Efficient enzyme-free method to assess the development and maturation of the innate and adaptive immune systems in the mouse colon

Researchers who aim to globally analyze the gastrointestinal immune system via flow cytometry have many protocol options to choose from, with specifics generally tied to gut wall layers of interest. To get a clearer idea of the approach we should use on full-thickness colon samples from mice, we first undertook a systematic comparison of three tissue dissociation techniques: two based on enzymatic cocktails and the other one based on manual crushing. Using flow cytometry panels of general markers of lymphoid and myeloid cells, we found that the presence of cell-surface markers and relative cell population frequencies were more stable with the mechanical method. Both enzymatic approaches were associated with a marked decrease of several cell-surface markers. Using mechanical dissociation, we then developed two minimally overlapping panels, consisting of a total of 26 antibodies, for serial profiling of lymphoid and myeloid lineages from the mouse colon in greater detail. Here, we highlight how we accurately delineate these populations by manual gating, as well as the reproducibility of our panels on mouse spleen and whole blood. As a proof-of-principle of the usefulness of our general approach, we also report segment- and life stage-specific patterns of immune cell profiles in the colon. Overall, our data indicate that mechanical dissociation is more suitable and efficient than enzymatic methods for recovering immune cells from all colon layers at once. Additionally, our panels will provide researchers with a relatively simple tool for detailed immune cell profiling in the murine gastrointestinal tract, regardless of life stage or experimental conditions.

CHD7 regulates craniofacial cartilage development via controlling HTR2B expression

Mutations in the Chromodomain helicase DNA-binding protein 7 - coding gene (CHD7) cause CHARGE syndrome (CS). Although craniofacial and skeletal abnormalities are major features of CS patients, the role of CHD7 in bone and cartilage development remain largely unexplored. Here, using a zebrafish (Danio rerio) CS model, we show that chd7-/- larvae display abnormal craniofacial cartilage development and spinal deformities. The craniofacial and spine defects are accompanied by a marked reduction of bone mineralization. At the molecular level, we show that these phenotypes are associated with significant reduction in the expression levels of osteoblast differentiation markers. Additionally, we detected a marked depletion of collagen 2α1 in the cartilage of craniofacial regions and vertebrae, along with significantly reduced number of chondrocytes. Chondrogenesis defects are at least in part due to downregulation of htr2b, which we found to be also dysregulated in human cells derived from an individual with CHD7 mutation-positive CS. Overall, this study thus unveils an essential role for CHD7 in cartilage and bone development, with potential clinical relevance for the craniofacial defects associated with CS.

Harnessing the Power of Enteric Glial Cells' Plasticity and Multipotency for Advancing Regenerative Medicine

The enteric nervous system (ENS), known as the intrinsic nervous system of the gastrointestinal tract, is composed of a diverse array of neuronal and glial cell subtypes. Fascinating questions surrounding the generation of cellular diversity in the ENS have captivated ENS biologists for a considerable time, particularly with recent advancements in cell type-specific transcriptomics at both population and single-cell levels. However, the current focus of research in this field is predominantly restricted to the study of enteric neuron subtypes, while the investigation of enteric glia subtypes significantly lags behind. Despite this, enteric glial cells (EGCs) are increasingly recognized as equally important regulators of numerous bowel functions. Moreover, a subset of postnatal EGCs exhibits remarkable plasticity and multipotency, distinguishing them as critical entities in the context of advancing regenerative medicine. In this review, we aim to provide an updated overview of the current knowledge on this subject, while also identifying key questions that necessitate future exploration.

The CHARGE syndrome-associated protein FAM172A controls AGO2 nuclear import

CHARGE syndrome is a neural crest-related disorder mainly caused by mutation of the chromatin remodeler-coding gene CHD7 Alternative causes include mutation of other chromatin and/or splicing factors. One of these additional players is the poorly characterized FAM172A, which we previously found in a complex with CHD7 and the small RNA-binding protein AGO2 at the chromatin-spliceosome interface. Focusing on the FAM172A-AGO2 interplay, we now report that FAM172A is a direct binding partner of AGO2 and, as such, one of the long sought-after regulators of AGO2 nuclear import. We show that this FAM172A function mainly relies on its classical bipartite nuclear localization signal and associated canonical importin-α/β pathway, being enhanced by CK2-induced phosphorylation and abrogated by a CHARGE syndrome-associated missense mutation. Overall, this study thus strengthens the notion that noncanonical nuclear functions of AGO2 and associated regulatory mechanisms might be clinically relevant.

Neural Crest Development in Health and Disease

The first volume of this Special Issue met its goal of covering several aspects regarding both the normal and abnormal development of neural crest cells, which form a truly unique multipotent and highly migratory cell population that only exists in vertebrates [...].

NR2F1 regulates a Schwann cell precursor-vs-melanocyte cell fate switch in a mouse model of Waardenburg syndrome type IV

Waardenburg syndrome type 4 (WS4) combines abnormal development of neural crest cell (NCC)-derived melanocytes (causing depigmentation and inner ear dysfunction) and enteric nervous system (causing aganglionic megacolon). The full spectrum of WS4 phenotype is present in Spot mice, in which an insertional mutation close to a silencer element leads to NCC-specific upregulation of the transcription factor-coding gene Nr2f1. These mice were previously found to develop aganglionic megacolon because of NR2F1-induced premature differentiation of enteric neural progenitors into enteric glia. Intriguingly, this prior work also showed that inner ear dysfunction in Spot mutants specifically affects balance but not hearing, consistent with the absence of melanocytes in the vestibule only. Here, we report an analysis of the effect of Nr2f1 upregulation on the development of both inner ear and skin melanocytes, also taking in consideration their origin relative to the dorsolateral and ventral NCC migration pathways. In the trunk, we found that NR2F1 overabundance in Spot NCCs forces dorso-laterally migrating melanoblasts to abnormally adopt a Schwann cell precursor (SCP) fate and conversely prevents ventrally migrating SCPs to normally adopt a melanoblast fate. In the head, Nr2f1 upregulation appears not to be uniform, which might explain why SCP-derived melanocytes do colonize the cochlea while non-SCP-derived melanocytes cannot reach the vestibule. Collectively, these data point to a key role for NR2F1 in the control of SCP-vs-melanocyte fate choice and unveil a new pathogenic mechanism for WS4. Moreover, our data argue against the proposed existence of a transit-amplifying compartment of melanocyte precursors in hair follicles.

CHARGE syndrome-associated proteins FAM172A and CHD7 influence male sex determination and differentiation through transcriptional and alternative splicing mechanisms

To gain further insight into chromatin‐mediated regulation of mammalian sex determination, we analyzed the role of the CHARGE syndrome‐associated proteins FAM172A and CHD7. This study is based on our prior discoveries that a subset of corresponding mutant mice display complete male‐to‐female sex reversal, and that both of these proteins regulate co‐transcriptional alternative splicing in neural crest cells. Here, we report that FAM172A and CHD7 are present in the developing gonads when sex determination normally occurs in mice. The interactome of FAM172A in pre‐Sertoli cells again suggests a role at the chromatin‐spliceosome interface, like in neural crest cells. Accordingly, analysis of Fam172a‐mutant pre‐Sertoli cells revealed transcriptional and splicing dysregulation of hundreds of genes. Many of these genes are similarly affected in Chd7‐mutant pre‐Sertoli cells, including several known key regulators of sex determination and subsequent formation of testis cords. Among them, we notably identified Sry as a direct transcriptional target and WNT pathway‐associated Lef1 and Tcf7l2 as direct splicing targets. The identified molecular defects are also associated with the abnormal morphology of seminiferous tubules in mutant postnatal testes. Altogether, our results thus identify FAM172A and CHD7 as new players in the regulation of male sex determination and differentiation in mice, and further highlight the importance of chromatin‐mediated regulatory mechanisms in these processes.

Chromatin remodeller CHD7 is required for GABAergic neuron development by promoting PAQR3 expression

Mutations in the chromatin remodeller‐coding gene CHD7 cause CHARGE syndrome (CS). CS features include moderate to severe neurological and behavioural problems, clinically characterized by intellectual disability, attention‐deficit/hyperactivity disorder and autism spectrum disorder. To investigate the poorly characterized neurobiological role of CHD7, we here generate a zebrafish chd7^−/− model. chd7^−/− mutants have less GABAergic neurons and exhibit a hyperactivity behavioural phenotype. The GABAergic neuron defect is at least in part due to downregulation of the CHD7 direct target gene paqr3b, and subsequent upregulation of MAPK/ERK signalling, which is also dysregulated in CHD7 mutant human cells. Through a phenotype‐based screen in chd7^−/− zebrafish and Caenorhabditis elegans, we show that the small molecule ephedrine restores normal levels of MAPK/ERK signalling and improves both GABAergic defects and behavioural anomalies. We conclude that chd7 promotes paqr3b expression and that this is required for normal GABAergic network development. This work provides insight into the neuropathogenesis associated with CHD7 deficiency and identifies a promising compound for further preclinical studies.

Treatment and Prevention of Neurocristopathies

Neurocristopathies form a heterogeneous group of rare diseases caused by abnormal development of neural crest cells. Heterogeneity of neurocristopathies directly relates to the nature of these migratory and multipotent cells, which generate dozens of specialized cell types throughout the body. Neurocristopathies are thus characterized by congenital malformations of tissues/organs that otherwise appear to have very little in common, such as the craniofacial skeleton and enteric nervous system. Treatment options are currently very limited, mainly consisting of corrective surgeries. Yet, as reviewed here, analyses of normal and pathological neural crest development in model organisms have opened up the possibility for better treatment options involving cellular and molecular approaches. These approaches provide hope that some neurocristopathies might soon be curable or preventable.

Vegetal diamine oxidase alleviates histamine-induced contraction of colonic muscles

Excess of histamine in gut lumen generates a pronounced gastrointestinal discomfort, which may include diarrhea and peristalsis dysfunctions. Deleterious effects of histamine can be alleviated with antihistamine drugs targeting histamine receptors. However, many antihistamine agents come with various undesirable side effects. Vegetal diamine oxidase (vDAO) might be a relevant alternative owing to its histaminase activity. Mammalian intestinal mucosa contains an endogenous DAO, yet possessing lower activity compared to that of vDAO preparation. Moreover, in several pathological conditions such as inflammatory bowel disease and irritable bowel syndrome, this endogenous DAO enzyme can be lost or inactivated. Here, we tested the therapeutic potential of vDAO by focusing on the well-known effect of histamine on gut motility. Using ex vivo and in vitro assays, we found that vDAO is more potent than commercial anti-histamine drugs at inhibiting histamine-induced contraction of murine distal colon muscles. We also identified pyridoxal 5′-phosphate (the biologically active form of vitamin B6) as an effective enhancer of vDAO antispasmodic activity. Furthermore, we discovered that rectally administered vDAO can be retained on gut mucosa and remain active. These observations make administration of vDAO in the gut lumen a valid alternative treatment for histamine-induced intestinal dysfunctions.

Dhh-expressing Schwann cell precursors contribute to skin and cochlear melanocytes, but not to vestibular melanocytes

For a long time, melanocytes were believed to be exclusively derived from neural crest cells migrating from the neural tube toward the developing skin. This notion was then challenged by studies suggesting that melanocytes could also be made from neural crest-derived Schwann cell precursors (SCPs) on peripheral nerves. A SCP origin was inferred from lineage tracing studies in mice using a Plp1 promoter-controlled Cre driver transgene (Plp1-CreERT2) and a fluorescent Rosa26 locus-controlled Cre reporter allele (Rosa26^FloxSTOP-YFP ). However, doubts were raised in part because another SCP-directed Cre driver controlled by the Dhh promoter (Dhh-Cre) was apparently unable to label melanocytes when used with a non-fluorescent Rosa26 locus-controlled Cre reporter (Rosa26^{FloxSTOP-LacZ} ). Here, we report that the same Dhh-Cre driver line can efficiently label melanocytes when used in a pure FVB/N background together with the fluorescent instead of the non-fluorescent Rosa26 locus-controlled Cre reporter. Our data further suggest that the vast majority of skin melanocytes are SCP-derived. Interestingly, we also discovered that SCPs contribute inner ear melanocytes in a region-specific manner, extensively contributing to the cochlea but not to the vestibule.

Glial Cell-Derived Neurotrophic Factor Induces Enteric Neurogenesis and Improves Colon Structure and Function in Mouse Models of Hirschsprung Disease

BACKGROUND & AIMS

Hirschsprung disease (HSCR) is a life-threatening birth defect in which the distal colon is devoid of enteric neural ganglia. HSCR is treated by surgical removal of aganglionic bowel, but many children continue to have severe problems after surgery. We studied whether administration of glial cell derived neurotrophic factor (GDNF) induces enteric nervous system regeneration in mouse models of HSCR.

METHODS

We performed studies with four mouse models of HSCR: Holstein (Hol^Tg/Tg, a model for trisomy 21-associated HSCR), TashT (TashT^Tg/Tg, a model for male-biased HSCR), Piebald-lethal (Ednrb^s-l//s-l, a model for EDNRB mutation-associated HSCR), and Ret^9/- (with aganglionosis induced by mycophenolate). Mice were given rectal enemas containing GDNF or saline (control) from postnatal days 4 through 8. We measured survival times of mice, and colon tissues were analyzed by histology, immunofluorescence, and immunoblots. Neural ganglia regeneration and structure, bowel motility, epithelial permeability, muscle thickness, and neutrophil infiltration were studied in colon tissues and in mice. Stool samples were collected, and microbiomes were analyzed by 16S rRNA gene sequencing. Time-lapse imaging and genetic cell-lineage tracing were used to identify a source of GDNF-targeted neural progenitors. Human aganglionic colon explants from children with HSCR were cultured with GDNF and evaluated for neurogenesis.

RESULTS

GDNF significantly prolonged mean survival times of Hol^Tg/Tg mice, Ednrb^s-l//s-l mice, and male TashT^Tg/Tg mice, compared with control mice, but not Ret^9/- mice (which had mycophenolate toxicity). Mice given GDNF developed neurons and glia in distal bowel tissues that were aganglionic in control mice, had a significant increase in colon motility, and had significant decreases in epithelial permeability, muscle thickness, and neutrophil density. We observed dysbiosis in fecal samples from Hol^Tg/Tg mice compared with feces from wild-type mice; fecal microbiomes of mice given GDNF were similar to those of wild-type mice except for Bacteroides. Exogenous luminal GDNF penetrated aganglionic colon epithelium of Hol^Tg/Tg mice, inducing production of endogenous GDNF, and new enteric neurons and glia appeared to arise from Schwann cells within extrinsic nerves. GDNF application to cultured explants of human aganglionic bowel induced proliferation of Schwann cells and formation of new neurons.

CONCLUSIONS

GDNF prolonged survival, induced enteric neurogenesis, and improved colon structure and function in 3 mouse models of HSCR. Application of GDNF to cultured explants of aganglionic bowel from children with HSCR induced proliferation of Schwann cells and formation of new neurons. GDNF might be developed for treatment of HSCR.

Male-biased aganglionic megacolon in the TashT mouse model of Hirschsprung disease involves upregulation of p53 protein activity and Ddx3y gene expression

Hirschsprung disease (HSCR) is a complex genetic disorder of neural crest development resulting in incomplete formation of the enteric nervous system (ENS). This life-threatening neurocristopathy affects 1/5000 live births, with a currently unexplained male-biased ratio. To address this lack of knowledge, we took advantage of the TashT mutant mouse line, which is the only HSCR model to display a robust male bias. Our prior work revealed that the TashT insertional mutation perturbs a Chr.10 silencer-enriched non-coding region, leading to transcriptional dysregulation of hundreds of genes in neural crest-derived ENS progenitors of both sexes. Here, through sex-stratified transcriptome analyses and targeted overexpression in ENS progenitors, we show that male-biased ENS malformation in TashT embryos is not due to upregulation of Sry-the murine ortholog of a candidate gene for the HSCR male bias in humans-but instead involves upregulation of another Y-linked gene, Ddx3y. This discovery might be clinically relevant since we further found that the DDX3Y protein is also expressed in the ENS of a subset of male HSCR patients. Mechanistically, other data including chromosome conformation captured-based assays and CRISPR/Cas9-mediated deletions suggest that Ddx3y upregulation in male TashT ENS progenitors is due to increased transactivation by p53, which appears especially active in these cells yet without triggering apoptosis. Accordingly, in utero treatment of TashT embryos with the p53 inhibitor pifithrin-α decreased Ddx3y expression and abolished the otherwise more severe ENS defect in TashT males. Our data thus highlight novel pathogenic roles for p53 and DDX3Y during ENS formation in mice, a finding that might help to explain the intriguing male bias of HSCR in humans.

Phosphorylation of GATA4 serine 105 but not serine 261 is required for testosterone production in the male mouse

BACKGROUND

GATA4 is a transcription factor essential for male sex determination, testicular differentiation during fetal development, and male fertility in the adult. GATA4 exerts part of its function by regulating multiple genes in the steroidogenic enzyme pathway. In spite of these crucial roles, how the activity of this factor is regulated remains unclear.

OBJECTIVES

Studies in gonadal cell lines have shown that GATA4 is phosphorylated on at least two serine residues-serine 105 (S105) and serine 261 (S261)-and that this phosphorylation is important for GATA4 activity. The objective of the present study is to characterize the endogenous role of GATA4 S105 and S261 phosphorylation in the mouse testis.

MATERIALS AND METHODS

We examined both previously described GATA4 S105A mice and a novel GATA4 S261A knock-in mouse that we generated by CRISPR/Cas9 gene editing. The male phenotype of the mutants was characterized by assessing androgen-dependent organ weights, hormonal profiles, and expression of multiple testicular target genes using standard biochemical and molecular biology techniques.

RESULTS

The fecundity of crosses between GATA4 S105A mice was reduced but without a change in sex ratio. The weight of androgen-dependent organs was smaller when compared to wild-type controls. Plasma testosterone levels showed a 70% decrease in adult GATA4 S105A males. This decrease was associated with a reduction in Cyp11a1, Cyp17a1, and Hsd17b3 expression. GATA4 S261A mice were viable and testis morphology appeared normal. Testosterone production and steroidogenic enzyme expression were not altered in GATA4 S261A males.

DISCUSSION AND CONCLUSION

Our analysis showed that blocking GATA4 S105 phosphorylation is associated with decreased androgen production in males. In contrast, S261 phosphorylation by itself is dispensable for GATA4 function. These results confirm that endogenous GATA4 action is essential for normal steroid production in males and that this activity requires phosphorylation on at least one serine residue.

Molecular dissection of CHARGE syndrome highlights the vulnerability of neural crest cells to problems with alternative splicing and other transcription-related processes

CHARGE syndrome is characterized by co-occurrence of multiple malformations due to abnormal development of neural crest cells. Here, we review the phenotypic and molecular overlap between CHARGE syndrome and similar pathologies, and further discuss the observation that neural crest cells appear especially sensitive to malfunction of the chromatin-transcription-splicing molecular hub.

HLX is a candidate gene for a pattern of anomalies associated with congenital diaphragmatic hernia, short bowel, and asplenia

Isolated congenital diaphragmatic hernia is often a sporadic event with a low recurrence risk. However, underlying genetic etiologies, such as chromosome anomalies or single gene disorders, are identified in a small number of individuals. We describe two fetuses with a unique pattern of multiple congenital anomalies, including diaphragmatic hernia, short bowel and asplenia, born to first-cousin parents. Whole exome sequencing showed that both were homozygous for a missense variant, c.950A>C, predicting p.Asp317Ala, in the H.20-Like Homeobox 1 (HLX1) gene. HLX is a homeobox transcription factor gene which is relatively conserved across species. Hlx homozygous null mice have a short bowel and reduced muscle cells in the diaphragm, closely resembling the anomalies in the two fetuses and we therefore suggest that the HLX mutation in this family could explain the fetal findings.

Toward a better understanding of enteric gliogenesis

Most of gastrointestinal functions are controlled by the enteric nervous system (ENS), which contains a vast diversity of neurons and glial cells. In accordance with its key role, defective ENS formation is the cause of several diseases that affect quality of life and can even be life-threatening. Treatment of these diseases would greatly benefit from a better understanding of the molecular mechanisms underlying ENS formation. In this regard, although several important discoveries have been made over the years, how the full spectrum of enteric neuronal and glial cell subtypes is generated from neural crest cells during development still remains enigmatic. Because they also have stem cell properties, such knowledge would be especially important for the enteric glial cell lineage. In a recent study, we identified the NR2F1 transcription factor as a new key regulator of enteric gliogenesis. Here we discuss our recent findings and briefly review what is already known about the mechanisms and signaling pathways involved in enteric gliogenesis, with an emphasis on Hedgehog and Notch signaling.

Male-specific colon motility dysfunction in the TashT mouse line

BACKGROUND

In Hirschsprung disease (HSCR), the absence of myenteric neural ganglia in the distal bowel prevents motility and thereby causes functional intestinal obstruction. Although surgical resection of the aganglionic segment allows HSCR children to survive this condition, a number of patients still suffer from impaired motility despite having myenteric ganglia in their postoperative distal bowel. Such phenomenon is also observed in patients suffering from other enteric neuropathies and, in both cases, colonic dysmotility is believed to result from abnormalities of myenteric ganglia and/or associated interstitial cells of Cajal (ICC). To better understand this, we used a recently described HSCR mouse model called TashT.

METHODS

Intestinal motility parameters were assessed and correlated with extent of aganglionosis and with neuronal density in ganglionated regions. The neural composition of the myenteric plexus and the status of ICC networks was also evaluated using immunofluorescence.

KEY RESULTS

TashT(Tg/Tg) mice display a strong male bias in the severity of both colonic aganglionosis and hypoganglionosis, which are associated with male-specific reduced colonic motility. TashT(Tg/Tg) male mice also exhibit a specific increase in nNos(+) neurons that is restricted to the most distal ganglionated regions. In contrast, Calretinin(+) myenteric neurons, Sox10(+) myenteric glial cells, and cKit(+) ICC are not affected in TashT(Tg/Tg) mice.

CONCLUSIONS AND INFERENCES

Male-specific impairment of colonic motility in TashT(Tg/Tg) mice is associated with both severe hypoganglionosis and myenteric neuronal imbalance. Considering these parameters in the clinic might be important for the management of postoperative HSCR patients.

Upregulation of the Nr2f1-A830082K12Rik gene pair in murine neural crest cells results in a complex phenotype reminiscent of Waardenburg syndrome type 4

Waardenburg syndrome is a neurocristopathy characterized by a combination of skin and hair depigmentation, and inner ear defects. In the type 4 form, these defects show comorbidity with Hirschsprung disease, a disorder marked by an absence of neural ganglia in the distal colon, triggering functional intestinal obstruction. Here, we report that the Spot mouse line - obtained through an insertional mutagenesis screen for genes involved in neural crest cell (NCC) development - is a model for Waardenburg syndrome type 4. We found that the Spot insertional mutation causes overexpression of an overlapping gene pair composed of the transcription-factor-encoding Nr2f1 and the antisense long non-coding RNA A830082K12Rik in NCCs through a mechanism involving relief of repression of these genes. Consistent with the previously described role of Nr2f1 in promoting gliogenesis in the central nervous system, we further found that NCC-derived progenitors of the enteric nervous system fail to fully colonize Spot embryonic guts owing to their premature differentiation in glial cells. Taken together, our data thus identify silencer elements of the Nr2f1-A830082K12Rik gene pair as new candidate loci for Waardenburg syndrome type 4.

A direct role for murine Cdx proteins in the trunk neural crest gene regulatory network

Numerous studies in chordates and arthropods currently indicate that Cdx proteins have a major ancestral role in the organization of post-head tissues. In urochordate embryos, Cdx loss-of-function has been shown to impair axial elongation, neural tube (NT) closure and pigment cell development. Intriguingly, in contrast to axial elongation and NT closure, a Cdx role in neural crest (NC)-derived melanocyte/pigment cell development has not been reported in any other chordate species. To address this, we generated a new conditional pan-Cdx functional knockdown mouse model that circumvents Cdx functional redundancy as well as the early embryonic lethality of Cdx mutants. Through directed inhibition in the neuroectoderm, we provide in vivo evidence that murine Cdx proteins impact melanocyte and enteric nervous system development by, at least in part, directly controlling the expression of the key early regulators of NC ontogenesis Pax3,Msx1 and Foxd3 Our work thus reveals a novel role for Cdx proteins at the top of the trunk NC gene regulatory network in the mouse, which appears to have been inherited from their ancestral ortholog.

Pigmentation-based insertional mutagenesis is a simple and potent screening approach for identifying neurocristopathy-associated genes in mice

Neurocristopathies form a specific group of rare genetic diseases in which a defect in neural crest cell development is causal. Because of the large number of neural crest cell derivatives, distinct structures/cell types (isolated or in combination) are affected in each neurocristopathy. The most important issues in this research field is that the underlying genetic cause and associated pathogenic mechanism of most cases of neurocristopathy are poorly understood. This article describes how a relatively simple insertional mutagenesis approach in the mouse has proved useful for identifying new candidate genes and pathogenic mechanisms for diverse neurocristopathies.

A collagen VI-dependent pathogenic mechanism for Hirschsprung's disease

Hirschsprung's disease (HSCR) is a severe congenital anomaly of the enteric nervous system (ENS) characterized by functional intestinal obstruction due to a lack of intrinsic innervation in the distal bowel. Distal innervation deficiency results from incomplete colonization of the bowel by enteric neural crest cells (eNCCs), the ENS precursors. Here, we report the generation of a mouse model for HSCR--named Holstein--that contains an untargeted transgenic insertion upstream of the collagen-6α4 (Col6a4) gene. This insertion induces eNCC-specific upregulation of Col6a4 expression that increases total collagen VI protein levels in the extracellular matrix (ECM) surrounding both the developing and the postnatal ENS. Increased collagen VI levels during development mainly result in slower migration of eNCCs. This appears to be due to the fact that collagen VI is a poor substratum for supporting eNCC migration and can even interfere with the migration-promoting effects of fibronectin. Importantly, for a majority of patients in a HSCR cohort, the myenteric ganglia from the ganglionated region are also specifically surrounded by abundant collagen VI microfibrils, an outcome accentuated by Down syndrome. Collectively, our data thus unveil a clinically relevant pathogenic mechanism for HSCR that involves cell-autonomous changes in ECM composition surrounding eNCCs. Moreover, as COL6A1 and COL6A2 are on human Chr.21q, this mechanism is highly relevant to the predisposition of patients with Down syndrome to HSCR.

Male-biased aganglionic megacolon in the TashT mouse line due to perturbation of silencer elements in a large gene desert of chromosome 10

Neural crest cells (NCC) are a transient migratory cell population that generates diverse cell types such as neurons and glia of the enteric nervous system (ENS). Via an insertional mutation screen for loci affecting NCC development in mice, we identified one line—named TashT—that displays a partially penetrant aganglionic megacolon phenotype in a strong male-biased manner. Interestingly, this phenotype is highly reminiscent of human Hirschsprung’s disease, a neurocristopathy with a still unexplained male sex bias. In contrast to the megacolon phenotype, colonic aganglionosis is almost fully penetrant in homozygous TashT animals. The sex bias in megacolon expressivity can be explained by the fact that the male ENS ends, on average, around a “tipping point” of minimal colonic ganglionosis while the female ENS ends, on average, just beyond it. Detailed analysis of embryonic intestines revealed that aganglionosis in homozygous TashT animals is due to slower migration of enteric NCC. The TashT insertional mutation is localized in a gene desert containing multiple highly conserved elements that exhibit repressive activity in reporter assays. RNAseq analyses and 3C assays revealed that the TashT insertion results, at least in part, in NCC-specific relief of repression of the uncharacterized gene Fam162b; an outcome independently confirmed via transient transgenesis. The transcriptional signature of enteric NCC from homozygous TashT embryos is also characterized by the deregulation of genes encoding members of the most important signaling pathways for ENS formation—Gdnf/Ret and Edn3/Ednrb—and, intriguingly, the downregulation of specific subsets of X-linked genes. In conclusion, this study not only allowed the identification of Fam162b coding and regulatory sequences as novel candidate loci for Hirschsprung’s disease but also provides important new insights into its male sex bias.

Hirschsprung’s disease (also known as aganglionic megacolon) is a severe congenital defect of the enteric nervous system (ENS) resulting in complete failure to pass stools. It is characterized by the absence of neural ganglia (aganglionosis) in the distal gut due to incomplete colonization of the embryonic intestines by neural crest cells (NCC), the ENS precursors. Hirschsprung’s disease has an incidence of 1 in 5000 newborns and a 4:1 male sex bias. Although many genes have been associated with this complex genetic disease, most of its heritability as well as its male sex bias remain unexplained. Here, we describe an insertional mutant mouse line (“TashT”) in which virtually all homozygotes display colonic aganglionosis due to defective migration of enteric NCC, but in which only a subset of homozygotes develops megacolon. Surprisingly, this group is almost exclusively male. The TashT ENS defect stems, at least in part, from the disruption of long-range interactions between evolutionarily conserved elements with silencer activity and Fam162b, resulting in NCC-specific upregulation of this uncharacterized protein coding gene. Global analysis of gene expression further revealed that several hundreds of genes are significantly deregulated in TashT enteric NCC. Interestingly, this dataset includes multiple X-linked candidate genes potentially underlying the male sex bias. Taken together, our data pave the way for a clearer understanding of the intriguing male sex bias of Hirschsprung’s disease.

[Transition in kidney transplantation]

Transition from pediatric to adult care in renal transplantation has emerged as a critical step in the life of a young kidney recipient. During this phase, young patients are faced with the physiological and psychological changes associated with adolescence that can lead to non-compliance and potentially graft loss. To date, there is not a unique accepted model of transition, however it has been proved that the presence of a multidisciplinary team including specialists in adolescent management and in the transition from pediatric to adult transplant care is beneficial during this at-risk phase. The goal of this team is to ensure a progressive transition of the patients according to a precise plan and time line.

[Factors influencing the return to work after transplantation in 61 renal or liver recipient]

The rate of return to work after transplantation is generally low, however this improves the quality of life of recipients. The aim of our study was to investigate the low rate after transplantation in 61 renal or liver patients followed at the Transplant Center (CTO) of the CHUV in Lausanne, and to analyse the occupational, individual and medical factors which may influence it. 39% of recipients returned to work after transplantation. The factors <being active pre-transplant), <with diploma> and <age <45 years olds were significantly related to return to work. In conclusion, knowledge of the factors influencing return to work after transplantation are important for medical practice, in order to propose early medico-socio-professional measures in order to maintain workability.

Induction and dorsal restriction of Paired-box 3 (Pax3) gene expression in the caudal neuroectoderm is mediated by integration of multiple pathways on a short neural crest enhancer

Pax3 encodes a paired-box transcription factor with key roles in neural crest and neural tube ontogenesis. Robust control of Pax3 neural expression is ensured by two redundant sets of cis-regulatory modules (CRMs) that integrate anterior-posterior (such as Wnt-βCatenin signaling) as well as dorsal-ventral (such as Shh-Gli signaling) instructive cues. In previous work, we sought to characterize the Wnt-mediated regulation of Pax3 expression and identified the Cdx transcription factors (Cdx1/2/4) as critical intermediates in this process. We identified the neural crest enhancer-2 (NCE2) from the 5'-flanking region of Pax3 as a Cdx-dependent CRM that recapitulates the restricted expression of Pax3 in the mouse caudal neuroectoderm. While this is consistent with a key role in relaying the inductive signal from posteriorizing Wnt ligands, the broad expression of Cdx proteins in the tailbud region is not consistent with the restricted activity of NCE2. This implies that other positive and/or negative inputs are required and, here, we report a novel role for the transcription factor Zic2 in this regulation. Our data strongly suggests that Zic2 is involved in the induction (as a direct Pax3NCE2 activator and Cdx neural cofactor) as well as the maintenance of Pax3 dorsal restriction (as a target of the ventral Shh repressive input). We also provide evidence that the inductive Cdx-Zic2 interaction is integrated on NCE2 with a positive input from the neural-specific transcription factor Sox2. Altogether, our data provide important mechanistic insights into the coordinated integration of different signaling pathways on a short Pax3 CRM.

A quantitative cell migration assay for murine enteric neural progenitors

Neural crest cells (NCC) are a transient and multipotent cell population that originates from the dorsal neural tube and migrates extensively throughout the developing vertebrate embryo. In addition to providing peripheral glia and neurons, NCC generate melanocytes as well as most of the cranio-facial skeleton. NCC migration and differentiation is controlled by a combination of their axial origin along the neural tube and their exposure to regionally distinct extracellular cues. Such contribution of extracellular ligands is especially evident during the formation of the enteric nervous system (ENS), a complex interconnected network of neural ganglia that locally controls (among other things) gut muscle movement and intestinal motility. Most of the ENS is derived from a small initial pool of NCC that undertake a long journey in order to colonize - in a rostral to caudal fashion - the entire length of the prospective gut. Among several signaling pathways known to influence enteric NCC colonization, GDNF/RET signaling is recognized as the most important. Indeed, spatiotemporally controlled secretion of the RET ligand GDNF by the gut mesenchyme is chiefly responsible for the attraction and guidance of RET-expressing enteric NCC to and within the embryonic gut. Here, we describe an ex vivo cell migration assay, making use of a transgenic mouse line possessing fluorescently labeled NCC, which allows precise quantification of enteric NCC migration potential in the presence of various growth factors, including GDNF.

Characterization of a novel transgenic mouse line expressing Cre recombinase under the control of the Cdx2 neural specific enhancer

Several genetically modified mouse models have been generated in order to drive expression of the Cre recombinase in the neuroectoderm. However, none of them specifically targets the posterior neural plate during neurulation. To fill this gap, we have generated a new transgenic mouse line in which Cre expression is controlled by a neural specific enhancer (NSE) from the Caudal-related homeobox 2 (Cdx2) locus. Analyses of Cre activity via breeding with R26R-YFP reporter mice have indicated that the Cdx2NSE-Cre mouse line allows for recombination of LoxP sites in most cells of the posterior neural plate as soon as from the head fold stage. Detailed examination of double-transgenic embryos has revealed that this novel Cre-driver line allows targeting the entire posterior neural tube with an anterior limit in the caudal hindbrain. Of note, the Cdx2NSE regulatory sequences direct Cre expression along the whole dorso-ventral axis (including pre-migratory neural crest cells) and, accordingly, YFP fluorescence has been also observed in multiple non-cranial neural crest derivatives of double-transgenic embryos. Therefore, we believe that the Cdx2NSE-Cre mouse line represents an important novel genetic tool for the study of early events occurring in the caudal neuroectoderm during the formation of both the central and the peripheral nervous systems.

The developmental genetics of Hirschsprung's disease

Hirschsprung's disease (HSCR), also known as aganglionic megacolon, derives from a congenital malformation of the enteric nervous system (ENS). It displays an incidence of 1 in 5000 live births with a 4:1 male to female sex ratio. Clinical signs include severe constipation and distended bowel due to a non-motile colon. If left untreated, aganglionic megacolon is lethal. This severe congenital condition is caused by the absence of colonic neural ganglia and thus lack of intrinsic innervation of the colon due in turn to improper colonization of the developing intestines by ENS progenitor cells. These progenitor cells are derived from a transient stem cell population called neural crest cells (NCC). The genetics of HSCR is complex and can involve mutations in multiple genes. However, it is estimated that mutations in known genes account for less than half of the cases of HSCR observed clinically. The male sex bias is currently unexplained. The objective of this review is to provide an overview of the pathophysiology and genetics of HSCR, within the context of our current knowledge of NCC development, sex chromosome genetics and laboratory models.

Transgenic mouse analysis of Sry expression during the pre- and peri-implantation stage

BACKGROUND

The SRY/Sry gene is expressed in pre-Sertoli cells of the male genital ridge and functions as the mammalian testis determining factor (TDF). In addition, expression of SRY/Sry outside the genital ridge has been reported, including preimplantation embryos, although the functional significance of this is not well understood.

RESULTS

Using Cre-mediated lineage studies and transgenic reporter mouse models, we now show that promoter sequences of human, pig and mouse SRY drive robust reporter gene expression in epiblast cells of peri-implantation embryos between embryonic day (E) 4.5 and E6.5. Analysis of endogenous Sry expression revealed that linear transcripts are produced by means of multiple polyadenylation sites in E4.5 embryos. Within the epiblast, SRY reporter expression mimics the expression seen using a Gata4 reporter model, but is dissimilar to that seen using an Oct4 reporter model. In addition, we report that overexpression of mouse Sry in embryonic stem cells leads to down-regulation of the core pluripotency markers Sox2 and Nanog.

CONCLUSION

We propose that SRY/Sry may function as a male-specific maturation factor in the peri-implantation mammalian embryo, providing a genetic mechanism to help explain the observation that male embryos are developmentally more advanced compared with female embryos, and suggesting a role for SRY beyond that of TDF.

Caudal-related homeobox (Cdx) protein-dependent integration of canonical Wnt signaling on paired-box 3 (Pax3) neural crest enhancer

One of the earliest events in neural crest development takes place at the neural plate border and consists in the induction of Pax3 expression by posteriorizing Wnt·β-catenin signaling. The molecular mechanism of this regulation is not well understood, but several observations suggest a role for posteriorizing Cdx transcription factors (Cdx1/2/4) in this process. Cdx genes are known as integrators of posteriorizing signals from Wnt, retinoic acid, and FGF pathways. In this work, we report that Wnt-mediated regulation of murine Pax3 expression is indirect and involves Cdx proteins as intermediates. We show that Pax3 transcripts co-localize with Cdx proteins in the posterior neurectoderm and that neural Pax3 expression is reduced in Cdx1-null embryos. Using Wnt3a-treated P19 cells and neural crest-derived Neuro2a cells, we demonstrate that Pax3 expression is induced by the Wnt-Cdx pathway. Co-transfection analyses, electrophoretic mobility shift assays, chromatin immunoprecipitation, and transgenic studies further indicate that Cdx proteins operate via direct binding to an evolutionarily conserved neural crest enhancer of the Pax3 proximal promoter. Taken together, these results suggest a novel neural function for Cdx proteins within the gene regulatory network controlling neural crest development.

An Ebox element in the proximal Gata4 promoter is required for Gata4 expression in vivo

GATA4 is an essential transcription factor required for the development and function of multiple tissues, including a major role in gonadogenesis. Despite its crucial role, the molecular mechanisms that regulate Gata4 expression in vivo remain poorly understood. We recently found that the Gata4 gene is expressed as multiple transcripts with distinct 5′ origins. These co-expressed alternative transcripts are generated by different non-coding first exons with transcripts E1a and E1b being the most prominent. Moreover, we previously showed that an Ebox element, located in Gata4 5′ flanking sequences upstream of exon 1a, is important for the promoter activity of these sequences in cell lines. To confirm the importance of this element in vivo, we generated and characterized Gata4 Ebox knockout mice. Quantitative PCR analyses realized on gonads, heart and liver at three developmental stages (embryonic, pre-pubertal and adult) revealed that the Ebox mutation leads to a robust and specific decrease (up to 89%) of Gata4 E1a transcript expression in all tissues and stages examined. However, a detailed characterization of the gonads revealed normal morphology and GATA4 protein levels in these mutants. Our qPCR data further indicate that this outcome is most likely due to the presence of Gata4 E1b mRNA, whose expression levels were not decreased by the Ebox mutation. In conclusion, our work clearly confirms the importance of the proximal Ebox element and suggests that adequate GATA4 protein expression is likely protected by a compensation mechanism between Gata4 E1a and E1b transcripts operating at the translational level.

Novel pre- and post-gastrulation expression of Gata4 within cells of the inner cell mass and migratory neural crest cells

GATA4 is a transcription factor known to be important for the development of many organs such as the heart, intestine, and gonads. However, information regarding the control of its expression is only now beginning to emerge. To further understand the regulation of Gata4 expression during mouse embryonic development, we have generated a novel knockin allele allowing expression of the Cre recombinase under the control of Gata4 regulatory sequences. When these Gata4(Cre/+) mice were crossed with the Cre reporter mouse R26R-YFP, we surprisingly found widespread mosaic YFP expression in e10.0 embryos. This particular expression pattern was traced back to the e5.5 stage via a cell lineage study, suggesting activation of transcription at the Gata4 locus around the blastocyst stage. In accordance with this hypothesis, we found that Gata4 is expressed in cultured embryonic stem (ES) cells and within the inner cell mass (ICM) of e4.5 blastocysts. Interestingly, such early Gata4 transcription can be recapitulated in transgenic reporter studies using 5 kb of the proximal rat Gata4 promoter. During mouse development, these 5-kb regulatory sequences were previously reported to direct reporter gene expression to Sertoli cells of the testes [Mazaud Guittot et al. (2007) Biol Reprod 76:85-95]. We now show that these regulatory sequences can also drive robust fluorescent reporter gene expression in migratory neural crest cells. Comparisons to Wnt1-Cre-mediated YFP labelling of neural crest cells suggest that most of the migratory neural crest cells are labelled in e9.5 to e11.5 Gata4p[5kb]-RFP or -GFP embryos. Analysis of GFP transcription via whole-mount in situ hybridization in e10.5 and e11.5 embryos demonstrated that the 5-kb Gata4 promoter is preferentially active in cells of the boundary caps at the dorsal root entry zone and motor exit points flanking the neural tube. RT-PCR gene expression analysis of FACS-purified GFP-positive cells from e9.5 Gata4p[5kb]-GFP embryos revealed co-expression of Gata4 with many neural crest stem cell markers. Together with sphere-forming and differentiation cell culture assays, our results indicate that the Gata4 promoter is active within at least a subset of the neural crest stem cells. Taken altogether, our studies have revealed new Gata4 expression patterns during mouse embryonic development, which are controlled by its 5-kb proximal 5' flanking sequences.

[Prevalence of undernutrition in 143 patients before liver transplantation. The Lausanne experience between 1997 and 2005]

The prevalence of undernutrition was prospectively studied in 143 patients before liver transplantation between 1997 and 2005. Nutritional assessment is a particularly tricky problem in cirrhosis and mid-arm muscle circumference is considered as the best reliable anthropometric tool. In this prospective study, prevalence rate is very high (61%) and undernutrition is more frequent in alcoholic cirrhotic patients. In conclusion, these patients should benefit from an early dietician intervention before liver transplantation.

Presumptive pre-Sertoli cells express genes involved in cell proliferation and cell signalling during a critical window in early testis differentiation

In mammals, the pre-Sertoli cell of the male genital ridge is the first cell type to display sex specific differentiation and differential gene expression. The genetic cascade driving the differentiation of pre-Sertoli cells and ultimately testis formation is beginning to be unravelled, but many questions remain. A better understanding of the transcriptome of pre-Sertoli cells immediately after sex determination is essential in order to further understand this differentiation process. A mouse model expressing Red Fluorescent Protein (RFP) under the control of a hybrid mouse/pig SRY promoter (HybSRYp-RFP) was used to purify cells from embryonic day 12.0 (e12.0) male genital ridges. To compare the transcriptomes of HybSRYp-RFP cell populations versus age matched whole female genital ridges, RNA was extracted and used to generate molecular probes that were hybridized onto Affymetrix Mouse Genome 430 2.0 micro-arrays. The expression of genes considered markers for pre-Sertoli cells, including Sox9, Mis, Dhh and Fgf9 were identified within the HybSRYp-RFP expressing cell population, while markers for germ cells (Oct4, SSEA-1) and endothelial cells (Ntrk3) were not identified. In contrast, markers for ovarian somatic cell expression, including Fst and Bmp2, were identified as overexpressed within the ovarian cell population. In a general fashion, genes identified as 2.5-fold over expressed in HybSRYp-RFP expressing cells coded notably for cell signalling and extra cellular proteins. The expression of Sox10, Stc2, Fgf18, Fgf13 and Wnt6 were further characterized via whole mount in situ hybridization (WISH) on male and female genital ridges between e11.5 and e14.5. Sox10, Fgf18, Fgf13 and Stc2 gene expression was detected within the male genital ridges while Wnt6 was found diffusely within both the male and female genital ridges. These data represent the earliest comprehensive microarray expression analysis of purified presumptive pre-Sertoli cells available to date.

Wnt signaling is a key mediator of Cdx1 expression in vivo

In the mouse, Cdx1 is essential for normal anteroposterior vertebral patterning through regulation of a subset of Hox genes. Retinoic acid (RA) and certain Wnts have also been implicated in vertebral patterning, although the relationship between these signaling pathways and the regulation of mesodermal Hox gene expression is not fully understood. Prior work has shown that Cdx1 is a direct target of both Wnt and retinoid signaling pathways,and might therefore act to relay these signals to the Hox genes. Wnt and RA are believed to impact on Cdx1 through an atypical RA-response element (RARE) and Lef/Tcf-response elements (LRE), respectively, in the proximal promoter. To address the roles of these regulatory motifs and pathways, we derived mice mutated for the LRE or the LRE plus the RARE. In contrast to RARE-null mutants, which exhibit limited vertebral defects,LRE-null and LRE+RARE-null mutants exhibited vertebral malformations affecting the entire cervical region that closely phenocopied the malformations seen in Cdx1-null mutants. Mutation of the LRE also greatly reduced induction of Cdx1 by RA, demonstrating a requirement for Wnt signaling in the regulation of this gene by retinoids. LRE and LRE+RARE mutants also exhibited vertebral fusions, suggesting a defect in somitogenesis. As Wnt signaling is implicated in somitogenesis upstream of the Notch pathway, it is conceivable that Cdx1 might play a role in this process. However, none of the Notch pathway genes assessed was overtly affected.

The proximal Gata4 promoter directs reporter gene expression to sertoli cells during mouse gonadal development

The GATA4 transcription factor is an important developmental determinant for many organs, such as the heart, gut, and testis. Despite this pivotal role, our understanding of the transcriptional mechanisms that control the proper spatiotemporal expression of the GATA4 gene remains limited. We have generated transgenic mice expressing a green fluorescent protein (GFP) marker under the control of rat Gata4 5' flanking sequences. Several GATA4-expressing organs displayed GFP fluorescence, including the heart, intestine, and pancreas. In the gonads, while GATA4 is expressed in pregranulosa, granulosa, and theca ovarian cells, and Sertoli, Leydig, and peritubular testicular cells, the first 5 kb of Gata4 regulatory sequences immediately upstream of exon 1 were sufficient to direct GFP reporter expression only in testis and, specifically, in Sertoli cells. Onset of GFP expression occurred after Sertoli cell commitment and was maintained in these cells throughout development to adulthood. In vitro studies revealed that the first 118 bp of the Gata4 promoter is sufficient for full basal activity in several GATA4-expressing cell lines. Promoter mutagenesis and DNA-binding experiments identified two GC-box motifs and, particularly, one E-box element within this -118-bp region that are crucial for its activity. Further analysis revealed that members of the USF family of transcription factors, especially USF2, bind to and activate the Gata4 promoter via this critical E-box motif.

Human and pigSRY 5′ flanking sequences can direct reporter transgene expression to the genital ridge and to migrating neural crest cells

Mechanisms for sex determination vary greatly between animal groups, and include chromosome dosage and haploid-diploid mechanisms as seen in insects, temperature and environmental cues as seen in fish and reptiles, and gene-based mechanisms as seen in birds and mammals. In eutherian mammals, sex determination is genetic, and SRY is the Y chromosome located gene representing the dominant testes determining factor. How SRY took over this function from ancestral mechanisms is not known, nor is it known what those ancestral mechanisms were. What is known is that SRY is haploid and thus poorly protected from mutations, and consequently is poorly conserved between mammalian species. To functionally compare SRY promoter sequences, we have generated transgenic mice with fluorescent reporter genes under the control of various lengths of human and pig SRY 5' flanking sequences. Human SRY 5' flanking sequences (5 Kb) supported reporter transgene expression within the genital ridge of male embryos at the time of sex determination and also supported expression within migrating truncal neural crest cells of both male and female embryos. The 4.6 Kb of pig SRY 5' flanking sequences supported reporter transgene expression within the male genital ridge but not within the neural crest; however, 2.6 Kb and 1.6 Kb of pig SRY 5' flanking sequences retained male genital ridge expression and now supported extensive expression within cells of the neural crest in embryos of both sexes. When 2 Kb of mouse SRY 5' flanking sequences (-3 to -1 Kb) were placed in front of the 1.6 Kb of pig SRY 5' flanking sequences and this transgene was introduced into mice, reporter transgene expression within the male genital ridge was retained but neural crest expression was lost. These observations suggest that SRY 5' flanking sequences from at least two mammalian species contain elements that can support transgene expression within cells of the migrating neural crest and that additional SRY 5' flanking sequences can extinguish this expression.

Cdx4 is a direct target of the canonical Wnt pathway

There is considerable evidence that the Cdx gene products impact on vertebral patterning by direct regulation of Hox gene expression. Data from a number of vertebrate model systems also suggest that Cdx1, Cdx2 and Cdx4 are targets of caudalizing signals such as RA, Wnt and FGF. These observations have lead to the hypothesis that Cdx members serve to relay information from signaling pathways involved in posterior patterning to the Hox genes. Regulation of Cdx1 expression by RA and Wnt in the mouse has been well characterized; however, the means by which Cdx2 and Cdx4 are regulated is less well understood. In the present study, we present data suggesting that Cdx4 is a direct target of the canonical Wnt pathway. We found that Cdx4 responds to exogenous Wnt3a in mouse embryos ex vivo, and conversely, that its expression is down-regulated in Wnt3a(vt/vt) embryos and in embryos cultured in the presence of Wnt inhibitors. We also found that the Cdx4 promoter responds to Wnt signaling in P19 embryocarcinoma cells and have identified several putative LEF/TCF response elements mediating this effect. Consistent with these data, chromatin immunoprecipitation assays from either embryocarcinoma cells or from the tail bud of embryos revealed that LEF1 and beta-catenin co-localize with the Cdx4 promoter. Taken together, these results suggest that Cdx4, like Cdx1, is a direct Wnt target.

Cdx1 autoregulation is governed by a novel Cdx1-LEF1 transcription complex

The Cdx1 gene product is essential for normal anterior-posterior vertebral patterning. Expression of Cdx1 is regulated by several pathways implicated in anterior-posterior patterning events, including retinoid and Wnt signaling. We have previously shown that retinoic acid plays a key role in early stages of Cdx1 expression at embryonic day 7.5 (E7.5), while both Wnt3a signaling and an autoregulatory loop, dependent on Cdx1 itself, are involved in later stages of expression (E8.5 to E9.5). This autoregulation is reflected by the ability of Cdx1 to affect expression from proximal Cdx1 promoter sequences in tissue culture. However, this region is devoid of a demonstrable Cdx response element(s). We have now found that Cdx1 and LEF1, a nuclear effector of Wnt signaling, synergize to induce expression from the Cdx1 promoter through previously documented LEF/T-cell factor response elements. We also found a direct physical interaction between the homeodomain of Cdx1 and the B box of LEF1, suggesting a basis for this synergy. Consistent with these observations, analysis of Cdx1 Wnt3a(vt) compound mutants demonstrated that Wnt and Cdx1 converged on Cdx1 expression and vertebral patterning in vivo. Further data suggest that Cdx-high-mobility group box interactions might be involved in a number of additional pathways.

Porcine SRY promoter is a target for steroidogenic factor 1

To study the process of mammalian sex determination and in particular to further understand the mechanisms of transcriptional regulation of the SRY gene, we have isolated a 4.5-kilobase (kb) pig SRY 5' flanking sequence. To facilitate the in vitro analysis of these sequences, we have generated a porcine genital ridge (PGR) cell line (9E11) that expresses SRY as well as SOX9, steroidogenic factor-1 (SF-1), and DAX1. Via primer extension analysis on RNA from this cell line, a transcription start site for porcine SRY was identified at -661 base pairs (bps) 5' from the translation initiation site. Deletion studies of the SRY 5' flanking sequences in PGR 9E11 cells demonstrated that -1.4 kb of 5' flanking sequences retained full transcriptional activity compared with the -4.5 kb fragment, but that transcriptional activity fell when further deletions were made. Sequences downstream of the transcriptional start site are important for promoter activity, because deleting transcribed but not translated sequences eliminated promoter activity. Sequence analysis of the -1.4 kb fragment identified two potential binding sites for SF-1, at -1369 and at -290 from the ATG. To address the role of SF-1 transactivation in SRY promoter activity, mutagenesis studies of the potential SF-1 binding sites were performed and revealed that these sites were indeed important for SRY promoter activity. Cotransfection studies in a heterologous cell system (mouse CV-1 cells) demonstrated that pig SF-1 was able to transactivate the pig SRY promoter. Gel shift assays confirmed that the upstream site was recognized by mouse SF-1 protein. We conclude that two sites for SF-1 transactivation exist within the pig SRY promoter, at -1369 bp and at -290 bp, and that the site at -1369 bp is quantitatively the most important.

The porcine SRY promoter is transactivated within a male genital ridge environment

In mammals the SRY gene functions as a dominant genetic switch for testis determination (Gubbay et al.: Nature 346:1128-1135, 1990; Koopman et al.: Nature 351:117-121, 1991; Sinclair et al.: Nature 346:240-244, 1990). To study SRY transcriptional regulation within an evolutionary context, we have generated transgenic mice that express green fluorescent protein (GFP) under the control of 4.5 kb of pig SRY 5' flanking sequences (pSRYp-GFP). Autofluorescence was observed in the genital ridges of e11.5 male embryos (18-21 tail somites), and by e12.5 (27 tail somites) autofluorescence was observed within the testes cords. The expression of the transgene did not display the abrupt termination characteristic of endogenous mouse SRY, but rather showed a gradual reduction in expression characteristic of human, pig and sheep SRY. Surprisingly, no autofluorescence was observed in normal XX genital ridges, although more sensitive RT-PCR analysis detected transgene transcription. When the transgene was bred into a constitutively male line of mice (Odsex; Bishop et al.: Nat Genet 26:490-494, 2000), autofluorescence was visible in genital ridges of XX animals, in the genetic absence of Sry protein. Via RT-PCR analysis, purified autofluorescent cells from e12.5 gonadal ridges expressed mouse SRY but not Oct4 transcripts, whereas autofluorescent cells from e14.5 gonadal ridges expressed MIS but not Oct4 transcripts, in each case consistent with a pre-Sertoli cell phenotype. In vitro expression studies performed in CV-1 cells demonstrated that pig SOX9 cDNA transactivated the pig SRY promoter but that pig SRY cDNA did not. When a SOX9 potential binding site identified at -205 of the pig SRY 5' flanking sequences was mutated, the SOX9 transactivation effect was reduced by 70%. This site is conserved in the 5' flanking sequences of bovine and human SRY genes but not in the mouse gene. Gel retardation assays using this binding site showed specific binding to SOX9-enriched nuclear extracts that was competed by excess unlabelled binding site but not by mutated binding site. We suggest that pig SRY gene is responsive to a testicular environment and propose a model of feedback amplification of pig SRY transcription by SOX9.

Genetic manipulation of sex differentiation and phenotype in domestic animals

In mammals, a gene based sex determination system ensures that approximately 50% of offspring will be of the male sex and 50% will be of the female sex. In domestic animal production systems, this ratio is not always ideal. Recent advances in our understanding of the molecular biology of sex determination and differentiation, as well as in the control of gene expression and the direct modification of animal genomes, allows us to consider methods for the direct genetic manipulation of sexual phenotype.

Expression and regulation of transcripts encoding two members of the NR5A nuclear receptor subfamily of orphan nuclear receptors, steroidogenic factor-1 and NR5A2, in equine ovarian cells during the ovulatory process

Steroidogenic factor-1 (SF-1, NR5A1a) is a member of the NR5A nuclear receptor subfamily and has been implicated as a key transcriptional regulator of all ovarian steroidogenic genes in vitro. To establish links between the expression of SF-1 and that of the steroidogenic genes in vivo, the objectives of this study were to clone equine SF-1 and examine the regulation of its messenger RNA (mRNA) in follicular cells during human CG (hCG)-induced ovulation. The equine SF-1 primary transcript was cloned by a combination of RT-PCR techniques. Results showed that the transcript was composed of a 5'-untranslated region (UTR) of 161 bp, an open reading frame (ORF) of 1386 bp that encodes a highly-conserved 461-amino acid protein, and a 3'-UTR of 518 bp. The cloning of SF-1 also led to the unexpected and serendipitous isolation of the highly-related orphan nuclear receptor NR5A2, which was shown to include a 5'-UTR of 243 bp, an ORF of 1488 bp, and a 3'-UTR of 1358 bp. The NR5A2 ORF encodes a 495-amino acid protein that is 60% identical to SF-1, including 99%-similar DNA-binding domains. Northern blot analysis revealed that SF-1 and NR5A2 were expressed in all major steroidogenic tissues, with the exception that NR5A2 was not present in the adrenal. Interestingly, NR5A2 was found to be, by far, the major NR5A subfamily member expressed in the preovulatory follicle and the corpus luteum. Using a semiquantitative RT-PCR/Southern blotting approach, the regulation of SF-1 and NR5A2 mRNAs in vivo was studied in equine follicular cells obtained from preovulatory follicles isolated between 0 and 39 h post hCG. Results showed that the theca interna was the predominant site of SF-1 mRNA expression in the follicle, and that hCG caused a significant decrease in SF-1 levels between 12-39 h in theca interna and between 24-39 h post hCG in granulosa cells (P < 0.05). In contrast, the granulosa cell layer was the predominant, if not the sole, site of NR5A2 mRNA expression in the follicle. Importantly, NR5A2 was much more highly expressed in granulosa cells than SF-1. The administration of hCG caused a significant decrease in NR5A2 transcripts in granulosa cells at 30, 36, and 39 h post hCG (P < 0.05). Thus, this study is the first to report the concomitant regulation of SF-1 in theca interna and granulosa cells throughout the ovulation/luteinization process, and to demonstrate the novel expression and hormonal regulation of NR5A2 in ovarian cells. Based on the marked expression of NR5A2 in equine granulosa and luteal cells and on mounting evidence of a functional redundancy between SF-1 and NR5A2 in other species, it is proposed that NR5A2 may play a key role in the regulation of gonadal steroidogenic gene expression.

Porcine steroidogenic factor-1 gene (pSF-1) expression and analysis of embryonic pig gonads during sexual differentiation

The porcine steroidogenic factor-1 gene (pSF-1) was cloned using a combination of genomic and RT-PCR based cloning methods. pSF-1 consists of an open reading frame of 1383 nt corresponding to a deduced amino acid sequence of 461 aa, similar to bovine and human SF-1. Sequence homologies between pSF-1 and human, bovine and mouse molecules indicate strong evolutionary conservation at both the nt and aa levels. Northern analysis of pSF-1 expression in adult steroidogenic tissues correlated with porcine steroidogenic acute regulatory protein gene (pStAR) and porcine side chain cleavage (pP450scc) gene expression. Notably, pSF-1 expression was readily detected in neonatal testes, absent at 3 weeks of age, and again readily detected at 3 months and in adult testes. pSF-1 expression was weak but detectable in placental tissues at various times of gestation, and was correlated with pStAR and pP450scc expression, indicating classical steroidogenesis in this organ. In developing gonads from 6-12 weeks of gestation, i.e. during the time of sex differentiation in the pig, Northern analysis demonstrated increasing expression of PSF-1 in fetal testes and no expression in ovaries. This expression pattern was paralleled for pStAR, pP450scc, and porcine Müllerian inhibitory substance (pMIS), consistent with pSF-1 involvement in both steroid and protein hormone secretions of the developing testes during sex differentiation. Porcine SRY HMG-box related gene-9 (pSOX-9) expression also paralleled that of pSF-1 in developing testes. In contrast, DSS-AHC critical region on the X chromosome, gene 1 (pDAX-1) was expressed predominantly in the developing ovaries, indicating a possible reciprocal regulation of pSF-1 and pDAX-1 genes in developing pig testes and ovaries.

Porcine and bovine steroidogenic acute regulatory protein (StAR) gene expression during gestation

We have generated complete complementary DNA (cDNA) sequences for the porcine steroidogenic acute regulatory protein (StAR) gene, using a combination of genomic PCR amplification and reverse transcription-PCR amplification of pig ovarian cDNA. Porcine StAR cDNA consists of 855 bp and shares 90.2%, 87.3%, 84.3%, and 83.9% homologies with bovine, human, mouse, and rat StAR cDNA at the nucleotide level, and 89.1%, 88.8%, 86.7%, and 86.3% homologies with bovine, human, mouse, and rat StAR protein at the deduced amino acid level. Northern analysis of porcine StAR showed that it is expressed in adult and fetal steroidogenic tissues, including adult testes and ovaries and adult adrenal glands as well as steroidogenic tissues of pregnancy, including developing fetal testes, corpus luteum, and pregnancy, but not the fetal ovary. Major hybridizing bands of 1.8 and 1.1 kilobases were demonstrated. In contrast to human StAR, porcine StAR was not expressed in adult or fetal kidneys. Expression of porcine StAR by the pig placenta is in contrast to human StAR, which is not expressed by the human placenta. Northern analysis of bovine cotyledons using a homologous probe for bovine StAR showed that StAR is also expressed by the placenta in the bovine animal. With respect to placental expression of StAR, variations may exist among mammalian species.

Analysis of T cell receptor beta chain expression by isoelectric focusing following gene amplification and in vitro translation

We describe a new approach to analysis of T cell receptor diversity based on isoelectric focusing of in vitro translation products of amplified V region genes. The method is illustrated by analysis of V beta 2 profiles in peripheral blood lymphocytes from normal donors. The primers used for V beta 2 analysis spanned the V-(D-)J junction and included the segment from amino acid residue position 53 in the variable region to residue 132 of the constant region. The isoelectric focusing patterns display approximately 13-14 bands of varying intensity. Differences in expression of V beta 2-derived peptides were detected in comparisons of the isoelectric focusing profiles from different individuals, suggesting that the method may be useful for detecting genetically determined, immune response related or disease associated differences in Tcr V region expression. The major isoelectric focusing bands have been interpreted as representing groups of V beta 2 sequences sharing J beta region and NDN region charge similarity. Quantitative differences were detected in V beta 2 profiles of CD4 and CD8 T cell subpopulations indicating there may be selection for different charge characteristics in NDNJ sequences in the two T cell subsets. The method provides a new dimension for the detection of perturbations in the T cell repertoire.