Chapter 11 Germ cells, fertilization and sex

Chapter 11 Germ cells, fertilization and sex The development of germ cells Gametes: eggs and sperm Determination of the sexual phenotype Sex chromosomes

Germ cell formation Divide less often Meiosis Primordial germ cell -special cytoplasm Germ plasm-polar granules, pole plasm Irradiated with UV light (RNA and proteins) Induce specification Specified Migration into the gonads Fig. 11-1, transplanted pole plasm

Figure 16.5 Localization of germ cell-less gene products in the posterior of the Drosophila egg and embryo

Germ plasm specification Oskar—organization and assembly of the pole plasm mRNA-posterior pole—3’ untranslated region Fig. 11-4, oskar alone is sufficient to initiate the specification of germ cells

Formation of germarium large germ cells are surrounded by smaller somatic cells , then the anterior somatic cells separate into 16 clusters about 10 disc-shaped cells (form the terminal filaments) Large eggs: arrest--double the diploid number of genes Insect—amplification of genes, yolk protein—liver, fat bodies Nurse cells

Figure 16.4 Formation of 16 interconnected cystocytes in Drosophila

Figure 16.4 Formation of 16 interconnected cystocytes in Drosophila (Part 1)

Figure 16.4 Formation of 16 interconnected cystocytes in Drosophila (Part 2)

Asymmetrical distribution of P granules in germline cells PGL-1—mRNA metabolism PIE-1: repress transcription Fig. 11-2

Figure 16.2 Inhibition of transcription in germ cell precursors of Caenorhabditiselegans

Germ-cell formation in the mouse Fig. 11-3, PGCs (Fragilis--TM), stella and Oct-4

Figure 16.8 Expression of Oct4 mRNA correlates with totipotency and ability to form germ cells in mammals

Figure 16.9 Photomicrograph of a section through a mouse teratocarcinoma, showing numerous differentiated cell types

Figure 16.10 Protocol for breeding mice whose genes are derived largely from tumor cells

Primordial germ cell migration in mouse White spotting: Kit receptor Migrating germ cells Steel: Ligand In the cells along which the germ cell migrate Fig. 11-5

Figure 16.14 Primordial germ cell migration in the mouse

Figure 16.11 Migration of germ cells in the Drosophila embryo Germ cell—extragonadal origin, migrate to reach the somatic gonad

Figure 16.11 Migration of germ cells in the Drosophila embryo (Part 1)

nanos, pumilio mutants stall at the outer gut surface differentiate prematurely---act as complete migration to the somatic gonads nanos target: RNA binding protein Sex lethal (Sxl)---splicing and translational regulation

PGC migration----Genes and mechanisms Genetic screen—somatically expressed genes Guidance (cues): Wunen: repulsive signal (exclude migrating pole cells from wrong places) Misexpression wunen: transform a tissue permissive to PGC to repulsive one Phosphatidic acid phosphatase 2 (transmembrane protein) Columbus: factor (gonadal mesoderm) attracts pole cells Misexpression Columbus—attract PGCs to tissues other than gonadal mesoderm 3-hydroxy-3-methylglutaryl coenzymeA reductase (cholesterol biosynthesis in human, Geranyl-geranyl group to Chemoattractant)

Figure 16.12 Specification and migration of germ cells in zebrafish

Meiosis produces haploid cells without replication Fig. 11-6

Oogenesis and spermatogenesis in mammals-I Fig. 11-7

Oogenesis and spermatogenesis in mammals-II Sexually mature complete Sexually mature at puberty Fig. 11-7

Figure 16.19 Regulation of the mitosis/meiosis decision in the adult germline of C. elegans (Part 1)

Figure 16.26 Retinoic acid (RA) determines the timing of meiosis and sexual differentiation of mammalian germ cells (Part 1)

Figure 16.26 Retinoic acid (RA) determines the timing of meiosis and sexual differentiation of mammalian germ cells (Part 2)

Paternal and maternal genomes Fig. 11-8

Imprinting of genes controlling embryonic growth Reversible process, DNA methylation IGF-2: placenta—growth hormone—large offspring Fig. 11-9 parental-conflict theory

Chapter 11 Germ cells, fertilization and sex