1. Germ Cells
Specification
Migration
Meiosis
Gamete Formation

2. Germ Cell Specification: Germ Plasm
Theodor Boveri ( )
Centrifugation and displacement of first cleavage.

3. Germ cell specification: Drosophila
Pole cells
germ cell-less (gcl)
polar granule component (pgc)
Oskar, Vasa, Aubergine

4. Germ cell specification: Drosophila
Fig 16.4

5. Germ cell specification: Frogs/Fish
Germ Plasm located in vegetal pole.
Nanos
Vasa

6. Germ cell specification: mammals
Wnts make cells competent for BMPs
BMPs Induce blimp1 and prdm14
Regulate Sox2, Nanog, and Nanos3.

7. 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

8. Cell Migration: Drosophila
Dpp- BMP2/4 homolog
Bag of Marbles (Bam)

9. Cell migration: Zebrafish
Sdf1 and CXCR4
Figure 16.12

10. Cell migration: Frogs
Fig

11. Cell migration: Mammals
Fig

12. Cell migration: Bird and Reptiles
Germinal crescent
Sdf1/CXCR4
Fig and 8.9

13. Cell migration: Bird and Reptiles
Germinal crescent
Sdf1/CXCR4
Fig and 8.9

14. Meiosis

15. Prophase I Chromatin condenses Spindle forms
Nuclear membrane breaks down
Homologous chromosomes pair
Chromosomes attach to spindle as tetrads

16. Homologous pairs form tetrads
While chromosomes are paired, crossing-over can occur
Tetrad

17. Metaphase I Tetrads line up at equator
Homologous chromosomes face opposite poles

18. Anaphase I Homologous chromosomes separate
Pulled apart by spindle shortening
Sister chromatids stay together

19. Telophase I Chromosomes reach poles Nucleus may re-form
Haploid cell
Chromosomes reach poles
Nucleus may re-form
Spindle breaks down
Cell divides (cytokinesis)
Two haploid daughter cells (N chromosomes)
Haploid cell

20. Meiosis I Daughters have one chromosome from each pair
Haploid: no homologous pairs
Still two copies of each chromosome (sister chromatids)
diploid cell:
N = 2
2N = 4
haploid cell:
2 chromosomes

21. Meiosis II Very similar to mitosis Sister chromatids separate
Telophase I
Interphase II
Prophase II
Metaphase II
Anaphase II
Telophase II
Cytokinesis

22. Results of meiosis Four haploid gametes One chromosome set each
Genetically different A a b B

23. Gamete Maturation: Frogs
Vitellogenin
Progesterone
Fig and 16.25

24. Gametogenesis in Mammals
Female oogenesis
Male spermatogenesis
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
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

25. Gametogenesis in Mammals
Fig

26. Gametogenesis in Mammals
Fig 16.27

27. Spermiogenesis

28. Mammalian Oogenesis Gonadotropin-releasing hormone (GRH)
Follicle –stimulating and lutenizing hormones (FSH and LH)