In tetrapod phylogeny, the dramatic modifications of the trunk have received less attention than the more obvious evolution of limbs. In somites, several waves of muscle precursors are induced by signals from nearby tissues. In both amniotes and fish, the earliest myogenesis requires secreted signals from the ventral midline carried by Hedgehog (Hh) proteins. To determine if this similarity rep...

The axial structures, the notochord and the neural tube, play an essential role in the dorsoventral patterning of somites and in the differentiation of their many cell lineages. Here, we investigated the role of the axial structures in the mediolateral patterning of the somite by using a newly identified murine homeobox gene, Nkx-3.1, as a medial somitic marker in explant in vitro assays. Nkx-3...

Gnathostomes (jawed vertebrates) possess skeletal muscles with unique functional and developmental features that are absent from cyclostomes-i.e., lamprey and hagfish. These gnathostome-specific traits include the epaxial and hypaxial division of myotomes, paired fin/limb muscles, shoulder girdle muscles, and the muscle associated with the tongue and the neck. Many of these muscles are derived ...

BACKGROUND The process of somitogenesis can be divided into three major events: the prepatterning of the mesoderm; the formation of boundaries between the prospective somites; and the cellular differentiation of the somites. Expression and functional studies have demonstrated the involvement of the murine Notch pathway in somitogenesis, although its precise role in this process is not yet well ...

During vertebrate development, the paraxial mesoderm becomes segmented, forming somites that will give rise to dermis, axial skeleton and skeletal muscles. Although recently challenged, the "clock and wavefront" model for somitogenesis explains how interactions between several cell-cell communication pathways, including the FGF, RA, Wnt and Notch signals, control the formation of these bilatera...

Somites give rise to a number of different embryonic cell types, including the precursors of skeletal muscle populations. The lateral aspect of amniote and fish somites have been shown to give rise specifically to hypaxial muscle, including the appendicular muscle that populates fins and limbs. We have investigated the morphogenetic basis for formation of specific hypaxial muscles within the ze...

1. Mackerel egg development was followed to hatching at constant temperatures of 10 degrees , 11 degrees , 12 degrees , 13 degrees , 14 degrees , 15 degrees , 16 degrees , 17 degrees , 18 degrees , 19 degrees , 20 degrees , 21 degrees , 22 degrees , and 24 degrees C. Experiment showed that typical development could be realized only between 11 degrees and 21 degrees . 2. The length of the develo...

This study provides evidence that cells destined to segment together into somites have a degree of cell division synchrony. We have measured the duration of the cell division cycle in somite and segmental plate cells of the chick embryo as 9.5 h using [3H]thymidine pulse- and-chase. Treatment of embryos with any of a variety of inhibitors known to affect the cell division cycle causes discrete ...

The role of somites and notochords in neuroectoderm differentiation from the embryonic ectoderm and its subsequent patterning into regional compartments along rostro-caudal and dorso-ventral axes, especially in humans, remains elusive. Here, we demonstrate the co-culture effect of somites and notochords isolated from chicken embryos on the neuronal differentiation and regional identity of an ad...

During vertebrate embryogenesis, paraxial mesoderm gives rise to somites, which subsequently develop into the dermis, skeletal muscle, ribs and vertebrae of the adult. Mutations that disrupt the patterning of individual somites have dramatic effects on these tissues, including fusions of the ribs and vertebrae. The T-box transcription factor, Tbx6, is expressed in the paraxial mesoderm but is d...