Mark Blaxter: Teaching Pages

Student Seminar: Evolution of development: the nematode vulva as a case study

Developmental Biology 4 2008

Evolution of vulval development in nematodes related to C. elegans

The idea of the seminar is
(a) for you to get practice in presenting and listening to journal papers...
(b) to begin to get an insight into the evolution of developmental mechanisms
EVERYONE should read everything, but you will be expected to have read this core paper:
Sommer, R. J. and P. W. Sternberg (1994). "Changes of induction and competence during the evolution of vulva development in nematodes." Science 265: 114-118.
There is background (and reminder) on C. elegans vulval induction on my DB3 web site (http://zeldia.cap.ed.ac.uk/teaching/devbio3/devbio3.html) and in the following paper:
Kornfeld, K. (1997) Vulval development in Caenorhabditis elegans.
Trends in Genetics 13, 55-61
The presenters will thus not have to reintroduce the Pn.p cells each time.

paper 1: Felix, M. A. and P. W. Sternberg (1997). "Two nested gonadal inductions of the vulva in nematodes." Development 124(1): 253-9.
         How do intercellular signals that pattern cell fates vary in evolution? During nematode vulva development, precursor cells acquire one of three fates in a pattern centered around the gonadal anchor cell. Non-vulval fates are at the periphery, outer and inner vulval fates are towards the center. In Caenorhabditis elegans, the three fates are specified around the same time by an induction by the anchor cell and lateral signaling between the vulva precursor cells. We find that, in three other nematode species (Panagrolaimus, Oscheius and Rhabditella spp.) spanning two families, the centered pattern is obtained by two temporally distinct gonadal inductions. The first induction specifies vulval fates; the second induction specifies the inner vulval fates in a subset of the precursors' daughters. This evolutionary change in the spatiotemporal connectivity of cell interactions allows centering of the pattern between two precursors in Panagrolaimus.

paper 2: Dichtel-Danjoy, M. L. and M. A. Felix (2004). "The two steps of vulval induction in Oscheius tipulae CEW1 recruit common regulators including a MEK kinase." Dev Biol 265(1): 113-26.
         The cell interactions that specify the spatial pattern of vulval precursor cell (VPC) fates differ between the nematodes Oscheius tipulae CEW1 and Caenorhabditis elegans. In the former, the centered pattern of fates is obtained by two successive inductions from the gonadal anchor cell, whereas in the latter, a single inductive step by the anchor cell (EGF-Ras-MAP kinase pathway) can act as a morphogen and is reinforced by lateral signaling between the vulval precursors (Notch pathway). We performed a genetic screen for vulva mutants in O. tipulae CEW1. Here we present the mutants that specifically affect the vulval induction mechanisms. Phenotypic and epistatic analyses of these mutants show that both vulval induction steps share common components, one of which appears to be MEK kinase(s). Moreover, the inductive pathway (including MEK kinase) influences the competence of the vulval precursor cells and more strikingly their division pattern as well, irrespective of their vulval fate. Finally, a comparison of vulval mutant phenotypes obtained in C. elegans and O. tipulae CEW1 highlights the evolution of vulval induction mechanisms between the two species.