Worm Breeder's Gazette 7(1): 81

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.

More on b245

L. Edgar, D. Hirsh

b245III is a temperature-sensitive mutation that blocks 
spermatogenesis and allows oogenesis in both males and hermaphrodites, 
and so appears to control an early switch between the two pathways of 
gamete differentiation.  Varied temperature pulses were used to 
determine the period at 25 C needed to initiate oogenesis in males.  A 
pulse of 8 to 10 hours, beginning at any time after 20 hours of age, 
will switch all males of a synchronized population to oogenesis as 
adults.  A six-hour pulse switches a fraction of the population and 
blocks spermatogenesis in the rest.  A four-hour pulse will similarly 
block spermatogenesis without initiating oogenesis, so that these 
worms as adults make a few sperm and then stop differentiating gametes.
A two-hour pulse does not block spermatogenesis.  Males from the six 
and eight-hour pulses that have switched to oogenesis consistently 
have 20 to 40 undifferentiated germ cells sandwiched between the sperm 
made initially and the oocytes made later.  Thus, there seems to be a 
level of gene product at which the initiation of spermatogenesis is 
permanently blocked, but the process of oogenesis is not initiated.
In a number of males given short pulses, so that oocytes were 
produced after some sperm was made, probable embryos were observed in 
Feulgen preparations.  Most males had single 'embryos'; sometimes two 
were seen.  These 'embryos' are spherical, appear to be membrane-
enclosed, and contain from about 30 to 200 nuclei.  None showed 
morphogenesis.  However, in one 'embryo' of approximately 100 nuclei, 
8 adjacent gut nuclei and a dead nucleus were distinguishable.  The 
most likely explanation is self-fertilization by the sperm present, as 
embryos are never observed in B245 25 C hermaphrodites, which have 
functional oocytes but no sperm.  It appears, then, that male oocytes 
can function to support at least early development, and that 
hermaphrodite gonadal structures may not be necessary for 
Double mutants were made of B245 with tra-1 (e1099)III and isx-1 (
hc17)IV to look at the interactions of this mutant, which appears to 
affect primarily gamete determination, with mutants that affect 
somatic and gonadal sex determination as well as gamete 
differentiation.  The b245 tra-1 (e1099) double mutant produced XX 
males as expected for the tra-1 mutant, and these males, if shifted to 
high temperature, produced oocytes like the b245 males.  This 
independent expression of the phenotypes of the two single mutants can 
be interpreted either that the two genes operate in independent 
pathways, or that tra-1 acts earlier in the same pathway, if the tra-1(
+) allele controls the hermaphroditic mode of expression of the b245(+)
The isx-1 and b245 mutations have very similar phenotypes, the only 
major difference being that isx-1 mutant males have feminized gonads, 
although their somatic sexual differentiation is male.  The double 
mutant b245; isx-1(hc17) shows a much more extreme phenotype than 
either of the single mutant strains.
At 16 C, most hermaphrodites make no sperm, showing the mutant 
phenotype even though both single mutants are temperature-sensitive.  
Males at 16 C have intersex gonads, but make sperm.  At 25 C, 
hermaphrodites, as would be expected, are totally spermless.  The 25 C 
males show an extreme phenotype with a very small intersex or 
undifferentiated gonad, and have no differentiated germ cells.  The 
male tail does not develop beyond the L4 stage.  This interaction 
suggests that the b245 gene is needed for male somatic and gonad 
differentiation as well as spermatogenesis, and that it acts in a 
common pathway with isx-1.