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.
III. GASTRULATION: DEVELOPMENT OF MESODERM,
ENDODERM, AND ECTODERM
Gastrulation (from the Greek term gastrula
meaning small stomach) is the process by which the
three somatic germ layers, ectoderm, mesoderm, and
endoderm, as well as the PGCs (see later) are formed.
3.1 The primitive streak
During Days 11-12 of gestation, the porcine
embryo initiates a dramatic elongation that over a
couple of days results in the transformation of the
spherical blastocyst to an approximately 1 m long,
extremely thin filamentous structure. Gastrulation in
the porcine embryo is initiated around the time, when
elongation is in its initial progress [45]. Porcine
gastrulation is not dependent on implantation, as it is
in man and mouse [3,10]. “True” gastrulation is defined
by the presence of the primitive streak (Figure
8). The porcine primitive streak apparently develops
as an anterior extension of the BRACHYURY and
GOOSECOID expressing crescent of epiblast cells
[3,45]. The streak elongates in an anterior direction
and forms a depression, termed the primitive groove,
at the midline. The porcine primitive streak expresses
BRACHYURY throughout its extension and
GOOSECOID at least in the anterior portion [23,45].
An example of a BRACHYURY expressing porcine
primitive streak is visualized in Figure 9. At approximately
Days 13-14 of gestation, the primitive
streak extends from the posterior pole of the epiblast
and approximately two thirds of the length of the
embryonic disc [42]. A key embryonic signalling cen-
Figure 7. Confocal laser scanning micrographs of Day 10 porcine blastocyst displaying mutually excluding epiblast cell populations expressing
OCT4 and NANOG. Modified from Wolf et al. (2011a)[46].
Figure 8. Median section though embryonic disc from Day 12-13 porcine embryo. The epiblast (Ep) is continuous with the trophectoderm (Te),
indicated by the arrows. In the posterior two third of the epiblast, more loosely arranged cells ingress through the primitive streak (PS) to the
space between the epiblast and the hypoblast (Hy/En), which is gradually exchanged by final endoderm. Loose mesoderm (Me) is also located
in this area. A: Anterior; P: Posterior; D: Dorsal; V: Ventral.
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