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© The Rockefeller University Press, 0021-9525/2001/9/1101-b $5.00
The Journal of Cell Biology, Volume 154, Number 6, September 17, 2001 1101-b-1101

Tagged From birth

Parallel gene expression orders during segmentation (top) and neurogenesis (bottom) determine cell fate. Doe/Elsevier

In the fly, the genes hunchback (hb), pdm1/pdm2 (pdm), and castor (cas) are expressed at different times in the embryonic central nervous system and have been suggested to specify temporal identity of neuroblast daughter cells. Now, Chris Doe and colleagues (University of Oregon, Eugene, OR) propose that sequential expression of these factors defines identity in neuroblast lineages.

Doe and colleagues first add the gene krüppel (Kr) to the proposed temporal cassette, and find that individual lineages sequentially make Hb, then Kr, then Pdm, and finally Cas. Hb and Kr are necessary and sufficient to specify the fate of first- and second-born progeny, respectively.

Birth order, not cell type, correlates with the layered expression of these gene. Thus, the same sequence of gene expression is followed regardless of whether the original progeny cell is a motorneuron, interneuron, or glial cell. First-born progeny express Hb and occupy the deepest cortical layers, whereas second-born progeny express Kr and reside in the next deepest layer.

A cell-cycle dependent clock, rather than a global timing mechanism, appears to regulate the sequential expression of these genes. If the cell cycle is stopped, the sequence of changes in gene expression also stops.

Reference:

Isshiki, T., et al. 2001. Cell. 106:511–521.[Medline]

Vicki Glaser

vpglaser{at}aol.com

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This Article Full Text (PDF, 125K) PPT slides of all figures Alert me when this article is cited Services Email this article Similar articles in this journal Alert me to new content in the JCB Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Glaser, V. Search for Related Content PubMed Articles by Glaser, V. Social Bookmarking                            What's this?