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Martin Scaal

Publications and source records attributed to Martin Scaal.

At least 19 recordsLinked to original sources
PubMed2006

Somite compartments in anamniotes.

Somites are a common feature of the phylotypic stage of embryos of all higher chordates. In amniote species like mouse and chick, somite development has been the subject of intense research over many decades, giving insight into the morphological and molecular processes leading to somite compartmentalization and subsequent differentiation. In anamniotes, somite development is much less understood. Except for recent data from zebrafish, and morphological studies in Xenopus, very little is known about the formation of somite compartments and the differentiation of somite derivatives in anamniotes. Here, we give a brief overview on the development of myotome, sclerotome and dermomyotome in various anamniote organisms, and point out the different mechanisms of somite development between anamniotes and the established amniote model systems.

Amphibians↗
PubMed2006

Regulation of ectodermal Wnt6 expression by the neural tube is transduced by dermomyotomal Wnt11: a mechanism of dermomyotomal lip sustainment.

Ectodermal Wnt6 plays an important role during development of the somites and the lateral plate mesoderm. In the course of development, Wnt6 expression shows a dynamic pattern. At the level of the segmental plate and the epithelial somites, Wnt6 is expressed in the entire ectoderm overlying the neural tube, the paraxial mesoderm and the lateral plate mesoderm. With somite maturation, expression becomes restricted to the lateral ectoderm covering the ventrolateral lip of the dermomyotome and the lateral plate mesoderm. To study the regulation of Wnt6 expression, we have interfered with neighboring signaling pathways. We show that Wnt1 and Wnt3a signaling from the neural tube inhibit Wnt6 expression in the medial surface ectoderm via dermomyotomal Wnt11. We demonstrate that Wnt11 is an epithelialization factor acting on the medial dermomyotome, and present a model suggesting Wnt11 and Wnt6 as factors maintaining the epithelial nature of the dorsomedial and ventrolateral lips of the dermomyotome, respectively, during dermomyotomal growth.

Animals↗
PubMed2006

Avian stanniocalcin-2 is expressed in developing striated muscle and joints.

The glycoprotein hormone stanniocalcin (STC) has originally been described in the teleost kidney. Since then, STC homologs have been identified in various genomes including human, mouse, rat, Xenopus and zebrafish. In mammals, two STC genes, STC1 and STC2, are known. We cloned a chicken STC homolog to analyze its expression pattern during chick development. Sequence analyses revealed a high sequence similarity of the chicken STC (cSTC) clone to mammalian STC2. Interestingly the expression pattern of cSTC2 largely resembles those of murine STC1: we found expression of cSTC2 in the nephric tubules, in the myocardium, in skeletal muscle cells from the onset of differentiation, and in synovial joint anlagen of the limbs.

Amino Acid Sequence↗
PubMed2005

Role of Wnt-6 in limb myogenesis.

Cells from the ventrolateral lip of the dermomyotome at limb levels undergo epithelio-mesenchymal transition and migrate as individual and undifferentiated cells into the limb buds. The precursor cells are under the influence of various signaling factors in the limb. Dorsal and ventral ectoderm influences various aspects of limb development. In addition to our previous studies, we investigated the influence of ectoderm and Wnt-6 on somitic cells in the limb bud. We show that in the absence of ectoderm the precursor cells never form muscle cells but differentiate into endothelial cells. In addition, we show that Wnt-6 that is secreted from the ectoderm influences the precursor cells to form muscle even in the absence of ectoderm. This indicates that Wnt-6 is an ectodermal signal that induces somite-derived progenitor cells to form muscle cells during limb development.

Animals↗
PubMed2005

Ectodermal Wnt-6 promotes Myf5-dependent avian limb myogenesis.

Limb muscles of vertebrates are derived from precursor cells that migrate from the lateral edge of the dermomyotome into the limb bud. Although several signaling molecules have been reported to be involved in the process of limb myogenesis, none of their activities has led to a consolidate idea about the limb myogenic pathway. Particularly, the role of ectodermal signals in limb myogenesis is still obscure. Here, we investigated the role of the ectoderm and ectodermal Wnt-6 during limb muscle development. We found that ectopic expression of Wnt-6 in the limb bud specifically extends the expression domains of Pax3, Paraxis, Myf5, Myogenin, Desmin and Myosin heavy chain (MyHC) but inhibits MyoD expression. Ectoderm removal results in a loss of expression of all of these myogenic markers. We show that Wnt-6 can compensate the absence of the ectoderm by rescuing the expression of Pax3, Paraxis, Myf5, Myogenin, Desmin and MyHC but not MyoD. These results show that, in chick, at least two signals from the limb ectoderm are necessary for muscle development. One of the signals is Wnt-6, which plays a unique role in promoting limb myogenesis via Pax3/Paraxis-Myf5, whereas the other putative signaling pathway involving MyoD expression is negatively regulated by Wnt-6 signaling.

Animals↗
PubMed2005

Differential regulation of avian pelvic girdle development by the limb field ectoderm.

Although limb development has been a subject of intense research over the last decades, development of the girdles has been poorly investigated. Particularly, a detailed analysis of pelvic girdle development including functional data is not available to date. Here, we describe the early steps of the formation of mesenchymal and cartilaginous anlagen of the pelvic elements using alcian blue staining in whole mount embryos and serial histological sections, and the expression pattern of several marker genes to provide an operative basis for further research in pelvis development. Moreover, we describe pelvis development after unilateral hindlimb bud amputation and somatopleural ectoderm extirpation. We show for the first time, that ectodermal signals at pre-limb bud stages are required for pelvis formation. We present evidence suggesting that the regulation of ilium development is different from the development of ischium and pubis.

Animals↗
PubMed2005

The formation of the avian scapula blade takes place in the hypaxial domain of the somites and requires somatopleure-derived BMP signals.

The avian scapula is a long bone located dorsally on the thorax. The cranial part that articulates with the upper limb is derived from the somatopleure of the forelimb field, while the caudal part, the scapula blade, originates from the dermomyotomes of brachial and thoracic somites. In previous studies, we have shown that scapula blade formation is intrinsically controlled by segment-specific information as well as extrinsically by ectoderm-derived signals. Here, we addressed the role of signals derived from the lateral plate mesoderm on scapula development. Chick-quail chimera experiments revealed that scapula precursor cells are located within the hypaxial domain of the dermomyotome adjacent to somatopleural cells. Barrier implantation between these two cell populations inhibited scapula blade formation. Furthermore, we identified BMPs as scapula-inducing signals from the somatopleure using injection of Noggin-producing cells into the hypaxial domain of scapula-forming dermomyotomes. We found that inhibition of BMP activity interfered with scapula-specific Pax1 expression and scapula blade formation. Taken together, we demonstrate that the scapula-forming cells located within the hypaxial somitic domain require BMP signals derived from the somatopleure for their specification and differentiation.

Animals↗
PubMed2005

BMP4 and noggin control embryonic blood vessel formation by antagonistic regulation of VEGFR-2 (Quek1) expression.

Regulation of VEGFR-2 (Quek1) is an important mechanism during blood vessel formation. In the paraxial mesoderm, Quek1 expression is restricted to the lateral portion of the somite and later to sclerotomal cells surrounding the neural tube. By grafting of either intermediate mesoderm or BMP4 beads into the paraxial mesoderm, we show that BMP4 is a positive regulator of VEGFR-2 (Quek1) expression in the quail embryo. Separation of somites from intermediate mesoderm leads to down-regulation of Quek1 expression. The expression of Quek1 in the medial somite half is normally repressed by the notochord and becomes up-regulated and lateromedially expanded after separation of the notochord. Our results show that up-regulation of BMP4 leads to an increase of the number of blood vessels, whereas inhibition of BMP4 by noggin results in a reduction of blood vessels.

Animals↗
PubMed2005

Comparative analysis of the expression patterns of Wnts during chick limb development.

Wnts control a number of processes during limb development-from initiating outgrowth and controlling patterning, to regulating cell differentiation in a number of tissues. We analyzed the expression pattern of various Wnts (4, 5a, 5b, 6, 11, and 14) in whole mount in situ hybridization during chick wing development. From HH stage 26, expression of Wnt 4 is observed in the central elbow region and wrist-forming regions, and during later stages, expression is seen in the joint-forming regions of the whole limb. Wnt 5a is expressed throughout the limb mesenchyme during early limb developmental stages, and later, at HH stage 23, it becomes predominantly confined to the distal tip, leaving low expression levels proximally. At HH stage 29, expression at the distal tip is restricted to the interdigital regions, and at day 8, expression is seen in the region surrounding the phalanges. Wnt 5b expression is first observed in the AER at HH stage 20 and later in the dorsal and ventral mesenchyme surrounding the cartilage elements of the limb. Expression of Wnt 6 is observed from HH stage 17 until day 8 in the dorsal and ventral ectoderm and also in the dorsoventral limb boundaries. Expression of Wnt 11 is observed in the proximal dorsal mesenchyme of the limb from HH stage 23 onward and later in the dorsal and ventral subectodermal mesenchyme and in the regions adjacent to the digits at day 8. Weak expression of Wnt 14 is observed at the proximal mesenchyme of the limb at HH stage 23; later, it extends as a transverse strip surrounding the cartilage elements as well as in the interdigital mesenchyme.

Animals↗
PubMed2005

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.

Animals↗
PubMed2005

Cells of all somitic compartments are determined with respect to segmental identity.

Development of somite cells is orchestrated by two regulatory processes. Differentiation of cells from the various somitic compartments into different anlagen and tissues is regulated by extrinsic signals from neighboring structures such as the notochord, neural tube, and surface ectoderm. Morphogenesis of these anlagen to form specific structures according to the segmental identity of each somite is specified by segment-specific positional information, based on the Hox-code. It has been shown that following experimental rotation of presomitic mesoderm or newly formed somites, paraxial mesodermal cells adapt to the altered signaling environment and differentiate according to their new orientation. In contrast, presomitic mesoderm or newly formed somites transplanted to different segmental levels keep their primordial segmental identity and form ectopic structures according to their original position. To determine whether all cells of a segment, including the dorsal and ventral compartment, share the same segmental identity, presomitic mesoderm or newly formed somites were rotated and transplanted from thoracic to cervical level. These experiments show that cells from all compartments of a segment are able to interpret extrinsic local signals correctly, but form structures according to their original positional information and maintain their original Hox expression in the new environment.

Animals↗
PubMed2005

Arthrotome: a specific joint forming compartment in the avian somite.

Somitocoele cells previously have been shown to form the proximal part of the ribs, the intervertebral discs, and the intervertebral joints (synovial joints). To determine whether the somitocoele cells are necessary for the development of axial skeleton joints, we microsurgically ablated the somitocoele cells in epithelial somites of 2-day-old chick embryos. The operated embryos were analyzed after whole-mount skeletal preparations and in sections. Removal of the somitocoele cells led to two major outcomes: (1) Intervertebral joints failed to develop and resulted in the fusion of the superior articular process and the inferior articular process; (2) Adjacent vertebral bodies fused and lacked the intervertebral disc. These results demonstrate that somitocoele cells specifically give rise to intervertebral joints and discs. Furthermore, these results suggest that neighboring sclerotome cells cannot adapt to form vertebral joints in the absence of the somitocoele compartment. Thus, we provide for the first time experimental evidence for the existence of a joint forming compartment in the somites, which we term the "arthrotome."

Animals↗
PubMed2004

Formation and differentiation of the avian dermomyotome.

During somite maturation, the ventral half of the epithelial somite disintegrates into the mesenchymal sclerotome, whereas the dorsal half forms a transitory epithelial sheet, the dermomyotome, lying in between the sclerotome and the surface ectoderm. The dermomyotome is the source of most of the mesodermal tissues in the body, giving rise to cell types as different as muscle, connective tissue, endothelium, and cartilage. Thus, the dermomyotome is the most important turntable of mesodermal cell fate choice in the vertebrate embryo. Here, we discuss the current knowledge on the formation of the dermomyotome and the mechanisms leading to the development of the various dermomyotomal derivatives, with special emphasis on the development of musculature and dermis.

Animals↗
PubMed2004

Formation and differentiation of the avian sclerotome.

The avian sclerotome forms by epitheliomesenchymal transition of the ventral half-somite. Sclerotome development is characterized by a craniocaudal polarization, resegmentation, and axial identity. Its formation is controlled by signals from the notochord, the neural tube, the lateral plate mesoderm, and the myotome. These signals and crosstalk between somite cells lead to the separation of various subdomains, such as the central and ventral sclerotomes that express Pax1 under the control of Sonic hedgehog and Noggin, and the dorsal and lateral sclerotome that do not express Pax1 and are controlled by Bmp-4. Further subdomains that give rise to specific derivatives are the syndetome, neurotome, meningotome, and arthrotome. The molecular control of subdomain formation and cell type specification is discussed.

Animals↗
PubMed2004

In ovo electroporation of avian somites.

In ovo electroporation is a well-established method of gene transfer into neural and mesenchymal tissue in chick embryos. Electroporation of somites, however, has been hampered by low efficiency due to technical difficulties. Here, we present a powerful technique to electroporate avian somites and subpopulations of somitic cells at high efficiency in ovo. We demonstrate specific targeting of distinct somitic compartments and their derivatives using single or combinations of plasmid expression vectors. This technique opens new perspectives to investigate the morphologic and genetic basis of somite development.

Animals↗
PubMed2004

A two-step mechanism for myotome formation in chick.

The study of the morphogenetic cell movements underlying myotome formation in the chick embryo has led to the emergence of highly controversial models. Here we report a real-time cell lineage analysis of myotome development using electroporation of a GFP reporter in newly formed chick somites. Confocal analysis of cell movements demonstrates that myotome formation involves two sequential steps. In a first phase, incremental myotome growth results from a contribution of myocytes derived solely from the medial border of the dermomyotome. In a second phase, myocytes are produced from all four borders of the dermomyotome. The relative distribution of myocytes demonstrates that the medial and the lateral borders of the somite generate exclusively epaxial and hypaxial muscles. This analysis also identified five myotomal regions, characterized by the origin of the myocytes that constitute them. Together, our results provide a comprehensive model describing the morphogenesis of the early myotome in higher vertebrates.

Animals↗
PubMed2002

BMPs induce dermal markers and ectopic feather tracts.

Bone morphogenetic protein (BMP) signaling is known to be involved in multiple inductive events during embryogenesis including the development of amniote skin. Here, we demonstrate that early application of BMP-2 to the lateral trunk of chick embryos induces the formation of dense dermis, which is competent to participate in feather development. We show that BMPs induce the dermis markers Msx-1 and cDermo-1 and lead to dermal proliferation, to expression of beta-catenin, and eventually to the formation of ectopic feather tracts in originally featherless regions of chick skin. Moreover, we present a detailed analysis of cDermo-1 expression during early feather development. The data implicate that cDermo-1 is located downstream of BMP in a signaling pathway that leads to condensation of dermal cells. The roles of BMP and cDermo-1 during development of dermis and feather primordia are discussed.

Animals↗