Embryology .pdf
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Gametogenesis Gametogenesis is the development of gametes – sperm, egg, pollen, ova, spores etc. Germ cells can derive from diverse tissues depending upon organism: Pole Plasm Plants: any stem cell will do...
Gametogenesis Gametogenesis is the development of gametes – sperm, egg, pollen, ova, spores etc. Germ cells can derive from diverse tissues depending upon organism: Pole Plasm Plants: any stem cell will do specialized cytoplasmic region zygote - or eggof the Insects, fish, nematodes, frogs: containsmmminants aa - 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 Pole Cells cytoplasm – pole cells - begin - cells that form germ polar the adult egg at the cells ends of Pole cells are the precursors to primordial germs cells & GIVE RISE TO GAMETES Insects (Drosophila melanogaster – fruit fly) Why Drosophila? functionality conserved very Cheap to feed, store, rear within genes network to are breeds quickly and in great quantities provide Function nuclei divide internally Short reproductive cycle (can breed traits quickly) Few chromosomes, well documented, mapped Sequenced Can knock out, mutate, knock in genes incomplete partioning 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/ Nematodesfruit only one to cell receives granules cell become like fys germ curoplasmdifwhereyou on a 3 p granules are only included in Pell ↳ become confined to Germ line is lineage the P-cell - lineage restricted We will come back Mosaic Development to this when we talk ↳ highly regulative about embryonic develoament potentials p. 400, Fig 9.3 : During gastulation Mouse to cells end move of posterior above the embryo primitive steah PGCs first detectable & inproximate PGCs to the Start migrate to gonads Cells move from the tube gut into the genital ridge via dorsal p. 402 fig. 9.5 mesentery Primordial Germ Cells (PGCs) migrate from outside the developing body (in the posterior primitive streak - discussed later during lectures on gastrulation), into the PGCs p. 403 fig 9.6 developing body when the gut begins to roll up to form a tube. in populate the genital ridge migrate through GI tract eventually become enclosed in developing gonadal tissue (testes or through body ovary) cality rest on two ridges overstrap Lord dep on organisms ↳ develop at diff times Spermatogenesis cells enter germ testes where embryonic will become they Sperm PGC differentiates into spermatogonia (puberty) unipotent Spermatogonia serve as stem cells for Spermatogenesis ↳ divide mitotically Golgi orient to tip of head and coalesce into acrosome Form top again - on forming a of population cells of Stem nucleus (spermatogonia) Globular actin between nucleus and Golgi globular and activ Mitochondria and centrosome with tubulin segregate 2NP diploid meiosis haploid to towards tail Stem cells G Flagella grows specialized form of Cilliq Spermatogonia d Cytoplasm sloughed off & Spermatocyte ↓ Spermatics ↓ Mature Sperm Hogarth and Griswold J Clin Invest. 2010;120(4):956-962 p. 406 Fig 9.9 Sperm become motile in epididymis Acrosome : atanterioendofthespensed to digest the protective coats around the a Simplified Structure of Spermatozoa Sperm moves by single - Flagellum powered by Mitochondria L actin hat the sitting Over head of nucleus haploid chromosome Set 40 80 - (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 depending upon species outside of sperm receptors Sperm structure adhere to help egg 9+2 arrangement of microtubules forms Flagella power movement of flagella Globular actin between nucleus and acrosome 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) Mitochondria mutations from Father Symmetric cell division yield 4 haploid spermatozoa Flagella and Cilia ↓Faganas I https://en.wikipedia.org/wiki/Flagellum#/media/File:Eukaryotic_flagellum.svg AMD Dynein - men Mutations locking action https://upload.wikimedia.org/wikipedia/commons/thumb/d/de/Chlamydomonas_TEM_17.jpg/ 1280px-Chlamydomonas_TEM_17.jpg lung infections receptiveenq can't occur 3 Flagella don't swim- accumulation neighboring in mis - immotile - infertile lungs Dynein Cytoskeleton motor protein ATP-dependent Mutation can cause immotility of flagella – also of cilia Immotile sperm = sterility meeting of sperm and Immotile cilia is egg absent 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) diff MiRNAs metabolic programming deposited in the Sperm Mammalian sperm require further (drinking smoring) affect way , processing in female reproductive tract are armed Capacitation destabilizes acrosome - now consequences sperm ready to fertilize on contact -allowsto penetrate for offsprin gas of egg Hyperactivation induced by near-oocyte A. Head of epididymus, B. Body of epididymus, 6) environment: ZP3 (zona pellucida ligand, progesterone (cumulus cells). Sperm flagella C. Tail of epididymis, and amplitude and frequency increases, sperm D. Vas deferens may be chemotactic at this point provides necessary required for penetration of zoapellucida Chemotaxis-movementofspermbeingguidedtoward theo is environment for sperm https://en.wikipedia.org/wiki/Epididymis#/media/File:Epididymis-KDS.jpg at the head After cells enter the germ , where they embryonic ovary will form oocytes they divide mitotically a few times and Oogenesis (Egg) thenenter theprophasa serision No more cell multiplication Further in In mice ; development occurs the adult female don't start eggs highly variable ovulating have sex until they 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. g Oocytes shed at species-specific times ie; rabbits ovulate only after stimulus of coitus, human on a monthly cycle I oave giving rise to legg cells Polar Bodies : small formed meiosis by during of development an Examples of Patterns of Oogenesis the oocyte an into egg. highly assymetic Egg growing in size - RNA - miRNA life proteinse support - until hatch yolk - or placental support complete cell division Arrest : 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 - - fertilized it ready When is RNAs (ribosomal, mRNA, miRNA) require genetic transc trans behaviour days before takes messages polypep , - stage embryo deposit early on wall Proteins including those necessary to support first few cell divisions – histones, enzymes, telomerases, yolk granules Full of Golgi forms thousands of vesicles that disperse to periphery (cortex) of cell – cortical granules viscous Fluid and proteins Cortical granules contain hyaline, glycosaminoglycans, proteoglycans, enzymes to cleave receptors, cross- attract water 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) tough after fertilization ↳ zone around Jelly, albumen, shell depending upon animal Off peripher ↳ protection egg clear ↳ Area of interdigitation (villi) with associated nursing cells in mammals all membrane 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 > - around peripheyis Ovarian Context Thecal cells hormones produce and secrete which is for estrogen crucial Follicular development 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
