Genetic Control of Nematode Development 
though many cells die during the course of 
C. elegans development, most cells survive; cell 
survival requires the inactivation of the cell death 
process, as a tenth gene functions to prevent the 
action of the nine cell death genes in surviving 
cells. In addition, this regulatory gene is itself 
controlled in a cell-specific fashion by other 
genes that determine which cells are to live and 
which are to die. Molecular analyses of genes in- 
volved in programmed cell deaths in C. elegans 
have suggested that the biochemical processes re- 
sponsible might be similar to those suspected to 
cause nerve cells to die in human neurological 
disorders. We hope that knowledge of what 
makes cells die and of what can block the cell 
death process in C. elegans will lead to methods 
that will prevent the cell deaths responsible for 
human disorders. 
Cell Migration 
During animal development, cells are often 
generated far from their final positions and must 
migrate considerable distances before being able 
to function. To understand what causes cells both 
to migrate and to stop migrating, we are analyzing 
two C. elegans cell migrations. The first involves 
a pair of muscle precursor cells that are born in 
the posterior body region and move to a central 
position along the animal's length, near its gonad. 
We have discovered that these migrations involve 
signaling between the migrating cells and go- 
nadal cells located at the termination site of the 
migration. We are characterizing genes that func- 
tion in this signaling process. 
The second migration we have studied involves 
a pair of neuronal cells that move from the tail 
region to the midbody region of the animal. Thir- 
teen genes have been identified that must func- 
tion for these neuronal migrations to occur prop- 
erly. Some of these genes probably act in the 
migration process per se, but some do not. The 
actions of some of these latter genes allow these 
neurons to acquire their identities; if these genes 
do not function, these neurons fail to express 
their normal characteristics, including their 
long-range cell migration. 
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