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Without Children (Woc) affects cystoblast differentiation and proper soma-germ line association by modulating Stat target gene expression.
Lilach
Gilboa, Iris Maimon, Malka Popliker. Biological Regulation, Weizmann Institute of Science, Rehovot, Israel.
In the Drosophila ovary, somatic cells and germ cells are tightly associated. How this association is achieved and its biological consequences remain
poorly understood. We show that the putative transcription/chromatin-binding factor, Without Children (Woc), is required for proper expression of Stat
target genes, which in turn affects soma-germ line association and the differentiation of germ line stem cell (GSC) daughter cells.
Woc is a zinc-finger transcription factor, which was also shown to bind and protect telomeres. It is expressed in both somatic cells and germ cells. We find
that Woc is required within somatic cells for correct cyst development. Removing Woc from somatic cells by tissue specific RNAi or in clones results in loss
of association between soma and germ line. In larval ovaries, the somatic Intermingled Cells fail to intermingle with primordial germ cells. In the adult
germarium, Escort Cells (ECs) fail to send cellular extensions that contact differentiating germ cells. Within such germaria, cystoblasts (the immediate
daughters of GSCs) do not form cysts, filling the ovary with single germ cells.
We find that the full range of phenotypes exhibited by Woc-deficient larval ovaries and germaria resemble ovaries in which Stat function or its target gene
zfh-1
have been removed. Indeed, in
woc
-mutant cells, the Stat target gene
zfh-1
is not properly expressed. Upd over-expression cannot rescue
woc
phenotypes. However, expression of Zfh-1 from a heterologus promoter does rescue cyst formation in
woc
mutant ovaries.
Our data suggest a novel role for Stat in regulating cystoblast differentiation and demonstrate a requirement for a transcription/chromatin factor, previously
associated with telomere integrity, in regulating ovarian Stat function.
153
Regulation of pachytene checkpoint in
Drosophila
ovaries via Polo-mediated phosphorylation of Maelstrom.
Jun Wei Pek, Toshie Kai. Temasek Life
Science Laboratory, 1 Research Link National University of Singapore Singapore 117604.
In
Drosophila
, Maelstrom is a conserved component of the perinuclear nuage, a germ-line-unique structure, which appears to serve as a site for piRNA
production to repress deleterious transposons. Maelstrom also functions in the nucleus as a transcription regulator to repress the expression of
microRNA-7
, a
process which is essential for proper differentiation of germ-line stem cells. Here, we report a novel function of Maelstrom in regulating the pachytene
checkpoint independent of its transposon silencing and germ-line stem cell differentiation activities.
Drosophila
Maelstrom is phosphorylated at a conserved
Serine 138 residue, and this phosphorylation event is required for repression of the pachytene checkpoint through repressing the checkpoint protein Sir2, but
not transposon silencing and germ-line stem cell differentiation. We identify Polo as a kinase which mediates phosphorylation of Maelstrom to regulate the
pachytene checkpoint. Therefore, our results suggest that Polo-mediated phosphorylation of Maelstrom may be a novel mechanism that controls the
pachytene checkpoint through repressing Sir2 in the
Drosophila
ovaries.
154
Tribbles is a kinase that directs a switch in gene expression to trigger follicle cell migration.
Leonard L. Dobens, Rahul Das, Venessa Masoner, Laramie
Pence. School of Biological Science, University Missouri-Kansas City, Kansas City, MO.
tribbles
(
trbl
) encodes the founding member of the Trb family of candidate pseudokinase molecules required for cell proliferation, growth and migration
throughout the metazoan lineage. During cell migration in flies,
trbl
drives protein turnover, notably of (1) the String cdc25 phosphatase in the mesoderm
during gastrulation and (2) the C/EBP homolog Slow Border Cells (Slbo) during border cell migration in the ovary. Here we re-examine the role of
trbl
in
follicle cell (FC) migration by testing (1) specific Trbl antisera, (2) site-directed mutants in the Trbl kinase-like domain and (3) a
trbl
null allele generated by
FRT-mediated deletion. During late stages of oogenesis, Trbl protein accumulates at high levels in the nuclei in non-migrating FC and at low levels in both
the migratory border cells and centripetal FC. During border cell migration, low levels of Trbl are maintained by
slbo
repression, but ectopic expression of
Slbo in posterior FC is not sufficient to repress Trbl expression. It has been shown previously that WT Trbl misexpression is sufficient to both block border
cell migration and enhance Slbo protein turnover and here we show that misexpression of a Trbl molecule bearing a site-directed mutant in the catalytic loop
of its kinase-like domain results in the opposite phenotype: a failure to block border cell migration and enhanced stability of the Slbo protein. Thus Trbl is a
bonafide kinase that mutually represses Slbo during border cell migration. During centripetal FC migration, clones of a
trbl
null allele lead to (1) a loss of FC
apico-basal polarity, (2) the disintegration of organized structures resembling actin cables and (3) reduced expression of the Slbo target Cut. These data
suggest that the
trbl
kinase regulates both the supracellular organization of the cytoskeleton and a gene expression switch from Slbo to Cut to coordinate the
migration of FC tissue sheets.