bs148h 13 November 2007Read: Text ch 21 & 47 • development• oogenesis•ovulation• fertilization• signals & cell “fate“• stem cells• sonic hedge hog• hox genes and segmentation• immunity and placental mammals• genomic imprinting • sex determination• mosaic XX in calico cats & womenHuman reproduction involves intricate anatomyintricate anatomy {see text}and complex behaviorcomplex behavior {next lecture}In the developing female embryo, oogonia, the stem cellsstem cells that give rise to ova, multiply and begin meiosis, but the process stops at prophase I. These primary oocytes, remain quiescent until puberty.Beginning at puberty, FSH (follicle-stimulating hormone) periodically stimulates afollicle to grow and induces the primary oocyte to complete meiosis I {reduction 2n=46 →n=23}& start meiosis II.Meiosis then stops again {secondary oocyte}; Penetration of the egg by a sperm ‘activates’ the secondary oocyte & triggers the completion of meiosis.OogenesisOogenesis (see text Fig 46.11)In humans, oogenesis differs from spermatogenesis in three major ways: 1. In meiotic divisions of oogenesisoogenesis, almost all the cytoplasm is monopolized by the oocyte and ovum; the polar bodies, degenerate.w/ spermatogenesis all four products of meiosis develop into mature sperm. 2.SpermatogenesisSpermatogenesis is continuous and prolific in the adult human males. Each ejaculation of a human male contains 100 to 650 million sperm cells, & males can ejaculate daily w/o loss of fertility {sperm is NOT limiting }.At birth, an ovary already contains all the primary oocytes it will ever have. 3. Oogenesis is cyclic, spermatogenesis is not. {age of egg & sperm of 40 yr old couple?}pubertyfetal developmentFertilization of egg initiates development; what initiates ovulationovulation? humanshumans and most vertebratesare spontaneous spontaneous ovulatorsovulators …Spontaneous ovulations are primarily the result of an LH surge from anterior pituitaryLH surge from anterior pituitaryinduced by ovarian steroid hormones …{regular cycling from + & {regular cycling from + & --FB: Fig 46.13}FB: Fig 46.13}{cats are reflex ovulators– in response to copulation}http://www.abc.net.au/science/descent/trans1b.htmDavid Buss: HumansHumans have what’s called concealed or cryptic ovulation,concealed or cryptic ovulation,... poses an especially important adaptive problem for men, ... how to know when to mate with the womanwhen to mate with the woman,Concealed ovulation makes the rhythm methodof contraception‘probabilistic.’These tests measure the increase in LH in urine, at the time of ovulation.But there are cues ...Hormone levels predict attractiveness of women.Hormone levels predict attractiveness of women.02 November 2005 NewScientist.comResearchers ... have found that womenwomen’’s facial attractiveness s facial attractiveness is directly related to their is directly related to their oestrogenoestrogenlevels.levels.composite faces of women at highest & lowest oestrogen levels - which do you find more attractive? (Image: Miriam Law Smith)October 11, 2006 ·Women Dress BestWomen Dress BestWhen When Ready to MateReady to Mate ...Haselton, M. G., et al. (2007). Ovulation and human female ornamentation: Near ovulation,Near ovulation,women dress to impresswomen dress to impress. Hormones and Behavior, 51, 40-45.{subjects asked “In which photo is the person trying to look more attractive?”tend to chose full body photos of self-dressed women taken closer to ovulation} Martie HaseltonOctober 10, 2007 By Abigail GoldmanScience says lap dancers send 'signals,' rake in cashOvulatoryOvulatorycycle effects on tip earnings by lapcycle effects on tip earnings by lap--dancers: dancers: Economic evidence for human estrus? Economic evidence for human estrus? Miller, G. F et al. 2007 Evolution and Human Behavior. {In humans}fertilizationfertilization takes about 24 hours.A sperm can survive for up to 48 hours. It takes ~10 hours to navigate the female repro tract, into the fallopian tube where fertilization begins. http://www.ucalgary.ca/UofC/eduweb/virtualembryo/db_tutorial.htmlOnly one sperm needs to bind with the protein receptors in the egg ZZonaPPellucidato triggerthe the AcrosomalAcrosomalreactionreaction allowing the zona to be pierced. {sperm surface molecule binds like peptide hormone to ZP receptor, triggers Na+ influx & cellular depolarization (like in neuron) - ‘fast block to fast block to polyspermypolyspermy:’the zona pellucida hardens trapping runner-up sperm;sperm receptors in the zona pellucida are destroyed.} Penetration of the zona pellucida takes about twenty minutes. Plan B® {estrogen and progestin}prevents pregnancy by stopping the release of an egg from the ovary, ... may also prevent the fertilization, and/or attachment of fertilized egg to the uterus. ... will not affect a fertilized egg already attached to the uterusThe Cortical ReactionThe Cortical Reaction: a signal transduction cascade causes the endoplasmic reticulum to release Ca2+,causing the cortical granules to fuse w/ the plasma membraneand release enzymes …viltelline layer becomes the fertilization envelope - ‘slow block to slow block to polyspermypolyspermy.’http://arbl.cvmbs.colostate.edu/hbooks/pathphys/reprod/fert/fert.htmlPrior to fertilization, the egg isarrested in metaphase of the 2ndmeiotic division.Upon binding of a sperm, the egg rapidly undergoes changes collectively called egg Activationegg Activation. including completion of the second meiotic division completion of the second meiotic division and the so-called cortical reactioncortical reaction. Sperm cells do not contribute any materials required for activationactivation. Unfertilized eggs can be artificially activated by a variety of mildly injurious treatments. It is possible to artificially activate an egg that has had its own nucleus removed: mRNA coding for new proteins are stockpiled in an inactive form in the cytoplasm of the unfertilized egg. {This mRNA is from mom, not egg DNA, early development is controlled pre-packaged maternal mRNA & proteins}Developmental biology:Developmental biology:Cell cycle unleashed.Cell cycle unleashed.Takeo Kishimoto Nature 437, 963-965 (13 October 2005){reports on advances in understanding molecular mechanisms of activation} ~30 hrs after fertilizationThe zygote now begins to cleavecleave, into two cells called blastomeresblastomeres.Within 11 hrs of fertilization the oocyte