Egg-Coat and Zona Pellucida Proteins of Chicken as a Typical Species of Aves

Proteo-transcriptomic profiles reveal key regulatory pathways and functions of LDHA in the ovulation of domestic chickens (Gallus gallus)

BACKGROUND

In poultry, the smooth transition of follicles from the preovulatory-to-postovulatory phase impacts egg production in hens and can benefit the poultry industry. However, the regulatory mechanism underlying follicular ovulation in avians is a complex biological process that remains unclear.

RESULTS

Critical biochemical events involved in ovulation in domestic chickens (Gallus gallus) were evaluated by transcriptomics, proteomics, and in vitro assays. Comparative transcriptome analyses of the largest preovulatory follicle (F1) and postovulatory follicle (POF1) in continuous laying (CL) and intermittent laying (IL) chickens indicated the greatest difference between CL_F1 and IL_F1, with 950 differentially expressed genes (DEGs), and the smallest difference between CL_POF1 and IL_POF1, with 14 DEGs. Additionally, data-independent acquisition proteomics revealed 252 differentially abundant proteins between CL_F1 and IL_F1. Perivitelline membrane synthesis, steroid biosynthesis, lysosomes, and oxidative phosphorylation were identified as pivotal pathways contributing to ovulation regulation. In particular, the regulation of zona pellucida sperm-binding protein 3, plasminogen activator, cathepsin A, and lactate dehydrogenase A (LDHA) was shown to be essential for ovulation. Furthermore, the inhibition of LDHA decreased cell viability and promoted apoptosis of ovarian follicles in vitro.

CONCLUSIONS

This study reveals several important biochemical events involved in the process of ovulation, as well as crucial role of LDHA. These findings improve our understanding of ovulation and its regulatory mechanisms in avian species.

Hepatic Transcriptomic Responses to Ethinylestradiol in Embryonic Japanese Quail and Double-Crested Cormorant

Understanding species differences in sensitivity to toxicants is a critical issue in ecotoxicology. We recently established that double-crested cormorant (DCCO) embryos are more sensitive than Japanese quail (JQ) to the developmental effects of ethinylestradiol (EE2). We explored how this difference in sensitivity between species is reflected at a transcriptomic level. The EE2 was dissolved in dimethyl sulfoxide and injected into the air cell of eggs prior to incubation at nominal concentrations of 0, 3.33, and 33.3 µg/g egg weight. At midincubation (JQ 9 days; DCCO 16 days), livers were collected from five embryos/treatment group for RNA sequencing. Data were processed and analyzed using EcoOmicsAnalyst and ExpressAnalyst. The EE2 exposure dysregulated 238 and 1,987 genes in JQ and DCCO, respectively, with 78 genes in common between the two species. These included classic biomarkers of estrogen exposure such as vitellogenin and apovitellenin. We also report DCCO-specific dysregulation of Phase I/II enzyme-coding genes and species-specific transcriptional ontogeny of vitellogenin-2. Twelve Kyoto Encyclopedia of Genes and Genomes pathways and two EcoToxModules were dysregulated in common in both species including the peroxisome proliferator-activated receptor (PPAR) signaling pathway and fatty acid metabolism. Similar to previously reported differences at the organismal level, DCCO were more responsive to EE2 exposure than JQ at the gene expression level. Our description of differences in transcriptional responses to EE2 in early life stage birds may contribute to a better understanding of the molecular basis for species differences. Environ Toxicol Chem 2024;00:1-12. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Zona pellucida family genes in Chinese pond turtle: identification, expression profiles, and role in the spermatozoa acrosome reaction†

The zona pellucida (ZP) is an extracellular matrix that surrounds all vertebrate eggs, and it is involved in fertilization and species-specific recognition. Numerous in-depth studies of the ZP proteins of mammals, birds, amphibians, and fishes have been conducted, but systematic investigation of the ZP family genes and their role during fertilization in reptiles has not been reported to date. In this study, we identified six turtle ZP (Tu-ZP) gene subfamilies (Tu-ZP1, Tu-ZP2, Tu-ZP3, Tu-ZP4, Tu-ZPD, and Tu-ZPAX) based on whole genome sequence data from Mauremys reevesii. We found that Tu-ZP4 had large segmental duplication and was distributed on three chromosomes, and we also detected gene duplication in the other Tu-ZP genes. To evaluate the role of Tu-ZP proteins in sperm-egg binding, we assessed the expression pattern of these Tu-ZP proteins and their ability to induce the spermatozoa acrosome reaction in M. reevesii. In conclusion, this is the first report of the existence of gene duplication of Tu-ZP genes and that Tu-ZP2, Tu-ZP3, and Tu-ZPD can induce acrosome exocytosis of spermatogenesis in the reptile.

Integrative analyses of the mRNA expression profile reveal the involvement of STC1 in chicken folliculogenesis

Efficient ovarian follicle development, maturation, and ovulation are critical for egg production performance. Previous research has underscored the importance of messenger RNAs (mRNAs) in regulating development and folliculogenesis in chicken ovarians. However, the molecular mechanism is not fully understood, especially in the late period of the laying cycle. In the present study, ovarian tissues from 80-week-old Hy-Line Brown layers (three with high and three with low rates of egg laying) were collected for transcriptome sequencing. A total of 306 differentially expressed genes (DEGs) were identified in this study, at a false discovery rate (FDR)-corrected P-value < 0.05 and a log2|fold change| (log2|FC|) ≥1.5. Among these DEGs, stanniocalcin 1 (STC1) was mainly related to cellular processes, single-organism processes, biological regulation, metabolic processes, developmental processes, and reproductive processes. Then, we further investigated the regulation of STC1 during chicken follicle development and found that STC1 inhibited the proliferation and stimulated the apoptosis of follicular granulosa cells (GCs), and decreased the expression of progesterone (P4) and estradiol (E2). Collectively, these results suggest that STC1 plays an important role in chicken follicle development by decreasing GC proliferation and steroidogenesis and stimulating GC apoptosis. This study contributes to the understanding of the reproductive biology of laying hens in the late period of the laying cycle and further lays a foundation for the improvement of egg production in poultry breeding.

New insights into the role of microheterogeneity of ZP3 during structural maturation of the avian equivalent of mammalian zona pellucida

The egg coat including mammalian zona pellucida (ZP) and the avian equivalent, i.e., inner-perivitelline layer (IPVL), is a specialized extracellular matrix being composed of the ZP glycoproteins and surrounds both pre-ovulatory oocytes and ovulated egg cells in vertebrates. The egg coat is well known for its potential importance in both the reproduction and early development, although the underlying molecular mechanisms remain to be fully elucidated. Interestingly, ZP3, one of the ZP-glycoprotein family members forming scaffolds of the egg-coat matrices with other ZP glycoproteins, exhibits extreme but distinctive microheterogeneity to form a large number of isoelectric-point isoforms at least in the chicken IPVL. In the present study, we performed three-dimensional confocal imaging and two-dimensional polyacrylamide-gel electrophoresis (2D-PAGE) of chicken IPVLs that were isolated from the ovarian follicles at different growth stages before ovulation. The results suggest that the relative proportions of the ZP3 isoforms are differentially altered during the structural maturation of the egg-coat matrices. Furthermore, tandem mass spectrometry (MS/MS) analyses and ZP1 binding assays against separated ZP3 isoforms demonstrated that each ZP3 isoform contains characteristic modifications, and there are large differences among ZP3 isoforms in the ZP1 binding affinities. These results suggest that the microheterogeneity of chicken ZP3 might be regulated to be associated with the formation of egg-coat matrices during the structural maturation of chicken IPVL. Our findings may provide new insights into molecular mechanisms of egg-coat assembly processes.

Diversity of sialic acids and sialoglycoproteins in gametes and at fertilization

Sialic acids are a family of 9-carbon monosaccharides with particular physicochemical properties. They modulate the biological functions of the molecules that carry them and are involved in several steps of the reproductive process. Sialoglycoproteins participate in the balance between species recognition and specificity, and the mechanisms of these aspects remain an issue in gametes formation and binding in metazoan reproduction. Sialoglycoproteins form a specific coat at the gametes surface and specific polysialylated chains are present on marine species oocytes. Spermatozoa are submitted to critical sialic acid changes in the female reproductive tract facilitating their migration, their survival through the modulation of the female innate immune response, and the final oocyte-binding event. To decipher the role of sialic acids in gametes and at fertilization, the dynamical changes of enzymes involved in their synthesis and removal have to be further considered.

Quantitative Protein Analysis of ZPB2, ZPB1 and ZPC in the Germinal Disc and a Non-Germinal Disc Region of the Inner Perivitelline Layer in Two Genetic Lines of Turkey Hens That Differ in Fertility

The avian inner perivitelline layer (IPVL), containing the zona pellucida (ZP) family of proteins, surrounds the ovulated ovum. In mammalian species, ZP proteins serve as key component(s) in binding sperm and initiating the acrosome reaction. Sperm binding at the germinal disc (GD) region of the IPVL initiates fertilization in avian species, and the amount of sperm binding at the GD reflects female fertility. The current research determined whether reported differences in mRNA expression in two genetic lines of turkey hens (E, high fertility and F, low fertility) translated to the protein level. ZPB2 in the IPVL is greater in the GD region compared with the nongerminal disc (NGD) region, as indicated by both mRNA and protein expression. However, protein expressions of ZPB1 and ZPC in the IPVL of E- and F-line turkey hens was in contrast to previously reported mRNA expression. The results indicate that the mRNA expression of ZP proteins at their site of synthesis in E- and F-line hens often does not directly correlate with the IPVL abundance of these proteins. The greater protein concentration of ZPB2 in the GD region compared with the NGD regions suggests that this protein may be critical for sperm binding at the GD region.

Quantitative Comparative Proteomic Analysis of Chicken Egg Vitelline Membrane Proteins during High-Temperature Storage

To explore the thermally induced alterations in chicken egg vitelline membrane (CEVM) protein abundances, a comparative proteomic analysis of CEVM after 10 days of storage at 30 °C was performed. Altogether, 981 proteins were identified, of which 124 protein abundances were decreased and 79 were increased. Bioinformatic analysis suggested that the altered proteins were related to structure (n = 10), mechanical properties (n = 13), chaperone (n = 15), antibacterial (n = 12), and antioxidant (n = 3). Alterations in abundances of structural proteins, possibly resulting from the disintegration of these complexes, were observed in this study, suggesting a loss in fibrous structure. Several proteins involved in mechanical strength (n = 10), elasticity (n = 3), and chaperone were decreased in abundances, which indicated that deficits in these proteins might affect the CEVM mechanical properties. These findings will extend our understanding of CEVM deterioration during high-temperature storage from a proteomic perspective.

Mammalian egg coat modifications and the block to polyspermy

Fertilization by more than one sperm causes polyploidy, a condition that is generally lethal to the embryo in the majority of animal species. To prevent this occurrence, eggs have developed a series of mechanisms that block polyspermy at the level of the plasma membrane or their extracellular coat. In this review, we first introduce the mammalian egg coat, the zona pellucida (ZP), and summarize what is currently known about its composition, structure, and biological functions. We then describe how this specialized extracellular matrix is modified by the contents of cortical granules (CG), secretory organelles that are exocytosed by the egg after gamete fusion. This process releases proteases, glycosidases, lectins and zinc onto the ZP, resulting in a series of changes in the properties of the egg coat that are collectively referred to as hardening. By drawing parallels with comparable modifications of the vitelline envelope of nonmammalian eggs, we discuss how CG‐dependent modifications of the ZP are thought to contribute to the block to polyspermy. Moreover, we argue for the importance of obtaining more information on the architecture of the ZP, as well as systematically investigating the many facets of ZP hardening.

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.

Molecular basis of egg coat cross-linking sheds light on ZP1-associated female infertility

Mammalian fertilisation begins when sperm interacts with the egg zona pellucida (ZP), whose ZP1 subunit is important for fertility by covalently cross-linking ZP filaments into a three-dimensional matrix. Like ZP4, a structurally-related component absent in the mouse, ZP1 is predicted to contain an N-terminal ZP-N domain of unknown function. Here we report a characterisation of ZP1 proteins carrying mutations from infertile patients, which suggests that, in human, filament cross-linking by ZP1 is crucial to form a stable ZP. We map the function of ZP1 to its ZP-N1 domain and determine crystal structures of ZP-N1 homodimers from a chicken homolog of ZP1. These reveal that ZP filament cross-linking is highly plastic and can be modulated by ZP1 fucosylation and, potentially, zinc sparks. Moreover, we show that ZP4 ZP-N1 forms non-covalent homodimers in chicken but not in human. Together, these data identify human ZP1 cross-links as a promising target for non-hormonal contraception.