stem cell biology of the central nervous system

Neural stem cells (NSCs) are multipotential progenitor cells that have self-renewal activities. A single NSC is capable of generating various kinds of cells within the central nervous system (CNS), including neurons, astrocytes, and oligodendrocytes. Because of these characteristics, there is increasing interest in NSCs and neural progenitor cells from the aspects of both basic developmental biology and therapeutic applications to the damaged brain. This special issue, dedicated to understanding the nature of the NSCs present in the CNS, presents an introduction to several avenues of research that may lead to feasible strategies for manipulating cells in situ to treat the damaged brain. The topics covered by these studies include the extracellular factors and signal transduction cascades involved in the differentiation and maintenance of NSCs, the population dynamics and locations of NSCs in embryonic and adult brains, prospective identification and isolation of NSCs, the induction of NSCs to adopt particular neuronal phenotypes, and their transplantation into the damaged CNS.