dx5 and various aspects of gonadogenesis. Marc Ginsburg and Eric Lambie. Department of Biological Sciences, Dartmouth College, Hanover NH 03755. One lucky day, we found a W-induced mutation (
dx5) that maps to IR and has strikingly obvious gonadogenesis defects. First, the
dx5/dx5 progeny of a
dx5/+ hermaphrodite often have proximal germline proliferation in one (and sometimes both) of the gonad arms. Despite such an abnormality, all of these animals are fertile. This phenotype is reminiscent of that seen in
lin-12(0) mutants, in which the anchor cell(s) induce proximal germline proliferation. However,
dx5 animals do not exhibit either the two-anchor-cell phenotype or vulva morphogenesis defects characteristic of
lin-12(0) mutants. To determine whether the anchor cell is responsible for inducing proximal proliferation in
dx5 animals, we tested the effect of
lin-12(
n302), which prevents specification of the anchor cell fate. None of 20 Unc progeny of
dx5 unc-75(
e950)/ + + I;
lin-12(
n302) III hermaphrodites had proximal proliferation. 19/49 Unc progeny of
dx5 unc-75(
e950)/+ + controls had proximal proliferation. This strongly suggests that the anchor cell is the culprit; however, we'll have to do some laser ablation experiments to be certain. The second glaringly obvious effect of
dx5 is seen among the progeny of
dx5/dx5 homozygotes. These animals have very small gonads and are usually vulvaless (presumably due to lack of an anchor cell). More detailed inspection will be necessary to determine exactly which cell divisions have gone awry. We are optimistic that we can make good progress towards determining the normal function of the gene defined by
dx5. For one thing, the
dx5 mutation is temperature sensitive, which should permit the isolation of additional alleles by clonal noncomplementation screening. Another good thing is that
dx5 maps very close to
lin-11 (probably to the left); this region is fairly well-covered on the physical map by cosmids and YACs.