Genes & Development Part 1: The Debate

Gene Theory Nuclear vs Cytoplasmic Inheritance Is control over development tied to the nucleus (chromatin) or to the cytoplasm? T Boveri & EB Wilson – Nuclear control TH Morgan – cytoplasmic control

Gene Theory Boveri’s support for nuclear control Polyspermy in sea urchins Embryos developing with multiple sets of chromosomes had defects Chromosome number (nucleus) important

Gene Theory EB Wilson & Nettie Stevens XO & XY = male XX = female Correlated chromosome absence/presence with sex determination Drosophila XO & XY = male XX = female

Gene Theory TH Morgan Chief proponent of cytoplasmic inheritance 1910 his lab accumulated data that supported chromosomal inheritance Discovered and characterized Drosophila white (w) mutant (has white eye) w phenotype had sex linked inheritance pattern – w male x wt female  F1 all wt offspring wt male x F1 female  only w-eyed males

Gene Theory Morgan’s conversion Since mutation was inherited together with the X chromosome, Morgan accepted the chromosomal inheritance theory wholeheartedly Went further to hypothesize that genes were arranged linearly on chromosomes

Gene Theory Nettie Stevens was a graduate student with Morgan at Columbia University Did postdoctoral studies with Wilson Wilson and Morgan were very good friends HOMEWORK: go online to devbio website and read material at website 4.1 Quiz on Monday!

Geneticist vs Embryologist Wilson and Morgan were embryologists Their combined support of the chromosomal inheritance theory brought more geneticists into embryological systems Influx of geneticists was disdained by classical embryologists EE Just, H Spemann, F Lillie et al

Geneticists vs Embryologists Embryologists set forth 3 criteria that must be satisfied by genetics in order to accept the dominance of the gene theory How can identical chromosomes give rise to differentiated cell types Demonstrate that genes control early developmental processes Explain environmentally influenced phenomena such as temperature dependent sex determination

Gene Action in Early Development Brachyury (brachy = short; ury = tail) Salome Gluecksohn-Schoenheimer Characterized the early embryos of mice with the Bra mutant Adult phenotype – deformed tails/pelvis Embryo phenotype – lack posterior notochord

Gene Action in Early Development Drosophila wing mutations Conrad Waddington Demonstrated defects in the imaginal disk formation

Gene Action in Early Development Both Waddington’s and Gluecksohn’s experiments established that genes did effect early developmental processes 1 down 2 to go

Genomic Equivalence Explain differential gene expression Establish that genomes of differentiated cells are equivalent Determine why only certain genes are expressed

Genomic Equivalence Regeneration of newt lens Remove lens Iris cells trans-differentiate to regenerate the lens Series of changes in iris cells Ribosome synthesis DNA replication mitosis exocytose melanosomes form a group of undifferentiated cells turn on crystalline genes

Genomic Equivalence Cloning – the ultimate equivalence test Generate an entire, normal animal from a the nucleus of a somatic cell Requires that somatic nucleus is totipotent

Genomic Equivalence Cloning of the frog Xenopus laevis by nuclear transplantation of albino gut cell nuclei into enucleated, wt oocytes. All progeny are albino & female

Genomic Equivalence Procedure for cloning frogs from differentiated nuclei. Successful cloning requires serial passage of donor nuclei through activated oocytes.

Genomic Equivalence Enucleate oocyte Isolate donor nuclei Inject nuclei into oocyte

Genomic Equivalence Totipotency of donor nuclei appears to decline with age

Genomic Equivalence Dolly 1st cloned mammal Mammary epithelial cell Cultured and maintained in G0 Fused with enucleated oocyte by electric shock 1/434 success rate (0.23%)

Genomic Equivalence Cloned Mice