Figure 2. Dynamic pattern of HLH-2 protein accumulation during the AC/VU decision. (A-F) Confocal micrographs of L2 hermaphrodite gonads. Hermaphrodites stained with antibodies against HLH-2 (green) and LacZ (red); cells in which both antibodies are detected appear yellow. Small yellow arrows indicate Z1.ppp and Z4.aaa. Larger white arrows indicate HLH-2 expression in the presumptive AC. Distal tip cells are marked with an asterisk. Photomicrographs are arranged in an inferred temporal sequence, on the basis of the observation that
lin-12::lacZ and
lag-2::lacZ are initially expressed in both Z1.ppp and Z4.aaa, but become restricted to the presumptive AC (
lag-2::lacZ expressing) or presumptive VU (
lin-12::lacZ expressing). Only (and all) animals that showed HLH-2 expression in both distal tip cells as well as
lin-12::lacZ expression in all six vulval precursor cells (Wilkinson and Greenwald 1995) or
lag-2::lacZ expression in both distal tip cells (Henderson et al. 1994) were counted, to be certain that the staining procedure had worked well in each animal scored. (A,C,E)
lin-12::lacZ animals (full genotype:
smg-1(
r861)
unc-54(
r293); arIs11[
lin-12::lacZ]). A total of 36 animals were observed with
lin-12::lacZ in both Z1.ppp and Z4.aaa. Of these, 20/36 animals showed no HLH-2 accumulation in either cell (A), and 16/36 showed HLH-2 accumulation in one cell (C). Seven animals were observed in which
lin-12::lacZ expression was already restricted to the presumptive VU. Of these, 7/7 showed HLH-2 accumulation in the other cell, the presumptive AC (E). (B,D,F)
lag-2::lacZ animals (full genotype:
smg-1(
r861)
unc-54(
r293); arIs13[
lag-2::lacZ]). Seven animals were observed with
lag-2::lacZ expressed in both Z1.ppp and Z4.aaa. Of these, 2/7 animals showed no HLH-2 accumulation in either cell (B), and 5/7 showed HLH-2 accumulation in one cell (D). A total of 21 animals were observed in which
lag-2::lacZ expression was restricted to the presumptive AC. Of these, 21/21 showed HLH-2 accumulation costaining the presumptive AC (F).