Program of the 2001 International Worm Meeting - Sternberg Lab ...

759
759. PGL-1, PGL-2, and PGL-3, a
family of P-granule proteins, function
redundantly to ensure fertility in both
sexes of C. elegans
Ichiro Kawasaki 1,2,3 , Anahita
Amiri 1 , Yuan Fan 1 , Takeshi
Karashima 4 , Yuji Kohara 2 , Susan
Strome 1
1 Dept. of Biology, Indiana University, USA
2 Genome Biology Lab., National Institute of
Genetics, Japan
3 PRESTO, JST, Japan
4 Dept. of Biophysics and Biochemistry,
University of Tokyo, Japan
P granules are distinctive ribonucleoprotein
complexes observed specifically in the
cytoplasm of germ cells throughout
development. We previously identified PGL-1
as being a constitutive protein component of P
granules. The presence of an RGG box predicts
that PGL-1 is an RNA-binding component of P
granules. pgl-1mutants contain defective P
granules and are sterile, due to defects in
proliferation and gametogenesis. Interestingly,
the sterility caused by null alleles of pgl-1 is
highly sensitive to temperature. Our
identification and analysis of two additional
pgl-1-related genes, termed pgl-2 and pgl-3,
demonstrate that the PGL proteins function
redundantly, and at low temperature, PGL-2 and
PGL-3 are sufficient for fertility.
PGL-2 has 34% identity with PGL-1 in its
N-terminal region. PGL-3 has 62% identity
with PGL-1 throughout its length and contains
an RGG box. Based on yeast two-hybrid and
GST pull-down results, the three PGL proteins
interact with each other. Furthermore, PGL-1
and PGL-3 are co-immunoprecipitated from
both embryo and oocyte extracts, indicating that
they are indeed in the same protein complex in
vivo. Immunofluorescence analysis has
demonstrated that in wild-type worms PGL-3 is
associated with P granules at most stages of
development, like PGL-1, but interestingly,
PGL-2 is associated with P granules only during
postembryonic development. Based on
molecular epistasis results, each PGL protein
associates with P granules independently of the
other two.
759
To address whether PGL-3 functions
redundantly with PGL-1, we isolated a pgl-3
deletion allele. We found that pgl-1; pgl-3
double mutant hermaphrodites and males show
significantly enhanced (but not 100%) sterility
at low temperature, compared to either single
mutant. Double mutant hermaphrodites contain
a severely underproliferated germline,
indicating that the primary defect is in
proliferation. Depletion of pgl-2 by RNAi did
not enhance sterility further.
Our findings suggest that both PGL-2 and
PGL-3 are components of P granules that
interact with PGL-1 and that at least PGL-3
functions redundantly with PGL-1 to ensure
fertility in both sexes during C. elegans
germline development.