Worm Breeder's Gazette 9(2): 72

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.

par-2, a Locus Essential for Early Cleavage Patterning and Germ-Line Function

N. Cheng, D. Morton, and K. Kemphues

We have been studying early cleavage in the worms trying to 
understand the contributions of the events of cleavage to the 
regulation of later development.  One locus we are concentrating on, 
par-2 III, has a maternal-effect on the early cleavage pattern and on 
germ-line function.  Recently, we have been screening intensively for 
new alleles at this locus.  Thus far we have a total of four alleles: 
e2030, it5, it46, and it49.  The mutations e2030 and it5 were isolated 
(e2030 by J.  Priess) using the general screen for maternal effect 
lethal mutations described in an earlier newsletter (vol.  8, #2, p5). 
The allele it46 was isolated by screening 2,652 chromosomes for 
failure to complement the grandchildless phenotype of e2030.  The 
allele it49 was isolated in a screen for mel mutations closely linked 
to daf-7 .u.  to the right of daf-7).  For 
the screen, 2452 F1 progeny from crosses of EMS treated daf-7 (e1372 
ts); dpy-11 (e224) hermaphrodites X N2 males were cloned at 25 C.  
Five F2 dauers were picked from each F1 plate and transferred to 16 C. 
Failure to produce F3 was scored as maternal-effect lethal.  The 
allele it49 was identified as a par-2 allele on the basis of its 
failure to complement e2030.
The range of phenotypes exhibited by these alleles are: 1) Cleavage, 
up to at least the 3rd division is synchronous.  2) The sizes of AB 
and P1 cells are nearly equal.  3) The spindles of AB and P1 are 
always perpendicular to the long axis of the embryo.  4) P granules 
localize abnormally or not at all.  5) Surviving progeny from 
homozygous mothers are sterile (i.e.  homozygotes are grandchildless).
The penetrance of the mutant phenotypes varies among alleles and is 
dependent upon temperature.  it5, it46, and it49 are leaky maternal-
effect lethal mutations.  The percentages of dead embryos generated by 
homozygous it46 worms are 99%, 91%, and 90% at 25 C, 20 C, and 16 C 
respectively.  Greater than 99.8% of surviving progeny at all 
temperatures are sterile.  it5 has a more striking temperature effect 
with 96% lethality at 25 C and 27% at 16 C with 75% of surviving 
progeny being sterile.  The allele e2030 produces a grandchildless 
phenotype but shows no maternal effect lethality as a homozygote (
Abstracts of 1985 C.  elegans meeting, p136).  We are now trying to 
determine the basis for the sterility.  Our preliminary results 
suggest that it is due to an absence or reduction in numbers of germ 
cells.  Temperature shift experiments with it5 demonstrate that the 
temperature-sensitive period for lethality is between the time of 
fertilization and the end of the first cleavage.  We have not yet 
determined the TSP for the sterility.  These results suggest that the 
function of par-2 is to insure normal cleavage pattern and cytoplasmic 
partitioning during early development.  Failure in one or both of 
these processes can lead to death or sterility.