Class Note for ECOL 182R at UA
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Date Created: 02/06/15
ECOL 182 Spring 2008 Lecture 5 Animal reproduction and development Dr Regis Ferriere Department of Ecology amp Evolutionary Biology University of Arizona What are the key terms and questions The three steps of sexual reproduction Gametogenesis Mating Fertilization How does qametoqenesis work VCellular mechanisms Hormonal control How does fertilization work Meeting Fusing From zygote to placenta How does fertilization activate deve0pment Cell hemispheres Cleavage Blastula How are tissue lavers generated Gastrulation Organizer Anteriorposterior body axis How do organs and orqan svstems develop Notochord Segmentation lox genes How does gametogenesis work Gametogenesis occurs in testes and ovaries Spermatogenesis production of sperm Oogenesis production of eggs Germ cells proliferate mitotically undergo meiosis and mature into gametes How does spermatogenesis work Each primary spermatocyte can produce 4 haploid sperm through the two divisions of meiosis A SPERMATOGENESIS Male germ cell Spermatogonium Primary 2 2n spermatocyte 4n J gt gt Mitosis Mitosis quot First meiotic division Embryo Aduh 589 Figure 423 Part 1 m Msmmuremo mmmmm Differentiation and maturation into gametes Spermatids n r Sperm cells in Secondary spermatocytes 2n Second meiotic division 39 How does oogenesis work Primary oocytes immediately enter prophase of the first meiotic division In many species including humans their development is arrested at this point Each oogonium produces only 1 egg l m Emb o W Adult Female germ primary Differentiation and growth cen en oogomum 2n oocyte 4 Secondary oocyte 2n Ootid n Ovum egg n s Mitosis Mitosis Second g v 39 First meiotic meiotic d39V395390quot Polar bodies division First Second degrade polar body polar body LIFE 3e Figure 423 Pan 4 How is spermatogenesis controlled Hormones Spermatogenesis depends on testosterone secreted by the Leydig cells of the testes under the control of other hormones produced by the hypothalamus which are themselves controlled by negative feedback from testosterone and inhibin lnhibin is produced by the Sertoli cells of the testes How does fertilization work Step 2 Fusion Then fertilization involves Sperm activation Speciesspecific binding of sperm to egg The acrosomal reaction xDigestion of a path thru protective coverings of the egg Fusion of sperm and egg plasma membranes LlF39E Be Figure 425 Sperm cell Mitochondria EV II in E P 3 O f u Acrosome E Sperm nucleus E D 5 no 7 V Vitelline envelope JG 003i ll 1 Egg plasma membrane Actin Protein bond 0 Cortical granule Digestive 39 enzymes Acrosomal process 55 03965 oooo 0 39 39 Sperm nucleus Centriol e Fertilization cone quot2quot m Fertilization envelopef fx i How does fertilization work Ste 2 Fusion Then fertilization involves Sperm activation Speciesspecific binding of sperm to egg The acrosomal reaction Digestion of a m thru protective coverings of the egg Fusion of sperm and egg plasma membranes Why only one winner This fusion triggers blocks to polyspermy prevents additional sperm from entering the egg In mammals the fusion signals the egg to complete meiosis and begin develooment How does fertilization work Step 3 From zvaote to placenta Sperm and egg contribute differentially to the zygote xSperm a haploid nucleus xqu a haploid nucleus nutrients ribosomes mitochondria mRNA proteins The zygote becomes a blastocyst as it passes down the oviduct Upon arrival in the uterus the blastocyst implants in the endometrium and form a placenta LIFE 32 gure 435 m msmwar amonnragm Earm u m How is female fertility regulated Edd maturation amp Uterus preparation Maturation and release of eggs occur with a periodicity of about 28 days in humans This is the ovarian cycle Uterus also undergoes a cycle that prepares it for receipt of a blastocyst If no blastocyst is implanted lining of the uterus sloughs off menstruation process Both cycles are coordinated by hormones including female sex steroids estrogen and progesterone Beginning with the onset of menstruation ovulation occurs at midcycle when uterus preparedness peaks How is female fertility regulated E Events in ovary Developing Ovulation Corpus luteum Developing Both cycles are om M a follicle I maturation coordinated by hormones Q G Q 0 Including female sex i S a C Ovarian hormones and tine uterine cycle progesterone Estrogen Progesterone onset of menstruation 39 ovulation occurs at D E d 39 n andwghmg midcycle when uterus K preparedness peaks 4 M Hum I 21 28 Day of uterine cycle LIFE 39 Figure 4214 Part 2 we rnzsmwcsoramoanmwmm m y 1w How does fertilization activate development Step 1 Rearranqement of eqq cytoplasmic content After fertilization egg cytoplasmic contents rearranged nutrients in vegetal hemisphere Vnucleus in animal hemisphere This defines the major axes of future embryo Anima The cortical cytoplasm cortical rotates relative to the cytoplasm Animal Inner cytoplasm pigmented pole A Sperm entry point vegteta cytoplasm The gray crescent is pole V unpigmentedl created by the rotation How does fertilization activate development Step 2 Cleavaqe Cleavage period of rapid cell division without cell expansion or gene expression Result of cleavage a ball or mass of cells called blastula In mammals cleavage results in a blastocyst Inner cell mass will become the embryo Outer cell mass called trophoblast helps implantation by secreting certain molecules How are multiple tissue layers generated Gastrulation massive cell movements Vproduce 3 germ layers endoderm mesoderm ectoderm place cells from various regions of the blastula into new associations with one another How are multiple tissue layers generated Model oroanisms for the study of development The sea urchin Certain blastomeres move inward at location called blastopore xCells that move inward form the endoderm and mesoderm VCells remaining on outside form the ectoderm Animal hemisphere Vegetal hemisphere Secondary mesenohyme Endoderm Arohenteron Primary rnesenchyrne LIFE Be Figure 438 m mscmmusmmmmsam a How do organs amp organ systems develop Organogenesis follows gastrulation Tissues interact to form organs and organ systems One group of cells that migrates over the blastopore lip is determined to become the notochord Notochord induces overlying ectoderm to thicken and form parallel ridges and fold in on itself to form a neural tube below the epidermal ectoderm The nervous system develops from this neural tube Neural plate 7 x C Neural tube Notochord Endoderm How do organs amp organ systems develop Notochord and neural crest cells participate in the formation of other organs and organ systems They play a major role in the orqanization of the mesoderm alonq the bodv aLis xdevelopment of seqmental structures called somites 2Day chick embryo ii Repeating segments or tissue somites form from rnesmlerr n on either side oi 1he neural tube Neural crest Neural IL be 3 Nolocl39rord 7 Each somite divides into three layers of cells The upper will contribute to skin 4Day chick embryo Neural crest cells Naural tube 1 i M lg rating mesenchvyme rsells term ca lhge oi the vertebrae and nibs 7Day chick embryo I migrate between the layers and will produce nerves and other tissue How do organs amp organ systems develop l l l l b b8 bQ and those closesl lo the 5 end are expressed more posteriorly The genes closest to the 339 end are expressed in the anteriorrnosl positions Hox genes V4 families of genes that determine the pattern Di 132 i 333 Dr bi DEF How of anteriorposterior it 30m I anterior o dlffe renCIatlon along posterioref 7 Embryo body axis in mammals Other genes contribute to dorsalventral differenciation sonic hedgehog and HOXI39JQ in the spinal cord For example Hoxb is exprer in the hindbrain Mujbrsnn 39 Faintrain Mouse embryo LIFE Se Figure 4316 U1 1 NE SCIERKEEO MMOGV Jan39s Emma r39 Mn Iv 3 r Suggested readings Karow J 2000 When sperm meets egg Scientific American August An examination of the molecular and cellular events that surround the fusion of sperm and egg Powledge T M 2002 Looking at ART Scientific American April An indepth look at assisted reproductive technology ART its challenges and promises Smith R 1999 The timing of birth Scientific American March Is it the fetus or the mother who initiates the birth process Recent research has revealed the basis for an interaction between the placenta the fetus and the mother which determines the onset of labor Dahm R 2006 The zebrafish exposed The American Scientist vol 92 page 3 The zebrafish has become a popular model system for studying development because the young fish are transparent De Robertis E M G Oliver and C V E Wright 1990 Homeobox genes and the vertebrate body plan Scientific American July A good discussion of the development of anatomy and a presentation of how a highly conserved family of genes directs important aspects of development NilssleinVolhard C 1996 Gradients that organize embryo development Scientific American August Presentation by a Nobel laureate of the exciting story of research on cytoplasmic determinants of development in fruit flies which are an important model in current developmental biology
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