Gametogenesis Lecture 5 PDF

Gametogenesis Lecture 5 Gametogenesis Gametogenesis is the development of gametes – sperm, egg, pollen, ova, spores etc. Germ cells can derive from diverse tissues depending upon organism: Plants: any stem cell will do Insects, fish, nematodes, frogs: specialized cytoplasm is localized to one po...

Gametogenesis Lecture 5 Gametogenesis Gametogenesis is the development of gametes – sperm, egg, pollen, ova, spores etc. Germ cells can derive from diverse tissues depending upon organism: Plants: any stem cell will do Insects, fish, nematodes, frogs: specialized cytoplasm is localized to one pole of the egg, or the freshly fertilized embryo – called pole plasm During early embryonic cell division, only some cells inherit that cytoplasm – pole cells Pole cells are the precursors to primordial germs cells Insects (Drosophila melanogaster – fruit fly) Why Drosophila? Cheap to feed, store, rear breeds quickly and in great quantities Short reproductive cycle (can breed traits quickly) Few chromosomes, well documented, mapped Sequenced Can knock out, mutate, knock in genes Many strains, probes, and reagents available to study Pole plasm segregates early Tale of Karl Illmansee (from teratocarcinoma, to fly, to mouse clones by nuclear transfer). http://www.zoology.ubc.ca/ Nematodes Germ line is lineage restricted We will come back to this when we talk about embryonic potentials p. 400, Fig 9.3  Mouse p. 402 fig. 9.5 Primordial Germ Cells (PGCs) migrate from outside the developing body (in the posterior primitive streak - discussed later during lectures p. 403 fig 9.6 on gastrulation), into the developing body when the gut begins to roll up to form a tube. populate the genital ridge eventually become enclosed in developing gonadal tissue (testes or ovary) Spermatogenesis PGC differentiates into spermatogonia (puberty) Spermatogonia serve as stem cells for Spermatogenesis Golgi orient to tip of head and coalesce into acrosome Globular actin between nucleus and Golgi Mitochondria and centrosome with tubulin segregate towards tail Flagella grows Cytoplasm sloughed off Hogarth and Griswold J Clin Invest. 2010; 120(4):956-962 p. 406 Fig 9.9 Simplified Structure of Spermatozoa (Axoneme) p. 413 Fig 9.14 Meiosis produces four symmetrically divided haploid cells Acrosome forms from Golgi, is membrane-bound, encapsulates some of nucleus Mitochondria move down to axoneme – 40-80 Sperm structure 9+2 arrangement of microtubules forms Flagella Globular actin Head Axoneme Tail End Piece Adapted from: https://en.wikipedia.org/wiki/Acrosome#/media/File:Simplified_spermatozoon_diagram.svg Globular actin concentrates between membranes of acrosome and nucleus External sperm head and interior membrane of acrosome hold receptors to stick to cumulous cells and/or oocyte At fertilization, all internal components transferred to oocyte Mitochondria degenerate – all mitochondria in zygote thought to derive from oocyte (mother) Symmetric cell division yield 4 haploid spermatozoa  Flagella and Cilia https://en.wikipedia.org/wiki/Flagellum#/media/File:Eukaryotic_flagellum.svg https://upload.wikimedia.org/wikipedia/commons/thumb/d/de/ Chlamydomonas_TEM_17.jpg/1280px-Chlamydomonas_TEM_17.jpg Dynein Cytoskeleton motor protein ATP-dependent Mutation can cause immotility of flagella – also of cilia Immotile sperm = sterility Immotile cilia Absence of bronchial tractoring of mucous – predisposition to lung infection Left-right asymmetry issues (laterality defects – situs inversus) Sperm Maturation Sperm must then mature via passage through epididymis – makes motile Maturation: is hormone mediated Sperm endocytose epididymosomes (epigenetic information in form of miRNA at least) Mammalian sperm require further processing in female reproductive tract Capacitation destabilizes acrosome - now ready to fertilize on contact Hyperactivation induced by near- A. Head of epididymus, oocyte environment: ZP3 (zona B. Body of epididymus, pellucida ligand, progesterone (cumulus C. Tail of epididymis, and cells). Sperm flagella amplitude and D. Vas deferens frequency increases, sperm may be chemotactic at this point https://en.wikipedia.org/wiki/Epididymis#/media/File:Epididymis-KDS.jpg  Oogenesis (Egg) Progression of oocyte through oogenesis varies from one species to the next Some arrest at oogonial stage, others at primary oocyte stage, others at secondary etc. Oocytes shed at species-specific times ie; rabbits ovulate only after stimulus of coitus, human on a monthly cycle Examples of Patterns of Oogenesis p. 405 Box 9A, Fig 1  Oogenesis Common Oogenesis steps Oogonia increases in size as it grows and as maternal cells deposit goods Mitochondria amplify to the 1000s RNAs (ribosomal, mRNA, miRNA) Proteins including those necessary to support first few cell divisions – histones, enzymes, telomerases, yolk granules Golgi forms thousands of vesicles that disperse to periphery (cortex) of cell – cortical granules Cortical granules contain hyaline, glycosaminoglycans, proteoglycans, enzymes to cleave receptors, cross-link vitelline coat Globular actin accumulates in the cortex just under the plasma memberane and around cortical granules Oocyte starts to deposit external protective materials: Sheath of protein called vitelline coat and also zona pellucida (glycoprotein) Jelly, albumen, shell depending upon animal Area of interdigitation (villi) with associated nursing cells in mammals Undergoes highly asymmetric cell divisions – 1 becomes 2 (one big cell, one polar body), becomes 4 (I big cell, 2-3 polar bodies) Meiosis reduces chromosomal complement to haploid in the remaining large oocyte cell. Cortical Granules Nilsson, B et al.(1981). Upsala journal of medical sciences 86: 225-232 Ovarian Context Thecal cells Cumulus cells Oocyte 3o or Graafian Follicle Mehlmann (2005). Reproduction. Vol 130 (6): 791–799 https://doi.org/10.1530/rep.1.00793 Mammalian Zona Pellucida Cumulus Cells Zona Pellucida Perivitelline Space Oocyte Kere et al. (2020) Animals 10(4), 664