The murine allantois is the future umbilical component of the placenta
, The base of the allantois is also thought to contain the future germ
line. We have examined the fate and developmental potency of cells wi
thin the murine allantois during gastrulation. lacZ-expressing headfol
d-stage allantoises (approximately 8.0 days postcoitum; dpc) were subd
ivided into three proximodistal regions and transplanted into three si
tes in synchronous non-transgenic host embryos: the primitive streak a
t the level of prospective paraxial mesoderm, the primitive streak at
the level of lateral plate mesoderm, and the base of the allantois, Af
ter 23 hours in culture, operated conceptuses were examined histologic
ally for contribution of donor allantoic cells to the conceptus, None
of the allantoic regions contributed to paraxial mesoderm when placed
into the fetus, but all three colonized the endothelium and adjacent m
esenchyme of the dorsal aorta, The mid-region was most efficient at co
lonizing endothelium, whereas the base was the only allantoic region t
o exhibit relative pluripotency, colonizing several derivatives of all
three primary germ layers. Differences in the state of differentiatio
n along the proximodistal axis of the allantois were further borne out
when the three allantoic regions were placed into the base of the all
antois of host conceptuses. Striking differences were observed in fina
l position along the proximodistal axis of the host allantois, Most gr
afted cells translocated distally from the base; however, basal donor
allantoic cells translocated typically only as far as the host's mid-r
egion, whereas donor allantoic tip cells typically returned to the tip
, often colonizing the chorioallantoic fusion junction. Together, our
data reveal that the headfold-stage allantois may contain a proximodis
tal gradient of differentiation, and raise intriguing questions about
how this gradient was established and the role it plays in umbilical v
asculogenesis.