germ cells
DESCRIPTION
Germ Cells. Specification Migration Meiosis Gamete Formation. Germ Cell Specification: Germ Plasm. Theodor Boveri (1862-1915) Centrifugation and displacement of first cleavage. Germ cell specification: Drosophila. Pole cells germ cell-less ( gcl ) polar granule component ( pgc ) - PowerPoint PPT PresentationTRANSCRIPT
Germ Cells• Specification• Migration• Meiosis• Gamete Formation
Germ Cell Specification: Germ Plasm• Theodor Boveri (1862-1915)• Centrifugation and displacement of first cleavage.
Germ cell specification: Drosophila• Pole cells• germ cell-less (gcl)• polar granule component (pgc)• Oskar, Vasa, Aubergine
Germ cell specification: Drosophila
Fig 16.4
Germ cell specification: Frogs/Fish• Germ Plasm located in
vegetal pole.• Nanos• Vasa
Germ cell specification: mammals• Wnts make cells competent
for BMPs• BMPs Induce blimp1 and
prdm14– Regulate Sox2, Nanog, and
Nanos3.
Cell Migration: Drosophila• Movement into posterior
midgut• Gut endoderm triggers
migration into visceral mesoderm
• PGCs split, each will associate with developing gonad.
• Germ cells migrate to gonads.– Attraction/repulsion
• HMG-CoA reductase
Cell Migration: Drosophila• Dpp- BMP2/4 homolog• Bag of Marbles (Bam)
Cell migration: Zebrafish• Sdf1 and CXCR4
Figure 16.12
Cell migration: Frogs
Fig. 16.13
Cell migration: Mammals
Fig. 16.14
Cell migration: Bird and Reptiles• Germinal crescent• Sdf1/CXCR4
Fig. 16.15 and 8.9
Cell migration: Bird and Reptiles• Germinal crescent• Sdf1/CXCR4
Fig. 16.15 and 8.9
Meiosis
• Chromatin condenses• Spindle forms• Nuclear membrane
breaks down• Homologous
chromosomes pair• Chromosomes attach
to spindle as tetrads
Prophase I
• While chromosomes are paired, crossing-over can occur
Homologous pairs form tetrads
Tetrad
• Tetrads line up at equator• Homologous chromosomes
face opposite poles
Metaphase I
• Homologous chromosomes separate• Pulled apart by spindle shortening• Sister chromatids stay together
Anaphase I
• Chromosomes reach poles• Nucleus may re-form• Spindle breaks down• Cell divides (cytokinesis)• Two haploid daughter cells
(N chromosomes)
Telophase I
Haploid cell
Haploid cell
• Daughters have one chromosome from each pair• Haploid: no homologous pairs• Still two copies of each chromosome (sister chromatids)
Meiosis I
diploid cell:N = 22N = 4
haploid cell:2 chromosomes
• Very similar to mitosis• Sister chromatids separate
Meiosis II
Telophase I Metaphase II Anaphase II Telophase II CytokinesisProphase IIInterphase II
Aa
a
A
a
A
A
A
a
a
b B B
b
bb
b
B B
B
• Four haploid gametes• One chromosome set each• Genetically different
Results of meiosis
Gamete Maturation: Frogs
• Vitellogenin• Progesterone
Fig. 16.22 and 16.25
Gametogenesis in MammalsFemale oogenesis• Meiosis initiated once in
finite population of cells• One gamete produced• Completion of meiosis
delayed months/years• Meiosis arrested in first
prophase.• Differentiation of gamete
occurs while diploid• All chromosomes exhibit
equivalent transcription
Male spermatogenesis• Meiosis initiated continuously
in mitotic stem cell• Four gametes produced• Meiosis completed in days or
weeks• Meiosis and differentiation
proceed continuously w/o cell cycle arrest
• Differentiation of gamete occurs while haploid
• Sex chromosomes excluded from recombination and transcription
Gametogenesis in Mammals
• Fig. 16.26
Gametogenesis in Mammals
• Fig 16.27
Spermiogenesis
Mammalian Oogenesis• Gonadotropin-releasing hormone (GRH)• Follicle –stimulating and lutenizing hormones (FSH and LH)