2011 (SBTE) 25th Annual Meeting Proceedings - International ...

R.C. Cheb
hebel.
el. 2011. Use of Applied Reproductive Technologies (FTAI, FTET) to Improve the Reproductive Efficiency in
Dairy Cattle. Acta Scientiae Veterinariae. 39(Suppl 1): s203 - s221.
tre during gastrulation, found at the anterior end of
the primitive streak, is the organizer region, termed
the node [37]. In the porcine embryo, the node is
morphologically evident as a thickening of cells in
the anterior part of the early primitive streak (Figure
9); [42].
3.2 Ingression of cells forming mesoderm and
endoderm
Formation of the primitive streak involves
extensive movement of cells, where the epiblast cells
first gather at the posterior end of the embryonic disc,
then rearrange to extend anteriorly in the streak itself,
and, finally, undergo an epithelial-mesenchymal
transition through the primitive streak to become
either mesoderm or definitive endoderm. When the
primitive streak has formed, epiblast cells continue
to enter this structure, which, thus, contains a dynamic
ever changing cell population. The cells, which ingress
to the space between the epiblast and hypoblast
form mesodermal and endodermal precursors. Until
recently it was generally believed that the definitive
endoderm derived from the primitive streak replaced
the hypoblast cell layer. Recently however, it was
shown that in the gastrulating murine embryo the newly
formed definitive endoderm cells insert themselves
into the hypoblast epithelium in a dispersed manner
N
Figure 9. Confocal laser scanning micrographs of Day 12-13 porcine embryo. (A–C) Side-view of the embryonic disc. Note the expression of
T (BRACHYURY) in the primitive streak and the posterior epiblast, the intensive FOXA2 expression in the hypoblast, and the co-expression
of the two markers in the node (arrow and arrowhead in C). The periphery of embryonic disc marked with open arrowheads in A. Note the
expression of T in the primitive streak as well as in intra- and extra embryonic mesoderm (EEM) underlying the epiblast and trophectoderm,
respectively. (D-F) Optical transversal sections of the embryonic disc corresponding to the broken line in A. Note the expression of T in the
primitive streak as well as in intra- and extra embryonic mesoderm underlying the epiblast and trophectoderm, respectively. A: Anterior; P:
Posterior.
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