October 22, 2003
NIH-funded researchers have identified a gene that appears to be a crucial signal for the beginning of puberty in human beings as well as in mice. Without a functioning copy of the gene, both humans and mice appear to be unable to enter puberty normally. The newly identified gene, known as GPR54, also appears necessary for normal reproductive functioning in human beings.
The study, funded in part by the National Institute of Child Health and Human Development (NICHD), appears in the October 23 issue of the New England Journal of Medicine. GPR54 is located on an autosomal chromosome (a chromosome that is not a sex chromosome). The study also was funded by the National Center for Research Resources and the National Institute of General Medical Sciences, both at NIH.
"The discovery of GPR54 is an important step in understanding the elaborate sequence of events needed for normal sexual maturation," said Duane Alexander, M.D., Director of the National Institute of Child Health and Human Development (NICHD). "Findings from this study may lead not only to more effective treatments for individuals who fail to enter puberty normally, but may provide insight into the causes of other reproductive disorders as well."
Puberty begins when a substance known as gonadotropin releasing hormone (GnRH) is secreted from a part of the brain called the hypothalamus. Individuals who fail to reach puberty because of inherited or spontaneous genetic mutations are infertile.
"The discovery of GPR54 as a gatekeeper for puberty across species is very exciting" said the study's first author, Stephanie B. Seminara, of the Reproductive Endocrine Unit, Massachusetts General Hospital, Boston and a member of the NICHD-funded, Harvard-wide Endocrine Sciences Center. "In the future, this work might lead to new therapies for the treatment of a variety of reproductive disorders."
The GPR54 gene contains the information needed to make a receptor. Receptors and the molecules that bind to them are analogous to a lock and a key mechanism. Like a key fits into a lock, certain molecules bind to their receptors, which usually sit atop a cell's surface. Once the binding takes place, the cell either will begin a new biochemical activity, or halt an ongoing activity. The researchers think that the molecule metastatin binds to the GPR54 receptor. As of yet, they do not know what precise effect the molecule may have on cells.
The researchers sought to learn which genes are involved in triggering the brain's release of GnRH at puberty. Two teams of researchers working independently of each other were involved in the discovery. One consisted of U.S. based researchers, the other, of British researchers.
The U.S. team included Scientists from Massachusetts General Hospital, Brigham and Women's Hospital, and Harvard Medical School who collaborated with a researcher at Kuwait University. The British team included researchers from the University of Cambridge and Paradigm Therapeutics Ltd. in Cambridge.
The U.S. researchers isolated the gene from members of a Saudi Arabian family that suffered from idiopathic hypogonadotropic hypogonadism (IHH), a rare inherited disease in which sexual development is incomplete or does not occur because of insufficient release of GnRH from the hypothalamus. If untreated, individuals with this disorder fail to develop sexually.
By analyzing genetic material from men and women with IHH using tools from the NIH-sponsored Human Genome Project, the U.S. researchers first discovered that a certain region of chromosome 19 carried the mutant gene responsible for IHH. The researchers then identified GPR54 as the possible gene.
Working independently of the U.S. and Kuwaiti researchers, the British researchers created mice lacking GPR54. The mice without GPR54 also failed to reach puberty. The study authors found, however, that the brains of the mice contained normal levels of GnRH. The researchers do not yet know why the animals were unable to enter puberty, despite producing normal amounts of the hormone.
The findings from the two research teams complement each other, explained NICHD project officer Louis De Paolo, Ph.D, of NICHD's Reproductive Sciences Branch.
"Through some careful detective work, the U.S. researchers pinpointed the gene that causes IHH in this family," said Louis De Paolo, Ph.D., project officer in NICHD's Reproductive Sciences Branch. "Using the mouse model, the British researchers gained an important insight into the function of the gene."
The NICHD is part of the National Institutes of Health (NIH), the biomedical research arm of the federal government. NIH is an agency of the U.S. Department of Health and Human Services. The NICHD sponsors research on development, before and after birth; maternal, child, and family health; reproductive biology and population issues; and medical rehabilitation. NICHD publications, as well as information about the Institute, are available from the NICHD Web site, http://www.nichd.nih.gov, or from the NICHD Information Resource Center, 1-800-370-2943; e-mail NICHDInformationResourceCenter@mail.nih.gov.