Worm Breeder's Gazette 7(1): 79

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.

Site of Yolk Protein Synthesis in C. elegans

J. Kimble, W. Sharrock

We have done several experiments which together indicate that yolk 
proteins are synthesized by the intestine, transported from the 
intestine into the pseudocoelom, and taken up by the gonad to reach 
the oocytes.  This is the simplest variation yet observed of the 
pattern of yolk protein synthesis typical of both invertebrates and 
vertebrates - where yolk proteins are normally synthesized by an 
endodermal derivative and they are transported to the ovary via the 
Our first bit of evidence is that animals with no gonads (obtained 
by laser ablation of the gonadal precursor cells soon after hatching) 
contain copious quantities of all three yolk proteins (yp170, yp115, 
and yp88, see Sharrock above).  The extragonadal synthesis observed in 
these animals suggested that the gonad is not the primary site of 
synthesis of yolk proteins.  Next, we dissected radioactively labelled 
animals into intestines, gonads, and body walls.  Each tissue exhibits 
a different pattern of bands on SDS gels.  Body walls contain mostly 
actin, myosin, and a series of bands of about 101K which we suspect 
are cuticle proteins.  Gonads contain all three yolk proteins as well 
as certain gonad specific proteins (bands that are missing in 
gonadless animals).  The major band in intestines is one at 170K that 
is probably yp170.  Intestines dissected from laser ablated gonadless 
animals possess bands at 170K, 115K, and 88K, suggesting that this 
tissue is the extragonadal site of yolk protein synthesis.  Finally, 
we incubated dissected intestines and gonads in [35S]-methionine to 
look at synthesis in isolated tissues.  Chan and Gehring's medium (C 
and G, 1971) turns out to be a successful medium for worm organ 
culture.  In such experiments, intestines made abundant 170K protein (
25% of the total protein), but synthesis of 115K and 88K protein was 
variable.  The gonads produce no proteins in organ culture that are 
170K, 115K, or 88K, though gonad specific proteins are made in 
quantity.  Thus, the intestine appears to be the primary site of 
synthesis of all three yolk proteins.  This is the only sign of sexual 
differentiation in the intestine so far detected.
Secretion of yolk proteins was observed by exposing the intestine to 
[35S]-methionine in the same medium.  This time the animal was cut 
midway through the pharynx so the intestine was not cut and so leakage 
would be minimized.  A comparison of gels of tissues and medium showed 
that yolk proteins were selectively found in the medium.
We have also examined the site of yolk protein synthesis in four 
mutants that alter sexual phenotype in a tissue specific way.  Each 
mutant appears morphologically to have male somatic tissues, but to 
make oocytes.  However, results from laser ablation and dissection 
experiments indicate that the intestine of these mutants makes yolk 
proteins.  Thus, the intestine and germ line tissues of these mutants 
are hermaphrodite, and the other somatic tissues are either completely 
male or primarily male - depending on the mutant.  We have therefore 
suggested that sexual differentiation in the endoderm and germ line 
tissues is coordinately controlled.