Cold Spring Harbor, NY - For many years, scientists studying gene expression in plants assumed that genes inherited from both male and female parental sources contribute equally to development after fertilization. A new study by scientists working at Cold Spring Harbor Laboratory challenges this view, and instead indicates that the first few days of embryonic development are controlled largely if not exclusively by the maternal genome.
The new study is reported in the March 3, 2000, issue of Nature. In it, Ueli Grossniklaus and his colleagues describe an unexpected and surprising finding. While carrying out a control experiment, they observed that none of the 20 paternally inherited genes they examined were transcribed (expressed) during early seed development in the plant Arabidopsis thaliana. Instead, only maternally inherited copies of the genes were transcribed. Significantly, the genes tested are distributed throughout the plant's genome and are involved in unrelated processes, suggesting that gene expression is shut down or "silenced" throughout the entire paternal genome during early stages of seed development. (Arabidopsis is a relative of the mustard plant that has emerged as an ideal model system for studying numerous features of plant and molecular biology.)
"We tried one gene we knew was active during early seed development. No expression from the paternally inherited allele. Then another. Still nothing. Finally, we tried all of the genes we had probes for, and none of paternally inherited alleles were expressed," says Grossniklaus.
The researchers found that silencing of the paternally inherited genome is eventually relieved three to four days after fertilization. Grossniklaus speculates, however, that the early period during which paternal genes are silenced may prolong the evolutionary window of opportunity in which deleterious mutations in the maternal genome (for example, embryonic lethal mutations) are uncovered and selected against.
The study was carried out at Cold Spring Harbor Laboratory by Jean-Philippe Vielle-Calzada, Ramamurthy Baskar, and Grossniklaus, who is currently at the Friedrich Miescher Institute in Basel, Switzerland and will assume a professorship at the University of Zurich in May 2000.
Cold Spring Harbor Laboratory is a private, non-profit basic research and educational institution with programs focusing on cancer, neurobiology, and plant biology. Its other areas of research expertise include molecular and cellular biology, genetics, structural biology, and bioinformatics. The Laboratory's new Watson School of Biological Sciences offers an innovative Ph.D. program for a small group of exceptional students. Located on the north shore of Long Island, 35 miles from Manhattan, the Laboratory was founded in 1890 as a field station for the study of evolution. Today, the Laboratory is headed by Director Bruce Stillman and President James D. Watson.
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