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. Author manuscript; available in PMC: 2018 May 15.
Published in final edited form as: Dev Biol. 2017 Apr 4;425(2):208–222. doi: 10.1016/j.ydbio.2017.03.032

Fig. 7. The primitive streak and VOC collaborate to drive fetal-placental union in the mouse via T and pFGFR1.

Fig. 7

Schematics in A-C are depicted entirely through the midsagittal plane, while the embryonic component in D, E is slightly lateral, to visualize one of the paired dorsal aortae. (A) As the allantoic bud (al) emerges (~E7.25), the T-positive primitive streak (dashed outline) has extended into the extraembryonic region, positioning the allantoic-yolk sac junction (arrows), where prospective VOC angioblasts (colored ovals) exhibit flk-1 (light blue), pFGFR1 and T (alternating brown and pink, respectively). T-dosage, i.e., the number of normal copies of T present, regulates extension of the primitive streak and thus, correct axial placement of the allantoic-yolk sac junction according to TC genotype (arrows) along the anteroposterior axis. (B) As the al elongates (~E7.75), the streak (dashed outline) expands into the ACD (red asterisk), where it ensures that the prospective VOC angioblasts (colored ovals), which are now beginning to lose T (pink), are organized to the midline. (C) By 2s (~E8.25), angioblasts have endothelialized (light blue flattenedovals) as a result of FGFR1 signaling to form the VOC (red, black asterisk), which now lacks both T (pink) and pFGFR1 (brown). (D) By 6–8s (~E8.5), the primitive streak (dashed outline)/ACD (red asterisk) regresses (Downs et al., 2009), and the VOC (red, black asterisk) branches as a result of pFGFR1 signaling to unite, in sequential order (red numbers), the omphalomesenteric artery (purple; 1), umbilical artery (yellow; 2), and dorsal aortae (dark blue; 3) to create the OUA connection. (E) Anterior movements during embryonic turning (11s, ~E9.0) cause the VOC (red, black asterisk) to curve around the hindgut (hg), creating the medial umbilical roots (mur). (F) Later, during the early-to-mid fetal period (~E13.5), the mur begin to regress, allowing the lateral umbilical roots (lur, dark blue; derived from the dorsal aortae) to assume prominence, connecting to the umbilical artery (yellow) at the VOC branchpoint (red, black asterisk). am, amnion; ch, chorion; em, embryo; ys, yolk sac.