
                         Roanoke Times
                 Copyright (c) 1995, Landmark Communications, Inc.

DATE: FRIDAY, December 2, 1994                   TAG: 9412020074
SECTION: NATIONAL/INTERNATIONAL                    PAGE: A2   EDITION: METRO 
SOURCE: ASSOCIATED PRESS
DATELINE: WASHINGTON                                 LENGTH: Medium

GENETIC SEX SWITCH FOUND

Researchers have isolated a genetic switch that separates the boys from the girls. It turns off the female in the human embryo and starts biological changes that eventually put hair on the chest.

Dr. Michael Weiss of the University of Chicago said the new study advances the understanding of the complex cascade that determines whether people are male or female and sheds new light on how this process can sometimes go awry.

In research to be published today in the journal Science, Weiss and his team use sophisticated imaging techniques to explore the biological pathway to manhood on an atomic level. Their research report traces the development of maleness, from the turning on of the SRY gene, which is on the Y chromosome, to the work of another gene called MIS, that removes the female parts of the original embryo.

Weiss said that science has long known that everybody at conception is female, but the precise biological mechanism that changes an embryo to male still is incompletely understood. Solving the puzzle on a molecular level may answer questions about other basic cellular changes, such as the development of cancer.

``If we can understand the general switches involved in sex determination, then we could possibly relate that to other basic processes, such as how organs differentiate or how cancer arises,'' he said.

For the first weeks after conception, all mammal embryos start forming the basic female structures: uterus, fallopian tubes and vagina.

``The embryo destined to become a boy begins as a female,'' Weiss said. ``It lays down first female structures and not male structures at a phase when the embryo looks like a recognizable mammal, with toes, fingers and eyes and a heart.''

After that, he said, the SRY gene switches on to start the embryo on its way toward manhood. The study shows that SRY also triggers the work of MIS, which dissolves the female parts of the original embryo.

``SRY is the master switch,'' Weiss said. ``For the first time we have shown that SRY can activate a male-specific pattern of gene expression leading to activation of MIS, which is the key signaling molecule for half of the male pathway.''

by CNB