The Fish Egg's Zona Pellucida

Towards a comprehensive understanding of the muscle proteome in Schizothorax labiatus: Insights from seasonal variations, metabolic responses, and reproductive signatures in the River Jhelum

Proteomics is a very advanced technique used for defining correlations, compositions and activities of hundreds of proteins from organisms as well as effectively used in identifying particular proteins with varying peptide lengths and amino acid counts. In the present study, an endeavour has been put forth to create muscle proteome expression of snow trout, Schizothorax labiatus. Liquid chromatography-mass spectrometry (LC-MS) using label free quantification (LFQ) technique has extensively been carried out to explore changes in protein metabolism and its composition to discriminate across species, clarify functions and pinpoint protein biomarkers from organisms. In LFQ technique, the abundances of proteins are determined based on the signal intensities of their corresponding peptides in mass spectrometry. The main benefit of using this method is that it doesn't require pre-labelling proteins with isotopic tags, which streamlines the experimental procedure and gets rid of any bias that might have been caused by the labelling process. LFQ techniques frequently offer a wider dynamic range, making it possible to detect and quantify proteins over a broad range of abundances obtained from the complex biological materials including fish muscle. The results of proteomic analysis could provide an insight in understanding about how various proteins are expressed in response to environmental challenges. For proteomic study, two different weight groups of S. labiatus were taken from River Jhelum based on biological, physiological and logistical factors. These groups corresponded to different life stages, such as younger size and adults/brooders in order to capture potential variations in the muscle proteome related to growth and development. The proteomic analysis of S. labiatus depicted that an overall of 220 proteins in male and 228 in female fish of group 1 were noted. However, when male and female S. labiatus were examined based on spectral count and peptide abundance using ProteinLynx Global Software, a total of 10 downregulated and 32 upregulated proteins were found. In group 2 of S. labiatus, a total of 249 proteins in male and 301 in female fish were documented. When the two genders of S. labiatus were likened to one another by LFQ technique, a total of 41 downregulated and 06 upregulated proteins were identified. The variability in the protein numbers between two fish weight groups reflected biological differences, influenced by factors such as age, developmental stages, physiological condition and reproductive activities. During the study, it was observed that S. labiatus exhibited downregulated levels of proteins that were involved in feeding and growth. The contributing factors to this manifestation could be explained by lower feeding and metabolic activity of fish and decreased food availability during winter in River Jhelum. Contrarily, the fish immune response proteins were found to be significantly over-expressed in S. labiatus, indicating that the environment was more likely to undergo increased microbial infection, pollution load and anthropogenic activities. In addition, it was also discovered that there was an upregulated expression of the reproductive proteins in S. labiatus, which could be linked to the fish's pre-spawning time as the fish used in this study was collected in the winter season which is the pre-spawning period of the fish. Therefore, the present study would be useful in obtaining new insights regarding the molecular makeup of species, methods of adaptation and reactions to environmental stresses. This information contributes to our understanding of basic science and may have applications in environmental monitoring, conservation and preservation of fish species.

Comparative gonad transcriptome analysis in cobia (Rachycentron canadum)

Background: Cobia (Rachycentron canadum) is a species of fish with high commercial potential particularly due to fast growth rates. The evidence of sexual size dimorphism favoring females indicate potential benefits in having a monosex culture. However, the involvement of genetic factors responsible for sexual development and gonadal maintenance that produces phenotypic sex in cobia is largely unknown. Methods: In the present study, we performed transcriptome sequencing of cobia to identify sex-biased significantly differentially expressed genes (DEGs) in testes and ovaries. The reliability of the gonad transcriptome data was validated by qPCR analysis of eight selected significantly differential expressed sex-related candidate genes. Results: This comparative gonad transcriptomic analysis revealed that 7,120 and 4,628 DEGs are up-regulated in testes or ovaries, respectively. Further functional annotation analyses identified 76 important candidate genes involved in sex determination cascades or sex differentiation, including 42 known testis-biased DEGs (dmrt1, amh and sox9 etc.), and 34 known ovary-biased DEGs (foxl2, sox3 and cyp19a etc.). Moreover, eleven significantly enriched pathways functionally related to sex determination and sex differentiation were identified, including Wnt signaling pathway, oocyte meiosis, the TGF-beta signaling pathway and MAPK signaling pathway. Conclusion: This work represents the first comparative gonad transcriptome study in cobia. The putative sex-associated DEGs and pathways provide an important molecular basis for further investigation of cobia's sex determination, gonadal development as well as potential control breeding of monosex female populations for a possible aquaculture setting.

A case study: temporal trends of environmental stressors and reproductive health of smallmouth bass (Micropterus dolomieu) from a site in the Potomac River Watershed, Maryland, USA

Decades of poor reproductive success and young-of-the-year survival, combined with adult mortality events, have led to a decline in the smallmouth bass (SMB; Micropterus dolomieu) population in sections of the Potomac River. Previous studies have identified numerous biologic and environmental stressors associated with negative effects on SMB health. To better understand the impact of these stressors, this study was conducted at the confluence of Antietam Creek and the Potomac River from 2013 to 2019 to identify temporal changes associated with SMB reproductive health. Surface water samples were collected and analyzed for over 300 organic contaminants, including pesticides, phytoestrogens, pharmaceuticals, hormones and total estrogenicity (E2Eq). Adult SMB were collected and sampled for multiple endpoints, including gene transcripts associated with reproduction (molecular), histopathology (cellular), and organosomatic indices (tissue). In males, biomarkers of estrogenic endocrine disruption, including testicular oocytes (TO) and plasma vitellogenin (Vtg) were assessed. Numerous agriculture-related contaminants or land use patterns were associated with gene transcript abundance in both male and female SMB. Positive associations between pesticides in the immediate catchment with TO severity and E2Eq with plasma Vtg in males were identified. In males, the prevalence of TO and detectable levels of plasma Vtg, liver vitellogenin transcripts (vtg) and testis vtg were high throughout the study. Peaks of complex mixtures of numerous contaminants occurred during the spring/early summer when spawning and early development occurs and to a lesser extent in fall/winter during recrudescence. Management practices to reduce exposure during these critical and sensitive periods may enhance reproductive health of these economically important sportfishes.

Comparative transcriptome sequencing analysis of female and male Decapterus macrosoma

Sexual growth dimorphism is a common phenomenon in teleost fish and has led to many reproductive strategies. Growth- and sex-related gene research in teleost fish would broaden our understanding of the process. In this study, transcriptome sequencing of shortfin scad Decapterus macrosoma was performed for the first time, and a high-quality reference transcriptome was constructed. After identification and assembly, a total of 58,475 nonredundant unigenes were obtained with an N50 length of 2,266 bp, and 28,174 unigenes were successfully annotated with multiple public databases. BUSCO analysis determined a level of 92.9% completeness for the assembled transcriptome. Gene expression analysis revealed 2,345 differentially expressed genes (DEGs) in the female and male D. macrosoma, 1,150 of which were female-biased DEGs, and 1,195 unigenes were male-biased DEGs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that the DEGs were mainly involved in biological processes including protein synthesis, growth, rhythmic processes, immune defense, and vitellogenesis. Then, we identified many growth- and sex-related genes, including Igf, Fabps, EF-hand family genes, Zp3, Zp4 and Vg. In addition, a total of 19,573 simple sequence repeats (SSRs) were screened and identified from the transcriptome sequences. The results of this study can provide valuable information on growth- and sex-related genes and facilitate further exploration of the molecular mechanism of sexual growth dimorphism.

Choriolytic and non-choriolytic proteases during hatching of Atlantic Salmon embryos

Fish embryonic hatching glands (HGs) secrete choriolysin-zymogens, which when activated degrade the chorion, allowing larval exit. Thus, hatching encompasses two dissimilar choriolysin-processes: pre-choriolysis including activated choriolysins accessing the perivitelline space (PVS), followed by choriolysis. Discovery of serine-proteolytic zonase in Atlantic salmon hatching fluid (HF) raises questions concerning its participation in hatching. This work aims to identify salmon choriolysins, and evaluate their role and that of zonase during hatching. Precocious salmon hatching occurs under alkaline conditions, producing an HF containing similar metallo- and serine- proteolytic activities. Purified zonase is selectively inhibited by peFabloc, whose MW (580 Da) allows diffusion through the chorion into the PVS. Without apparent toxicity, brief peFabloc-pretreatment (2 mM) of salmon eggs reduced precocious hatching substantially, compatible with a zonase-relevance for hatching. Atlantic salmon differed from other fishes since their HGs were not immuno-stained by polyclonal antibodies against pike choriolysins. However, cloning and sequencing experiments revealed a single low choriolytic enzyme (LCE) of 69% identity to pike LCE. Similar experiments with high choriolytic enzymes (HCEs) revealed two types (HCE-1 and HCE-2) with respectively 71% and 91% identity to pike HCE-1 & HCE-2. In situ hybridization revealed typical HGs. However, zebrafish-choriolysis is achieved by HCE-class choriolysins alone. Another zebrafish choriolysin (HE2) was not expressed. Peptide-bond hydrolysis by non-choriolytic zonase mimicks HCE-action generating hydrophilic sites for LCE-choriolytic catalysis. Ultimately, precise definitions of choriolytic and pre-choriolytic catalysis requires developmental genetics. Our data are compatible with a complex pre-choriolytic hatching-stage in Atlantic salmon, before LCE-choriolysis degrades the chorion.

The bisphenol A metabolite MBP causes proteome alterations in male Cyprinodon variegatus fish characteristic of estrogenic endocrine disruption

The toxicological status of bisphenol A (BPA) is under strong debate. Whereas in vitro it is an agonist of the estrogen receptor with a potency ca. 10⁵-fold lower than the natural female hormone estradiol, in vivo exposure causes only mild effects at concentration thresholds environmentally not relevant and inconsistent among species. By using a proteomic approach, shotgun liver proteome analysis, we show that 7-d exposure to 10 μg/L of the BPA metabolite, 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP), and not the same exposure to the parental molecule BPA, alters the liver proteome of male Cyprinodon variegatus fish. Different physiological and environmental conditions leading to biotransformation of BPA to MBP may partly explain the conflicting results so far reported for in vivo BPA exposures. The pattern of alteration induced by MBP is similar to that caused by estradiol, and indicative of estrogenic endocrine disruption. MBP enhanced ribosomal activity, protein synthesis and transport, with upregulation of 91% of the ribosome-related proteins, and 12 proteins whose expression is regulated by estrogen-responsive elements, including vitellogenin and zona pellucida. Whey acidic protein (WAP) was the protein most affected by MBP exposure (FC = 68). This result points at WAP as novel biomarker for xenoestrogens.

Targeted deletion of liver-expressed Choriogenin L results in the production of soft eggs and infertility in medaka, Oryzias latipes

Egg envelopes (chorions) in medaka, Oryzias latipes, are composed of three major glycoproteins: ZI-1, - 2, and - 3. These gene-encoded chorion glycoproteins are expressed in the liver and/or ovarian oocytes of sexually mature female fish. In medaka, the glycoproteins produced in the female liver are induced by estrogen as Choriogenin (Chg.) H and Chg. H minor (m), which correspond to the zona pellucida (ZP) B (ZPB) protein in mammals, and Chg. L, which corresponds to ZPC in mammals. Chg. H, Chg. Hm, and Chg. L, are then converted to ZI-1, - 2, and - 3, respectively, during oogenesis in medaka ovaries.In the present study, we established a medaka line in which the chg.l gene was inactivated using the transcription activator-like effector nuclease (TALEN) technique. Neither intact chg.l transcripts nor Chg. L proteins were detected in livers of sexually mature female homozygotes for the mutation (homozygous chg.l knockout: chg.l-/-). The chg.l-/- females spawned string-like materials containing "smashed eggs." Closer examination revealed the oocytes in the ovaries of chg.l-/- females had thin chorions, particularly at the inner layer, despite a normal growth rate. In comparing chorions from normal (chg.l+/+) and chg.l-/- oocytes, the latter exhibited abnormal architecture in the chorion pore canals through which the oocyte microvilli pass. These microvilli mediate the nutritional exchange between the oocyte and surrounding spaces and promote sperm-egg interactions during fertilization. Thus, following in vitro fertilization, no embryos developed in the artificially inseminated oocytes isolated from chg.l-/- ovaries. These results demonstrated that medaka ZI-3 (Chg.L) is the major component of the inner layer of the chorion, as it supports and maintains the oocyte's structural shape, enabling it to withstand the pressures exerted against the chorion during spawning, and is essential for successful fertilization. Therefore, gene products of oocyte-specific ZP genes that may be expressed in medaka oocytes cannot compensate for the loss Chg. L function to produce offspring for this species.

The effects of gallic acid and metformin on male reproductive dysfunction in diabetic mice induced by methylglyoxal: An experimental study

BACKGROUND

Diabetes mellitus is a disease that has reached a dangerous point. Today, nearly 500 million men and women around the world live with diabetes. Gallic acid (Gal) affects diabetes.

OBJECTIVE

To evaluate the effects of Gal and metformin (met) on the levels of glucose, insulin, testosterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), sperm count, antioxidant status, and histological changes in the testes of diabetic mice induced by methylglyoxal (MGO).

MATERIALS AND METHODS

In this experimental study, 50 male adult NMRI mice, weighting 25-30 gr, aged 3-4 months were randomly divided into five equal groups (n = 10/each). (i) Control (vehicle, normal saline), (ii) MGO (600 mg/kg/d) orally for 28 days, (iii) Gal (50 mg/kg/d), (iv) MGO+Gal, and (v) MGO+met (200 mg/kg/d). Gal and met were administered orally for 21 consecutive days after the induction of diabetes. Blood samples were taken at 24 hr after the latest doses of treatment. Histological assessment of the testis was done, and the epididymis sperm count was obtained. Antioxidant indices, glucose, insulin, LH, FSH, and testosterone levels were measured.

RESULTS

In the MGO group compared to the control group, insulin, glucose (p = 0.001), LH (p = 0.04) and malondialdehyde (p = 0.001) were increased. However, the level of testosterone (p = 0.001), seminiferous tubule diameters, epithelial height, sperm count, superoxide dismutase activity (p = 0.02), and testis volume (p = 0.01) were decreased. The results indicated that Gal and met ameliorated the MGO effects.

CONCLUSION

These findings suggested that the animals receiving MGO became diabetic. According to the results, Gal and met can effectively prevent MGO-induced diabetes. The effect of Gal was equivalent and sometimes better than metformin.

Does combination of estradiol and sesame oil improve the oocyte quality, embryo development and expressions of Zp3, E-cad, and Ctnnb1 genes in mice? An experimental study

BACKGROUND

Aging may reduce oocyte maturation, embryo quality, and fertility potential.

OBJECTIVE

To compare the effect of estradiol (E2) and sesame oil on oocyte and embryo quality between young and old mice.

MATERIALS AND METHODS

Sixty old and young female mice were divided in to two groups (30 mice/group, grouped by age). Each group was divided into three subgroups of mice treated with sesame oil, E2 + sesame oil, and normal saline as control group. After ovulation induction, some oocytes were considered for in vitro fertilization and the rest were assessed for morphological status. After obtaining the two-cell embryos, the embryos were collected to determine the expression of zona pellucida (ZP) glycoprotein 3, E-cadherin, and β-catenin genes and some of them followed until the blastocysts stage to evaluate the viability.

RESULTS

The findings showed that the mean ZP and perivitelline space thickness increased in the old mice that received the E2 + sesame oil treatment. The number of 2-cell embryos, blastocysts, and live cells were significantly higher in the old group treated with sesame oil respectively (p = 0.018, 0.002, and < 0.0001, respectively). The normal ZP shape and refractile body numbers increased in the old mice that were treated with sesame oil, respectively. The E-cadherin gene was downregulated in the treatment groups compared to the controls.

CONCLUSION

Sesame oil showed a better response in the old mice, because aging is associated with an increased rate of reactive oxygen species, causing deficiencies in both oocyte and embryo qualities.

Proteomics support the threespine stickleback egg coat as a protective oocyte envelope

Ancestrally marine threespine stickleback fish (Gasterosteus aculeatus) have undergone an adaptive radiation into freshwater environments throughout the Northern Hemisphere, creating an excellent model system for studying molecular adaptation and speciation. Ecological and behavioral factors have been suggested to underlie stickleback reproductive isolation and incipient speciation, but reproductive proteins mediating gamete recognition during fertilization have so far remained unexplored. To begin to investigate the contribution of reproductive proteins to stickleback reproductive isolation, we have characterized the stickleback egg coat proteome. We find that stickleback egg coats are comprised of homologs to the zona pellucida (ZP) proteins ZP1 and ZP3, as in other teleost fish. Our molecular evolutionary analyses indicate that across teleosts, ZP3 but not ZP1 has experienced positive Darwinian selection. Mammalian ZP3 is also rapidly evolving, and surprisingly some residues under selection in stickleback and mammalian ZP3 directly align. Despite broad homology, however, we find differences between mammalian and stickleback ZP proteins with respect to glycosylation, disulfide bonding, and sites of synthesis. Taken together, the changes we observe in stickleback ZP protein architecture suggest that the egg coats of stickleback fish, and perhaps fish more generally, have evolved to fulfill a more protective functional role than their mammalian counterparts.

Cellular and molecular modification of egg envelope hardening in fertilization

Fertilization is an essential process that fundamentally impacts fitness. An egg changes dramatically after fertilization mediating the beginning of life, which mainly includes the transformation of the egg envelope via hardening, which is thought to be due to complex reactions involved in the conversion of cellular and molecular. This review highlights the mechanisms of egg envelope hardening in teleost fish. We conclude that the egg envelope hardening might be carried out in two steps. (a) A metalloprotease (alveolin) hydrolyzes the N-terminal proline-glutamine (Pro-Gln) region of zona pellucida (ZP) 1 and (b) triggers intermolecular cross-linking to ZP3 catalyzed by transglutaminase (TGase). The post-fertilization hardening of the egg envelope is an evolutionarily conserved phenomenon across species. We discuss the biochemical function and interaction of some factors reported to be essential to egg envelope hardening in mammalian and nonmammalian species, including metalloprotease, TGase, peroxidase/ovoperoxidase, and other factors (carbohydrate moieties, zinc and Larp6 proteins), and the relevant data suggest that egg envelope hardening is crucial to block polyspermy in internal fertilization, in addition to protecting the developing embryo from mechanical shock and preventing bacterial infection in external fertilization. Increased knowledge of the processes of egg envelope hardening and fertilization is likely to make a remarkable contribution to reproduction and aquaculture.

Structural analysis and characterization of egg-envelope in the Indian freshwater murrel, Channa punctatus

Egg-envelope, an acellular coat, surrounds the egg and is essential for vitellogenin incorporation. It also plays a pivotal role during fertilization and provides protection to the developing embryo. In the present study, scanning electron microscopy was used to elucidate the structural details of isolated egg-envelopes from the Indian freshwater murrel, Channa punctatus. Several pores and single micropyle were observed on outer surface, whereas inner layer indicated deposition of proteinaceous material. The constituent proteins of egg-envelope were further characterized by Fourier transform infrared (FT-IR) spectroscopy, and electrophoresis and mass-spectrometry (MALDI-TOF-MS/MS). The secondary structure of egg-envelope proteins showed the presence of antiparallel ß-pleated sheets and aromatic amino acids. These proteins resolved into two peptides (130 kDa and 68 kDa) under denaturing conditions, which exhibited glycoprotein nature. The peptide band with low molecular mass showed significant similarity with transmembrane protein, whereas peptide band with high molecular mass matched with choriogenin protein of other fishes. These results confirm that chorion is derived from precursor protein, Choriogenin, in murrel. Chemical composition of egg-envelope supports that chorion is responsible exchange material and chemical defence during embryogenesis.

Unravelling the changes during induced vitellogenesis in female European eel through RNA-Seq: What happens to the liver?

The life cycle of European eel (Anguilla anguilla), a catadromous species, is complex and enigmatic. In nature, during the silvering process prior to their long spawning migration, reproductive development is arrested, and they cease feeding. In studies of reproduction using hormonal induction, eels are equivalently not feed. Therefore, in female eels that undergo vitellogenesis, the liver plays different, essential roles being involved both in vitellogenins synthesis and in reallocating resources for the maintenance of vital functions, performing the transoceanic reproductive migration and completing reproductive development. The present work aimed at unravelling the major transcriptomic changes that occur in the liver during induced vitellogenesis in female eels. mRNA-Seq data from 16 animals (eight before induced vitellogenesis and eight after nine weeks of hormonal treatment) were generated and differential expression analysis was performed comparing the two groups. This analysis detected 1,328 upregulated and 1,490 downregulated transcripts. Overrepresentation analysis of the upregulated genes included biological processes related to biosynthesis, response to estrogens, mitochondrial activity and localization, while downregulated genes were enriched in processes related to morphogenesis and development of several organs and tissues, including liver and immune system. Among key genes, the upregulated ones included vitellogenin genes (VTG1 and VTG2) that are central in vitellogenesis, together with ESR1 and two novel genes not previously investigated in European eel (LMAN1 and NUPR1), which have been linked with reproduction in other species. Moreover, several upregulated genes, such as CYC1, ELOVL5, KARS and ACSS1, are involved in the management of the effect of fasting and NOTCH, VEGFA and NCOR are linked with development, autophagy and liver maintenance in other species. These results increase the understanding of the molecular changes that occur in the liver during vitellogenesis in this complex and distinctive fish species, bringing new insights on European eel reproduction and broodstock management.

Zona Pellucida Proteins, Fibrils, and Matrix

The zona pellucida (ZP) is an extracellular matrix that surrounds all mammalian oocytes, eggs, and early embryos and plays vital roles during oogenesis, fertilization, and preimplantation development. The ZP is composed of three or four glycosylated proteins, ZP1–4, that are synthesized, processed, secreted, and assembled into long, cross-linked fibrils by growing oocytes. ZP proteins have an immunoglobulin-like three-dimensional structure and a ZP domain that consists of two subdomains, ZP-N and ZP-C, with ZP-N of ZP2 and ZP3 required for fibril assembly. A ZP2–ZP3 dimer is located periodically along ZP fibrils that are cross-linked by ZP1, a protein with a proline-rich N terminus. Fibrils in the inner and outer regions of the ZP are oriented perpendicular and parallel to the oolemma, respectively, giving the ZP a multilayered appearance. Upon fertilization of eggs, modification of ZP2 and ZP3 results in changes in the ZP's physical and biological properties that have important consequences. Certain structural features of ZP proteins suggest that they may be amyloid-like proteins.

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.

Matrix Metalloproteinase 13 Activity is Required for Normal and Hypoxia-Induced Precocious Hatching in Zebrafish Embryos

Hypoxia induces precocious hatching in zebrafish, but we do not have a clear understanding of the molecular mechanisms regulating the activation of the hatching enzyme or how these mechanisms trigger precocious hatching under unfavorable environmental conditions. Using immunohistochemistry, pharmacological inhibition of matrix metalloproteinase 13 (Mmp13), and in vivo zymography, we show that Mmp13a is present in the hatching gland just as embryos become hatching competent and that Mmp13a activity is required for both normal hatching and hypoxia-induced precocious hatching. We conclude that Mmp13a likely functions in activating the hatching enzyme zymogen and that Mmp13a activity is necessary but not sufficient for hatching in zebrafish. This study highlights the broad nature of MMP function in development and provides a non-mammalian example of extra-embryonic processes mediated by MMP activity.

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.

A chromosome-level genome of black rockfish, Sebastes schlegelii, provides insights into the evolution of live birth

The black rockfish (Sebastes schlegelii) is a teleost in which eggs are fertilized internally and retained in the maternal reproductive system, where they undergo development until live birth (viviparity). In the present study, we report a chromosome-level black rockfish genome assembly. High-throughput transcriptome analysis (RNA-seq and ATAC-seq) coupled with in situ hybridization (ISH) and immunofluorescence reveal several candidate genes for maternal preparation, sperm storage and release, and hatching. We propose that zona pellucida (ZP) proteins retain sperm at the oocyte envelope, while genes in two distinct astacin metalloproteinase subfamilies serve to release sperm from the ZP and free the embryo from chorion at prehatching stage. We present a model of black rockfish reproduction, and propose that the rockfish ovarian wall has a similar function to the uterus of mammals. Together, these genomic data reveal unprecedented insights into the evolution of an unusual teleost life history strategy, and provide a sound foundation for studying viviparity in nonmammalian vertebrates and an invaluable resource for rockfish ecological and evolutionary research.