Embryonic Ethanol but Not Cannabinoid Exposure Affects Zebrafish Cardiac Development via Agrin and Sonic Hedgehog Interaction

Recent studies demonstrate the adverse effects of cannabinoids on development, including via pathways shared with ethanol exposure. Our laboratory has shown that both the nervous system and cardiac development are dependent on agrin modulation of sonic hedgehog (shh) and fibroblast growth factor (Fgf) signaling pathways. As both ethanol and cannabinoids impact these signaling molecules, we examined their role on zebrafish heart development. Zebrafish embryos were exposed to a range of ethanol and/or cannabinoid receptor 1 and 2 agonist concentrations in the absence or presence of morpholino oligonucleotides that disrupt agrin or shh expression. In situ hybridization was employed to analyze cardiac marker gene expression. Exposure to cannabinoid receptor agonists disrupted midbrain-hindbrain boundary development, but had no effect on heart development, as assessed by the presence of cardiac edema or the altered expression of cardiac marker genes. In contrast, exposure to 1.5% ethanol induced cardiac edema and the altered expression of cardiac marker genes. Combined exposure to agrin or shh morpholino and 0.5% ethanol disrupted the cmlc2 gene expression pattern, with the restoration of the normal expression following shh mRNA overexpression. These studies provide evidence that signaling pathways critical to heart development are sensitive to ethanol exposure, but not cannabinoids, during early zebrafish embryogenesis.

Ethanol Effects on Early Developmental Stages Studied Using the Zebrafish

Fetal alcohol spectrum disorder (FASD) results from prenatal ethanol exposure. The zebrafish (Danio rerio) is an outstanding in vivo FASD model. Early development produced the three germ layers and embryonic axes patterning. A critical pluripotency transcriptional gene circuit of sox2, pou5f1 (oct4; recently renamed pou5f3), and nanog maintain potency and self-renewal. Ethanol affects sox2 expression, which functions with pou5f1 to control target gene transcription. Various genes, like elf3, may interact and regulate sox2, and elf3 knockdown affects early development. Downstream of the pluripotency transcriptional circuit, developmental signaling activities regulate morphogenetic cell movements and lineage specification. These activities are also affected by ethanol exposure. Hedgehog signaling is a critical developmental signaling pathway that controls numerous developmental events, including neural axis specification. Sonic hedgehog activities are affected by embryonic ethanol exposure. Activation of sonic hedgehog expression is controlled by TGF-ß family members, Nodal and Bmp, during dorsoventral (DV) embryonic axis establishment. Ethanol may perturb TGF-ß family receptors and signaling activities, including the sonic hedgehog pathway. Significantly, experiments show that activation of sonic hedgehog signaling rescues some embryonic ethanol exposure effects. More research is needed to understand how ethanol affects early developmental signaling and morphogenesis.

BMP Signaling Interferes with Optic Chiasm Formation and Retinal Ganglion Cell Pathfinding in Zebrafish

Decussation of axonal tracts is an important hallmark of vertebrate neuroanatomy resulting in one brain hemisphere controlling the contralateral side of the body and also computing the sensory information originating from that respective side. Here, we show that BMP interferes with optic chiasm formation and RGC pathfinding in zebrafish. Experimental induction of BMP4 at 15 hpf results in a complete ipsilateral projection of RGC axons and failure of commissural connections of the forebrain, in part as the result of an interaction with shh signaling, transcriptional regulation of midline guidance cues and an affected optic stalk morphogenesis. Experimental induction of BMP4 at 24 hpf, resulting in only a mild repression of forebrain shh ligand expression but in a broad expression of pax2a in the diencephalon, does not per se prevent RGC axons from crossing the midline. It nevertheless shows severe pathologies of RGC projections e.g., the fasciculation of RGC axons with the ipsilateral optic tract resulting in the innervation of one tectum by two eyes or the projection of RGC axons in the direction of the contralateral eye.

LncRNA BLACAT1 Accelerates Non-small Cell Lung Cancer Through Up-Regulating the Activation of Sonic Hedgehog Pathway

Recently, increasing evidence has displayed that lncRNAs can exhibit crucial function in cancer progression, including lung cancer. LncRNA bladder cancer-associated transcript 1 (BLACAT1) is reported to participate in various cancers. The aim of our current study was to investigate the function of BLACAT1 in non-small cell lung cancer progression and study the functional pathway. Here, we reported BLACAT1 was significantly up-regulated in lung cancer tissues in comparison to the adjacent normal tissues, which suggested BLACAT1 might act as an oncogene in lung cancer. Then, A549 and PC9 cells were infected with BLACAT1 overexpression plasmid and shRNA. As shown, we proved up-regulation of BLACAT1 greatly induced the growth of non-small cell lung cancer cells. Reversely, knockdown of BLACAT1 reduced A549 and PC9 cell proliferation, migration and invasion. Sonic hedgehog (shh) signaling is able to exert a significant role in carcinogenesis, including lung cancer. Currently, we proved that up-regulation of BLACAT1 activated shh signaling pathway, via inducing shh, Gli-1 and Smo expression. shh pathway inhibitor GANT-61 reversed the effect of overexpression of BLACAT1 on non-small cell lung cancer. Moreover, we manifested that loss of BLACAT1 remarkably reduced the in vivo growth and metastasis of A549 cells via enhancing infiltrating CD3+ T cells. In conclusion, our research revealed a critical role of BLACAT1 in the modulation of non-small cell lung cancer via modulating shh pathway.

Glial cell ecology in zebrafish development and regeneration

Zebrafish have been found to be the premier model organism in biological and biomedical research, specifically offering many advantages in developmental biology and genetics. The zebrafish (Danio rerio) has the ability to regenerate its spinal cord after injury. However, the complete molecular and cellular mechanisms behind glial bridge formation in zebrafish remains unclear. In our review paper, we examine the extracellular and intracellular molecular signaling factors that control zebrafish glial cell bridging and glial cell development in the forebrain. The interplay between initiating and terminating molecular feedback cycles deserve future investigations during glial cell growth, movement, and differentiation.

microRNAs Regulating Human and Mouse Naïve Pluripotency

microRNAs are ~22bp nucleotide non-coding RNAs that play important roles in the post-transcriptional regulation of gene expression. Many studies have established that microRNAs are important for cell fate choices, including the naïve to primed pluripotency state transitions, and their intermediate state, the developmentally suspended diapause state in early development. However, the full extent of microRNAs associated with these stage transitions in human and mouse remain under-explored. By meta-analysis of microRNA-seq, RNA-seq, and metabolomics datasets from human and mouse, we found a set of microRNAs, and importantly, their experimentally validated target genes that show consistent changes in naïve to primed transitions (microRNA up, target genes down, or vice versa). The targets of these microRNAs regulate developmental pathways (e.g., the Hedgehog-pathway), primary cilium, and remodeling of metabolic processes (oxidative phosphorylation, fatty acid metabolism, and amino acid transport) during the transition. Importantly, we identified 115 microRNAs that significantly change in the same direction in naïve to primed transitions in both human and mouse, many of which are novel candidate regulators of pluripotency. Furthermore, we identified 38 microRNAs and 274 target genes that may be involved in diapause, where embryonic development is temporarily suspended prior to implantation to uterus. The upregulated target genes suggest that microRNAs activate stress response in the diapause stage. In conclusion, we provide a comprehensive resource of microRNAs and their target genes involved in naïve to primed transition and in the paused intermediate, the embryonic diapause stage.

[Expression and significance of Shh and Wnt5a genes in Cornelia de Lange syndrome]

OBJECTIVE

To study the expression of Shh and Wnt5a genes in the limb buds of NIPBL^+/- fetal rats and the association of these two genes with Cornelia de Lange syndrome (CdLS).

METHODS

A total of 72 NIPBL^+/- fetal rats were divided into an experimental group and a control group, with 36 rats in each group. The limb buds were collected from 12 fetal rats each on embryonic days 10, 11 and 12 (E10, E11 and E12) respectively. Real-time PCR and Western blot were used to measure the mRNA and protein expression of Shh and Wnt5a.

RESULTS

The mRNA and protein expression of Shh and Wnt5a was detected in the limb buds on E10, E11 and E12, and the experimental group had significantly lower expression than the control group (P<0.01). The mRNA and protein expression of Shh and Wnt5a in limb buds was at a low level on E10, followed by an increase on E11 and a reduction on E12, and the expression on E12 was still lower than that on E10 (P<0.01).

CONCLUSIONS

The mRNA and protein expression of Shh and Wnt5a are consistent. The pathogenesis of CdLS may be associated with the low mRNA and protein expression of Shh and Wnt5a inhibited by the low expression of NIPBL gene.

Genetic linkage between altered tooth and eye development in lens-ablated Astyanax mexicanus

The phenotype of lens-ablated Mexican tetra (Astyanax mexicanus) compared to wild-type surface fish has been described and includes, among other effects, eye degeneration, changes in tooth number and cranial bone changes. Here, we investigate the spatiotemporal expression patterns of several key genes involved in the development of these structures. Specifically, we show that the expression of pitx2, bmp4 and shh is altered in the eye, oral jaw, nasal pit and forebrain in these lens-ablated fish. Furthermore, for the first time, we show altered pitx2 expression in the cavefish, which also has altered eye and tooth phenotypes. We thus provide evidence for a genetic linkage between the eye and tooth modules in this fish species. Furthermore, the altered pitx2 expression pattern, together with the described morphological features of the lens-ablated fish suggests that Astyanax mexicanus could be considered as an alternative teleost model organism in which to study Axenfeld-Rieger syndrome (ARS), a rare autosomal dominant developmental disorder that is associated with PITX2 and which has both ocular and non-ocular abnormalities.

Expression of a hindlimb-determining factor Pitx1 in the forelimb of the lizard Pogona vitticeps during morphogenesis

With over 9000 species, squamates, which include lizards and snakes, are the largest group of reptiles and second-largest order of vertebrates, spanning a vast array of appendicular skeletal morphology. As such, they provide a promising system for examining developmental and molecular processes underlying limb morphology. Using the central bearded dragon (Pogona vitticeps) as the primary study model, we examined limb morphometry throughout embryonic development and characterized the expression of three known developmental genes (GHR, Pitx1 and Shh) from early embryonic stage through to hatchling stage via reverse transcription quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry (IHC). In this study, all genes were found to be transcribed in both the forelimbs and hindlimbs of P. vitticeps. While the highest level of GHR expression occurred at the hatchling stage, Pitx1 and Shh expression was greatest earlier during embryogenesis, which coincides with the onset of the differentiation between forelimb and hindlimb length. We compared our finding of Pitx1 expression—a hindlimb-determining gene—in the forelimbs of P. vitticeps to that in a closely related Australian agamid lizard, Ctenophorus pictus, where we found Pitx1 expression to be more highly expressed in the hindlimb compared with the forelimb during early and late morphogenesis—a result consistent with that found across other tetrapods. Expression of Pitx1 in forelimbs has only rarely been documented, including via in situ hybridization in a chicken and a frog. Our findings from both RT-qPCR and IHC indicate that further research across a wider range of tetrapods is needed to more fully understand evolutionary variation in molecular processes underlying limb morphology.

Expression analysis of Shh signaling members in early stages of chick lung development

Lung organogenesis is guided by epithelial-mesenchymal interactions that coordinate cellular events responsible for the formation of the respiratory system. Several signaling pathways have been implicated in this process; among them, sonic hedgehog (Shh) signaling has emerged as a crucial regulator of branching morphogenesis in the mammalian lung. Canonical Shh signaling requires the presence of patched (Ptch) and smoothened (Smo) transmembrane receptors in order to induce the activation of glioblastoma (Gli) zinc finger transcription factors that are the true effectors of the pathway. Signal transduction is finely regulated by Ptch1, Gli, and Hhip (hedgehog-interacting protein). The present work characterizes, for the first time, the expression pattern of shh, ptch1, smo, gli1, and hhip in early stages of the embryonic chick lung. In situ hybridization studies revealed that these genes are expressed in the same cellular compartments as their mammalian counterparts, although their proximo-distal distribution is slightly changed. Moreover, the molecular interactions between fibroblast growth factor (FGF) and Shh signaling pathway were assessed, in vitro, by grafting beads soaked in SU5402 (an FGF receptor inhibitor). In the chick lung, Shh signaling seems to have some features that are species specific since shh is not a downstream target of FGF signaling. Nonetheless and despite the observed differences, these findings suggest a role for Shh signaling in the epithelial-mesenchymal interactions that control chick lung morphogenesis.

Making teeth to order: conserved genes reveal an ancient molecular pattern in paddlefish (Actinopterygii)

Ray-finned fishes (Actinopterygii) are the dominant vertebrate group today (+30 000 species, predominantly teleosts), with great morphological diversity, including their dentitions. How dental morphological variation evolved is best addressed by considering a range of taxa across actinopterygian phylogeny; here we examine the dentition of Polyodon spathula (American paddlefish), assigned to the basal group Acipenseriformes. Although teeth are present and functional in young individuals of Polyodon, they are completely absent in adults. Our current understanding of developmental genes operating in the dentition is primarily restricted to teleosts; we show that shh and bmp4, as highly conserved epithelial and mesenchymal genes for gnathostome tooth development, are similarly expressed at Polyodon tooth loci, thus extending this conserved developmental pattern within the Actinopterygii. These genes map spatio-temporal tooth initiation in Polyodon larvae and provide new data in both oral and pharyngeal tooth sites. Variation in cellular intensity of shh maps timing of tooth morphogenesis, revealing a second odontogenic wave as alternate sites within tooth rows, a dental pattern also present in more derived actinopterygians. Developmental timing for each tooth field in Polyodon follows a gradient, from rostral to caudal and ventral to dorsal, repeated during subsequent loss of teeth. The transitory Polyodon dentition is modified by cessation of tooth addition and loss. As such, Polyodon represents a basal actinopterygian model for the evolution of developmental novelty: initial conservation, followed by tooth loss, accommodating the adult trophic modification to filter-feeding.

Activity-dependent expression of neuronal PAS domain-containing protein 4 (npas4a) in the developing zebrafish brain

In rodents, the Npas4 gene has recently been identified as being an important regulator of synaptic plasticity and memory. Homologs of Npas4 have been found in invertebrate species though their functions appear to be too divergent for them to be studied as a proxy for the mammalian proteins. The aim of this study, therefore, was to ascertain the suitability of the zebrafish as a model organism for investigating the function of Npas4 genes. We show here that the expression and regulation of the zebrafish Npas4 homolog, npas4a, is remarkably similar to that of the rodent Npas4 genes. As in mammals, expression of the zebrafish npas4a gene is restricted to the brain where it is up-regulated in response to neuronal activity. Furthermore, we also show that knockdown of npas4a during embryonic development results in a number of forebrain-specific defects including increased apoptosis and misexpression of the forebrain marker genes dlx1a and shha. Our work demonstrates that the zebrafish is a suitable model organism for investigating the role of the npas4a gene and one that is likely to provide valuable insights into the function of the mammalian homologs. Furthermore, our findings highlight a potential role for npas4a in forebrain development.

FGF signalling through Fgfr2 isoform IIIb regulates adrenal cortex development

Developmental signalling pathways are implicated in the formation and maintenance of the adrenal gland, but their roles are currently not well defined. In recent years it has emerged that Sonic hedgehog (Shh) and Wnt/β catenin signalling are crucial for the growth and development of the adrenal cortex. Here we demonstrate that Fibroblast growth factor receptor (Fgfr) 2 isoforms IIIb and IIIc are expressed mainly in the adrenal subcapsule during embryogenesis and that specific deletion of the Fgfr2 IIIb isoform impairs adrenal development, causing reduced adrenal growth and impaired expression of SF1 and steroidogenic enzymes. The hypoplastic adrenals also have thicker, disorganised capsules which retain Gli1 expression but no longer express Dlk1. Fgfr2 ligands were detected in both the capsule and the cortex, suggesting the importance of signalling between the capsule and the cortex in adrenal development.

Protein kinase Cα and integrin-linked kinase mediate the negative axon guidance effects of Sonic hedgehog

In addition to its role as a morphogen, Sonic hedgehog (Shh) has also been shown to function as a guidance factor that directly acts on the growth cones of various types of axons. However, the noncanonical signaling pathways that mediate the guidance effects of Shh protein remain poorly understood. We demonstrate that a novel signaling pathway consisting of protein kinase Cα (PKCα) and integrin-linked kinase (ILK) mediates the negative guidance effects of high concentration of Shh on retinal ganglion cell (RGC) axons. Shh rapidly increased Ca(2+) level and activated PKCα and ILK in the growth cones of RGC axons. By in vitro kinase assay, PKCα was found to directly phosphorylate ILK on threonine-173 and -181. Inhibition of PKCα or expression of a mutant ILK with the PKCα phosphorylation sites mutated (ILK-DM), abolished the Shh-induced macropinocytosis, growth cone collapse and repulsive axon turning. In vivo, expression of a dominant negative PKCα or ILK-DM disrupted RGC axon pathfinding at the optic chiasm but not the projection toward the optic disk, supporting that this signaling pathway plays a specific role in Shh-mediated negative guidance effects.

Adrenocortical stem and progenitor cells: implications for adrenocortical carcinoma

The continuous centripetal repopulation of the adrenal cortex is consistent with a population of cells endowed with the stem/progenitor cell properties of self-renewal and pluripotency. The adrenocortical capsule and underlying undifferentiated cortical cells are emerging as critical components of the stem/progenitor cell niche. Recent genetic analysis has identified various signaling pathways including Sonic Hedgehog (Shh) and Wnt as crucial mediators of adrenocortical lineage and organ homeostasis. Shh expression is restricted to the peripheral cortical cells that express a paucity of steroidogenic genes but give rise to the underlying differentiated cells of the cortex. Wnt/β-catenin signaling maintains the undifferentiated state and adrenal fate of adrenocortical stem/progenitor cells, in part through induction of its target genes Dax1 and inhibin-α, respectively. The pathogenesis of ACC, a rare yet highly aggressive cancer with an extremely poor prognosis, is slowly emerging from studies of the stem/progenitor cells of the adrenal cortex coupled with the genetics of familial syndromes in which ACC occurs. The frequent observation of constitutive activation of Wnt signaling due to loss-of-function mutations in the tumor suppressor gene APC or gain-of-function mutation in β-catenin in both adenomas and carcinomas, suggests perhaps that the Wnt pathway serves an early or initiating insult in the oncogenic process. Loss of p53 might be predicted to cooperate with additional genetic insults such as IGF2 as both are the most common genetic abnormalities in malignant versus benign adrenocortical neoplasms. It is unclear whether other factors such as Pod1 and Pref1, which are implicated in stem/progenitor cell biology in the adrenal and/or other organs, are also implicated in the etiology of adrenocortical carcinoma. The rarity and heterogeneous presentation of ACC makes it difficult to identify the cellular origin and the molecular progression to cancer. A more complete understanding of adrenocortical stem/progenitor cell biology will invariably aid in characterization of the molecular details of ACC tumorigenesis and may offer new options for therapeutic intervention.

Morphogens and hepatic stellate cell fate regulation in chronic liver disease

Hepatic stellate cells (HSC) are the liver mesenchymal cell type which responds to hepatocellular damage and participates in wound healing. Although HSC myofibroblastic trans-differentiation (activation) is implicated in excessive extracellular matrix deposition, molecular understanding of this phenotypic switch from the viewpoint of cell fate regulation is limited. Recent studies demonstrate the roles of anti-adipogenic morphogens (Wnt, Necdin, Shh) in epigenetic repression of the HSC differentiation gene Pparγ as a causal event in HSC activation. These morphogens have positive cross-interactions which converge to epigenetic repression of Pparγ involving the methyl-CpG binding protein MeCP2. However, these morphogens expressed by activated HSC may also participate in cross-talk between HSC and hepatoblasts/hepatocytes to support liver regeneration, and their aberrant regulation may contribute to liver tumorigenesis. Implications of HSC-derived morphogens in these possibilities are discussed.

Analysis of sphingosine-1-phosphate signaling mutants reveals endodermal requirements for the growth but not dorsoventral patterning of jaw skeletal precursors

Development of the head skeleton involves reciprocal interactions between cranial neural crest cells (CNCCs) and the surrounding pharyngeal endoderm and ectoderm. Whereas elegant experiments in avians have shown a prominent role for the endoderm in facial skeleton development, the relative functions of the endoderm in growth versus regional identity of skeletal precursors have remained unclear. Here we describe novel craniofacial defects in zebrafish harboring mutations in the Sphingosine-1-phospate (S1P) type 2 receptor (s1pr2) or the S1P transporter Spinster 2 (spns2), and we show that S1P signaling functions in the endoderm for the proper growth and positioning of the jaw skeleton. Surprisingly, analysis of s1pr2 and spns2 mutants, as well as sox32 mutants that completely lack endoderm, reveals that the dorsal-ventral (DV) patterning of jaw skeletal precursors is largely unaffected even in the absence of endoderm. Instead, we observe reductions in the ectodermal expression of Fibroblast growth factor 8a (Fgf8a), and transgenic misexpression of Shha restores fgf8a expression and partially rescues the growth and differentiation of jaw skeletal precursors. Hence, we propose that the S1P-dependent anterior foregut endoderm functions primarily through Shh to regulate the growth but not DV patterning of zebrafish jaw precursors.

New findings for phenotype-genotype correlations in a large European series of holoprosencephaly cases

BACKGROUND

Holoprosencephaly (HPE) is the most common forebrain defect in humans. It results from incomplete midline cleavage of the prosencephalon.

METHODS

A large European series of 645 HPE probands (and 699 relatives), consisting of 51% fetuses and 49% liveborn children, is reported.

RESULTS

Mutations in the four main genes involved in HPE (SHH, ZIC2, SIX3, TGIF) were identified in 25% of cases. The SHH, SIX3, and TGIF mutations were inherited in more than 70% of these cases, whereas 70% of the mutations in ZIC2 occurred de novo. Moreover, rearrangements were detected in 22% of the 260 patients screened by array comparative genomic hybridisation. 15 probands had two mutations providing additional support for the 'multiple-hit process' in HPE. There was a positive correlation between the severity of the brain malformation and facial features for SHH, SIX3, and TGIF, but no such correlation was found for ZIC2 mutations. The most severe HPE types were associated with SIX3 and ZIC2 mutations, whereas microforms were associated with SHH mutations. The study focused on the associated brain malformations, including neuronal migration defects, which predominated in individuals with ZIC2 mutations, and neural tube defects, which were frequently associated with ZIC2 (rachischisis) and TGIF mutations. Extracraniofacial features were observed in 27% of the individuals in this series (up to 40% of those with ZIC2 mutations) and a significant correlation was found between renal/urinary defects and mutations of SHH and ZIC2.

CONCLUSIONS

An algorithm is proposed based on these new phenotype-genotype correlations, to facilitate molecular analysis and genetic counselling for HPE.

The inductive role of Wnt-β-Catenin signaling in the formation of oral apparatus

Proper patterning and growth of oral structures including teeth, tongue, and palate rely on epithelial-mesenchymal interactions involving coordinated regulation of signal transduction. Understanding molecular mechanisms underpinning oral-facial development will provide novel insights into the etiology of common congenital defects such as cleft palate. In this study, we report that ablating Wnt signaling in the oral epithelium blocks the formation of palatal rugae, which are a set of specialized ectodermal appendages serving as Shh signaling centers during development and niches for sensory cells and possibly neural crest related stem cells in adults. Lack of rugae is also associated with retarded anteroposterior extension of the hard palate and precocious mid-line fusion. These data implicate an obligatory role for canonical Wnt signaling in rugae development. Based on this complex phenotype, we propose that the sequential addition of rugae and its morphogen Shh, is intrinsically coupled to the elongation of the hard palate, and is critical for modulating the growth orientation of palatal shelves. In addition, we observe a unique cleft palate phenotype at the anterior end of the secondary palate, which is likely caused by the severely underdeveloped primary palate in these mutants. Last but not least, we also discover that both Wnt and Shh signalings are essential for tongue development. We provide genetic evidence that disruption of either signaling pathway results in severe microglossia. Altogether, we demonstrate a dynamic role for Wnt-β-Catenin signaling in the development of the oral apparatus.

The unfolding clinical spectrum of holoprosencephaly due to mutations in SHH, ZIC2, SIX3 and TGIF genes

Holoprosencephaly is a severe malformation of the brain characterized by abnormal formation and separation of the developing central nervous system. The prevalence is 1:250 during early embryogenesis, the live-born prevalence is 1:16 000. The etiology of HPE is extremely heterogeneous and can be teratogenic or genetic. We screened four known HPE genes in a Dutch cohort of 86 non-syndromic HPE index cases, including 53 family members. We detected 21 mutations (24.4%), 3 in SHH, 9 in ZIC2 and 9 in SIX3. Eight mutations involved amino-acid substitutions, 7 ins/del mutations, 1 frame-shift, 3 identical poly-alanine tract expansions and 2 gene deletions. Pathogenicity of mutations was presumed based on de novo character, predicted non-functionality of mutated proteins, segregation of mutations with affected family-members or combinations of these features. Two mutations were reported previously. SNP array confirmed detected deletions; one spanning the ZIC2/ZIC5 genes (approx. 100 kb) the other a 1.45 Mb deletion including SIX2/SIX3 genes. The mutation percentage (24%) is comparable with previous reports, but we detected significantly less mutations in SHH: 3.5 vs 10.7% (P=0.043) and significantly more in SIX3: 10.5 vs 4.3% (P=0.018). For TGIF1 and ZIC2 mutation the rate was in conformity with earlier reports. About half of the mutations were de novo, one was a germ line mosaic. The familial mutations displayed extensive heterogeneity in clinical manifestation. Of seven familial index patients only two parental carriers showed minor HPE signs, five were completely asymptomatic. Therefore, each novel mutation should be considered as a risk factor for clinically manifest HPE, with the caveat of reduced clinical penetrance.

Genetic evidence that SOST inhibits WNT signaling in the limb

SOST is a negative regulator of bone formation, and mutations in human SOST are responsible for sclerosteosis. In addition to high bone mass, sclerosteosis patients occasionally display hand defects, suggesting that SOST may function embryonically. Here we report that overexpression of SOST leads to loss of posterior structures of the zeugopod and autopod by perturbing anterior-posterior and proximal-distal signaling centers in the developing limb. Mutant mice that overexpress SOST in combination with Grem1 and Lrp6 mutations display more severe limb defects than single mutants alone, while Sost(-/-) significantly rescues the Lrp6(-/-) skeletal phenotype, signifying that SOST gain-of-function impairs limb patterning by inhibiting the WNT signaling through LRP5/6.

Smad4-Shh-Nfic signaling cascade-mediated epithelial-mesenchymal interaction is crucial in regulating tooth root development

Transforming growth factor beta (TGF-beta)/bone morphogenetic protein (BMP) signaling is crucial for regulating epithelial-mesenchymal interaction during organogenesis, and the canonical Smad pathway-mediated TGF-beta/BMP signaling plays important roles during development and disease. During tooth development, dental epithelial cells, known as Hertwig's epithelial root sheath (HERS), participate in root formation following crown development. However, the functional significance of HERS in regulating root development remains unknown. In this study we investigated the signaling mechanism of Smad4, the common Smad for TGF-beta/BMP signaling, in HERS in regulating root development. Tissue-specific inactivation of Smad4 in HERS results in abnormal enamel and dentin formation in K14-Cre;Smad4(fl/fl) mice. HERS enlarges but cannot elongate to guide root development without Smad4. At the molecular level, Smad4-mediated TGF-beta/BMP signaling is required for Shh expression in HERS and Nfic (nuclear factor Ic) expression in the cranial neural crest (CNC)-derived dental mesenchyme. Nfic is crucial for root development, and loss of Nfic results in a CNC-derived dentin defect similar to the one of K14-Cre;Smad4(fl/fl) mice. Significantly, we show that ectopic Shh induces Nfic expression in dental mesenchyme and partially rescues root development in K14-Cre;Smad4(fl/fl) mice. Taken together, our study has revealed an important signaling mechanism in which TGF-beta/BMP signaling relies on a Smad-dependent mechanism in regulating Nfic expression via Shh signaling to control root development. The interaction between HERS and the CNC-derived dental mesenchyme may guide the size, shape, and number of tooth roots.

A direct cross-talk between interferon-gamma and sonic hedgehog signaling that leads to the proliferation of neuronal precursor cells

Interferon-gamma (IFN-gamma) is a pleiotropic cytokine that is critical for innate and adaptive immunity. Recent evidence suggests a connection between IFN-gamma signaling and the sonic hedgehog (Shh) pathway in the developing brain with CNS-targeted expression of IFN-gamma transgene in mice. To determine the relationship between these distinct pathways, we have found that IFN-gamma induces a rapid Shh transcription in cultured primary granular neuron precursor (GNP) cells. The transcriptional induction of Shh by IFN-gamma is resistant to protein synthesis inhibition. Chromatin immunoprecipitation (ChIP) analysis reveals a direct binding of signal transducer and activator of transcription (STAT) 1 to the Shh promoter. Functional analyses, including dual immunofluorescent labeling with 5-bromodeoxyuridine (BrdU) incorporation indicate that IFN-gamma treatment leads to significant GNP proliferation. This mitogenic effect of IFN-gamma is blocked by inhibition of Shh signaling. Therefore, Shh is an IFN-gamma target gene and is responsible for IFN-gamma-induced GNP proliferation. This previously unrecognized cross-talk between IFN-gamma and Shh highlights a potential importance of this immune mediator in the pathogenesis of human developmental and psychiatric disorders.

Loss of glypican-3 function causes growth factor-dependent defects in cardiac and coronary vascular development

Glypican-3 (Gpc3) is a heparan sulfate proteoglycan (HSPG) expressed widely during vertebrate development. Loss-of-function mutations cause Simpson-Golabi-Behmel syndrome (SGBS), a rare and complex congenital overgrowth syndrome with a number of associated developmental abnormalities including congenital heart disease. We found that Gpc3-deficient mice display a high incidence of congenital cardiac malformations like ventricular septal defects, common atrioventricular canal and double outlet right ventricle. In addition we observed coronary artery fistulas, which have not been previously reported in SGBS. Coronary artery fistulas are noteworthy because little is known about the molecular basis of this abnormality. Formation of the coronary vascular plexus in Gpc3-deficient embryos was delayed compared to wild-type, and consistent with GPC3 functioning as a co-receptor for fibroblast growth factor-9 (FGF9), we found a reduction in Sonic Hedgehog (Shh) mRNA expression and signaling in embryonic mutant hearts. Interestingly, we found an asymmetric reduction in SHH signaling in cardiac myocytes, as compared with perivascular cells, resulting in excessive coronary artery formation in the Gpc3-deficient animals. We hypothesize that the excessive development of coronary arteries over veins enables the formation of coronary artery fistulas. This work has broad significance to understanding the genetic basis of coronary development and potentially to molecular mechanisms relevant to revascularization following ischemic injury to the heart.

The mutational spectrum of holoprosencephaly-associated changes within the SHH gene in humans predicts loss-of-function through either key structural alterations of the ligand or its altered synthesis

Mutations within either the SHH gene or its related pathway components are the most common, and best understood, pathogenetic changes observed in holoprosencephaly patients; this fact is consistent with the essential functions of this gene during forebrain development and patterning. Here we summarize the nature and types of deleterious sequence alterations among over one hundred distinct mutations in the SHH gene (64 novel mutations) and compare these to over a dozen mutations in disease-related Hedgehog family members IHH and DHH. This combined structural analysis suggests that dysfunction of Hedgehog signaling in human forebrain development can occur through truncations or major structural changes to the signaling domain, SHH-N, as well as due to defects in the processing of the mature ligand from its pre-pro-precursor or defective post-translation bi-lipid modifications with palmitate and cholesterol.

Sonic hedgehog signaling regulates reciprocal epithelial-mesenchymal interactions controlling palatal outgrowth

The mammalian secondary palate arises by outgrowth from the oral side of the paired maxillary processes flanking the primitive oral cavity. Palatal growth depends on reciprocal interactions between the oral ectoderm and the underlying neural-crest-derived mesenchyme. Previous studies have implicated sonic hedgehog (Shh) as an important epithelial signal for regulating palatal growth. However, the cellular and molecular mechanisms through which Shh regulates palatal development in vivo have not been directly analyzed, due in part to early embryonic lethality of mice lacking Shh or other essential components of the Shh signaling pathway. Using Cre/loxP-mediated tissue-specific inactivation of the smoothened (Smo) gene in the developing palatal mesenchyme, we show that the epithelially expressed Shh signals directly to the palatal mesenchyme to regulate palatal mesenchyme cell proliferation through maintenance of cyclin D1 (Ccnd1) and Ccnd2 expression. Moreover, we show that Shh-Smo signaling specifically regulates the expression of the transcription factors Foxf1a, Foxf2 and Osr2 in the developing palatal mesenchyme. Furthermore, we show that Shh signaling regulates Bmp2, Bmp4 and Fgf10 expression in the developing palatal mesenchyme and that specific inactivation of Smo in the palatal mesenchyme indirectly affects palatal epithelial cell proliferation. Together with previous reports that the mesenchymally expressed Fgf10 signals to the palatal epithelium to regulate Shh mRNA expression and cell proliferation, these data demonstrate that Shh signaling plays a central role in coordinating the reciprocal epithelial-mesenchymal interactions controlling palatal outgrowth.

Molecular signaling pathways that regulate prostate gland development

Prostate gland development is a complex process that involves coordination of multiple signaling pathways including endocrine, paracrine, autocrine, juxtacrine and transcription factors. To put this into proper context, the present manuscript will begin with a brief overview of the stages of prostate development and a summary of androgenic signaling in the developing prostate, which is essential for prostate formation. This will be followed by a detailed description of other transcription factors and secreted morphogens directly involved in prostate formation and branching morphogenesis. Except where otherwise indicated, results from rodent models will be presented since studies that examine molecular signaling in the developing human prostate gland are sparse at the present time.

Molecular evidence for an activator-inhibitor mechanism in development of embryonic feather branching

The developmental basis of morphological complexity remains a central question in developmental and evolutionary biology. Feathers provide a unique system to analyze the development of complex morphological novelties. Here, we describe the interactions between Sonic hedgehog (Shh) and bone morphogenetic protein 2 (Bmp2) signaling during feather barb ridge morphogenesis. We demonstrate that activator-inhibitor models of Shh and Bmp2 signaling in the tubular feather epithelium are sufficient to explain the initial formation of a meristic pattern of barb ridges and the observed variation in barb morphogenesis in chick natal down feathers. Empirical tests support the assumptions of the model that, within the feather ectoderm, Shh (activator) up-regulates its own transcription and that of Bmp2 (inhibitor), whereas Bmp2 signaling down-regulates Shh expression. More complex models incorporating a second activator and dorsal/ventral polarized modification of activator signaling can produce all of the barb morphogenesis patterns observed during the growth of more complex branched pennaceous feathers: new barb ridge formation, helical growth, and barb ridge fusion. An integrated model of feather morphogenesis and evolution suggests that plumulaceous feather structure evolved by the establishment of activator-inhibitor interactions between Shh and Bmp2 signaling in the basal epithelium of the feather germ. Subsequently, pennaceous feather structure evolved through the integration of barb ridge morphogenesis with a second, local inhibitor and a dorsal/ventral signal gradient within the feather. The model is congruent with paleontological evidence that plumulaceous feathers are primitive to pennaceous feathers.

Wnt regulation of progenitor maturation in the cortex depends on Shh or fibroblast growth factor 2

In the embryonic mouse cerebral cortex, progenitors in the ventricular zone (VZ) undergo a developmental change between embryonic day 13 (E13) and E15. This results in the generation of a secondary proliferative population and the appearance of a second germinal layer, the subventricular zone (SVZ). We have shown previously that bone morphogenetic proteins (BMPs) and fibroblast growth factor 2 (FGF2) act antagonistically to regulate the development of a subset of SVZ progenitors that normally express a high level of epidermal growth factor (EGF) receptors and divide in response to EGF. In the present study, we show that Wnt 7a, Wnt 7b, and Sonic hedgehog (Shh) promote progenitor maturation in explant cultures, as reported for FGF2. Wnts 7a and 7b also stimulate the proliferation of neurogenic progenitors and increase the number of cells that can generate primary neurospheres. To determine whether Wnts, FGF2, and Shh act independently or in a common pathway, each factor was inhibited in cortical explants. This revealed that endogenous Wnts, FGF2, and Shh normally contribute to progenitor maturation. Moreover, Wnt 7a depends on FGF2 or Shh to promote maturation but not proliferation. Maturation induced by blocking BMPs also depends on Shh. In contrast, FGF2 promotes maturation by a Shh-independent mechanism. In vivo, progenitors infected with a Wnt 7a retrovirus at E10.5 were found preferentially in the SVZ at E16.5. These findings suggest that Wnts depend on Shh or FGF2 to promote progenitor maturation to an SVZ state in the embryonic cortex.

Tbx1 is regulated by tissue-specific forkhead proteins through a common Sonic hedgehog-responsive enhancer

Haploinsufficiency of Tbx1 is likely a major determinant of cardiac and craniofacial birth defects associated with DiGeorge syndrome. Although mice deficient in Tbx1 exhibit pharyngeal and aortic arch defects, the developmental program and mechanisms through which Tbx1 functions are relatively unknown. We identified a single cis-element upstream of Tbx1 that recognized winged helix/forkhead box (Fox)-containing transcription factors and was essential for regulation of Tbx1 transcription in the pharyngeal endoderm and head mesenchyme. The Tbx1 regulatory region was responsive to signaling by Sonic hedgehog (Shh) in vivo. We show that Shh is necessary for aortic arch development, similar to Tbx1, and is also required for expression of Foxa2 and Foxc2 in the pharyngeal endoderm and head mesenchyme, respectively. Foxa2, Foxc1, or Foxc2 could bind and activate transcription through the critical cis-element upstream of Tbx1, and Foxc proteins were required, within their expression domains, for Tbx1 transcription in vivo. We propose that Tbx1 is a direct transcriptional target of Fox proteins and that Fox proteins may serve an intermediary role in Shh regulation of Tbx1.

Sonic hedgehog-dependent activation of Gli2 is essential for embryonic hair follicle development

Sonic hedgehog (Shh) signaling plays a critical role in hair follicle development and skin cancer, but how it controls these processes remains unclear. Of the three Gli transcription factors involved in transducing Shh signals in vertebrates, we demonstrate here that Gli2 is the key mediator of Shh responses in skin. Similar to Shh(-/-) mice, Gli2(-/-) mutants exhibit an arrest in hair follicle development with reduced cell proliferation and Shh-responsive gene expression, but grossly normal epidermal differentiation. By transgenic rescue experiments, we show that epidermal Gli2 function alone is sufficient to restore hair follicle development in Gli2(-/-) skin. Furthermore, only a constitutively active form of Gli2, but not wild-type Gli2, can activate Shh-responsive gene expression and promote cell proliferation in Shh(-/-) skin. These observations indicate that Shh-dependent Gli2 activator function in the epidermis is essential for hair follicle development. Our data also reveal that Gli2 mediates the mitogenic effects of Shh by transcriptional activation of cyclin D1 and cyclin D2 in the developing hair follicles. Together, our results suggest that Shh-dependent Gli2 activation plays a critical role in epithelial homeostasis by promoting proliferation through the transcriptional control of cell cycle regulators.

Developmental mechanisms underlying polydactyly in the mouse mutant Doublefoot

The pre-axial polydactylous mouse mutant Doublefoot has 6-9 digits per limb but lacks anteroposterior polarity (there is no biphalangeal digit 1). It differs from other polydactylous mutants in showing normal Shh expression, but polarizing activity (shown by mouse-chick grafting experiments) and hedgehog signalling activity (shown by expression of Ptc1) are present throughout the distal mesenchyme. The Dbf mutation has not yet been identified. Here we review current understanding of this mutant, and briefly report new results indicating (1) that limb bud expansion is concomitant with ectopic lhh expression and with extension of the posterior high cell proliferation rate into the anterior region, and (2) that the Dbf mutation is epistatic to Shh in the limb.

Regulation of myogenic differentiation in the developing limb bud

The limb myogenic precursors arise by delamination from the lateral dermomyotome in response to signals from the lateral plate mesoderm. They subsequently migrate into the developing limb bud where they switch on the expression of the myogenic regulatory factors, MyoD and Myf5, and coalese to form the dorsal and ventral muscle masses. The myogenic cells subsequently undergo terminal differentiation into slow or fast fibres which have distinct contractile properties determining how a muscle will function. In general, fast fibres contract rapidly with high force and are characterized by the expression of fast myosin heavy chains (MyHC). These fibres are needed for movement. In contrast, slow fibres express slow MyHC, contract slowly and are required for maintenance of posture. This review focuses on the molecular signals that control limb myogenic development from the initial delamination and migration of the premyogenic cells to the ultimate formation of the complex muscle pattern and differentiation of slow and fast fibres.

Patterning the limb before and after SHH signalling

The vertebrate limb is one of the most relevant experimental models for analysing cell-cell signalling during patterning of embryonic fields and organogenesis. Recently, the combination of molecular and genetic studies with experimental manipulation of developing limb buds has significantly advanced our understanding of the complex molecular interactions co-ordinating limb bud outgrowth and patterning. Some of these studies have shown that there is a need to revise some of the textbook views of vertebrate limb development. In this review, we discuss how signalling by the polarizing region is established and how limb bud morphogenesis is controlled by both long-range and signal relay mechanisms. We also discuss recent results showing that differential mesenchymal responsiveness to SHH signalling is established prior to its expression by the polarizing region.

Specification of the mammalian cochlea is dependent on Sonic hedgehog

Organization of the inner ear into auditory and vestibular components is dependent on localized patterns of gene expression within the otic vesicle. Surrounding tissues are known to influence compartmentalization of the otic vesicle, yet the participating signals remain unclear. This study identifies Sonic hedgehog (Shh) secreted by the notochord and/or floor plate as a primary regulator of auditory cell fates within the mouse inner ear. Whereas otic induction proceeds normally in Shh(-/-) embryos, morphogenesis of the inner ear is greatly perturbed by midgestation. Ventral otic derivatives including the cochlear duct and cochleovestibular ganglia failed to develop in the absence of Shh. The origin of the inner ear defects in Shh(-/-) embryos could be traced back to alterations in the expression of a number of genes involved in cell fate specification including Pax2, Otx1, Otx2, Tbx1, and Ngn1. We further show that several of these genes are targets of Shh signaling given their ectopic activation in transgenic mice that misexpress Shh in the inner ear. Taken together, our data support a model whereby auditory cell fates in the otic vesicle are established by the direct action of Shh.

Shh establishes an Nkx3.2/Sox9 autoregulatory loop that is maintained by BMP signals to induce somitic chondrogenesis

Prior work has established that transient Shh signals from the notochord and floor plate confer a competence in somitic tissue for subsequent BMP signals to induce chondrogenesis. We have therefore proposed that Shh induces a factor(s) that renders somitic cells competent to chondrify in response to subsequent BMP signals. Recently, we have shown that forced expression of Nkx3.2, a transcriptional repressor induced by Shh, is able to confer chondrogenic competence in somites. In this work, we show that administration of Shh or forced Nkx3.2 expression induces the expression of the transcription factor Sox9 in the somitic tissue. Forced expression of Sox9 can, in turn, induce robust chondrogenesis in somitic mesoderm, provided that BMP signals are present. We have found that in the presence of BMP signals, Sox9 and Nkx3.2 induce each other's expression. Thus, Nkx3.2 may promote axial chondrogenesis by derepressing the expression of Sox9 in somitic mesoderm. Furthermore, forced expression of either Sox9 or Nkx3.2 not only activates expression of cartilage-specific genes in somitic mesoderm, but also promotes the proliferation and survival of the induced chondrocytes in the presence of BMP signals. However, unlike Nkx3.2, Sox9 is able to induce de novo cartilage formation in non-cartilage-forming tissues. Our findings suggest that Shh and BMP signals work in sequence to establish a positive regulatory loop between Sox9 and Nkx3.2, and that Sox9 can subsequently initiate the chondrocyte differentiation program in a variety of cellular environments.

Transcriptional regulation of lung development: emergence of specificity

The lung is the product of a set of complex developmental interactions between two distinct tissues, the endodermally derived epithelium and the mesoderm. Each tissue contributes to lung development by fine-tuning the spatial and temporal pattern of gene expression for a distinct array of signaling molecules, transcriptional molecules and molecules related to the extracellular matrix. Morphoregulatory transcriptional factors such as NKX2.1 have the crucial role of connecting the cell-cell crosstalk to the activation or repression of gene expression through which processes such as cellular proliferation, migration, differentiation and apoptosis can be controlled. Although none of the factors participating in lung development are exclusively lung-specific, their unique combinations and interactions constitute the basis for emergence of lung structural and functional specificities. An understanding of the individual molecules and their unique interactions in the context of lung development is necessary for the construction of a morphogenetic map for this vital organ as well as for the development of rational and innovative approaches to congenital and induced lung disease.

Spinal cord neuronal precursors generate multiple neuronal phenotypes in culture

Neuronal restricted precursors (NRPs) () can generate multiple neurotransmitter phenotypes during maturation in culture. Undifferentiated E-NCAM+ (embryonic neural cell adhesion molecule) immunoreactive NRPs are mitotically active and electrically immature, and they express only a subset of neuronal markers. Fully mature cells are postmitotic, process-bearing cells that are neurofilament-M and synaptophysin immunoreactive, and they synthesize and respond to different subsets of neurotransmitter molecules. Mature neurons that synthesize and respond to glycine, glutamate, GABA, dopamine, and acetylcholine can be identified by immunocytochemistry, RT-PCR, and calcium imaging in mass cultures. Individual NRPs also generate heterogeneous progeny as assessed by neurotransmitter response and synthesis, demonstrating the multipotent nature of the precursor cells. Differentiation can be modulated by sonic hedgehog (Shh) and bone morphogenetic protein (BMP)-2/4 molecules. Shh acts as a mitogen and inhibits differentiation (including cholinergic differentiation). BMP-2 and BMP-4, in contrast, inhibit cell division and promote differentiation (including cholinergic differentiation). Thus, a single neuronal precursor cell can differentiate into multiple classes of neurons, and this differentiation can be modulated by environmental signals.