DEVBIOL Gametogenesis

• Gametogenesis refers to the generation and maturation of gametes, including oogenesis and foliculogenesis in females, and spermatogenesis in males.
• Oogenesis is the generation and maturation of gametes in females.
• Foliculogenesis is the generation and maturation of gametes in females.
• Spermatogenesis is the generation and maturation of male sex cells, including sperms and spermatozoa.
• Gametogenesis involves a series of changes or processes, starting from primordial germ cells to specialized sex cells.
• In mammals, there are no obvious germplasm, but in animals other than mammals, germplasm can be easily distinguished as a cell-dense association of mRNAs and mRNA-binding proteins such as VASA, DAZL, and MILI homologues.
• There is a need for nutrients just in case the egg gets fertilized during the phases of gametogenesis.
• The phases of gametogenesis include the generation of germ cells and migration to the gonads, multiplication of germ cells in the gonads (mitosis), reduction in chromosome # by ½ (meiosis), and maturation and differentiation of sex cells to becoming specialized ones.
• Gametogenesis involves the generation of germ cells and migration to the gonads, which occur somewhere else and are distinguishable at an early stage of development.
• Primordial germ cells become spermatozoa through mitotic multiplication, meiosis, and spermeiogenesis (maturation of spermatids).
• Mitosis in male occurs throughout life.
• PGCs at the genital ridge migrate to sex cords, seminiferous tubules, and tubular epithelium (where Sertoli cells form).
• Once within the genital ridges, PGC undergo a series of divisions to generate waves of different subpopulations of spermatogonia.
• Stem cells undergo synchronized cell division and self-renewal.
• Type A4 (last batch) have the option to have another round of cell division or undergo apoptosis or others have the option to becoming committed to becoming a primary spermatocyte.
• Committed cells will undergo another self-renewal to become Type B spermatogonia.
• Type B are committed to becoming primary spermatocytes.
• They will undergo Meiosis 1 and become secondary spermatocytes.
• Secondary spermatocytes undergo Meiosis 2 and become spermatids.
• Spermatids will undergo spermeiogenesis.
• Cytoplasmic bridges interconnect everything and make sure that per batch will mature synchronously.
• At spermiogenesis, there are residual bodies.
• Changes during spermeiogenesis include reorganization of the cytoplasm, Golgi apparatus, centrioles, mitochondria, and the formation of the acrosome cap.
• At spermiogenesis, the nucleus undergoes progressive reduction in nuclear size/compaction, loss of water, elimination of RNA, and not all histones are replaced.
• In humans, 15-20% of histones remain in nucleosomal configuration.
• In anuran amphibians, an unfertilized egg undergoes cleavage and gastrulation.
• In amniotes (birds, reptiles, mammals), primordial germ cells identify in the yolk sac endoderm.
• In humans, primordial germ cells are recognizable at 24-day post-fertilization in the yolk sac endoderm.
• Gametogenesis is the process that results in the production of mature oocytes.
• Oogenesis is the process that results in the production of oocytes.
• Oocytes undergo arrested stages during oogenesis.
• Unequal cytoplasmic division occurs during oogenesis.
• Only one functional oocyte is produced per cycle, with polar bodies produced during oogenesis.
• Mammalian oogenesis is a reference point for understanding the effects of prolonged arrested stages and puberty on oocyte maturation.
• Hormonal control of oocyte maturation sets in during puberty, when females start producing hormones.
• Primary follicles gradually become secondary follicles during puberty.
• FSH, or follicle-stimulating hormone, LH, or luteinizing hormone, and FSH act on the granulosa cells and as a response, granulosa cells increase in population.
• When there is an increase in granulosa cells, there is an increase in estrogen, which further activates more granulosa cells to increase.
• The peak of estrogen levels occurs during the mid-cycle of mammalian oogenesis.
• LH increases at a lower level than FSH, with its release being further activated by the level of estrogen released by granulosa cells.