The cell biological events that guide early embryonic development occur with great precision within species but can be quite diverse across species. How these cellular processes evolve and which molecular components underlie these changes is poorly understood.
To begin to address these questions, we used two approaches. In the first approach, we systematically investigated early embryogenesis in 35 nematode species by time-lapse microscopy. We found 40 cell-biological characters that displayed phenotypic differences among the species. By tracing the evolutionary changes on the species phylogeny, we found that these characters evolved multiple times and independently of one another. Comparisons with genome-wide RNAi data from C. elegans revealed that individual aspects of the observed inter-species diversity are mirrored by single-gene phenotypes in C. elegans, thus leading to hypotheses about the specific molecular subnetworks that may have been altered during the evolution of early embryogenesis. For example, we predicted that a cell polarity module was altered during the evolution of the Protorhabditis group and showed that PAR-1, a kinase localized asymmetrically in C. elegans early embryos and many other cell types, is symmetrically localized in the one-cell stage of Protorhabditis group species.
In the second approach, we used RNAi in C. briggsae, a species that displays no major phenotypic difference when compared with C. elegans during wild-type development. We tested the C. briggsae role of genes belonging to the par-network by RNAi and identified several cases where the resulting phenotypes differed between the two species. This approach identified hidden genetic variability only visible by comparing the effect of gene perturbations.
Together, these results are consistent with the idea that the molecular networks underlying early embryogenesis are evolving significantly, even in cases where wild-type phenotypes are similar. They also suggest that embryogenesis comprises loosely interconnected functional modules that allow cellular events to evolve independently of one another thereby facilitating the exploration of phenotypic space.
|Commitee:||Desplan, Claude, Fitch, Dave HA, Nance, Jeremy, Siegal, Mark, de Salle, Rob|
|School:||New York University|
|School Location:||United States -- New York|
|Source:||DAI-B 70/01, Dissertation Abstracts International|
|Keywords:||Embryology, Evolution, Nematodes, Rhabditids|
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