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.
cord. This organ system is the first to initiate its
development; functionally, however, it is overtaken
by the later developing vascular system. Timewise,
the process of neurulation overlaps with that of
gastrulation: Along with the posterior retraction of
the primitive streak, neurulation progresses in an anterior
to posterior direction. Hence, over a certain
period of time, the embryonic disc presents both the
primitive streak posteriorly and the developing neural
system anteriorly.
4.1 Neural ectoderm
The epiblast cells anterior to the primitive node
are induced to differentiate at the second gestational
week [44]. The notochord’s signalling molecules,
including Sonic hedgehog, induce the overlying
epiblast to differentiate into neuroectoderm, whereas
the remaining more lateral portion of the epiblast
differentiates into surface ectoderm. This notochordinduced
neurulation is referred to as primary neurulation.
The first morphological sign of primary
neurulation is a dorsal thickening in the anterior ectoderm
forming an elliptical region referred to as the
neural plate. Subsequently, the neural plate undergoes
a shaping which converts it into a more elongated
key-hole shaped structure with broad anterior and
narrow posterior regions. Neural plate shaping is
followed by the development of two lateral elevations,
the neural folds, on either side of a depressed
midregion referred to as the neural groove. In pigs
and cattle the neural folds become clear during the
third week of development (Figure 11).
N
Figure 11: Porcine Day 14-15 embryos. (A) Stereo micrograph of the embryonic disc showing the primitive streak (PS) posteriorly, delineated
by arrowheads, and the neural groove (NG) anteriorly, delineated by arrows. CAF: Chorioamniotic folding. (B) Section of embryonic disc along
the broken line in A. Note the thick neural ectoderm (NE) continuous with the trophectoderm at the arrows. The mesoderm (Me) is seen between
the neural ectoderm and the endoderm (En). The mesoderm also forms extra-embryonic portions lining both the trophectoderm and the yolk sac
(YS) with the extra-embryonic coelom (EC) between the layers. The latter opens into the primitive gut forming the hindgut (Hg) and the foregut
(Fg). CAF: Chorioamniotic folding. (C) Section through the dorsal portion of the neural tube (NT) showing the neural ectoderm (NE)
overlaid by the surface ectoderm (SE) characterized by expression of Pankeratin. Note the PAX7 expressing neural crest cells.
A: Anterior; P: Posterior; D:Dorsal; V: Ventral.
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