Worm Breeder's Gazette 7(1): 78

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.

Yolk Proteins of C. elegans

W. Sharrock

I have been working on the adult-hermaphrodite-specific proteins 
initially described by Klass et al.  (Develop.  Biol.  69: 329).  
These proteins are: a doublet species of approximately 170,000 daltons;
a species of approximately 115,000 daltons which occasionally 
migrates as a doublet; and a single band of approximately 88,000 
daltons.  The abundance, presence in eggs, and specific synthesis of 
these proteins in adult hermaphrodites suggest that they are the 
principal yolk proteins of C.  elegans.  My results and others (see 
Kimble & Sharrock, below) are consistent with this idea.  I therefore 
refer to these proteins as yp170, yp115, and yp88.
Homogenates of C.  elegans produced by passage through a Stansted 
cell disruptor at 1500-2500 psi yield a substantial pellet on 
centrifugation at 1000 x g.  Extraction of the pellet with 0.1% 
Nonidet P-40 solubilizes the yolk proteins in enriched form.  I have 
isolated the yp170 doublet by fractionating the NP-40 extract on a 
column of Bio-gel A5m in the presence of 0.1% SDS.  An anti-serum 
against the purified yp170 doublet does not bind either yp115 or yp88. 
In indirect immunofluorescence experiments, this anti-serum 
illuminates particles uniformly distributed throughout the cytoplasm 
of embryonic cells.  As hatching approaches, the yp170 antigen is 
segregated in the posterior of the worm, probably the intestine.
All three yolk protein species bind the lectin concanavalin A, 
indicating that they are glycoproteins.  Peptide mapping experiments 
with [35S]-labeled proteins indicate that yp170, yp115, and yp88 are 
structurally distinct polypeptide species.  As in the immunoabsorption 
experiment described above, however, it is not clear how much of this 
apparent dissimilarity may be attributed to glycosylation or other 
post-translational modifications.  The two bands of the yp170 doublet 
are closely related, though some differences are evident.
In other organisms, yolk proteins are present in the egg in membrane-
enclosed globules or platelets.  The extraction of yp170, yp115, and 
yp88 from a particulate fraction by detergent is consistent with a 
similar sort of packaging in C.  elegans eggs.  Segregation of yolk to 
the embryonic intestine is observed in amphibians and insects.  It 
remains to be seen whether modifications, such as the glycosylation 
indicated by Con A binding, are as extensive in C.  elegans as 
elsewhere.  Also, yolk proteins are typically derived by proteolytic 
cleavage of larger precursors; there is as yet no evidence for such 
processing in C.  elegans.