Characterization of structure and protein of vitelline membranes of precocial (ring-necked pheasant, gray partridge) and superaltricial (cockatiel parrot, domestic pigeon) birds

Of all the known oviparous taxa, female birds lay the most diverse types of eggs that differ in terms of shape, shell pigmentation, and shell structure. The pigmentation of the shell, the weight of the egg, and the composition of the yolk correlate with environmental conditions and the needs of the developing embryos. In this study, we analyzed the structure and protein composition of the vitelline membrane (VM) of ring-necked pheasant, gray partridge, cockatiel parrot, and domestic pigeon eggs. We found that the VM structure is characteristic of each species and varies depending on whether the species is precocial (ring-necked pheasant and gray partridge) or superaltrical (cockatiel parrot and domestic pigeon). We hypothesize that a multilayer structure of VM is necessary to counteract the aging process of the egg. The multilayer structure of VM is only found in species with a large number of eggs in one clutch and is characterized by a long incubation period. An interesting discovery of this study is the three-layered VM of pheasant and partridge eggs. This shows that the formation of individual layers of VM in specific sections of the hen’s reproductive system is not confirmed in other species. The number of protein fractions varied between 19 and 23, with a molecular weight ranging from 15 to 250 kDa, depending on the species. The number of proteins identified in the VM of the study birds’ eggs is as follows: chicken—14, ring-necked pheasant—7, gray partridge—10, cockatiel parrot—6, and domestic pigeon—23. The highest number of species-specific proteins (21) was detected in the VM of domestic pigeon. This study is the first to present the structure and protein composition in the VM of ring-necked pheasant, gray partridge, cockatiel parrot, and domestic pigeon eggs. In addition, we analyzed the relationship between the hatching specification of birds and the structure of the VM.在已知的卵生类群中，雌性鸟类所产的卵类型最为多样，其差异体现在卵的形状、卵壳色素沉着以及卵壳结构等方面。卵壳色素沉着、卵重以及卵黄组成均与环境条件以及发育中胚胎的需求相关联。本研究针对环颈雉、灰山鹑、鸡尾鹦鹉以及家鸽的卵黄膜（vitelline membrane，VM）结构与蛋白质组成展开分析。研究发现，VM结构具有物种特异性，且会因物种属于早成雏类群（环颈雉与灰山鹑）还是极度晚成雏类群（鸡尾鹦鹉与家鸽）而存在差异。我们提出假说：卵黄膜的多层结构可抵御卵的老化过程。仅在窝卵数较多且孵化周期较长的物种中，才会存在VM的多层结构。本研究的一项有趣发现是，环颈雉与灰山鹑的卵黄膜为三层结构。这表明此前认为的“鸟类生殖系统特定区域可形成VM各层”的结论，在其他物种中并未得到证实。根据物种不同，蛋白质组分的数量在19至23之间波动，分子量范围为15至250千道尔顿（kDa）。本次研究涉及的鸟类卵黄膜中已鉴定出的蛋白质数量如下：家鸡——14种，环颈雉——7种，灰山鹑——10种，鸡尾鹦鹉——6种，家鸽——23种。其中家鸽卵黄膜中检测到的物种特异性蛋白质数量最多，达21种。本研究首次报道了环颈雉、灰山鹑、鸡尾鹦鹉以及家鸽的卵黄膜结构与蛋白质组成。此外，我们还分析了鸟类孵化特征与VM结构之间的关联。