The nematode worm Caenorhabditis elegans (C.Elegans, so called because of its "elegant" curving movement) has recently had its entire genome sequenced. (available from NCBI). Early embryological studies of this worm characterized the fate of each and every cell in the worm through all stages of development. That is, an adult cell could be accurately tracked back through its ancestors to the earliest stage of development. This allowed important questions to be asked about mechanisms determining cell fate and regulation of cell movement in development. See also a movie of early cell division in this embryo from the 2 cell stage.
3 adult worms
The reseaerchers were investigating how gene expression is regulated in C. elegans and identified the novel regulation method of RNA interference (RNAi), gene silencing by double-stranded RNA. This discovery was awarded the 2006 Nobel Prize in Physiology or Medicine.
Geanacopoulos M. The determinants of lifespan in the nematode Caenorhabditis elegans: a short primer. Sci Prog. 2004;87(Pt 4):227-47. Review.
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(According to Sulston et al. (1983)
P0 Single cell zygote
AB Embryonic founder cell
MS Embryonic founder cell
MS.a AVFL/R; Interneuron, processes in ventral cord and ring, few synapses
P0.pap E; Embryonic founder cell
P1.apa AS1; Ventral cord motor neuron, innervates dorsal muscles, no ventral counterpart
P1.app VD2; Vent cord motor neuron, innervates vent body muscles, probably reciprocal inhibitor
P1.p hyp7; Postembryonic large hypodermal syncytium
P0.ppa C; Embryonic founder cell
P2.p hyp7; Postembryonic large hypodermal syncytium
P0.pppa D; Embryonic founder cell
P3.p hyp7; Postembryonic large hypodermal syncytium, male
P0.pppp P4; Embryonic founder cell of germ line
Data from KEGG Last updated: January 19, 2000 (According to Sulston et al. (1983)