多年来，培育鸟的人知道，偶尔会自然地出现一种“半边鸟”。这些外观奇特的鸟（亦称为“雌雄嵌合体”）在羽毛、大小和其他特征上会极不对称，因为身体的一边像雄性，而另一边则像雌性。有关性别确定的哺乳动物模型（按照该模型，一个胚胎在性别上是中性的，直到一个基因开关使产生性激素的性腺的发育启动）过去一般被假设适用于所有脊椎动物。现在，对三个“半边鸡”所做的一项研究表明，至少对鸟类来说，性别确定并不仅仅依赖于性腺，而是整个身体中所有细胞的一个功能。“半边种”被发现是真正的雌雄嵌合体，在它们当中，各个细胞对性激素的同一混合物有不同反应。这项工作提出了关于性别确定和性发育之性质的普遍性问题，这些问题此前似乎或多或少都已经解决了。
生物谷推荐原文出处：
Nature vol.464 (7286), (11 Mar 2010) doi:10.1038/nature08852
Somatic sex identity is cell autonomous in the chicken
D. Zhao1,5, D. McBride1,5, S. Nandi1, H. A. McQueen3, M. J. McGrew1, P. M. Hocking2, P. D. Lewis4, H. M. Sang1 " M. Clinton1
1 Division of Developmental Biology and,
2 Division of Genetics and Genomics, The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Roslin, Midlothian EH25 9PS, UK
3 Institute of Cell Biology, University of Edinburgh, West Mains Road, Edinburgh EH9 3JR, UK
4 Animal and Poultry Science Department, University of KwaZulu-Natal, Pietermaritzburg, South Africa
5 These authors contributed equally to this work.
In the mammalian model of sex determination, embryos are considered to be sexually indifferent until the transient action of a sex-determining gene initiates gonadal differentiation. Although this model is thought to apply to all vertebrates, this has yet to be established. Here we have examined three lateral gynandromorph chickens (a rare, naturally occurring phenomenon in which one side of the animal appears male and the other female) to investigate the sex-determining mechanism in birds. These studies demonstrated that gynandromorph birds are genuine male:female chimaeras, and indicated that male and female avian somatic cells may have an inherent sex identity. To test this hypothesis, we transplanted presumptive mesoderm between embryos of reciprocal sexes to generate embryos containing male:female chimaeric gonads. In contrast to the outcome for mammalian mixed-sex chimaeras, in chicken mixed-sex chimaeras the donor cells were excluded from the functional structures of the host gonad. In an example where female tissue was transplanted into a male host, donor cells contributing to the developing testis retained a female identity and expressed a marker of female function. Our study demonstrates that avian somatic cells possess an inherent sex identity and that, in birds, sexual differentiation is substantively cell autonomous.
