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Fig. 7. Models for the role for BMPRIA in mesoderm development. (A)
In wild-type embryos, epiblast cells that are recruited to the anterior
primitive streak (red arrow) or to the middle primitive streak (green arrow)
are fated to form somites (red square) or LPM (green hexagon), respectively,
at the late streak stage. (B,C) Mutant embryos. (B) In mutant
embryos, epiblast cells recruited to the anterior primitive streak probably
form somites as in wild-type embryos (red arrows and red square). However,
many epiblast cells passing through the middle primitive streak (green arrow),
which should form LPM, change their fate to form ectopic somites (yellow arrow
and yellow square); LPM is consequently reduced (green arrow and hexagon). (C)
Alternatively, some of the prospective PXM cells are abnormally recruited to
the middle primitive streak (yellow arrow) and form ectopic somites (yellow
square). LPM is reduced owing to loss of contributing cells (green hexagon)
resulting from reduced BMP signaling.