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Fig. 1. (A) Wild-type Q lineage and cell migration. (Top) Q neuroblast lineage. QL
and QR generate identical cell lineages to produce three neurons: the two
Q.pax cells are filled circles whereas the Q.ap cell is an unfilled circle.
`X' indicates cell death. (Middle) Left and right Q cells (QL in blue, QR in
pink) are located in approximately the same position at hatching. Anterior is
towards the left and ventral is downwards. Shortly after hatching but before
division, the QL cell migrates a short distance posteriorly, while the QR cell
migrates a short distance anteriorly. (Bottom) Final positions of Q
descendants. QL.pax cells (filled blue circles) are located near the position
of QL at hatching, whereas the QL.ap (unfilled blue circle) cell migrates into
the tail. QR.pax cells (filled pink circles) migrate to the anterior body,
whereas the QR.ap cell (unfilled pink circle) migrates into the head. (B)
Wild-type vulva development. (Top) A schematic view of a late L1 larva with 11
of the 12 ventral Pn.p cells shown. Some of the Pn.p cells fuse with the
hypodermal syncytium, hyp7, as indicated by dashes in the third row of the top
panel. The unfused cells are indicated by ovals, and these are the vulval
precursor cells (VPCs). The oval around P3.p is dashed because this cell
remains unfused in about 50% of wild-type animals. Anterior is towards the
left and ventral is downwards. (Middle) In the L3 stage, an inductive signal
(green arrows) from the anchor cell (AC, also shown in the top panel), lateral
signaling (blue arrow) among the VPCs and an inhibitory signal (red T) from
hyp7 impose a 3°-3°-2°-1°-2°-3° pattern of cell fates.
The three fates can be distinguished by the expression pattern of several
markers and by cell lineage pattern. The 1° fate is characterized by three
rounds of cell division, with the last divisions being all transverse (T). The
2° fate is characterized by three rounds of cell division, with the Pn.pxx
cells dividing longitudinally (L), dividing transversely (T) or not dividing
(N). The 3° fate is characterized by a single round of division followed
by fusion with hyp7, as indicated by the dashed Pn.px circles. The descendants
of P5.p-P7.p form the vulva. (Bottom) In the L4 stage, the vulval cells
migrate towards the center of the animal to form seven vulval rings and begin
the process of intratoroidal fusion. Vulval eversion at the end of the vulva
formation process is not shown.
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