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Hitoshi SAWA, Ph. D. 
The
development of multicellular organisms involves a single cell (such as
a fertilized egg) which gives rise to a diverse progeny through successive
cell divisions. The process of cell division in which the resulting daughter
cells are of different characters or “fates” is known as asymmetric
cell division. One example of this form of cell division is seen in stem
cells, which can produce one copy of themselves and one more specialized
(differentiated) cell in a single division. Asymmetric cell division is
central to the generation of cellular diversity, but because in higher
organisms a given cell's “family relations” (known as cell
lineage) are frequently unclear, it can be difficult to study the process
in detail.
In
the nematode, C. elegans, however, thanks to the transparency
of the worm's body it is possible to track the division and other
activity of individual cells in the living animal using only a low-magnification
light microscope. In our laboratory, we take advantage of this ability
to monitor developmental processes in real time, a method which we use
in combination with genetic studies to investigate the mechanisms that
underlie asymmetric division. We have determined that nearly every asymmetric
cell division in C. elegans is mediated by β-catenins acting
in the Wnt signaling pathway. This pathway works to polarize cells fated
to undergo asymmetric division; we seek to gain a better understanding
of how it achieves this by studying the intracellular localization of
the Wnt pathway's molecular components.
We
have also discovered numerous mutant C. elegans phenotypes in
which the asymmetric division of specific cells is disturbed, allowing
us to identify more than 50 genes involved in this process. By investigating
the function of these genes, we hope to clarify the biological mechanisms
of asymmetric cell division even further.
