Mutations in two genes,
mab-1 I and
mab-11 I, have a conspicuous effect on morphogenesis of the male tail, leading to an abnormal swollen bursa (the 'Morpho-mab' phenotype). Vulval morphogenesis is also affected, so that
mab-1 and
mab-11 hermaphrodites have an enlarged, protrusive vulva (the 'P-vul' phenotype). Surprisingly, these mutations act as weak recessive suppressors of mutations in tra- 3 which cause partial masculinization of XX animals. One hypomorphic mutation of
tra-2 e1209 is also weakly suppressed, but strong ( putative null) alleles of
tra-2 are not affected (WBG 9#2:94; 1987 Meeting Abstr. p.111). Selection for reversion of
lin-29 mutants, which have a retarded heterochronic hypodermal phenotype, led to the isolation of several unlinked suppressors that acted as recessive suppressors of one
lin-29 mutant,
n546, but did not affect other
lin-29 alleles (1987 Meeting Abstr. p. 84; WBG contribution by A.P. & V.A., this issue). Conversations at the 1987 Worm Meeting (also involving Michael Shen and Andrew Fire) suggested that some of the
lin-29 suppressors might be morpho-mabs. This is the case:
ma129 is an allele of
mab-1 and
ma123 is an allele of
mab-11. Both were isolated as
n546 suppressors, but also suppress
tra-2(
e1209). Conversely, the reference alleles of
mab-1 and
mab-11 (
e1228 and
e2008) act as good suppressors of
n546. Two other suppressors obtained by the
n546 reversion also have a Morpho-mab phenotype and suppress
e1209. These identify new loci:
ma117 maps to LGIV, near
unc-5 and is assigned to
mab-13 while
ma116 maps to LGV, near
dpy-11 and is assigned to
mab-14. All mutations at these four loci (
mab-1 (seven alleles),
mab-11 (seven alleles),
mab-13 ( two alleles),
mab-14 (one allele)) appear to have much the same Morpho- mab and P-vul phenotypes and (when tested) act equally well as suppressors of
e1209 or
n546 irrespective of how they were isolated. Mutations of
mab-1 and
mab-11 appear to be fairly frequent, and their phenotypes are recessive, but we do not know if they are simple loss- of-function alleles. These mutations behave as allele-specific suppressors for two apparently unrelated genes, which makes it possible that they are informational suppressors of some kind. If this is so, then they may be encountered in the course of other reversion screens. How the suppression is working is entirely unclear, but it may be significant that the suppressed
tra-2 allele is hypomorphic (and
tra-3 mutations can be regarded as honorary
tra-2 hypomorphs). Perhaps
e1209 and
n546 both produce very unstable proteins, and the suppression occurs because protein degradation occurs more slowly in
mab-1 etc. Other possibilities can be envisaged. None of these hypotheses provides a good explanation of the bursal and vulval abnormalities. Other unexplained interactions have been encountered. For example,
mab-1 and
mab-11 enhance, rather than suppress, the paralysed phenotype of
unc-54 mutations such as
e190 and
e1300. Enhancement effects have also been observed with certain
tra-1 alleles (see WBG contribution by J.H., this issue).