Browsing by Subject "Oogenesis"

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    Diversity and dynamics of fish ovaries: Insights into reproductive strategies, hormonal regulation, and ovarian development
    (Universidad de Murcia, Departamento de Biologia Celular e Histiologia, 2025) Mokhtar, Doaa M.
    Fish ovaries exhibit a remarkable diversity in shape, size, and organization, reflecting the myriad reproductive strategies employed by different species. This review delves into the intricate biology of fish ovaries, highlighting their structural diversity and the hormonal regulation that governs ovarian development and oocyte maturation. Key hormones include pituitary gonadotropins (GTHs) and maturation-inducing hormones (MIHs), which initiate oocyte growth and maturation. GTHs stimulate ovarian production of estradiol-17β and 17α,20β-DP, which induce oocyte maturation via MPF formation. Sex steroids like estrogens and progestogens, synthesized from cholesterol, play crucial roles. Other hormones, including growth hormone, prolactin, thyroid hormones, IGFs, ACTH, and melatonin, influence ovarian activity. The review also explores the varied reproductive strategies among fish, including oviparity and viviparity, and discusses how environmental factors like water temperature and photoperiod influence ovarian histology. Understanding the complex interplay between these factors is essential for advancing fisheries management, conservation, and aquaculture practices. Additionally, the evolutionary trajectory of fish ovaries underscores their adaptation to diverse ecological niches, contributing to the survival and reproductive success of fish species. The ovarian stroma provides structural support and houses various cell types, including dendritic cells (DCs), endocrine cells, and telocytes, contributing to follicle growth and hormone production, essential for reproductive success in fish. Fish ovaries are a crucial aspect of fish biology, with their structure and function intricately regulated by hormonal, environmental, and seasonal factors.
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    Female fertility and the mammalian egg’s zona pellucida
    (Universidad de Murcia. Departamento de Biología Celular e Histología, 2024) Wassarman, Paul M.; Litscher, Eveline S.
    All mammalian eggs are surrounded by a relatively thick extracellular matrix (ECM) or zona pellucida (ZP) to which free-swimming sperm bind in a species-restricted manner during fertilization. The ZP consists of either three (e.g., Mus musculus) or four (e.g., Homo sapiens) glycosylated proteins, called ZP1-4. These proteins are unlike those found in somatic cell ECM, are encoded by single-copy genes on different chromosomes, and are well conserved among different mammals. Mammalian ZP proteins are synthesized as polypeptide precursors by growing oocytes that will become ovulated, unfertilized eggs. These precursors are processed to remove a signal-sequence and carboxyterminal propeptide and are secreted into the extracellular space. Secreted ZP proteins assemble into long, crosslinked fibrils that exhibit a structural repeat due to the presence of ZP2-ZP3 dimers every 140 Å or so along fibrils. Fibrils are crosslinked by ZP1 and are oriented either perpendicular, parallel, or randomly to the plasma membrane of eggs depending on their position in the ZP. Free-swimming mouse sperm recognize and bind to ZP2 or ZP3 that serve as sperm receptors. Acrosome-intact sperm bind to ZP3 oligosaccharides and acrosome-reacted sperm bind to ZP2 polypeptide. ZP fibrils fail to assemble in the absence of either nascent ZP2 or ZP3 and results in mouse eggs that lack a ZP and female infertility. Gene sequence variations in genes encoding ZP1-4 result in human eggs that lack a ZP or have an abnormal ZP and female infertility. These and other features of the mouse and human egg’s ZP are discussed here.