CHAMPAIGN, Ill. -- Researchers studying the nuclei of frog oocytes in early stages of meiosis -- the cell division that gives rise to germ cells -- have found that two key proteins remain apart at a crucial time before condensation occurs. One of the proteins, they say, may be important in the early organization of chromosomes and later may recruit the other.

In the August issue of the journal Chromosome Research, scientists at the University of Illinois at Urbana-Champaign detail how they used antibodies to the proteins, XCAP-E and XCAP-D2, and confocal laser scanning microscopy to zero in on the proteins' precise locations inside the nuclei of gametes of the African frog Xenopus laevis.

(The research will be on display as a poster presentation Aug. 17-22 during the Gorden Research Conference on Plasmid & Chromosome Dynamics in Tilton, N.J.)

The proteins are from two subcomplexes of chromosome condensation proteins known as condensins. One group of the Xenopus Chromosome Associated Proteins (XCAP), including XCAP-D2, consists of regulatory proteins, while XCAP-E is among those directly involved in condensation.

"On the chromosomes, XCAP-D2 was only found associated with the chromomeres," said Michel Bellini, a professor of cell and structural biology at Illinois. That location features highly compacted chromatin, or fibers of DNA, suggesting XCAP-D2 is directly involved early in meiotic chromatin organization.

Immunofluorescent staining showed XCAP-D2 proteins on the 18 easily recognizable chromosomes of the frog oocyte. These extended chromosomes stretch out long loops of chromatin -- regions of extensive RNA synthesis -- causing them to resemble a lampbrush, and, more importantly, allowing for detailed cytological studies of the major components implicated in both RNA transcription and chromatin organization.

"When we looked for XCAP-E, we did not see it on the chromosomes," Bellini said. "Instead, it was accum
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Contact: Jim Barlow
jebarlow@uiuc.edu
217-333-5802
University of Illinois at Urbana-Champaign
14-Aug-2003

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