Abstract
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.
Highlights
The vitelline membrane (VM) is a multilayered structure that protects and gives shape to the egg yolk and separates it from the egg white
The specific structure of the VM helps it performs the aforementioned functions. It consists of an inner layer (IL; lamina perivitellina), which is formed before ovulation from the follicular epithelium, and an outer layer (OL; lamina extravitellina), which is formed after ovulation from the mucinous secretion of infundibulum glands [3,4,5,6]
The highest proportion of the weight of VM in the weight of egg yolk was found to be in pigeon eggs, followed by the ring-necked pheasant and cockatiel parrot eggs, and the lowest proportion was found in gray partridge eggs (P < 0.05)
Summary
The vitelline membrane (VM) is a multilayered structure that protects and gives shape to the egg yolk and separates it from the egg white. VM keeps the egg yolk in the central part of the egg, thereby preventing its integration with the shell membranes It acts as a diffusion barrier by transporting water and nutrients between the egg yolk and the egg white. Mann conducted a proteomic analysis and has expanded the number of known VM proteins from 13 [10,11,12] to 137 [2]. Many of these proteins are VM-specific (ovocalyxin-36, apolipoprotein A-I, ovocleidin-116, semaphorin C3, actin, filamin, clusterin), but their functions remain to be elucidated
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