1-Germ cell development, gametogenesis and fertilisation

Developmental biology

Understanding the mechanisms that control embryo development

Gene expression

Genes that are actively transcribing mRNA

Genetic equivalence

Genetic material in almost all cells is the same with the exception of immune cells which have more variation in their DNA for generating antibodies

Somatic cells

Cells of the body

Limited life

Germ line cells

Reproductive cells

Immortal

Oocytes, sperm

What cells are germ line cells derived from

Primordial germ cells

What does BMP4 stand for

Bone morphogenic protein 4

Where is BMP4 secreted from

Extraembryonic tissue

Effect of BMP4

Comes into contact with the closest cells in the epiblast

Triggers these cells to become PGCs

BMP4 receptors

Transmembrane proteins

Binding to extracellular part which triggers phosphorylation in the cytoplasmic region

Cascade

Genes turned on

What days are PGCs generated

Day 6-7

What day do the PGCs migrate into the gut

Day 8

What day do PGCs enter the genital ridges

Day 11

What do the genital ridges give rise to

Ovaries and testes

Anne McLaren’s work

Worked on PGC differentiation

Importance of RA

IVF

Lipophilic

Easily passes over the membrane

Retinoic acid

Needed for PGCs to become oocytes

Cytochrome P450

Expressed in male gonads and degrades RA

Inhibits differentiation into oocytes

Where does spermatogenesis occur

Seminiferous tubes of the testes

Order of cells in spermatogenesis

PGCs

Spermatogonial stem cells

Primary spermatocytes

Meiosis

Secondary spermatocytes

Spermatids

Effect of too much SSC proliferation

Tumour formation

Effect of too little SSC proliferation

Male infertility

Acrosome

Contains that digest proteins and sugars so the sperm can lyse the outer egg layers

Where is the sperm acrosome derived from

Golgi

Nucleus DNA content in sperm

Haploid number of chromosomes

Sperm midpiece

Contains mitochondria that produce energy for motility

Sperm flagellum

Required for propulsion

What is the name of the motion portion of the flagellum

Axoneme

Where does oogenesis occur

Ovaries

What happens when oogonia form

Mitosis

Begin meiosis

Stops at prophase 1

What stimulates division of some primary oocytes

Follicle stimulating hormone

What stage is a secondary oocyte arrested in if no fertilisation takes place

Metaphase 2

Successful fertilisation

Complete second division

Gives rise to second polar body

Zona pellucida

Thick extracellular matrix that binds sperm

Cumulus

Layer of ovarian follicular cells surrounding oocyte

What does oocyte cytoplasm contain

Proteins, ribosomes, tRNA, mRNA

Step 1 in fertilisation

Attraction and activation of sperm by contents of female reproductive tract

What secretes chemo-attractants to attract sperm in reproductive tract

Ovarian follicle

Step 2 in fertilisation

Binding of sperm to zona pellucida

What needs to be present in order for mice sperm to bind to the egg

ZP3 glycoprotein

Step 3 of fertilisation

Release of enzyme from acrosome to lyse hole in zona

Step 4 of fertilisation

Fusion of sperm and oocyte pronuclei

What happens when the sperm and oocyte pronuclei fuse

Completion of 2nd meiotic division

Chromatin of male pronucleus uncoils

Breakdown of both nuclear envelopes

Chromosomes orientate themselves on the mitotic spindle

Creation of a zygote

Hydatiform mole

Only has male chromosomes

Effect of hydatiform mole

Mass of placenta like cells

Embryo doesn’t develop

Can lead to tumours

Parthenogenetic embryos

Only has female chromosomes

Effect of parthenogenetic embryos

Sometimes organs form

Chaotic development

Grossly disorganised embryo

Prevention of polyspermy

Cortical reaction occurs after fusion

Egg releases enzymes that harden zona pellucida so no more sperm can penetrate