Showing papers by "Charles P. Ordahl published in 1997"

Location and growth of epaxial myotome precursor cells

Abstract: The skeletal muscle progenitor cells of the vertebrate body originate in the dermomyotome epithelium of the embryonic somites. To precisely locate myotome precursor cells, fluorescent vital dyes were iontophoretically injected at specific sites in the dermomyotome in ovo and the fates of dye-labeled cells monitored by confocal microscopy. Dye-labeled myotome myofibers were generated from cells injected along the entire medial boundary and the medial portion of the cranial boundary of the dermomyotome, regions in close proximity to the dorsal region of the neural tube where myogenic-inducing factors are thought to be produced. Other injected regions of the dermomyotome did not give rise to myotome fibers. Analysis of nascent myotome fibers showed that they elongate along the embryonic axis in cranial and caudal directions, or in both directions simultaneously, until they reach the margins of the dermomyotome. Finally, deposition of myotome fibers and expansion of the dermomyotome epithelium occurs in a lateral-to-medial direction. This new model for early myotome formation has implications for myogenic specification and for growth of the epaxial domain during early embryonic development.

The fate of the first avian somite.

Abstract: We have studied the derivatives of the first somite using the quail-chick marking technique. After transplantation of the somite, the chick embryos were reincubated for periods ranging from 4 h to 11 days. Coronal and sagittal sections of the embryos were prepared for parallel staining with Feulgen-reaction, anti-quail antibody, anti-desmin antibody and QH-1 antibody. The first somite consists of an epithelial envelope surrounding somitocoele cells. Like other somites, it forms sclerotome, dermatome and myotome. Cells contribute to the occipital and parasphenoid bone, the meninges, the dermis in the occipital region and the pharyngeal connective tissue. The contribution of the first somite to bones, meninges, dermis and pharyngeal connective tissue is characterised by sharp anterior and posterior boundaries. In contrast, other derivatives such as connective tissue surrounding the vagus nerve, the carotid artery, and jugular vein exceed 10 to 18 segments. This is also true for myogenic cells participating in the formation of the cucullaris capitis muscle that extends from the temporal bone to the shoulder. In one third of the embryos, myocytes of the intrinsic laryngeal muscles are derived from the grafted first somite. Moreover, endothelial cells originate from this somite and migrate into the head (hindbrain, meninges, dermis), neck (pharynx, connective tissue surrounding the vagus nerve, carotid artery and jugular vein) and thorax. With respect to differentiation and derivatives the first somite is similar to other somites.

Emergence of determined myotome precursor cells in the somite.

Abstract: Myotome and sclerotome precursor cells are derived, respectively, from cells in the dorsomedial and ventromedial regions of the somite. To assay changes in the specification of myotomal precursor cells during somite maturation, we implanted dorsomedial quadrant fragments, from staged quail somites, next to the notochords of host chick embryos, and superimposed two additional notochords on these implants. In this notochord signalling environment, dorsomedial quadrant cells that are developmentally plastic are expected to differentiate as cartilage, while cells determined to a myogenic fate are expected to differentiate as skeletal muscle. Large numbers of differentiated chondrocytes developed from dorsomedial quadrant grafts of all stages of paraxial mesoderm development tested, indicating that persistent chondrogenic potential in cells fated to form muscle and dermis can be elicited by notochord signals. Differentiated myocytes, however, appeared in two somite-stage-dependent phases. In the first phase, dorsomedial quadrants from segmental plate and early stage somites (II and IV) form small, disorganized clusters of individual myocytes. The frequency of first-phase myocluster formation increases as myogenic factor expression begins in the dorsomedial quadrant, indicating that myogenic determination assayed by this method is closely linked to the expression of myogenic factors in the dorsomedial quadrant. In the second phase, dorsomedial quadrants from somite stages XI-XIII consistently form morphologically organized muscle tissue containing large numbers of parallel-oriented, multinucleated myotubes. Mitotic labelling demonstrated that muscle precursors were determined to the muscle phenotype prior to withdrawal from the cell cycle. Thus, myogenic determination in cells of the dorsomedial quadrant is acquired at earlier stages of somite maturation than the ability to proliferate and form muscle tissue. These results are consistent with the hypothesis that successive lineages of myotome precursor cells with different mitotic and morphogenetic properties arise in the dorsomedial quadrant during somite maturation.

Avian somite transplantation: a review of basic methods.

Abstract: Publisher Summary This chapter outlines two basic procedures for the transplantation of quail embryo somites into chick embryos. Although the two methods were developed independently, both employ a remarkably similar surgical strategy, even down to the sequence of incisions. The similarity in incision sequence reflects mechanical constraints inherent to the tissues within the avian embryo. Nevertheless, combining materials or techniques from both procedures can exploit advantages and minimize disadvantages. In addition, these basic procedures can also be used to perform modified somite transplantations or transplantations of somite fragments. Tranplantation of somite fragments can be used to elucidate the fate of different portions of the developing somite. Half-somite transplantation has proven particularly useful in this regard because the somite can easily be divided in half along each of its three axes. The connections between half-somite fragments, however, are somewhat more fragile than those between whole somites, so more care must be taken in their isolation and transfer. The chapter also outlines half-somite transplantation strategies that have proven useful in revealing novel aspects of early development.