The formation of the primitive streak in early avian development marks the onset of gastrulation, during which large scale cell movement leads to a trilaminar blastoderm comprising prospective endodermal, mesodermal and ectodermal tissue. During streak formation a specialized group of cells first moves anteriorly as a coherent column, beginning from the posterior end of the prospective anterior...

The establishment of anteroposterior (AP) polarity in the early mouse epiblast is crucial for the initiation of gastrulation and the subsequent formation of the embryonic (head to tail) axis. The localization of anterior and posterior determining genes to the appropriate region of the embryo is a dynamic process that underlies this early polarity. Several studies indicate that morphological and...

Homozygous tW18 embryos die prior to organogenesis. They develop gross abnormalities shortly after primitive streak formation. Anatomically, the lesion appears to be confined to the mesoderm with that tissue showing ultrastructural deficiencies and abnormal migration (Spiegelman & Bennett, 1974), and failing to develop in teratomas produced from mutant embryos (Artzt & Bennett, 1972). Analysis ...

During gastrulation, epiblast cells are pluripotent and their fate is thought to be constrained principally by their position. Cell fate is progressively restricted by localised signalling cues from areas including the primitive streak. However, it is unknown whether this restriction accompanies, at the individual cell level, a reduction in potency. Investigation of these early transition event...

The establishment of the primitive streak and its derivative germ layers, mesoderm and endoderm, are prerequisite steps in the formation of many tissues. To model these developmental stages in vitro, an ES cell line was established that expresses CD4 from the foxa2 locus in addition to GFP from the brachyury locus. A GFP-Bry(+) population expressing variable levels of CD4-Foxa2 developed upon d...

During early embryogenesis, the transcription factor HNF3beta is expressed in visceral and definitive endoderm, node, notochord and floorplate. A targeted mutation in the HNF3&bgr ; gene results in the lack of a definitive node and notochord. Furthermore, lack of HNF3beta results in failure of proper primitive streak elongation. To address whether HNF3beta is required in visceral endoderm, we h...