Fertilization Structure of Gametes External vs Internal Fertilization Sperm Attraction Sperm Binding to Egg and subsequent fusion Activation of Egg Fusion of Nuclear material

What is the purpose of Fertilization? Transmit genes from Parent to offspring Initiate functions in egg cytoplasm that

permits development to occur

Common Elements of Fertilization Contact and Recognition between Sperm and

Egg Regulation of sperm entry Fusion of Genetic Material Activation of egg metabolism to start

development

Sperm Cell First observed by

Leeuwenhoek (Sperma, Semen= seed)

Homunculus Believed to contain all

information for embryo Work demonstrated that

Semen required sperm cells for fertilization of egg

1876, Hertwig and Fol demonstrate sperm entering egg and fusion of their genetic material. Studies in Sea Urchin

Spermatogenesis

Sperm Structure Haploid Nucleus and

Acrosome. Flagellum- axoneme “9+2” arrangement Dynein-Force

generator! Mitochondria

Egg Cell- Oocyte All material needed for beginning of growth

and development. Large cytoplasm Synthesis and absorption of proteins (yolk) Other cytoplasmic factors:

Nutritive proteins Ribosomes and tRNAs Accumulated mRNA Morphogenic factors (transcription and paracrine

factors) Protective elements against UV, give egg bad

taste, and yolk contains antibodies.

Oocyte Structure

Fertilization patterns External Internal

Overview of External: Sea Urchin Many Marine animals use this method Chemotaxis main targeting mechanism. Species specific sperm attraction and species

specific sperm activation.

Overview of Internal: Mammals Difficult to study Sperm Heterogeneous at first. Both gametes use biochemical and

mechanical means to reach site of Fertilization(Ampula).

Translocation Capacitation

External Sperm Attraction to Egg Species specific Resact (14 a.a.) Regulates Calcium influx Increases ATP formation from Mitochondria:

increase flagellar motive force.

Internal: Sperm attraction to Egg Regionally specific molecules-motility and

capacitation During capacitation, flagellum hyperactive Directional cues: Heat and Chemotaxis

(progesterone).

Capacitation of Mammalian Sperm

External: Recognition/fusion Initial binding to Egg Jelly,

Bindin Species specific EBR-1 interacts with Bindin. Acrosome reaction Once membranes fuse

(Bindin), polymerization of actin in Egg: Fertilization cone.

Actin from gametes form a connection, sperm nucleus and tail pass into egg cell.

All regions of Egg can interact with sperm.

Internal: Recognition/fusion Sperm binds to

glycoprotein matrix of Zona Pellucida (ZP).

Second interaction occurs with ZP via SED1 protein of sperm

Final interaction between proteins (ADAM3, ADAM2) interact with ZP3. Crosslinking of galactosyltransferasesCa influx and acrosome reaction

Internal Recognition/Fusion Interaction slightly

different Acrosomal fusion:

proteolytic enzymes Secondary contacts:

Zonadhesion Other inner acrosomal

proteins bind to ZP2. Fusion not clear.

Possible interaction with CD9 of oocyte.

External: Block of Polyspermy Effects of Polyspermy Fast block

Membrane potential switches from negative to positive

Transient (1 min) Slow block

Shortly after fast block Cortical Granules Increase in Calcium,

from internal stores. Fertilization envelope

Slow-block for Polyspermy

Internal: Block of Polyspermy No observed fast block Slow block- similar to Sea Urchin N-acetylglucosaminidase cleave NAG from

ZP3. Other proteins cleave proteins from cell

surface.

External and Internal: Activation of Egg Calcium-major signal. Releases inhibitors from

stored mRNAs-Maskin protein

IP3 created by phospholipase C, DAG also created

G proteins and Src induce PLC activity

IP3 causes Ca release from ER

Ca required for Na/H pump that regulates Egg internal pH.

Mammals similar…multiple waves of Ca release.

External: Fusion of Genetic material. Nucleus/centriole

separate from mitochondria and tail.

Nuclear envelope vesiculates into small packets. Expose chromatin

Phosphorylation of nuclear lamin and histones-starts early

Pronucleus rotates 180o, placing centriole between sperm and egg pronuclei

Zygote nucleus formed.

Internal: Fusion of Genetic material. Takes longer in mammals Sperm DNA bound by

Protamines (disulfide bonds hold complex together)

Glutathione reduces protamine-relax chromatin

Ca release in waves. As pronuclei meet, DNA

condenses into chromosomes and orient on common mitotic spindle.

True zygote nucleus: 2 cell stage.