Worm Breeder's Gazette 10(1): 110

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Further Notes on mab-9

A. Chisholm

Figure 1

mab-9(e1245) males have highly abnormal tails, with internal 
structures (spicules, gubernaculum) missing, constipation and 
defective tail morphogenesis.  A small percentage of mab-9 
hermaphrodites are also constipated.  As reported at the worm meeting 
this May, analysis of the tail lineages of mab-9 males indicated that 
the primary defect was in the B lineage, which appears partially 
transformed towards a Y-like lineage (see figure).  Ventral and 
lateral hypodermal lineages are wild-type.  Observations on mab-9 
hermaphrodites suggested that an analogous B-to-Y transformation was 
also occurring.  Such transformations could account for the gross 
mutant phenotypes observed.  nDf3 (Greenwald & Horvitz, 1980) does not 
complement e1245.  Of 5 e1245/nDf3 males lineaged, 2 showed a 
virtually complete transformation of B to Y, including the division of 
the most posterior daughter in L3 (see figure).  The other 3 worms had 
lineage patterns typical of e1245 homozygotes.  No new lineage defects 
were seen; the terminal phenotype of the deficiency heterozygote is 
within the observed range of e1245.  Therefore e1245 is not null, but 
it is probably close.
Analysis of the U and F lineages up to the L3 moult in 3 mab-9 males 
revealed that the divisions of F.lv and F.rv at about 1.5h after their 
formation (i.e., at 30.5h) does not occur.  Variable divisions of the 
dorsal and ventral daughters of F.l and F.r occur at around 34h, 
synchronously with the divisions of U.la and U.ra (if they occur).  
Thus, F appears to execute a U-like lineage; whether this is a primary 
or secondary effect of the mab-9 mutation is not clear.  The lineage 
defect in e1245 males is suppressed by one or two copies of the amber 
suppressor sup-5(e1464).  The B lineage in mab-9;sup-5 males is wild-
type as far as late L3: good spicules are made.  However tail 
morphogenesis is not perfect, and the spicules are slightly protruding 
(even at 15 C), probably due to incomplete suppression.  Other amber 
suppressors are being tested.
In lin-12(0) males, Y is transformed into the neuron DA9 (Greenwald 
et al. 1983).  If B is being transformed into Y in mab-9, one might 
predict a further transformation in the double mutant, or at least 
some reduction in cell proliferation.  To test this prediction, the 
strain e1245:lin-12(n137n720)unc-32(e189);e1490 was constructed.  
Males of this strain are very ill (most die before or during L1), but 
partial lineages from two worms showed no such interaction: B still 
executes a Y-like lineage.  This is confirmed by spot checks of 
several worms of this genotype and of an analogous strain using lin-12(
n676n909).  This negative result may indicate that B is not being 
transformed into Y in mab-9, but alternative explanations are possible.
For instance, it could be argued that the wildtype role of lin-12 is 
not to specify Y-ness but to control a more basic decision (e.g., 
blast cell/neuron).  The information necessary to execute a Y lineage 
would therefore be extant in the double mutant, and could be used by 
the transformed B cell.  To clarify the nature of the null phenotype 
of mab-9, I am currently screening for more alleles of the locus.

Figure 1