Worm Breeder's Gazette 8(3): 12

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Genetic Analysis of a Long Life-Span Mutant Strain

D.B. Friedman, T. Johnson

Figure 1

Klass isolated and completed preliminary characterization of several 
long-lived mutants isolated in DH26 by a brute force screening 
procedure (Mech.  Age.  Dev.  22:279).  Mike ascribed the extended 
life-span to the secondary effects of either dauer formation or a 
decreased rate of food ingestion.  Those mutants with decreased food 
ingestion also looked uncoordinated.  We have asked which Unc locus(i) 
was involved in this increase in life-span (Age) and begun an attempt 
to map the Age locus.
MK546, one of the longest-lived isolates, was crossed to N2 males 
and the F1 were allowed to self for four generations yielding stocks 
for analysis.  We chose this procedure because pilot experiments 
suggested that few F2 animals were longer-lived; inbreeding to the F5 
produces progeny which are 94% homozygous.  Our data shows that the 
Unc phenotype is a single nuclear gene and maps to linkage group IV 
near dpy-13.  It is allelic with unc-31 (e169).  Complementation tests 
between e169 and Unc's of MR546, MR542, and MR31 (all isolated by 
Klass) showed that the Unc's were all allelic.  Tests to determine 
allelism of the Age loci are currently underway.
We tested the F5 for life-span and found that the Age phenotype 
segregates as two unlinked nuclear genes (X =0.140; p=0.7); this 
assumes that life-spans 1.26 times those of wild-type and above are 
Age and all others are non-Age and that there is no selection against 
the Age phenotype (see Figure).  MR546, in addition to being Unc and 
Age, developed slowly, had small brood sizes and high frequencies of 
bags.  We tested for correlations between Age and these other 
phenotypes in the F5.  We found that Age is not linked to Unc (X2 =4.
12; p=0.25, see Figure).  Age and small brood size do not cosegregate, 
nor do Age and high incidence of bags, nor do Age and slow development 
rate, nor do Age and b26.  Not surprising was the correlation between 
Unc and both higher incidence of bags and slow development rate.  Food 
uptake was monitored by ingestion of [35S] labeled 0P50 and compared 
with N2 controls and zero time samples; pharyngeal pump rate was also 
monitored.  We found no difference between food uptake in MR546 and 
the other Mk strains as compared with wild-type or DH26.  Comparisons 
of Age reisolates and wild-type reisolates also failed to detect 
differences in rate of food uptake.  Extensive repeats of these 
observations lead us to accept their validity.
We are attempting to localize the two genes responsible for the Age 
phenotype to their respective linkage groups (not an easy task).  Age 
strains containing Unc's shown to have wild-type life-span 
representing each linkage group have been constructed by four rounds 
of backcrossing F2 Unc hermaphrodites with a male fertile, Age 
reisolate strain (TJ401).  This eliminates the need for life-span 
analyses until stock construction is completed.  Analysis of these 
strains with respect to life-span are in progress.  We expect that if 
the tester Unc locus and the Age loci are unlinked we should see 82% 
of such Unc he linkage would result in lower 
frequencies of Unc  Linkage group assignments 
will be confirmed by the standard technique of crossing the Unc 
utants to wild type, reisolating F5 Unc's and 
testing their life-span.  The age (hx546) allele prolongs life-span so 
dramatically that genotype determination can be reliably estimated 
from shoulder heights on survival curves.  Therefore map distances can 
be estimated directly from survival curves of large populations.
[See Figure 1]

Figure 1