Sex determination in birds: HINTs from the W sex chromosome?

Sex in birds is controlled genetically ( ZZ male: ZW female), but the genetic mechanism remains unclear. While some evidence points to the involvement of Z sex chromosome dosage, other data favour a dominant female- determining gene carried on the W sex chromosome. An intriguing candidate gene located on the chicken W chromosome is HINTW, which encodes an aberrant form of a hydrolase enzyme. In chicken embryos, HINTW is strongly expressed in the gonads and other tissues of ZW ( female) embryos. In vitro biochemical data show that HINTW can interfere with the action of a Z-linked orthologue, HINTZ, which is a bona fide hydrolase enzyme. HINTW is conserved among carinate ( flying) birds, and recent molecular analysis indicates that it has undergone positive selection over evolution. However, a differentiated HINTW gene appears to be absent in the flightless ratites. This review examines the evidence for and against a role for HINTW in avian sex determination. Copyright (C) 2007 S. Karger AG, Basel.