Worm Breeder's Gazette 9(3): 90

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.

Cell Interactions and dth-1

J.R. Priess

dth-1 ('deep-throat' or 'demi-throat', e2072, e2141, e2142, e2144) 
is a maternal-effect lethal mutant that makes only the posterior half 
of the pharynx as an embryo (and supernumerary hypodermal cells- see 
Abstracts of 1985 C. and H.Schnabel and R. 
Schnabel, WBG 9-2, p. 78). In trying to interpret the mutant phenotype,
I have examined whether pharyngeal development normally is 'cell-
autonomous' or involves cellular interactions. Both the AB and Pl 
blastomeres of a normal two-cell embryo produce descendants that 
become pharyngeal muscles; AB produces most of the anterior half of 
the pharynx, and Pl produces most of the posterior half. I have 
removed either the AB or the Pl blastomeres with a microneedle and 
stained the resulting partial embryo with an antibody that recognizes 
pharyngeal muscles. Pl-derived partial embryos contain pharyngeal 
muscles (14/14), and some of these embryos develop a fairly well-
formed posterior pharynx (including the grinder). However AB-derived 
partial embryos do not make any pharyngeal muscles (0/25), suggesting 
an interaction with Pl-derived cells is necessary for descendants of 
AB to become these muscles.
Because all of the AB-derived pharyngeal muscles originate from just 
one of the AB daughters, ABa, I was interested in whether the other 
daughter, ABp, could produce pharyngeal muscles if it occupied the 
position of the ABa blastomere. In normal development, the AB 
blastomere initially divides transversely, then skews toward the 
anterior-posterior axis of the egg. This results in an anterior 
daughter, ABa, and a posterior daughter, ABp. It turns out to be 
relatively simple to reverse the direction of skewing in a dividing AB 
blastomere with a blunt-ended micropippete needle, such that the 
daughter that normally becomes ABp instead becomes ABa. These embryos 
form an apparently normal pharynx, hatch, and develop into fertile 
adults. This result explicitly rules out the possibilites that the 
nuclei, peripheral cytoplasm or membranes, of the AB daughters are 
qualitatively different when these cells are born. Instead, it appears 
likely that the different fates of ABa and ABp descendants normally 
arise from cellular interactions in the embryo. Therefore my current 
favorite model for the dth-1 gene product is that it plays some role 
in the interaction between AB- and Pl-derived cells (rather than being 
a pharyngeal 'determinant' partitioned into ABa, as I speculated at 
the last worm meeting.)
Andrew Fire and I are now trying to clone dth-1 with the goal of 
determining the nature and embryonic localization of the gene product. 
dth-1 maps near lin-12 and within the Tc1 polymorphisms eP6 and eP7, 
an area now covered entirely by a contig (Greenwald et al., WBG 9-2). 
We have isolated DNA from the majority of the cosmids in the region, 
and are attempting to rescue the mutant using the general protocols 
for transient expression (no luck yet) and stable integration 
previously described by Andy (EMBO, Oct. issue).