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.
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 circulation. 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.