Halves of Epithelial Somites and Segmental Plate Show Distinct Muscle Differentiation Behaviorin VitroCompared to Entire Somites and Segmental Plate

Abstract

Medial and lateral halves of the somite are known to differ with respect to their developmental fates: Cells from the medial half of the somite give rise to the epaxial muscle of the back and cells from the lateral half of the somite give rise to the skeletal muscles of the limbs and the ventrolateral body wall. To get a better insight into myogenic determination of somite hemispheres, isolated entire somites as well as medial and lateral parts of somites and of segmental plate from 2 day chick embryos were explanted in vitro. These parts of the paraxial mesoderm were also cocultured in contact with somite surrounding tissues such as neural tube lacking floorplate, neural tube including notochord-floorplate complex, and intermediate mesoderm, which were examined with respect to their muscle promoting or inhibiting influences. Skeletal muscle differentiation was monitored by the use of anti-myosin heavy chain antibody (MF20). It is shown that medial and lateral halves of segmental plate and epithelial somites are capable of undergoing myogenesis in the absence of axial organs. In contrast, cultures of intact segmental plate and epithelial somites from the same levels did not show muscle differentiation. Neural tube lacking floorplate promoted muscle differentiation in the medial halves especially of epithelial somites and also of segmental plate, but not in the lateral halves of the paraxial mesoderm at these levels. Intermediate mesoderm was found to inhibit muscle differentiation in medial and lateral halves of segmental plate and of epithelial somites. We further demonstrate that the arrangement of the myoblasts within tissue cultures is influenced by the presence or absence of axial organs.

Normal and aberrant craniofacial myogenesis by grafted trunk somitic and segmental plate mesoderm

“…Classical explant experiments indicate that commitment coincides with the formation of somites, and autonomous competence to differentiate is acquired shortly thereafter Ordahl and Le Douarin, 1992). This conclusion is consistent with segmental plate cell culture experiments (Buffinger and Stockdale, 1994;Gamel et al, 1995;Stern and Hauschka, 1995). However, PCR assays have found myf5 or myod transcripts in cranial segmental plate mesodermal cells in the chick (Kiefer and Hauschka, 2001), suggestive of an earlier bias towards myogenesis.…”

“…Indeed, somite rotation experiments have shown that medial and lateral domains of newly-formed somites are labile (Aoyama and Asamoto, 1988;Dockter and Ordahl, 2000). It is possible that grafted half somites undergo regulation, restoring the entire mediolateral complement of myogenic lineages (Gamel et al, 1995). However, this alone would not account for the widespread expression of lbx1.…”

Regulation of dorsal somitic cell fates: BMPs and Noggin control the timing and pattern of myogenic regulator expression

“…In vitro experiments with mouse and chick somites have indicated that both the axial tissues and the surface ectoderm are capable of inducing the expression of both dermomyotomal and myotomal genes in cocultured paraxial mesoderm (Avery et al 1956;Vivarelli and Cossu 1986;Kenny-Mobbs and Thorogood 1987;Christ et al 1992;Rong et al 1992;Buffinger andStockdale 1994, 1995;Fan and Tessier-Lavigne 1994;Gamel et al 1995;Cossu et al 1996;Spence et al 1996). Myogenesis can be induced in somites IV-IX isolated from a stage 10 chick embryo when explanted with either the dorsolateral neural tube or the surface ectoderm.…”

“…It has been shown that signals from either the axial tissues (i.e., the neural tube and notochord) or the surface ectoderm are capable of inducing the expression of Pax3 and somitic myogenesis in explants of paraxial mesoderm (Avery et al 1956;Vivarelli and Cossu 1986;Kenny-Mobbs and Thorogood 1987;Christ et al 1992;Rong et al 1992;Buffinger andStockdale 1994, 1995;Fan and Tessier-Lavigne 1994;Gamel et al 1995;Cossu et al 1996;Spence et al 1996). The combination of Wnt1 or Wnt3 plus Sonic hedgehog (Shh) can mimic the axial signals and induce expression of both Pax3 and somitic myogenesis Maroto et al 1997).…”

Sonic hedgehog promotes somitic chondrogenesis by altering the cellular response to BMP signaling

“…The various cell fates within the somite are plastic and appear to depend on signals from surrounding tissues. In particular, dorsally generated derivatives such as muscle require signals from either the dorsal neural tube or surface ectoderm (Avery et al 1956;Vivarelli and Cossu 1986;Kenny-Mobbs and Thorogood 1987;Rong et al 1992;Buffinger and Stockdale 1994;Fan and Tessier-Lavigne 1994;Buffinger and Stockdale 1995;Cossu et al 1995;Gamel et al 1995;Mü nsterberg et al 1995;Spence et al 1996;Dietrich et al 1997), whereas the ventrally situated sclerotome is generated in response to a common signal from the floor plate and notochord (Holtzer and Detwiler 1953;Watterson et al 1954;Grobstein and Holtzer 1955;Hall 1977;Brand-Saberi et al 1993;Dietrich et al 1993Dietrich et al , 1997Goulding et al 1993;Koseki et al 1993;Pourquié et al 1993;Ebensperger et al 1995). The dorsal and ventral signals appear to be antagonistic: embryos genetically or surgically manipulated to lack both floor plate and notochord show a ventral expansion of the domain of dermomyotomal gene expression and a subsequent absence of sclerotome and vertebrae (Watterson et al 1954;Dietrich et al 1993Dietrich et al , 1997Goulding et al 1993;Monsoro-Burq et al 1994;Ebensperger et al 1995).…”