Worm Breeder's Gazette 14(4): 47 (October 1, 1996)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
| 1 | Division of Biological Sciences, University of Missouri, Columbia MO 65211 |
| 2 | Andrus Gerontology Center, University of Southern California, Los Angeles, CA 90089 |
All daf-2 mutants thus far studied show a number of mutant defects,
including constitutive dauer larva formation (Daf-c), increased adult
life span (Age) and increased intrinsic thermotolerance (Itt). Some
alleles also display additional defects such as reduced brood size,
production of progeny long after the end of the normal egg laying
period, increased death due to internal hatching, and embryonic and L1
arrest. We have characterized in detail the phenotypes resulting from 16
daf-2 alleles of which 15 are ts for Daf-c. We did this in order to a )
discover the full range of daf-2 phenotypes and b) establish which
mutant traits are correlated with which, especially with the Age trait.
The 15 ts alleles fell into two groups: eight Class A alleles,
e1365, e1368, e1369, e1371, m41, m577 and sa193, which were Daf-c, Itt
and Age; and seven Class B alleles (see below), which displayed the
Class A defects and also one or more of the other defects mentioned
above, plus 'dauer-like' shrinkage of the adult body, abnormal gonads
and greatly reduced adult movement accompanied by coiling behavior. The
ranking of severity of alleles with respect to Daf-c defined the
following series, in order of increasing severity:
e1365 < m577 < sa193 < e1371 < e1368 < sa223 < m120 < e1370 < m596 <
m579 < m41 < e1391 < e979 < m212 < e1369
The Class B-specific defects defined a second series:
m596 < m120 < m579 < e1370 < e979 < e1391 < sa223
The ranking of severity with respect to the Daf-c and 15C Age defects
was the same in all the Class A alleles, excluding m41, plus the two
weakest alleles of the Class B series, m596 and m120. Class B-specific
defects are largely ts, except for sa223, and alleles of increasing
severity displayed more defects, such that the defects present in weaker
mutants were almost always present in more severe mutants. For instance,
all alleles resulting in greatly reduced brood sizes also showed reduced
adult movement. This suggests that increasing severity in the Class B
series corresponds to a progressively greater defect in a single
component of daf-2 function. Thus daf-2 may be considered genetically
bifunctional, comprised of daf-2A and daf-2B, such that Class A alleles
are daf-2A(-)daf-2B(+), and Class B alleles daf-2A(-)daf-2B(-).
Ranking of alleles with respect to severity of Itt (measured in
animals raised at 15C) largely coincided with those of Daf-c and Age,
with a striking exception: m120 is wild type with respect to Itt. Thus,
life span extension is possible without Itt. Conversely, the severity of
Class B defects showed no correlation with Age or Daf-c phenotype.
A further difference between Class A and all but the weakest
Class B alleles is that in Class A mutants increases in median and
maximum life span at 22.5C relative to N2 are similar, whereas in Class
B mutants the increase in maximum life span is disproportionately
greater. This suggests that in Class B mutant populations at 22.5C a
large proportion of mortality (perhaps all?) is not due to senescence
per se, but instead is the result of deleterious Class B-specific
defects.
m41 was distinct from all other Class A alleles in certain
respects. For example, the Daf-c phenotype was maternally rescued at
25.5C in the case of m41 alone. Based on its Daf-c phenotype m41 is a
moderately strong allele, but it is wild type with respect to all
phenotypes at 15C. This suggests that while most ts daf-2 alleles are
hypomorphic, being ts due to the temperature dependence of wild type
dauer formation, m41 may encode a thermolabile protein.