Supplementary Material for: Avian sex determination: a chicken egg conundrum

Background Primary sex-determination is the developmental process that results in the sex determination of the gonads. Vertebrate sex determination is generally considered to follow the model based on the mammalian system, where a sex-specific master regulatory gene activates one of the two different gene networks that underlie testis and ovary differentiation. Summary It is now known that, while many of the molecular components of these pathways are conserved across different vertebrates, a wide variety of different trigger factors are utilised to initiate primary sex determination. In birds, the male is the homogametic sex (ZZ), and significant differences exist between the avian system of sex determination and that of mammals. For example, DMRT1, FOXL2 and estrogen are key factors in gonadogenesis in birds, but none are essential for primary sex determination in mammals. Key Message Gonadal sex determination in birds is thought to depend on a dosage-based mechanism involving expression of the Z-linked DMRT1 gene, and it may be that this ‘mechanism’ is simply an extension of the cell autonomous sex identity (CASI) associated with avian tissues, with no sex-specific trigger required.

背景：初级性别决定是促使性腺完成性别分化的发育过程。目前脊椎动物的性别决定普遍被认为遵循基于哺乳动物系统的模型，即由性别特异性主调控基因激活两套分别介导睾丸与卵巢分化的基因网络中的一套。
摘要：现有研究表明，尽管这些通路的诸多分子组分在不同脊椎动物间保守存在，但启动初级性别决定的触发因子种类却存在显著多样性。在鸟类中，雄性为同配性别（ZZ），其性别决定系统与哺乳动物存在显著差异。例如，DMRT1、FOXL2与雌激素是鸟类性腺发生的关键因子，但这些因子均非哺乳动物初级性别决定所必需。
关键结论：学界普遍认为鸟类的性腺性别决定依赖于一种基于剂量的调控机制，该机制涉及Z染色体连锁的DMRT1基因的表达。且该「机制」或许只是鸟类组织相关的细胞自主性性别认同（cell autonomous sex identity, CASI）的延伸，并不需要特异性的性别触发因子。