Bhagwati Gupta

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===== VPC competence and lin-39 in worms =====

//**Panigault and Felix, Developmental Biology, 2011, 357:428-438**//\\
In this paper authors have quantified the levels of the Homeodomain protein LIN-39 in //C. elegans// vulval cells. The results revealed an interesting distribution pattern, leading to an improved understanding of //lin-39// function during development. 

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//(excerpt from the paper)//\\
We have quantified the LIN-39 protein profile in vulval precursor cells of early L2 stage larvae, prior to P3.p fusion and inductive signaling. We show that LIN-39 levels are very low in P3.p and P4.p, peak in P5.p and progressively decrease until P8.p. This unexpectedly centered profile arises independently from the gonad. P3.p and P4.p competence and division are sensitive to the already low LIN-39 and Wnt doses; most dramatically, each of the //cwn-1/Wnt// and //egl-20/Wnt// genes show haplo-insuficience for P3.p fate. In contrast to previous results, we find that these Wnts maintain P3.p and P4.p competence without affecting their LIN-39 level.\\
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{{ :lin-39_panigault-felix-2011.jpg?nolink&500 |}}
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//**(from Panigault and Felix, Developmental Biology, 2011, 357:419-427)**//\\
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{{ :lin-39-in-nematodes.jpg?nolink&500 |}}
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{{ :lin-39-in-cbr.jpg?nolink&500 |}}
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Two other papers (below) also describe the role of //lin-39// in vulval development.

//**(from Seetharaman et al., Developmental Biology, 2010, 346:128-139)**//\\
The vulva develops from three of six ventral hypodermal cells (termed P3.p to P8.p) that escape fusion to the surrounding hypodermal syncytium, hyp7, during the L1 stage and become vulval precursor cells (VPCs). This process is mediated by //lin-39// since all Pn.p cells in //lin-39// mutants fuse to hyp7 in the L1 stage. The //lin-39// activity is also required during the L2 stage to prevent VPCs from fusing to hyp7, and maintaining their competence to respond to patterning signals. The L2-stage expression of //lin-39// is positively regulated by the BAR-1 (β-Catenin)-mediated canonical Wnt signaling pathway. In //bar-1// mutants //lin-39// activity is greatly reduced which causes VPCs to inappropriately fuse with hyp7 (Eisenmann et al., 1998).\\
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//**(from Myers and Greenwald, PNAS, 2007, 104:20368-20373)**//\\
During the L3 stage P5.p, P6.p and P7.p receive patterning signals (inductive and lateral) and divide to produce the correct number and types of vulval cells. The other VPCs (P3.p, P4.p and P8.p) do not receive these signals and produce daughters that fuse with hyp7. //lin-39// appears to be involved in induction and is a direct transcriptional target of the inductive signaling pathway.\\
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