Fertilization Structure of Gametes External vs Internal Fertilization Sperm Attraction Sperm Binding to Egg and subsequent fusion Activation of Egg Fusion of Nuclear material
Dec 17, 2015
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.