Munkácsy Mihály: Poros út (Dusty road) II. Munkácsy Mihály: Poros út (Dusty road) I.

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Fertilization, cleavage Homeobox genes

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GnRH (LHRH)

LH FSH E P every month 10-15 follicles enter the cycle - only 1 ovulates! -

FSH - 200-300 million spermatozoa 300-500 reach the site of fertilization - 1-3 mm/minute

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6-7 months!! 3

Fertilization Spatium perivitellinum

- capacitation - activation in female genital tract, glycoprotein and protein coat removed (7h) - passes through corona radiata cells - acrosome reaction - species specific receptors for spermatozoa trypsin-like enzymes, acrosin - crosses the zona pellucida - fusion of the sperm cell membrane and membrana vitellina, the head and fibrous structures of tail enter the oocyte - cortical and zona reaction prevents polyspermia - Ca++ wave 2. meiotic division resumes - perivitellin space - spermatozoon brings centriole and essential enzymes metabolic activation, transcription of preformed RNA → Embryogenesis starts 4

- the 2nd meiotic division finishes: definitive oocyte and 2nd polar body - male and female pronucleus, DNA replication (but the pronuclei do not unite) - mitotic spindle, (2x23 chromosomes, each with 2 chromatids

- 1st division – 2-cell stage The main results of fertilization 1. diploid chr. No. restored 2. determination of sex 3. initiation of cleavage

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spermatozoa after the acrosome reaction

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1st week: • morula • blastocyst • implantation begins •2nd week : • bilaminar germ disk • implantation finished

•3rd week: • gastrulation • trilaminar germ disk

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Cleavage

blastomeres 2 cells: 30 h

4 cells: 40 h

compaction: 8-cell stage (E-cadherin)

polarization: apical cytocortex inner basolateral surface

inner cell mass: embryo outer cell mass: trophoblast (placenta!) 12-16 cells: 3rd day 8

fluid penetrates

late morula: 4th day

blastocyst: 5th-6th day polar trophoblast embryoblast blastocyst cavity mural trophoblast zona pellucida 9

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HOX (homeobox) genes - 1984 invertebrates – max. 13 HOX genes vertebrates – 3-8 copies (clusters) of max. 13/chromosome HOX genes mammals: 39 HOX genes, in 4 clusters (a,b,c,d,parallel series) - contain homeobox domain (conservative, 180 bp) that codes the homeodomain protein segment (60 AA) regulating gene expression

human: HOXa13: mutant stop-code: defective fingers and uterus

- defines the body pattern along the A-P axis, creates diversity - these genes are responsible for morphogenesis, expressed in sequences that correlate with development of specific regions

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HOX GENES: Mutation in Michigan Family

Defects: thumbs and toes Women: uterine abnormalites & sterility DNA examination: Mutation present in HOXa13 Dickman, 1997. Science 245: 1568

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Mouse experiment: HOXa3 – voice box, thyroid, parathyroid glangs, thymus HOX d3 – atlantooccipital joint Analogous HOX genes can replace the proper function on a different chromosome

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VICTOR VASARELLY VÁSÁRHELYI GYŐZŐ 1908-1997

OP-ART

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