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.
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).