Growth, hedgehog and the price of GAS

Ptch2/Gas1 and Ptch1/Boc differentially regulate Hedgehog signalling in murine primordial germ cell migration

Gas1 and Boc/Cdon act as co-receptors in the vertebrate Hedgehog signalling pathway, but the nature of their interaction with the primary Ptch1/2 receptors remains unclear. Here we demonstrate, using primordial germ cell migration in mouse as a developmental model, that specific hetero-complexes of Ptch2/Gas1 and Ptch1/Boc mediate the process of Smo de-repression with different kinetics, through distinct modes of Hedgehog ligand reception. Moreover, Ptch2-mediated Hedgehog signalling induces the phosphorylation of Creb and Src proteins in parallel to Gli induction, identifying a previously unknown Ptch2-specific signal pathway. We propose that although Ptch1 and Ptch2 functionally overlap in the sequestration of Smo, the spatiotemporal expression of Boc and Gas1 may determine the outcome of Hedgehog signalling through compartmentalisation and modulation of Smo-downstream signalling. Our study identifies the existence of a divergent Hedgehog signal pathway mediated by Ptch2 and provides a mechanism for differential interpretation of Hedgehog signalling in the germ cell niche.

How co-receptors Gas1 and Boc interact with Ptch1/2 receptors and regulate Hh signalling is unclear. Here, the authors demonstrate that the spatiotemporal expression of Gas1 and Boc determines how Hh signalling affects the dynamic migration of murine primordial germ cells.

Functions and roles of a protein-associated factor

The divergence of protein (Hedgehog) in different organisms remains an unresolved issue to comprehend how the pathway in Hh signaling evolves. Insights into this question can help one identify the key molecules in Hh signaling. This work proposes a protein-associated factor in cells. The development of a non-reductionist theory of cellular functions in medicine is not sufficient. It is necessary to find the parameters with regards to molecules/genes that can elicit functions. This work shows that molecular interactions of gene products can be accomplished by biophysics logic. Defining the protein-associated factors in molecular activities and identifying its roles in molecular transduction are important. A misregulation in molecular switch can account for complex biomolecular consequences. This work shows the potential of the factor on homo-sapiens and unlocks its implications to gene multi-tasking functionality. The associated factor notion should facilitate the medical development in cancer therapeutics.

Trps1, a regulator of chondrocyte proliferation and differentiation, interacts with the activator form of Gli3

Trps1, the gene mutated in human Tricho-Rhino-Phalangeal syndrome, represents an atypical member of the GATA-family of transcription factors. Here we show that Trps1 interacts with Indian hedgehog (Ihh)/Gli3 signaling and regulates chondrocyte differentiation and proliferation. We demonstrate that Trps1 specifically binds to the transactivation domain of Gli3 in vitro and in vivo, whereas the repressor form of Gli3 does not interact with Trps1. A domain of 185aa within Trps1, containing three predicted zinc fingers, is sufficient for interaction with Gli3. Using different mouse models we find that in distal chondrocytes Trps1 and the repressor activity of Gli3 are required to expand distal cells and locate the expression domain of Parathyroid hormone related peptide. In columnar proliferating chondrocytes Trps1 and Ihh/Gli3 have an activating function. The differentiation of columnar and hypertrophic chondrocytes is supported by Trps1 independent of Gli3. Trps1 seems thus to organize chondrocyte differentiation interacting with different subsets of co-factors in distinct cell types.

Muscle-epidermis interactions affect exoskeleton patterning in Caenorhabditis elegans

The C. elegans hypodermis is a single epithelial cell layer separated from the musculature by a thin basement membrane on its basal surface. The hypodermis secretes the extracellular material of the cuticle from its apical surface. The regulation of cuticle synthesis and apical secretion is not well understood. UNC-95 is a component of the muscle dense bodies and M-lines, which are integrin-based adhesion complexes required for force transduction to the cuticle. Using gene expression profiling and in vivo assays, we show that, in unc-95 mutant worms, there is an increase in expression levels of a group of hypodermal and pharyngeal genes related to cuticle structure and molting. Moreover, the cuticle structure of unc-95 mutant adult is impaired. Our findings suggest that aberrant force transduction from the structurally impaired muscle attachments across the basement membrane to the underlying hypodermis elicits intercellular signaling that plays a role in regulating cuticle synthesis and patterning.

Adenoviral vector-mediated transfer of the Indian hedgehog gene modulates lymphomyelopoiesis in vivo

Indian hedgehog (Ihh) plays an essential role in angiogenesis, hematogenesis, and epiphysis formation during embryogenesis. In the present study, we injected an adenoviral vector (Adv) carrying the mock-control (Adv-control) or Ihh (Adv-Ihh) gene into severe combined immunodeficiency (SCID) or BALB/c mice to evaluate the effects of lhh on the regulation of postnatal hematopoiesis in vivo. After the i.v. injection of Adv-Ihh, the expression of vector-derived Ihh mRNA was detected in the liver. Four weeks after administration of Adv-Ihh to SCID mice, we observed an increase in the number of c-Kit+ cells and clonogenic cells per 10(5) mononuclear cells in the bone marrow compared with Adv-control-administered mice. Moreover, after administration of Adv-Ihh to BALB/c mice, the number of splenic B220+IgM(low)CD23(int)CD21(int) B lymphocytes and CD4+ T lymphocytes was strongly increased. Furthermore, the number of thymic double-negative (DN)2, DN3, CD8+ immature single-positive, and CD4+/CD8- cells was significantly elevated relative to the number in mice that received the control Adv vector. Our results suggest that enhanced signaling by Ihh can modulate the proliferation and differentiation of splenic B lymphocytes and thymic T lymphocytes during bone marrow hematopoiesis in vivo. Thus, modulation of the hedgehog signaling pathway may provide a therapeutic strategy to stimulate lymphomyelopoiesis in vivo.

Targeted-simultaneous expression of Gas1 and p53 using a bicistronic adenoviral vector in gliomas

The targeted expression of transgenes is one of the principal goals of gene therapy, and it is particularly relevant for the treatment of brain tumors. In this study, we examined the effect of the overexpression of human gas1 (growth arrest specific 1) and human p53 cDNAs, both under the transcriptional control of a promoter of the human glial fibrillary acidic protein (gfa2), employing adenoviral expression vectors, in glioma cells. We showed that the targeted overexpression of gas1 and p53 (AdSGas1 and AdSp53, respectively) in rat glioma cells (C6) reduced the number of viable cells and induced apoptosis. Moreover, the adenovirally targeted expression of these genes also reduced tumor growth in vivo. Unexpectedly, there was no additive effect when both gas1 and p53 were simultaneously expressed in the same cells using a bicistronic adenoviral vector. We suggest that Gas1 does not act in combination with p53 in the C6 and U373 glioma cell lines, inducing apoptosis and cell cycle arrest. Our results indicate that the targeted expression of tumor suppressor genes (gas1 and p53) regulated by the gfa2 promoter, together with adenoviral vectors may provide an interesting approach for adjuvant selective glioma gene therapy.

Comparative morphometrics of embryonic facial morphogenesis: implications for cleft-lip etiology

Cleft lip (CL) with or without cleft palate (CL[P]) has a complex etiology but is thought to be due to either genetic or environmentally induced disruptions of developmental processes affecting the shape and size of the facial prominences (medial nasal, lateral nasal, and maxilla). Recent advances in landmark-based morphometrics enable a rigorous reanalysis of phenotypic shape variation associated with facial clefting. Here we use geometric morphometric (GM) tools to characterize embryonic shape variation in the midface and head of six strains of mice that are both cleft-liable (A, A/WySn, CL/Fr) and normal (BALB/cBy, C57BL, CD1). Data were comprised of two-dimensional landmarks taken from frontal and lateral photographs of embryos spanning the time period in which the facial prominences fuse (GD10-12). Results indicate that A/- strain mice, and particularly A/WySn, have overall smaller midfaces compared to other strains. The A/WySn strain also has significant differences in facial shape related to retarded development. Overall, CL/Fr strain mice are normal-sized, but tend to have undersized maxillary prominences that do not project anteriorly and have a small nasal contact area. These results suggest that the etiology of clefting differs in A/WySn and CL/Fr strains, with the former strain suffering disruptions to developmental processes affecting overall size (e.g., neural crest migration deficiencies and lower mitotic activity), while the latter strain has defects restricted to the shape and size of the maxilla. A combination of molecular experimentation and phenotypic analysis of shape is required to test these hypotheses further.

Gas1 is a modifier for holoprosencephaly and genetically interacts with sonic hedgehog

Holoprosencephaly (HPE) is a clinically heterogeneous developmental anomaly affecting the CNS and face, in which the embryonic forebrain fails to divide into distinct halves. Numerous genetic loci and environmental factors are implicated in HPE, but mutation in the sonic hedgehog (Shh) gene is an established cause in both humans and mice. As growth arrest-specific 1 (Gas1) encodes a membrane glycoprotein previously identified as a Shh antagonist in the somite, we analyzed the craniofacial phenotype of mice harboring a targeted Gas1 deletion. Gas1(-/-) mice exhibited microform HPE, including midfacial hypoplasia, premaxillary incisor fusion, and cleft palate, in addition to severe ear defects; however, gross integrity of the forebrain remained intact. These defects were associated with partial loss of Shh signaling in cells at a distance from the source of transcription, suggesting that Gas1 can potentiate hedgehog signaling in the early face. Loss of a single Shh allele in a Gas1(-/-) background significantly exacerbated the midline craniofacial phenotype, providing genetic evidence that Shh and Gas1 interact. As human GAS1 maps to chromosome 9q21.3-q22, a region previously associated with nonsyndromic cleft palate and congenital deafness, our results establish GAS1 as a potential locus for several human craniofacial malformations.

Functional annotation prediction: all for one and one for all

In an era of rapid genome sequencing and high-throughput technology, automatic function prediction for a novel sequence is of utter importance in bioinformatics. While automatic annotation methods based on local alignment searches can be simple and straightforward, they suffer from several drawbacks, including relatively low sensitivity and assignment of incorrect annotations that are not associated with the region of similarity. ProtoNet is a hierarchical organization of the protein sequences in the UniProt database. Although the hierarchy is constructed in an unsupervised automatic manner, it has been shown to be coherent with several biological data sources. We extend the ProtoNet system in order to assign functional annotations automatically. By leveraging on the scaffold of the hierarchical classification, the method is able to overcome some frequent annotation pitfalls.

Is GAS1 a co-receptor for the GDNF family of ligands?

Glial-cell-line-derived neurotrophic factor (GDNF) is a survival and maintenance factor for dopamine-containing neurons and motoneurons. GDNF belongs to a family of structurally related factors that includes neurturin (NRTN), artemin (ARTN) and persephin (PSPN). An initial step in the activation of signaling via the GDNF family of ligands (GFLs) is their binding to their cognate co-receptor GFR alpha. GAS1, an apparently unrelated protein, exhibits homology to GFR alpha and thus we hypothesize that GAS1 can serve as an alternative receptor for GFLs. The functional similarity between GFR alpha and GAS1 extends to their role in embryogenesis, differentiation and glia maintenance, and is substantiated by overlap in their expression profile, subcellular localization and structural details. We propose that the relative expression and localization of the two remote receptors, GFR alpha and GAS1, on the membranes of neuronal and glial cells determines whether these cells survive or undergo apoptotic death.

Retinoic acid induces CDK inhibitors and growth arrest specific (Gas) genes in neural crest cells

Retinoic acid (RA), the active metabolite of vitamin A, regulates cellular growth and differentiation during embryonic development. In excess, this vitamin is also highly teratogenic to animals and humans. The neural crest is particularly sensitive to RA, and high levels adversely affect migration, proliferation and cell death. We investigated potential gene targets of RA associated with neural crest proliferation by determining RA-mediated changes in gene expression over time, using microarrays. Statistical analysis of the top ranked RA-regulated genes identified modest changes in multiple genes previously associated with cell cycle control and proliferation including the cyclin-dependent kinase inhibitors Cdkn1a (p21), Cdkn2b (p15(INK4b)), and Gas3/PMP22. The expression of p21 and p15(INK4b) contribute to decreased proliferation by blocking cell cycle progression at G1-S. This checkpoint is pivotal to decisions regulating proliferation, apoptosis, or differentiation. We have also confirmed the overexpression of Gas3/PMP22 in RA-treated neural crests, which is associated with cytoskeletal changes and increased apoptosis. Our results suggest that increases in multiple components of diverse regulatory pathways have an overall cumulative effect on cellular decisions. This heterogeneity contributes to the pleiotropic effects of RA, specifically those affecting proliferation and cell death.

Sulfatases: Structure, Mechanism, Biological Activity, Inhibition, and Synthetic Utility

Sulfatases, which cleave sulfate esters in biological systems, play a key role in regulating the sulfation states that determine the function of many physiological molecules. Sulfatase substrates range from small cytosolic steroids, such as estrogen sulfate, to complex cell-surface carbohydrates, such as the glycosaminoglycans. The transformation of these molecules has been linked with important cellular functions, including hormone regulation, cellular degradation, and modulation of signaling pathways. Sulfatases have also been implicated in the onset of various pathophysiological conditions, including hormone-dependent cancers, lysosomal storage disorders, developmental abnormalities, and bacterial pathogenesis. These findings have increased interest in sulfatases and in targeting them for therapeutic endeavors. Although numerous sulfatases have been identified, the wide scope of their biological activity is only beginning to emerge. Herein, accounts of the diversity and growing biological relevance of sulfatases are provided along with an overview of the current understanding of sulfatase structure, mechanism, and inhibition.

Restriction of sonic hedgehog signalling during early tooth development

The signalling peptide encoded by the sonic hedgehog gene is restricted to localised thickenings of oral epithelium, which mark the first morphological evidence of tooth development, and is known to play a crucial role during the initiation of odontogenesis. We show that at these stages in the murine mandibular arch in the absence of epithelium, the Shh targets Ptc1and Gli1 are upregulated in diastema mesenchyme, an edentulous region between the sites of molar and incisor tooth formation. This ectopic expression is not associated with Shh transcription but with Shh protein, undetectable in the presence of epithelium. These findings suggest that, in diastema mesenchyme, restriction of Shh activity is dependent upon the overlying epithelium. This inhibitory activity was demonstrated by the ability of transplanted diastema epithelium to downregulate Ptc1 in tooth explants, and for isolated diastema mesenchyme to express Ptc1. A candidate inhibitor in diastema mesenchyme is the glycosylphosphatidylinositol-linked membrane glycoprotein Gas1. Gas1is normally expressed throughout mandibular arch mesenchyme; however, in the absence of epithelium this expression was downregulated specifically in the diastema where ectopic Shh protein was identified. Although Shh signalling has no effect upon Gas1 expression in mandibular arch mesenchyme,overexpression of Gas1 results in downregulation of ectopic Ptc1. Therefore, control of the position of tooth initiation in the mandibular arch involves a combination of Shh signalling at sites where teeth are required and antagonism in regions destined to remain edentulous.

Expression of hedgehog proteins in the human thymus

The Hedgehog (Hh) family of secreted proteins includes intercellular signaling molecules that specify cell fate and patterning during the development of many tissues. In this study we show that the different components of the Hh signaling pathway are expressed in human thymus. The three mammalian Hh proteins, Sonic (Shh), Indian (Ihh), and Desert (Dhh) hedgehog, are produced by thymic epithelial cells. Shh-expressing epithelial cells are restricted to the thymic subcapsula and medulla, whereas Ihh- and Dhh-producing epithelial cells are distributed throughout the thymus. The requisite Hh receptors, Patched 1(Ptc1) and Smoothened (Smo), and the Gli transcription factors are expressed by thymocytes and also by epithelial cells. Ptc1 is expressed in most thymocyte subsets, whereas Smo expression is mainly associated with immature thymocytes. The isoform of the Ptc receptor, Ptc2, is expressed only by intrathymic progenitor cells and epithelial cells. Other Hh-binding proteins with modulating functions, such as Hedgehog-interacting protein (Hip) and growth arrest-specific gene-1 (Gas-1), are also expressed in human thymus. Our study shows that the intrathymic expression pattern of the Hh signaling pathway components is complex and suggests that Hh proteins may regulate human thymocyte differentiation from the earliest developmental stages, as well as thymic epithelial cell function.

Hedgehog-Gli signalling and the growth of the brain

The development of the vertebrate brain involves the creation of many cell types in precise locations and at precise times, followed by the formation of functional connections. To generate its cells in the correct numbers, the brain has to produce many precursors during a limited period. How this is achieved remains unclear, although several cytokines have been implicated in the proliferation of neural precursors. Understanding this process will provide profound insights, not only into the formation of the mammalian brain during ontogeny, but also into brain evolution. Here we review the role of the Sonic hedgehog-Gli pathway in brain development. Specifically, we discuss the role of this pathway in the cerebellar and cerebral cortices, and address the implications of these findings for morphological plasticity. We also highlight future directions of research that could help to clarify the mechanisms and consequences of Sonic hedgehog signalling in the brain.