African Pygmy Mice: Females Are XY ... Researchers Find out Why
ScienceDaily (Feb. 25, 2010) — In a great majority of cases, the Y chromosome determines sex in mammals. The African pygmy mouse M. minutoides is an exception to this rule. In this species, which is a close relative of the house mouse, it is the X chromosome that determines sex.
An XY female Mus minutoides. (Credit: Copyright Frédéric Veyrunes / CNRS 2009)
The research is published in the 7 April issue of the journal Proceedings of the Royal Society B.
In the great majority of mammals, sex determination follows a simple rule: an XX chromosome arrangement defines a female while an XY arrangement produces a male. However, some situations may deviate from this principle, in which case reference is made to chromosomal anomalies that most generally cause sterility. On the Y chromosome, sex is determined by the presence or absence of a single gene called Sry. Located in 1990, this gene initiates the development of male characteristics; without this gene, the gonads become ovaries.
However, some mammal species do not obey this rule. Until now, only seven cases of atypical sex determination had been observed, all in rodents. The team coordinated by Frédéric Veyrunes has just identified a new case, the first to be described for 30 years, in Mus minutoides, an African pygmy mouse species which is particularly interesting as it is very closely related to the house mouse, the principal mammal model used in biology. By studying different populations of African Mus minutoides, the researchers observed a very high proportion of fertile females carrying XY chromosomes (between 74% and 100%).
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Frederic Veyrunes1,*, Pascale Chevret2, Josette Catalan1, Riccardo Castiglia3, Johan Watson4, Gauthier Dobigny5, Terence J. Robinson6 and Janice Britton-Davidian1
-Author Affiliations
1Institut des Sciences de l'Evolution (UMR CNRS/Université Montpellier II),Montpellier, France
2Institut de Génomique Fonctionnelle de Lyon (UMR CNRS/INRA/Université Lyon 1/ENS Lyon), Lyon, France
3Dipartimento di Biologia Animale e dell'Uomo, Università di Roma ‘La Sapienza’, Rome, Italy
4Free State Department of Economic Development, Tourism and Environmental Affairs, Bloemfontein, South Africa
5Institut de Recherche pour le Développement, Centre de Biologie pour la Gestion des Populations (UMR IRA/INRA/SupAgro/Cirad), Centre Régional Agrhymet BP11011, Niamey, Niger
6Evolutionary Genomics Group, Department of Botany and Zoology, University of Stellenbosch, Stellenbosch, South Africa
*Author for correspondence (frederic.veyrunes@univ-montp2.fr).
Abstract
Therian mammals have an extremely conserved XX/XY sex determination system. A limited number of mammal species have, however, evolved to escape convention and present aberrant sex chromosome complements. In this study, we identified a new case of atypical sex determination in the African pygmy mouse Mus minutoides, a close evolutionary relative of the house mouse. The pygmy mouse is characterized by a very high proportion of XY females (74%, n = 27) from geographically widespread Southern and Eastern African populations. Sequencing of the high mobility group domain of the mammalian sex determining gene Sry, and karyological analyses using fluorescence in situ hybridization and G-banding data, suggest that the sex reversal is most probably not owing to a mutation of Sry, but rather to a chromosomal rearrangement on the X chromosome. In effect, two morphologically different X chromosomes were identified, one of which, designated X*, is invariably associated with sex-reversed females. The asterisk designates the still unknown mutation converting X*Y individuals into females. Although relatively still unexplored, such an atypical sex chromosome system offers a unique opportunity to unravel new genetic interactions involved in the initiation of sex determination in mammals.
African pygmy mouse Mus minutoides atypical sex determination system; sex-reversed females
Sry gene X* chromosome
Footnotes
Received October 21, 2009.
Accepted November 17, 2009.
© 2009 The Royal Society
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