The origin and development of the amphibian somitie mesoderm is summarized and reviewed with the ... more The origin and development of the amphibian somitie mesoderm is summarized and reviewed with the goal of identifying issues most profitably pursued in these organisms. The location of the prospective somitic mesoderm as well as the cell movements bringing this tissue into ...
Page 1. MECHANICAL DEVELOPMENT OF THE NOTOCHORD IN XENOPUS EARLY TAIL-BUD EMBRYOS MAR Koehl, Dany... more Page 1. MECHANICAL DEVELOPMENT OF THE NOTOCHORD IN XENOPUS EARLY TAIL-BUD EMBRYOS MAR Koehl, Dany S. Adams, and Ray E. Keller Department of Zoology University of California Berkeley, CA 94720 U.SA. ...
In this paper we will discuss some recent work on the cell motility underlying the convergence an... more In this paper we will discuss some recent work on the cell motility underlying the convergence and extension movements during gastrulation and neurulation of Xenopus laevis. We will also discuss some of the tissue interactions controlling this motility, and we will refine our previous ideas on how convergence and extension functions in gastrulation of Xenopus.
Time‐lapse cinemicrography was used to show what changes in the number, size, shape, arrangement ... more Time‐lapse cinemicrography was used to show what changes in the number, size, shape, arrangement and what movements of apices of superficial cells occur during epiboly, extension, convergence and blastopore formation in the blastula or gastrula of Xenopus laevis. Epiboly of the animal region occurs by apical expansion of superficial cells at a nearly constant rate from the midblastula to the midgastrula stage. Egression of deep cells into the superficial layer does not occur. Extension of the dorsal marginal zone begins in the late blastula stage with the rapid spreading of the apices of cells in this region and this continues until the onset of neurulation when rapid shrinkage begins. Extension and convergence of the dorsal marginal zone occurs by a rearrangement in which individual cells exchange neighbors and by a change in the shape of the cell apices. Regional differences in apical expansion are accompanied by differences in rate of anticlinal division of superficial cells such that cells in all sectors of the animal region and the marginal zone show similar patterns of decrease in apparent apical area. Shrinkage of the apices of bottle cells during blastopore formation is described. From this and other studies, a model of the cellular behavior of epiboly, extension and convergence is constructed and several hypotheses as to how these activities might generate the mechanical forces of the gastrulation movements are presented.
The origin and development of the amphibian somitie mesoderm is summarized and reviewed with the ... more The origin and development of the amphibian somitie mesoderm is summarized and reviewed with the goal of identifying issues most profitably pursued in these organisms. The location of the prospective somitic mesoderm as well as the cell movements bringing this tissue into ...
Page 1. MECHANICAL DEVELOPMENT OF THE NOTOCHORD IN XENOPUS EARLY TAIL-BUD EMBRYOS MAR Koehl, Dany... more Page 1. MECHANICAL DEVELOPMENT OF THE NOTOCHORD IN XENOPUS EARLY TAIL-BUD EMBRYOS MAR Koehl, Dany S. Adams, and Ray E. Keller Department of Zoology University of California Berkeley, CA 94720 U.SA. ...
In this paper we will discuss some recent work on the cell motility underlying the convergence an... more In this paper we will discuss some recent work on the cell motility underlying the convergence and extension movements during gastrulation and neurulation of Xenopus laevis. We will also discuss some of the tissue interactions controlling this motility, and we will refine our previous ideas on how convergence and extension functions in gastrulation of Xenopus.
Time‐lapse cinemicrography was used to show what changes in the number, size, shape, arrangement ... more Time‐lapse cinemicrography was used to show what changes in the number, size, shape, arrangement and what movements of apices of superficial cells occur during epiboly, extension, convergence and blastopore formation in the blastula or gastrula of Xenopus laevis. Epiboly of the animal region occurs by apical expansion of superficial cells at a nearly constant rate from the midblastula to the midgastrula stage. Egression of deep cells into the superficial layer does not occur. Extension of the dorsal marginal zone begins in the late blastula stage with the rapid spreading of the apices of cells in this region and this continues until the onset of neurulation when rapid shrinkage begins. Extension and convergence of the dorsal marginal zone occurs by a rearrangement in which individual cells exchange neighbors and by a change in the shape of the cell apices. Regional differences in apical expansion are accompanied by differences in rate of anticlinal division of superficial cells such that cells in all sectors of the animal region and the marginal zone show similar patterns of decrease in apparent apical area. Shrinkage of the apices of bottle cells during blastopore formation is described. From this and other studies, a model of the cellular behavior of epiboly, extension and convergence is constructed and several hypotheses as to how these activities might generate the mechanical forces of the gastrulation movements are presented.
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