Unit 3 Gametogenesis Meiosis Review Recombination crossing over occurs here Gilbert 10e Meiosis Review Gilbert 10e Meiosis Review Conclusion Meiosis separates genetic material from one diploid meiotic Gilbert 10e gametes equally precursor to four haploid Symmetry of Meiotic Divisions Spermatogenesis Meiosis separates cytoplasm equally Purves et al 6e Fig 42 4 Asymmetry of Meiotic Divisions Oogenesis Meiosis separates cytoplasm unequally Purves et al 6e Fig 42 4 Polar bodies are the small products of meiosis Almost all cytoplasm remains in the oocyte 1 of 4 haploid products of meiosis Testis Sperm maturation occurs in the epididymis In order to fertilize efficiently capacitation must occur in the female reproductive tract adapted from Gilbert 10e Fig 17 28 Spermatogonia Spermatogonial stem cells Gilbert 10e Fig 17 29 Spermatogonia Gilbert 10e Fig 17 29 Testis Sertoli cells are connected to and provide nutrients for developing spermatids Leydig cells not shown make testosterone Gilbert 10e Fig 17 28 Spermatogenesis Gilbert 10e Fig 4 2 Spermatogene sis Gilbert 10e Fig 4 2 Spermatogene sis Mitochondria are needed to produce ATP for flagellar dynein The acrosomal vesicle contains enzymes released during fertilization Gilbert 10e Fig 4 2 Sperm structure CROSS SECTION OF SPERM TAIL The sperms flagellum Gilbert 10e Fig 4 3 uses microtubule sliding within the axoneme to accomplish bending Sperm The axoneme has a 9 2 arrangement of microtubules outer doublet Gilbert 10e Fig 4 3 Flagellar dyneins are positioned so that outer Flagella Dyneins are positioned to slide adjacent doublets which are locked together into an integrated Campbell 6e Fig 7 25 Broadcast Spawning Broadcast spawning release of large numbers of gametes into an aquatic environment Courtesy Kathy Foltz Spawning in Amphibians Oogenesis in Xenopus Externally fertilized oocytes eggs typically have a large amount of yolk Example Xenopus oocytes are 1 mm in diameter Oocyte Structure Stage IV VI oocyte 0 8 1 2 mm diameter animal Xenopus oocyte Unfertilized egg arrested in M II MII spindle germinal vesicle mRNAs vegetal Gilbert and Raunio Embryology Fig 20 1 Oocytes in meiosis I have a large nucleus germinal vesicle Many oocytes contain localized determinants typically mRNAs For historical reasons the less yolky end of the oocyte is called the animal pole the opposite is the vegetal pole The Ovary One follicle per ovulatory cycle matures in humans follicular dominance Dominance may involve local production of growth factors by the follicle that wins Campbell et al 5e Fig 46 13 Oogenesis in Mammals PRIMORDIAL FOLLICLE Gilbert 10e Fig 17 31 Oogenesis in Mammals The mature follicle must rupture to release the oocyte which normally is swept into the Fallopian tube Gilbert 10e Fig 17 31 Female Reproductive Structure fimbriae Fallopian Tube Fimbriae sweep the oocyte cumulus complex into the open end of the Fallopian tube Adapted from Campbell et al 5e Fig 46 9 Ovulation Hormonal Feedback Control The hypothalamus stimulates the anterior pituitary via the release of gonadotropin releasing hormones GnRHs specific for particular gonadotropins e g luteinizing hormone LH or follicle stimulating hormone FSH Purves et al 6e Fig 42 14 Ovulation Hormonal Feedback Control Gonadotropins positively regulate cells in the ovary Estrogen is made by connective tissue cells in the ovary Progesterone is made by the follicle but especially by the remnant of the follicle corpus luteum Estrogen and progesterone inhibit hormone production by the hypothalamus and pituitary Progesterone stimulates thickening of the uterine lining Purves et al 6e Fig 42 14 Control of Ovulation Hormonal Regulation Gonadotropins Ovary Gilbert 7e Fig 19 30 A surge of LH and FSH stimulates ovulation Control of Ovulation Hormonal Regulation Ovarian hormones A surge of estrogen contributes the FSH LH surge progesterone stimulates uterine lining thickening Uterine lining Gilbert 7e Fig 19 30 Human Chorionic Gonadotropin Progesterone hCG progesterone supports endometrium inhibits contraction firms cervix hCG is made by the embryo and stimulates the corpus luteum to maintain progesterone production Ulmann et al 1990 Sci Am 262 6 42 48 RU486 and Progesterone progesterone RU486 RU486 mifepristone binds the progesterone receptor but does not activate signaling thereby competing with progesterone Sea Urchin Egg Structure Egg jelly produces molecules that attract sperm Sperm must digest it Gilbert 10e Fig 4 4 Sea Urchin Egg Structure Vitelline Envelope The vitelline envelope will be remodelled after fertilization to form the fertilization envelope Gilbert 10e Fig 4 6 Mammalian Oocyte Structure Sperm bind to and digest through the zona pellucida Purves et al 6e Fig 43 2 The cumulus complex contains proteoglycans Sperm must digest it Mammalian Oocyte Structure polar body cumulus cells Gilbert 10e Fig 4 7 The Zona Pellucida Paul Wassarman Stages of Oocyte Meiotic Arrest Oocytes have not completed meiosis when they are fertilized Eggs have completed meiosis Gilbert 10e Fig 4 5 Stages of Oocyte Meiotic Arrest Gilbert 10e Fig 4 5 Most mammalian and amphibian oocytes are arrested in metaphase II MPF and CSF Yoshio Masui Maturation promoting factor MPF causes oocyte maturation cytostatic factor causes arrest at metaphase II by preventing destruction of MPF Meiotic Maturation MPF Micropipette Cytoplasm is extracted from a mature egg cell Extracted cytoplasm is injected into an oocyte Hardin et al World of the Cell 8e Fig 19 34 Meiotic Maturation MPF Meiosis is triggered Mature egg cell results Conclusion MPF promotes maturation but results in arrest at metaphase II Hardin et al World of the Cell 8e Fig 19 34 MPF Activation cyclin Cdk Cdk cyclin complex INACTIVE MPF consists of a cyclin and a cyclin dependent kinase Cdk Hardin et al World of the Cell 8e Fig 19 36 MPF Activation Cdk MPF is active when the Cdk is appropriately phosphorylated Hardin et al World of the Cell 8e Fig 19 36 MPF Activation Cdk MPF is active when the Cdk is appropriately phosphorylated Hardin et al World of the Cell 8e Fig 19 36 MPF Components Nobel Prize 2001 Lee Hartwell Paul Nurse Tim Hunt courtesy Nobel Foundation CSF causes metaphase arrest no division One blastomere injected at 2 cell stage Spindle arrested at metaphase Conclusion CSF must prevent inactivation of MPF since the injected cell arrests at the next metaphase Courtesy Ellen Shibuya MPF Regulation in Frog Oocytes Progesterone leads to activated MPF and