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Dissection of Gene Regulatory Networks Underlying Patterning and Morphogenesis in the C. elegans Vulva


Fernandes, Jolene Sabrina (2007) Dissection of Gene Regulatory Networks Underlying Patterning and Morphogenesis in the C. elegans Vulva. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/AKNB-Q161.


During development, in the course of which the single-celled egg generates a whole organism, cells become different from each other and form patterns of types of cells. It is these spatially defined cell-fate patterns that underlie the generation of complex organs. The mechanisms that establish these precise spatial patterning events depend on the implementation of diverse ‘gene regulatory networks’ (a consequence of functional interconnections between regulatory genes (transcription factors) and their target genes). Dissection of gene regulatory networks that control patterning of gene expression and differentiation would thus help us understand how cells generate a spatially defined pattern of cell fates during organ formation. Resources such as diverse spatial and temporal cell-fate markers, reverse genetics (RNAi), trans-genesis, and the ease of manipulation at the single-cell level make C. elegans a tractable system for studying the execution of cell-type-specific gene expression programs that occur during organogenesis. Consider the C. elegans vulva, a postembryonically derived organ that invariantly consists of seven distinct vulval cell types (vulA, vulB1, vulB2, vulC, vulD, vulE and vulF), each with its own unique gene expression profile. These features make the C. elegans vulva a particularly attractive model for dissecting the postembryonic gene regulatory networks involved in patterning and organ morphogenesis. This thesis focuses on elucidating the regulatory networks that control gene expression in the seven vulval cell types of C. elegans during organogenesis. The transcription factors lin-11(LIM), cog-1(Nkx6.1/6.2), and egl-38(Pax2/5/8) have been previously implicated as key regulators of gene expression in the vulva. Identification of additional regulatory factors is warranted, so as to rigorously dissect the mechanisms that specify the spatial fate patterns of terminally differentiated cell types. To this end, I systematically disrupted the gene activity of 508 transcription factors via RNAi and assayed the expression of ceh-2, a readout for vulB fate during the L4 stage. From this screen, I identified the tailless ortholog nhr-67 as a novel regulator of vulval gene expression. nhr-67 acts in combination with cog-1, egl-38, and lin-11 to execute accurate patterning of gene expression of their downstream targets. The pair-wise interactions between these regulatory genes are complex and vary among the seven cell types. One of the ways in which nhr-67 maintains cell identity is through restriction of inappropriate cell fusion events in specific vulval cells (namely vulE and vulF). The cell fusion defects observed in an nhr-67 RNAi background can be partially attributed to deregulation of fusogens. cog-1 and lin-11 (but not egl-38) mutants also show heterotypic fusion defects to different degrees. I also discovered a striking regulatory circuit that affects a subset of the vulval lineages: cog-1 and nhr-67 inhibit both one another and themselves. We argue that the 1° vulval cells (vulE and vulF) utilize this novel regulatory motif to rapidly switch fates in response to transient inputs. We also speculate that the built-in flexibility of this circuit acts as a failsafe mechanism (in the event of cell damage) in the vulE and vulF cells. We postulate that the differential levels and combinatorial patterns of lin-11, cog-1, egl-38, and nhr-67 expression are a part of a regulatory code for the mature vulval cell types

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:C. elegans vulva; gene regulatory networks; morphogenesis; transcription factors
Degree Grantor:California Institute of Technology
Major Option:Biology
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Sternberg, Paul W.
Thesis Committee:
  • Rothenberg, Ellen V. (chair)
  • Zinn, Kai George
  • Sternberg, Paul W.
  • Fraser, Scott E.
Defense Date:18 May 2007
Non-Caltech Author Email:jfernandes (AT)
Record Number:CaltechETD:etd-05242007-164706
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2028
Deposited By: Imported from ETD-db
Deposited On:31 May 2007
Last Modified:22 Feb 2020 00:36

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