Gametogenesis and Puberty 2024 - ROSS UNIVERSITY PDF

Gametogenesis and puberty L. Segabinazzi 2024  Oogenesis Somatic cells Pairs of homologous chromosomes Each chromosome has one chromatid X Y Oogenesis Theriogenology...

Gametogenesis and puberty L. Segabinazzi 2024  Oogenesis Somatic cells Pairs of homologous chromosomes Each chromosome has one chromatid X Y Oogenesis Theriogenology MM Mitosis Part of cell cycle Two genetically identical daughter cells No crossing over  Oogenesis Mitosis OH Chromatids get separated Generate 2 diploid cells (46 chromosomes) with 46 chromatids of each 2n & 2c 2chvoro.cn pair 2C chromatid  Meiosis Theriogenology MM Special form of cell division that reduces chromosome Creates 4 haploid daughter cells Each genetically distinct Crossing over (Prophase I) Lechage the material genitic n betweratids Meiosis II Meiosis n I n 2n n n n  Oogenesis Before parturition, the fetus’ oogonia (2n) starts meiosis I – prophase I (duplication of DNA – 2n & 4C) Meiosis I Homologous chromosomes 1 get separated Generate 2 haploid cells 1 (23 chromosomes) but 46 41 chromatids N & 2C 1 eachchuowsougoestfoesi.de 5  Oogenesis Before parturition, the fetus’ oogonia (2n) starts meiosis I – gets arrested in Prophase I (duplication of DNA – 2n & 4C) Meiosis II Chromatids get separated Generate 2 haploid cells (23 chromosomes) with 23 chromatids N&C T T  Physiology MM II Fetal life Ovum development in fetal life Primary germ cells originate near yolk sac and migrate to developing ovary (genital ridge) Differentiate to oogonia and multiply by mitosis Oogonia: diploid cells (2N & 2C). Absence of Enter prophase of first meiotic division (primary oocytes) – ✔Testis determining factor most mammals are born ✔AMH ✔Testosterone  Physiology MM II Oocyte developmental events Most mammals are born with oogenesis at the beginning of Meiosis I – Primary oocyte Oocytes get arrested until puberty in prophase I (2N & 4C)  Physiology MM II Meiosis Prophase Homologous recombination (“Chromosomal crossover”) Not at random points: chiasma (chiasmata) Multiple crossovers occur per homologue pair Introduces variation into sexual reproduction Many genetically different daughter cells are possible. Homologous pairs line up in random orientation For each chromosome, it is random as to whether the maternally or paternally derived chromosome goes to each daughter cell For human, with 23 chromosome pairs, this allows over 8 million variations Add in recombination (“crossover”) and you have a virtually infinite number of genetically distinct gametes  Physiology MM II Postnatal oocyte development Primary oocyte (Meiosis I) Duplicates the DNA (Interphase) - Chromosomal complement is 2N & 4C Crossing over (Prophase) Meiosis resumed at the ovulatory surge of LH (Puberty) Meiosis I results in a Secondary oocyte (n & 2C) and a polar body (will degenerate) Polar body  Physiology MM II Oocytes Polar body Formed after meiotic divisions Important for reducing the genetic material Embryo development requires the oocyte cytoplasm Polar bodies degenerate Meiosis I – First Polar body  Physiology MM II Postnatal oocyte development Secondary oocyte (Meiosis II) The secondary oocyte is the cell that is formed by meiosis I in oogenesis. Thus, it has only one of each pair of homologous chromosomes (after crossing over). However, each chromosome still has two chromatids, making a total of 46 chromatids (2C). The secondary oocyte continues the second stage of meiosis (meiosis II), however, gets arrested at metaphase II; until they meet the sperm in the fallopian tube. n 2C Ovulation occurs during the second Meiotic division Meiosis II is completed at the time of fertilization. Results in an Ovum (n) and a polar body (will degenerate)  Physiology MM II Ovulation Release of the oocyte from the follicle Oocyte and cumulus mass moved into infundibulum of uterine tube by fimbria Meiosis continues to second meiotic metaphase (blocked there unless fertilized) Fertilization occurs in ampulla of uterine tube Short window for fertilization (6-12 h)  Male fetal life Physiology MM II - Reproduction ✔Testis determining factor Testis development (Sertoli cells) ✔AMH Development of the Leydig cells – Testosterone – Male duct system  Fetal life Theriogenology MM Spermatogonium development in fetal life Primary germ cells originate near the yolk sac and migrate to the developing ovary (genital ridge) Differentiate to spermatogonium and multiply by mitosis ✔Testis determining factor Diploid cells (2N). ✔AMH Male mammals are born with spermatogonium that can undergo multiple mitosis ✔Testosterone Spermatogenesis Physiology MM II AMHdungfetal AMH to adult producingin Sertoli cells - a "nurse" cell of the life testicles that is part of a seminiferous seminiferous tubules tubule and helps in the process of Inside the spermatogenesis – produces inhibin and estradiol; Phagocytose residual cytoplasm Spermatogonium - undifferentiated male germ cel (2n) Blood testis barrier (Lamina propria) seminiferous tubules - Prevents autoimmune response to Outside the sperm Leydig cells - primary source of testosterone or androgens in males.  Physiology MM II Spermatogenesis Sperm function requires development and maturation through the testis and epididymis Temperature Overall 60ish days Lower than body temperature (34 °C/93 °F) Hormone-dependent Testosterone Spermatocytogenesis Formation of spermatid from spermatogonia Spermiogenesis Morphological change of spermatid into spermatozoa  Physiology MM II Spermatogenesis Inside of the seminiferous tubules First haploid cell – secondary spermatocyte Spermatid is the last cell after cell Division Spermatids undergo morphological changes to become a spermatozoa days  Physiology MM II Sperm cell A Head fixation Acrosome Miedpiece Mitocoidia Tail Mount  Spermatogenesis Physiology MM II Epididymis Transit takes about 2 weeks Sperm acquire capability for motility and fertilization Sperm are stored in tail of epididymis  Physiology MM II Puberty The acquisition of reproductive competence Production of gametes Mating behavior Ability to produce sufficient GnRH - LHBothsexes wallandfeal Decreased hypothalamic sensitivity to negative feedback by testosterone/estradiol - FSH Onset of cyclicity in females Mature sperm in males There is no “intrinsic immaturity” of Gonads Pituitary Animals may be forced to ovulate by appropriate stimulation of prepubertal ovaries Pituitary transplants (!!) in mice prove that prepubertal pituitary can drive cyclicity when transferred to adult recipient  Lorenzo Segabinazzi, DVM, MSc, PhD Ross University School of Veterinary Medicine THANK YOU [email protected] VETERINARY.ROSSU.EDU ©2021 Ross University School of Veterinary Medicine. 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