Analysis of extraembryonic mesodermal structure formation in the absence of morphological primitive streak.
During mouse gastrulation, the primitive streak is formed on the posterior side of the embryo. Cells migrate out of the primitive streak to form the future mesoderm and endoderm. Fate mapping studies revealed a group of cell migrate through the proximal end of the primitive streak and give rise to the extraembryonic mesoderm tissues such as the yolk sac blood islands and allantois. However, it is not clear whether the formation of a morphological primitive streak is required for the development of these extraembryonic mesodermal tissues. Loss of the Cripto gene in mice dramatically reduces, but does not completely abolish, Nodal activity leading to the absence of a morphological primitive streak. However, embryonic erythrocytes are still formed and assembled into the blood islands. In addition, Cripto mutant embryos form allantoic buds. However, Drap1 mutant embryos have excessive Nodal activity in the epiblast cells before gastrulation and form an expanded primitive streak, but no yolk sac blood islands or allantoic bud formation. Lefty2 embryos also have elevated levels of Nodal activity in the primitive streak during gastrulation, and undergo normal blood island and allantois formation. We therefore speculate that low level of Nodal activity disrupts the formation of morphological primitive streak on the posterior side, but still allows the formation of primitive streak cells on the proximal side, which give rise to the extraembryonic mesodermal tissues formation. Excessive Nodal activity in the epiblast at pre-gastrulation stage, but not in the primitive streak cells during gastrulation, disrupts extraembryonic mesoderm development.
Department of Molecular, Cellular & Craniofacial Biology and Birth Defects Center, University of Louisville, Louisville, Kentucky, USA.
Jiu-Zhen
JZ
Jin
Department of Molecular, Cellular & Craniofacial Biology and Birth Defects Center, University of Louisville, Louisville, Kentucky, USA.
Yuanqi
Y
Zhu
Department of Molecular, Cellular & Craniofacial Biology and Birth Defects Center, University of Louisville, Louisville, Kentucky, USA.
Dennis
D
Warner
Department of Molecular, Cellular & Craniofacial Biology and Birth Defects Center, University of Louisville, Louisville, Kentucky, USA.
Jixiang
J
Ding
D000818:Animals; D004815:Epidermal Growth Factor / Q000235:genetics / Q000378:metabolism; D055458:Left-Right Determination Factors / Q000235:genetics / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D008648:Mesoderm / Q000166:cytology* / Q000196:embryology*; D051379:Mice; D008817:Mice, Mutant Strains; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D055457:Nodal Protein / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism
C484382:Drap1 protein, mouse; D055458:Left-Right Determination Factors; C526162:Lefty2 protein, mouse; D008562:Membrane Glycoproteins; D009363:Neoplasm Proteins; D055457:Nodal Protein; C526008:Nodal protein, mouse; D012097:Repressor Proteins; C489450:Tdgf1 protein, mouse; D004815:Epidermal Growth Factor
Cripto; Drap1; Lefty2; allantois; blood island; primitive streak