Somite

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somite

[′sō‚mīt]
(zoology)

Somite

 

a paired metameric formation in the embryos of such invertebrates as annelids and insects and in the embryos of man and all other chordates. The middle germ layer, or mesoderm, is segmented into somites during embryonic development. The somites are arranged along the longitudinal axis of the body alongside the neural tube and the chorda. The entire mesoderm is segmented in invertebrates, whereas in man and other chordates only its dorsal section is segmented, with the remaining mesoderm forming lateral plates, or splanchnotomes. Segmentation begins from the anterior section of the body and gradually extends to the posterior section. In the process of development, each somite decomposes into a myotome, a sclerotome, and a dermatome, from which are formed, respectively, the truncal musculature, the axial skeleton (in fish, also the skeleton of the fins), and the connective-tissue portion of the skin and its derivatives.

T. A. DETLAF

References in periodicals archive ?
Tabin, "Ectopic expression of sonic hedgehog alters dorsal-ventral patterning of somites," Cell, vol.
This action suggests that sound production occurred by rubbing the narrow posterior edges of the somite exoskeleton against the anterior edges of the other somite exoskeleton.
Flemminger, 1985) rather than on the genital somite. Intersex individuals were described in species of Acartidae, Calanidae, Diaptomidae, Euchaetidae, Metridinidae and Paracalanidae (Ferrari, 1985 among others).
(B): Sagittal section through an embryo in (A) showing normal development of the somites (arrows) and neural tube (asterisks).
As described above, during embryonic myogenesis, somites and dermomyotomes receive secreted signals such as Wnts, Notch ligands, Shh, FGF, BMP, and retinoic acid (RA) with morphogen gradients from surrounding tissues in order to induce the formation of myogenic cells (Figure 2).
The vertebral column is formed from the sclerotome of the somites. Normal segmentation of the sclerotomes is important for the development of a normal vertebral column.
In contrast to [EE.sub.2] and [E.sub.2] exposures, GFP expression in liver and somite muscle were relatively weak in response to BPA.
Although it is possible to inject fluid into somites, and culture the embryos through hatching with a 60% successful hatch rate for a stage 15 embryo (Giamario et al., 2003), the more invasive procedure of somite cross-transplantation was not attempted in the previous study.
Utilizing a more primitive group of cell type isolated from the somites of E11.5 mice and a less invasive procedure of injection into the uterine continuation of medial circumflex femoral veins of mdx mice, Torrente et al.