Journal article

Publication year: 1990

Pages: 14-30

Journal: Roux's archives of developmental biology

Volume number: 199

Issue number: 1

ISSN: 0930-035X

DOI Link: https://doi.org/10.1007/BF01681530

Publisher: Springer

Abstract: 
As in many spiralian embryos with unequal cleavage, cleavage inPlatynereis
follows an invariant pattern. Preceding each cleavage the cytoplasm is
reorganized, allowing the spiral cleavage mode to produce cells with
different cytoplasmic composition. The fertilized egg undergoes a
dramatic ooplasmic segregation after the completion of the cortical
reaction. As a consequence, a plug of clear cytoplasm becomes located at
the animal pole. Once the four quadrants of the embryo have been
established, the cleavage sequence of the D quadrant differs clearly
from that of the other three quadrants. The results presented here
suggest that differential distribution of the clear cytoplasm governs
this sequence. The first quartet of micromeres, which will form the
ectoderm and the cerebral ganglia of the head, is clearly bilaterally
symmetrical from the onset of the third cleavage. Dorsoventral polarity
and bilateral symmetry in the ectoderm of the trunk is expressed most
markedly by the dorsal location of the large 2d cell, whose rapid
proliferation is bilaterally symmetrical with respect to the median
plane. As a result of this proliferation it comes to fill most of the
posttrochal region (ectoderm, three pairs of anlagen for the setal sacs,
and the ventral plate which forms the nerve cord). The other micromeres
contribute only a minor portion of the ventral ectoderm and are
involved in the formation of the stomodaeum. The mesentoblast, 4d, i.e.
the stem cell of the primary mesoderm, forms at the sixth cleavage, also
in a position on the dorsal mid-line. The daughter cells, which arise
from 4d by strictly bilaterally symmetrical cleavage, form the
mesodermal germ bands, which lie beneath the ectoderm. The trochoblasts
are formed by asynchronously cleaving founder cells, but further
cleavages in these cells are synchronous. This suggests that cell-cell
interaction is involved in the development of this alleged mosaic
embryo.

Harvard Citation style: Dorresteijn, A. (1990) Quantitative analysis of cellular differentiation during early embryogenesis ofPlatynereis dumerilii, Roux's archives of developmental biology, 199(1), pp. 14-30. https://doi.org/10.1007/BF01681530

APA Citation style: Dorresteijn, A. (1990). Quantitative analysis of cellular differentiation during early embryogenesis ofPlatynereis dumerilii. Roux's archives of developmental biology. 199(1), 14-30. https://doi.org/10.1007/BF01681530