OR2AT4 and OR1A2 counterregulate molecular pathophysiological processes of steroid-resistant inflammatory lung diseases in human alveolar macrophages.

BACKGROUND: Therapeutic options for steroid-resistant non-type 2 inflammation in obstructive lung diseases are lacking. Alveolar macrophages are central in the progression of these diseases by releasing proinflammatory cytokines, making them promising targets for new therapeutic approaches. Extra nasal expressed olfactory receptors (ORs) mediate various cellular processes, but clinical data are lacking. This work investigates whether ORs in human primary alveolar macrophages could impact pathophysiological processes and could be considered as therapeutic targets. METHODS: Human primary alveolar macrophages were isolated from bronchoalveolar lavages of 50 patients with pulmonary diseases. The expression of ORs was validated using RT-PCR, immunocytochemical staining, and Western blot. Changes in intracellular calcium levels were analyzed in real-time by calcium imaging. A luminescent assay was used to measure the cAMP concentration after OR stimulation. Cytokine secretion was measured in cell supernatants 24 h after stimulation by ELISA. Phagocytic ability was measured by the uptake of fluorescent-labeled beads by flow cytometry. RESULTS: We demonstrated the expression of functional OR2AT4 and OR1A2 on mRNA and protein levels. Both ORs were primarily located in the plasma membrane. Stimulation with Sandalore, the ligand of OR2AT4, and Citronellal, the ligand of OR1A2, triggered a transient increase of intracellular calcium and cAMP. In the case of Sandalore, this calcium increase was based on a cAMP-dependent signaling pathway. Stimulation of alveolar macrophages with Sandalore and Citronellal reduced phagocytic capacity and release of proinflammatory cytokines. CONCLUSION: These are the first indications for utilizing olfactory receptors as therapeutic target molecules in treating steroid-resistant lung diseases with non-type 2 inflammation.

CREB, NF-Y and MEIS1 conserved binding sites are essential to balance Myostatin promoter/enhancer activity during early myogenesis.

Myostatin (MSTN) is a strong inhibitor of skeletal muscle growth in human and other vertebrates. Its transcription is controlled by a proximal promoter/enhancer (Mstn P/E) containing a TATA box besides CREB, NF-Y, MEIS1 and FXR transcription factor binding sites (TFBSs), which are conserved throughout evolution. The aim of this work was to investigate the role of these TFBSs on Mstn P/E activity and evaluate the potential of their putative ligands as Mstn trans regulators. Mstn P/E mutant constructs were used to establish the role of conserved TFBSs using dual-luciferase assays. Expression analyses were performed by RT-PCR and in situ hybridization in C2C12 myoblasts and E10.5 mouse embryos, respectively. Our results revealed that CREB, NF-Y and MEIS1 sites are required to balance Mstn P/E activity, keeping Mstn transcription within basal levels during myoblast proliferation. Furthermore, our data showed that NF-Y site is essential, although not sufficient, to mediate Mstn P/E transcriptional activity. In turn, CREB and MEIS1 binding sites seem to depend on the presence of NF-Y site to induce Mstn P/E. FXR appears not to confer any effect on Mstn P/E activity, except in the absence of all other conserved TFBS. Accordingly, expression studies pointed to CREB, NF-Y and MEIS1 but not to FXR factors as possible regulators of Mstn transcription in the myogenic context. Altogether, our findings indicated that CREB, NF-Y and MEIS1 conserved sites are essential to control basal Mstn transcription during early myogenesis, possibly by interacting with these or other related factors.

Retrograde migration of pectoral girdle muscle precursors depends on CXCR4/SDF-1 signaling.

In vertebrates, muscles of the pectoral girdle connect the forelimbs with the thorax. During development, the myogenic precursor cells migrate from the somites into the limb buds. Whereas most of the myogenic precursors remain in the limb bud to form the forelimb muscles, several cells migrate back toward the trunk to give rise to the superficial pectoral girdle muscles, such as the large pectoral muscle, the latissimus dorsi and the deltoid. Recently, this developing mode has been referred to as the "In-Out" mechanism. The present study focuses on the mechanisms of the "In-Out" migration during formation of the pectoral girdle muscles. Combining in ovo electroporation, tissue slice-cultures and confocal laser scanning microscopy, we visualize live in detail the retrograde migration of myogenic precursors from the forelimb bud into the trunk region by live imaging. Furthermore, we present for the first time evidence for the involvement of the chemokine receptor CXCR4 and its ligand SDF-1 during these processes. After microsurgical implantations of CXCR4 inhibitor beads in the proximal forelimb region of chicken embryos, we demonstrate with the aid of in situ hybridization and live-cell imaging that CXCR4/SDF-1 signaling is crucial for the retrograde migration of pectoral girdle muscle precursors. Moreover, we analyzed the MyoD expression in CXCR4-mutant mouse embryos and observed a considerable decrease in pectoral girdle musculature. We thus demonstrate the importance of the CXCR4/SDF-1 axis for the pectoral girdle muscle formation in avians and mammals.

Wnt11 is required for oriented migration of dermogenic progenitor cells from the dorsomedial lip of the avian dermomyotome.

The embryonic origin of the dermis in vertebrates can be traced back to the dermomyotome of the somites, the lateral plate mesoderm and the neural crest. The dermal precursors directly overlying the neural tube display a unique dense arrangement and are the first to induce skin appendage formation in vertebrate embryos. These dermal precursor cells have been shown to derive from the dorsomedial lip of the dermomyotome (DML). Based on its expression pattern in the DML, Wnt11 is a candidate regulator of dorsal dermis formation. Using EGFP-based cell labelling and time-lapse imaging, we show that the Wnt11 expressing DML is the source of the dense dorsal dermis. Loss-of-function studies in chicken embryos show that Wnt11 is indeed essential for the formation of dense dermis competent to support cutaneous appendage formation. Our findings show that dermogenic progenitors cannot leave the DML to form dense dorsal dermis following Wnt11 silencing. No alterations were noticeable in the patterning or in the epithelial state of the dermomyotome including the DML. Furthermore, we show that Wnt11 expression is regulated in a manner similar to the previously described early dermal marker cDermo-1. The analysis of Wnt11 mutant mice exhibits an underdeveloped dorsal dermis and strongly supports our gene silencing data in chicken embryos. We conclude that Wnt11 is required for dense dermis and subsequent cutaneous appendage formation, by influencing the cell fate decision of the cells in the DML.

ATOH8, a regulator of skeletal myogenesis in the hypaxial myotome of the trunk.

The embryonic muscles of the axial skeleton and limbs take their origin from the dermomyotomes of the somites. During embryonic myogenesis, muscle precursors delaminate from the dermomyotome giving rise to the hypaxial and epaxial myotome. Mutant studies for myogenic regulatory factors have shown that the development of the hypaxial myotome differs from the formation of the epaxial myotome and that the development of the hypaxial myotome depends on the latter within the trunk region. The transcriptional networks that regulate the transition of proliferative dermomyotomal cells into the predominantly post-mitotic hypaxial myotome, as well as the eventual patterning of the myotome, are not fully understood. Similar transitions occurring during the development of the neural system have been shown to be controlled by the Atonal family of helix-loop-helix transcription factors. Here, we demonstrate that ATOH8, a member of the Atonal family, is expressed in a subset of embryonic muscle cells in the dermomyotome and myotome. Using the RNAi approach, we show that loss of ATOH8 in the lateral somites at the trunk level results in a blockage of differentiation and thus causes cells to be maintained in a predetermined state. Furthermore, we show that ATOH8 is also expressed in cultured C2C12 mouse myoblasts and becomes dramatically downregulated during their differentiation. We propose that ATOH8 plays a role during the transition of myoblasts from the proliferative phase to the differentiation phase and in the regulation of myogenesis in the hypaxial myotome of the trunk.

A thymosin beta15-like peptide promotes intersegmental myotome extension in the chicken embryo.

Beta-thymosins constitute a group of small actin-sequestering peptides. These highly conserved peptides are involved in cytoskeleton dynamics and can influence different cell properties such as motility, substrate adhesion, shape and chemotaxis. As a marker for tumour metastasis, the mammalian thymosin beta15 is believed to have an important diagnostic relevance in cancer prognosis, although little is known about its physiological function. In order to study the role of thymosin beta15(avian) in embryogenesis, we cloned the chicken and quail orthologues of thymosin beta15 and used the chicken as a model for vertebrate development. Avian thymosin beta15, the first known non-mammalian thymosin beta15-like gene, encodes a peptide that possesses a cysteine at position one after the methionine which is a significant difference compared to its mammalian counterparts. Thymosin beta15(avian) expression starts at an early stage of development. The expression pattern changes rapidly with development and differs from that of the related thymosin beta4 gene. The most prominent expression domain is seen in developing muscles of limbs and trunk. Gain-of-function experiments revealed that thymosin beta15(avian) has a function in normal myotome development. Ectopic over-expression of thymosin beta15(avian) leads to premature elongation of myotome cells trespassing segment borders. We conclude that thymosin beta15(avian) has a still undescribed function in promoting myocyte elongation.

Myogenesis and muscle regeneration.

Skeletal muscle has received much attention with regard to developmental origin, control of cell differentiation and regeneration. In this article, early landmarks in skeletal muscle research are reviewed and recent findings on myogenesis are addressed with particular focus on novel regulatory molecules including miRNAs, as well as on the topographical heterogeneity of skeletal muscle origin. The latter has developed into a central theme of keen interest in the past years, particularly since overlaps in genetic and embryological background between head muscle subsets and heart muscle have been described. As embryonic myogenesis and regenerating myofibers employ common molecules, the heterogeneity in embryonic sources from which skeletal muscle groups in the vertebrate body take origin is closely reflected by differences in the susceptibility to particular muscle dystrophies as well as their regeneration potential. In the regeneration chapter of this review the progress that has been made in the field of muscle stem cell biology, with special focus on the satellite cells, is outlined. Satellite cells are considered the most promising source of muscle stem cells possessing a high regenerative potential. We shall discuss recent insights into the heterogeneous nature of these satellite cells not just in terms of their expression profile but also their regeneration potential. Latest findings about the motility of the satellite cell shall also be discussed. Furthermore, we shall outline the impact of an improved understanding of muscle stem cells within their environment, and of satellite cells in particular, on efficient stem cell replacement therapies for muscular dystrophies, putting embryological findings and stem cell approaches into context.

Comparative analysis of Neph gene expression in mouse and chicken development.

Neph proteins are evolutionarily conserved members of the immunoglobulin superfamily of adhesion proteins and regulate morphogenesis and patterning of different tissues. They share a common protein structure consisting of extracellular immunoglobulin-like domains, a transmembrane region, and a carboxyl terminal cytoplasmic tail required for signaling. Neph orthologs have been widely characterized in invertebrates where they mediate such diverse processes as neural development, synaptogenesis, or myoblast fusion. Vertebrate Neph proteins have been described first at the glomerular filtration barrier of the kidney. Recently, there has been accumulating evidence suggesting a function of Neph proteins also outside the kidney. Here we demonstrate that Neph1, Neph2, and Neph3 are expressed differentially in various tissues during ontogenesis in mouse and chicken. Neph1 and Neph2 were found to be amply expressed in the central nervous system while Neph3 expression remained localized to the cerebellum anlage and the spinal cord. Outside the nervous system, Neph mRNAs were also differentially expressed in branchial arches, somites, heart, lung bud, and apical ectodermal ridge. Our findings support the concept that vertebrate Neph proteins, similarly to their Drosophila and C. elegans orthologs, provide guidance cues for cell recognition and tissue patterning in various organs which may open interesting perspectives for future research on Neph1-3 controlled morphogenesis.

Diversification and molecular evolution of ATOH8, a gene encoding a bHLH transcription factor.

ATOH8 is a bHLH domain transcription factor implicated in the development of the nervous system, kidney, pancreas, retina and muscle. In the present study, we collected sequence of ATOH8 orthologues from 18 vertebrate species and 24 invertebrate species. The reconstruction of ATOH8 phylogeny and sequence analysis showed that this gene underwent notable divergences during evolution. For those vertebrate species investigated, we analyzed the gene structure and regulatory elements of ATOH8. We found that the bHLH domain of vertebrate ATOH8 was highly conserved. Mammals retained some specific amino acids in contrast to the non-mammalian orthologues. Mammals also developed another potential isoform, verified by a human expressed sequence tag (EST). Comparative genomic analyses of the regulatory elements revealed a replacement of the ancestral TATA box by CpG-islands in the eutherian mammals and an evolutionary tendency for TATA box reduction in vertebrates in general. We furthermore identified the region of the effective promoter of human ATOH8 which could drive the expression of EGFP reporter in the chicken embryo. In the opossum, both the coding region and regulatory elements of ATOH8 have some special features, such as the unique extended C-terminus encoded by the third exon and absence of both CpG islands and TATA elements in the regulatory region. Our gene mapping data showed that in human, ATOH8 was hosted in one chromosome which is a fusion product of two orthologous chromosomes in non-human primates. This unique chromosomal environment of human ATOH8 probably subjects its expression to the regulation at chromosomal level. We deduce that the great interspecific differences found in both ATOH8 gene sequence and its regulatory elements might be significant for the fine regulation of its spatiotemporal expression and roles of ATOH8, thus orchestrating its function in different tissues and organisms.

Etiopathogenesis of hyperostosis frontalis interna: a mystery still.

Hyperostosis frontalis interna is a morphological pattern characterized by single or multiple bony nodules situated on the inner lamina of the frontal bone. It is seldom found in males, but it is a common phenomenon among post-menopausal females in modern societies but relatively rare in antiquity. The etiopathogenesis of the trait is a matter of debate and ranges from genetic predisposition to epigenetic, while endocrine disturbances, aging, and dietary factors are also listed among the causes. We studied the frequency, characteristic features, and etiopathogenesis of the disease in recent cadaveric and dry skull specimens. The frequency of hyperostosis frontalis interna in cadavers and dry skull materials was almost identical, 12.5% and 12.3%, respectively. In cadavers, 87.5% of severe hyperostosis frontalis interna cases were found in females over 65 years-old. Interestingly, in two cadavers we found hyperostotic lesions spreading onto adjacent tissues such as the dura and falx cerebri. We provide some new aspects that may help in better understanding of the etiopathogenesis of hyperostosis frontalis interna. Thereby, we discuss the various etiopathogenesis models found in the literature.

Sternalis muscle: a new crossed subtype, classification, and surgical applications.

The sternalis muscle is an anatomic variation well known to anatomists, but relatively unknown to clinicians and surgeons. It is localized superficially to the pectoralis major and can cause a diagnostic dilemma during breast surgery, mammography, and computed tomography and magnetic resonance imaging scans, as its appearance mimics tumor pathology of the region. We studied the presence of longitudinally placed muscles in the anterior thoracic wall in 45 cadavers (90 hemithoraces). In an 83-year-old white male, a rare case of crossed-type sternalis was detected on the left side. The muscle originated from the sternal head of the right sternocleidomastoid, crossed into the opposite parasternal half, and split into 2 tendons and 2 muscle bellies that inserted into the left subcostal arch region. This variant was not included in the available sternalis classifications, and an update is suggested. The muscle is of utmost importance and diagnostic value in routine mammogram screening. Moreover, it is of great value for the plastic surgeon, because identification of the variant can aid the differential diagnosis among other regional lesions. Likewise, its superficial location makes it an ideal candidate for utilization as a muscular flap in plastic reconstruction of the head and neck region.

A novel role of CXCR4 and SDF-1 during migration of cloacal muscle precursors.

The cloaca acts as a common chamber into which gastrointestinal and urogenital tracts converge in lower vertebrates. The distal end of the cloaca is guarded by a ring of cloacal muscles or sphincters, the equivalent of perineal muscles in mammals. It has recently been shown that the development of the cloacal musculature depends on hindlimb muscle formation. The signaling molecules responsible for the outward migration of hindlimb myogenic precursors are not known. Based on the expression studies for CXCR4 and SDF-1, we hypothesized a role of this signaling pair during cloacal muscle precursor migration. The aim of our study was to investigate the role of SDF-1/CXCR4 during cloacal muscle precursor migration in the chicken embryos. We show that SDF-1 is expressed in the cloacal region, and by experimentally manipulating the SDF-1/CXCR4 signaling, we can show that SDF-1 guides the migration of CXCR4-expressing cloacal muscle precursors.

Histone deacetylase inhibitor, trichostatin A, affects gene expression patterns during morphogenesis of chicken limb buds in vivo.

Acetylation is one of the key chromatin modifications that control gene transcription during embryonic development and tumorigenesis. The types of genes sensitive to such modifications in vivo are not known to date. We investigated the expression of a number of genes involved in embryonic development after treatment with trichostatin A (TSA), a histone deacetylase (HDAC) inhibitor, in the limbs of chicken embryos. Our results show that TSA affects the expression profiles of some genes that play important roles during limb development. The expression of BMP4, SF/HGF and Twist1 increased, whereas the expression of BMP2, FGF8, Shh, Scleraxis, Myf5 and MyoD was decreased or even inhibited. In contrast, the expression of Pax3, Paraxis, Msx1, CREB, and PCNA was not affected. Our results indicate that the chicken embryo can serve as an effective in vivo model for studying the effect of HDAC inhibitors on gene expression and can be helpful for understanding the role of chromatin remodeling and epigenetic control of gene expression.

Stromal-derived factor-1 (SDF-1) expression during early chick development.

Cell migration plays a fundamental role in a wide variety of biological processes including development, tissue repair and disease. These processes depend on directed cell migration along and through cell layers. Chemokines are small secretory proteins that exert their effects by activating a family of G-protein coupled receptors and have been shown to play numerous fundamental roles in the control of physiological and pathological processes during development and in adult tissues, respectively. Stromal-derived factor-1 (SDF-1/CXCL12), a ligand of the chemokine receptor, CXCR4, is involved in providing cells with directional cues as well as in controlling their proliferation and differentiation. Here we studied the expression pattern of SDF-1 in the developing chick embryo. We could detect a specific expression of SDF-1 in the ectoderm, the sclerotome, the intersomitic spaces and the developing limbs. The expression domains of SDF-1 reflect its role in somitic precursor migration and vessel formation in the limbs.

The eventful somite: patterning, fate determination and cell division in the somite.

The segmental somites not only determine the vertebrate body plan, but also represent turntables of cell fates. The somite is initially naive in terms of its fate restriction as shown by grafting and rotation experiments whereby ectopically grafted or rotated tissue of newly formed somites yielded the same pattern of normal derivatives. Somitic derivatives are determined by local signalling between adjacent embryonic tissues, in particular the neural tube, notochord, surface ectoderm and the somitic compartments themselves. The correct spatio-temporal specification of the deriving tissues, skeletal muscle, cartilage, endothelia and connective tissue is achieved by a sequence of morphogenetic changes of the paraxial mesoderm, eventually leading to the three transitory somitic compartments: dermomyotome, myotome and sclerotome. These structures are specified along a double gradient from dorsal to ventral and from medial to lateral. The establishment and controlled disruption of the epithelial state of the somitic compartments are crucial for development. In this article, we give a synopsis of some of the most important signalling events involved in somite patterning and cell fate decisions. Particular emphasis has been laid on the issue of epithelio-mesenchymal transition and different types of cell division in the somite.

Expression of the avian gene cNOC2 encoding nucleolar complex associated protein 2 during embryonic development.

Genetic information that directs a cell during different phases of embryogenesis is locked up in the genome. Therein is contained the road map for growth, proliferation, differentiation and morphogenesis. The cellular transportation machinery plays a major role to ensure that all the components for transcription and translation are available at the right place at the right time. Nucleolar complex associated protein2 (NOC2) has a highly conserved UPF0120 domain, and is an element involved in ribosome transportation from the nucleoplasm to the cytoplasm. However, its gene expression pattern is still unknown. We chose the developing chick embryo to investigate the possible involvement of avian NOC2 (cNOC2) in developmental processes, particularly neurogenesis and myogenesis. For this purpose, we constructed a fragment of chicken cNOC2, which contains the UPF0120 domain coding sequence, into pDrive vector, and performed in situ hybridization on chicken embryos of different stages with this gene probe. A dynamic expression pattern of cNOC2 transcripts can be seen beginning as early as from stage HH7 until stage HH32. Using in situ hybridization we could detect that cNOC2 transcripts were expressed ubiquitously, but prominent expression could be found in the neural tissue, the somites and in the developing limbs. Comparison of cNOC2 gene expression with the proliferation marker gene cPCNA, muscle specific marker genes cMyf5 and cMyoD in single or double in situ hybridisation show that cNOC2 is expressed in the myotome, similar to cMyf5 and cMyoD, but not like cPCNA, which is hardly detectable in the myotome. Our results suggest that cNOC2 is involved in the development of neural tissue, somites and limbs.

Inhibitors of CXCR4 affect the migration and fate of CXCR4+ progenitors in the developing limb of chick embryos.

Chemokines and their receptors play major roles in numerous physiological and pathological processes during development and disease. CXCR4 is the most abundantly expressed chemokine receptor during development. In contrast to other chemokine receptors, CXCR4 binds and is activated exclusively by its ligand stromal derived factor-1 (SDF-1) or CXCL12. SDF-1 signaling has a wide range of effects on CXCR4-expressing cells depending on the cell type ranging from cell growth to adhesion, chemotaxis, and migration. CXCR4 also serves as a co-receptor for HIV-1 entry into T-cells and has been implicated in the pathogenesis of rheumatoid arthritis and cancer growth and invasion. Numerous inhibitors and antagonists of CXCR4 have been produced and are being tested for their efficiency to target its role in pathogenesis. Our initial expression analysis revealed that CXCR4 is expressed by the migrating myogenic and angiogenic precursors in the developing chick limb. In this study, we used the most specific peptidic inhibitors of CXCR4, T140 and its analog TN14003, to analyse the effect of blocking CXCR4/SDF-1 signaling on the undetermined bioptent migratory progenitors in the developing chick limb. Our results point to defects in migration and an altered differentiation program of these CXCR4-expressing progenitor pool in the limb.

RNAi-induced targeted silencing of developmental control genes during chicken embryogenesis.

The RNA interference technique is a powerful tool to understand gene function. Intriguingly, RNA interference cannot only be used for cells in vitro, but also in living organisms. Here, we have adapted the method for use in the chick embryo. However, this technique is limited by the uncertainty in predicting the RNAi transfection efficiency and site in the embryo. Hence, we elaborated a modified vector system, pEGFP-shRNA, which can coexpress enhanced green fluorescent protein (EGFP) and short hairpin RNA (shRNA) simultaneously to facilitate analysis of gene silencing in chicken embryos. We tested the silencing of two highly conserved genes (cAxin2, cParaxis), which play crucial roles in chicken embryonic developmental processes. For each target gene, four to five small DNA inserts, each of them encoding one shRNA, were selected and cloned individually to the vector downstream of the Pol III promoter (either human H1 or U6 promoter), which shared with highly conserved motifs in human and chicken. The pEGFP-shRNA constructs were electroporated into the neural tube or somites. After subsequent re-incubation of 24 h, the EGFP expression, with green fluorescent signal, indicated the transfected regions in the neural tube or somites. The EGFP expressing embryos were further submitted into the process of in situ hybridization for examination of the silencing effects. The results show that the EGFP signal in transfected areas correlated with the silencing of the target genes (cAxin2, cParaxis). The cAxin2 expression was inhibited by shRNAs of either targeting the RGS domain or the DAX domain coding region. The cParaxis mRNA level in transgenic somites and the related migratory myogenic population was also reduced. The results suggest that our novel dual expression EGFP-shRNA system opens a new possibility to study gene function in a convenient and efficient way.

Expression of chemokine receptor CXCR4 during chick embryo development.

The chemokine receptor CXCR4 plays a decisive role in physiological cell migration both in developmental processes and adult tissues; it has also been implicated in metastasis formation of different human cancers (Balkwill 2004) and in HIV pathogenesis (Murdoch 2000). Here we present the expression pattern of this important chemokine receptor CXCR4 in the chick embryo. A dynamic expression pattern can be detected beginning as early as the gastrulation stages until the observed stage of HH28. During gastrulation, expression was observed in the epiblast at the level of the primitive streak and in the endoderm. Later, expression was noticeable in the ventral foregut portal, developing somites, tail bud, neural tube, the intermediate mesoderm, Wolffian duct, the lateral plate mesoderm and the developing blood vessels. Our descriptive data suggest a role for CXCR4 in gastrulation and other morphogenetic events connected with angiogenesis and kidney development.

cDermo-1 misexpression induces dense dermis, feathers, and scales.

Reciprocal epithelio-mesenchymal interactions between the prospective epidermis and the underlying dermis are the major driving forces in the development of skin appendages. Feather development is initiated by a still unknown signal from the dermis in feather-forming skin. The morphological response of the ectoderm to this signal is the formation of an epidermal placode, which signals back to the mesenchyme to induce dermal condensations. Together, epidermal and dermal components constitute the outgrowing feather bud. The bHLH transcription factor cDermo-1 is expressed in developing dermis and is the earliest known marker of prospective feather tracts. To test its function during feather development, we forced cDermo-1 expression in embryonic chicken dermis using a retroviral expression vector. In featherless (apteric) regions, cDermo-1 misexpression induced dense, thickened dermis normally observed in feathered skin (pterylae), and leads to the development of regularly spaced and normally shaped ectopic feather buds. In pterylae, cDermo-1 misexpression enhanced feather growth. In hindlimb skin, according to the local skin identity, misexpression of cDermo-1 induced ectopic scale formation. Thus, we show that forced cDermo-1 expression in developing dermis is sufficient to launch the developmental program leading to skin appendage formation. We propose a role of cDermo-1 at the initial stages of feather induction upstream of FGF10.