Hypoblast controls mesoderm generation and axial patterning in the gastrulating rabbit embryo.
Gastrulation in higher vertebrate species classically commences with the generation of mesoderm cells in the primitive streak by epithelio-mesenchymal transformation of epiblast cells. However, the primitive streak also marks, with its longitudinal orientation in the posterior part of the conceptus, the anterior-posterior (or head-tail) axis of the embryo. Results obtained in chick and mouse suggest that signals secreted by the hypoblast (or visceral endoderm), the extraembryonic tissue covering the epiblast ventrally, antagonise the mesoderm induction cascade in the anterior part of the epiblast and thereby restrict streak development to the posterior pole (and possibly initiate head development anteriorly). In this paper we took advantage of the disc-shape morphology of the rabbit gastrula for defining the expression compartments of the signalling molecules Cerberus and Dickkopf at pre-gastrulation and early gastrulation stages in a mammal other than the mouse. The two molecules are expressed in novel expression compartments in a complementary fashion both in the hypoblast and in the emerging primitive streak. In loss-of-function experiments, carried out in a New-type culturing system, hypoblast was removed prior to culture at defined stages before and at the beginning of gastrulation. The epiblast shows a stage-dependent and topographically restricted susceptibility to express Brachyury, a T-box gene pivotal for mesoderm formation, and to transform into (histologically proven) mesoderm. These results confirm for the mammalian embryo that the anterior-posterior axis of the conceptus is formed first as a molecular prepattern in the hypoblast and then irrevocably fixed, under the control of signals secreted from the hypoblast, by epithelio-mesenchymal transformation (primitive streak formation) in the epiblast.
Department of Anatomy and Cell Biology, Martin-Luther-University, Grosse Steinstrasse 52, 06097, Halle, Germany.
Jan
J
Idkowiak
Gunnar
G
Weisheit
Juliane
J
Plitzner
Christoph
C
Viebahn
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019521:Body Patterning; D017124:Conserved Sequence; D046508:Culture Techniques; D047108:Embryonic Development; D004707:Endoderm / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D005260:Female; D005326:Fetal Proteins / Q000032:analysis / Q000378:metabolism*; D005775:Gastrula / Q000737:chemistry / Q000166:cytology / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D008648:Mesoderm / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D011506:Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits / Q000196:embryology*; D015398:Signal Transduction; D020825:T-Box Domain Proteins / Q000032:analysis / Q000378:metabolism*; D029867:Xenopus Proteins; D000098908:Brachyury Protein
D005326:Fetal Proteins; D036341:Intercellular Signaling Peptides and Proteins; D011506:Proteins; D020825:T-Box Domain Proteins; D029867:Xenopus Proteins; D000098908:Brachyury Protein; C501126:DKK1 protein, human; C501127:Dkk1 protein, mouse; C100866:cer1 protein, Xenopus