Department of Comparative Anatomy, Institute of Zoology and Biomedical Research, Jagiellonian University, Gronostajowa 9, 30-387 Krakow, Poland; Doctoral School of Exact and Natural Sciences, Jagiellonian University, Krakow, Poland.
Department of Comparative Anatomy, Institute of Zoology and Biomedical Research, Jagiellonian University, Gronostajowa 9, 30-387 Krakow, Poland.
Ann Anat. 2023 Oct;250:152151. doi: 10.1016/j.aanat.2023.152151. Epub 2023 Aug 18.
The developing gonads constitute a valuable model for studying developmental mechanisms because the testes and ovaries, while originating from the same primordia, undergo two different patterns of development. So far, gonadal development among birds has been described in detail in chickens, but literature on the earliest stages of gonadogenesis is scarce. This study presents changes in the structure of the gonads in three species of breeding birds (chicken, duck, and pigeon), starting from the first signs of gonadal ridge formation, that is, the thickenings of the coelomic epithelium. It appears that both gonads show asymmetry from the very beginning of gonadal ridge formation in both genetic sexes. The left gonadal ridge is thicker than the right one, and it is invaded by a higher number of primordial germ cells. Undifferentiated gonads, both left and right, consist of the primitive cortex and the medulla. The primitive cortex develops from the thickened coelomic epithelium, while the primitive medulla - by the aggregation of mesenchymal cells. This study also describes the process of sex differentiation of the testes and ovaries, which is initiated at the same embryonic stage in all three studied species. The first sign of gonadal sex differentiation is the decrease in the number of cortical germ cells and a reduction in cortical thickness in the differentiating testes. This is followed by an increase in the number of germ cells in the medulla. The cortical asymmetry and difference in size between the left and right testes diminishes during later development. However, the differentiating left ovary shows an increase in the number of cortical germ cells and cortical thickness. No regression is seen in the right ovary, although its development is slower. The right ovarian cortex undergoes testis-specific reduction, while the medulla undergoes ovary-specific development. The process of gonadogenesis is similar in the three studied species, with only slight differences in gonadal structure.
正在发育的性腺是研究发育机制的有价值的模型，因为睾丸和卵巢虽然起源于相同的原基，但经历了两种不同的发育模式。到目前为止，鸟类的性腺发育在鸡中已经有详细的描述，但关于性腺发生的最早阶段的文献很少。本研究介绍了三种繁殖鸟类（鸡、鸭和鸽子）的性腺结构变化，从性腺嵴形成的第一个迹象开始，即体腔上皮的增厚。似乎在遗传性别中，从性腺嵴形成的最初阶段开始，两个性腺就表现出不对称性。左侧性腺嵴比右侧厚，并且有更多的原始生殖细胞侵入。未分化的性腺，无论是左侧还是右侧，都由原始皮质和髓质组成。原始皮质由增厚的体腔上皮发育而来，而原始髓质则由间充质细胞聚集而成。本研究还描述了睾丸和卵巢的性别分化过程，在所有三种研究的物种中，这一过程在同一胚胎阶段开始。性腺性别分化的第一个迹象是皮质生殖细胞数量减少和分化睾丸皮质厚度减小。随后，髓质中生殖细胞数量增加。在后期发育过程中，左侧睾丸的皮质不对称性和大小差异减小。然而，分化的左侧卵巢显示出皮质生殖细胞数量和皮质厚度的增加。右侧卵巢没有出现退化，尽管其发育较慢。右侧卵巢皮质经历了睾丸特异性减少，而髓质经历了卵巢特异性发育。在三种研究的物种中，性腺发生过程相似，只有在性腺结构上存在细微差异。
