Worm Breeder's Gazette 13(4): 53 (October 1, 1994)

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.

Maternally-Encoded Factors Are Required to Repress Zygotic pes-10 Expression in the Embryonic Germ Lineage.

Geraldine Seydoux, Andy Fire

Carnegie Institution, Baltimore MD 21210.

  In the previous WBG, we described the expression pattern of the pes-10 gene, one
of the first genes to be transcribed in embryos (WBG 13.3, p 33). Starting in the
four-cell stage, pes-10 RNA is expressed transiently in each somatic founder lineage.
pes-10 RNA was never detected in the gerrn lineage (P[1]-P[4]). To test whether
regulation of pes-10 expression is dependent on maternally-encoded products, we have
analyzed by in situ hybridization the distribution of pes-10 or pes-10 ::lacZtranscripts
in embryos derived from mothers homozygous for maternal-effect mutations that affect
the fate of embryonic blastomeres. The observed pes-10 expression patterns are
summarized below.
  skn-1 ( zu67 ): Skn-1 is a maternally-encoded putative transcription factor
required for the specification of the fate of the EMS blastomere(1). (In skn-1
(-)embryos, EMS descendants adopt fates resembling those of the somatic descendants
of P2 .)In skn-1 (-)embryos, pes-10 expression appears unaffected at least to the 8-cell
stage. This result indicates that skn-1 (+)activity is not required for pes-10
transcription in EMS .
  pie-1 ( zu154 ): Pie-1 is required for the specification of the fate of the P2 blasto
mere2 .(In pie-1 (-)embryos, the P2 germline blastomere adopts a fate resembling that
of its somatic sister EMS.) In pie-1 (-)embryos, pes-10 RNA is ectopically expressed in
P[2] and P[3], in addition to its normal expression in somatic cells. This result
indicates that pie-1 (+) activity is required to keep pes-10 expression off in the germ (P)
lineage. This observation suggest a model for the mechanism of PIE-1 action: PIE-1
may function generally to keep zygotic transcription off in the germ lineage. This
would counteract the action of transcription factors, including pes-10 regulator(s) and
skn-1 .( Skn-1 is present in both P[2] and EMS but seems to act only in EMS to specify
its fate(3)).
  mex-3 ( zu155 ): MEX-3 is required to repress myogenic fates in the AB lineage(4).
(In mex-3 (-)embryos, AB descendants develop muscle.) pes-10 expression is abnormal
in mex-3 (-)embryos. In particular, we frequently saw pes-10 expression in P[2] (12/19
four-cell embryos), although no pes-10 expression was seen in P3 (18/18 eight-cell
embryos). In the 28-cell stage, a time when pes-10 expression is normally restricted to
the C and D lineages, we observed instead pes-10 expression in a subset of cells in the
AB/EMS lineages. These observations suggest that mex-3 (+)activity is required for the
regulation of pes-10 expression in both somatic and germ lineages.
 (1) Bowerman et al. (1992). Cell 68, 1-20.
 (2) Mello et al. (1992). Cell 70, 163-176.
 (3) Bowerman et al. (1993). Cell 74, 443-452.
 (4) Draper and Priess, pers. communication.