Fertilisation © 2016 Paul Billiet ODWS

William Harvey (1578-1657) Sceptical about spontaneous generation Observed embryo development of: chicks in eggs deer in uterus omne vivum ex ovo Two parents must come together physically to ensure reproduction Leewenhoek’s microscope (1677) showed he was on the right track. © 2016 Paul Billiet ODWS

The spermatozoan Head 50µm Midpiece Acrosome Haploid Nucleus Flagellum Gray’s Anatomy Flagellum Mitochondria Acrosome Midpiece Head Haploid Nucleus 50µm Sperms (photomicrograph) Sperms (SEM) © 2016 Paul Billiet ODWS

Preparing the sperm cells Storage in the epididymis → Maturation Ejaculation → Activation Ascension to the ovary → Capacitation Near the oocyte → Acrosome reaction. © 2016 Paul Billiet ODWS

Maturation Storage in epididymis DNA condenses further (sperm head smaller) Cytoplasm reduced (slender sperms) Motility achieved but switched off Plasma membrane composition changes. © 2016 Paul Billiet ODWS

Activation During ejaculation 2-6 ml of secretions are added to the sperm In a set sequence Epididymis Seminal vesicle – gelatinous, fructose rich, prostaglandins Prostate - protease Urethra – alkaline pH 7-8. © 2016 Paul Billiet ODWS

Capacitation The journey from the vagina to the end of the fallopian tube The sperms become motile The secretions of the cervix change at ovulation They become sperm friendly The sperm rest at staging posts en route (crypts) The plasma membrane changes so the acrosome reaction is possible. © 2016 Paul Billiet ODWS

Acrosome reaction The acrosome releases hydrolytic enzymes Digest through the zona pellucida surrounding the oocyte. © 2016 Paul Billiet ODWS

The oocyte Human oocyte 100µm Mouse oocyte © 2016 Paul Billiet ODWS

Fertilisation sea urchin Sperm acrosomes digest surrounding jelly © 2016 Paul Billiet ODWS

Fertilisation Horse zygote Fertilisation (SEM) © 2016 Paul Billiet ODWS

Fertilisation Tip of acrosome process attaches to sperm cell receptor site © 2016 Paul Billiet ODWS

Fertilisation Vitelline layer lifts © 2016 Paul Billiet ODWS

Fertilisation Microvilli form to wrap around sperm head © 2016 Paul Billiet ODWS

Fertilisation Sperm head drawn into oocyte © 2016 Paul Billiet ODWS

Fertilisation © 2016 Paul Billiet ODWS

Fertilisation Cortical granules (vesicles) fuse with oocyte plasma membrane Cortical reaction lifts away vitelline layer Enzymes change the receptor site proteins Other sperms excluded © 2016 Paul Billiet ODWS

Cortical reaction Reaction spreads across the oocyte surface in 20s Fertilization the calcium wave © 2016 Paul Billiet ODWS

Fertilisation Sperm head drawn in Membrane disintegrates Sperm mitochondria digested © 2016 Paul Billiet ODWS

Fertilisation Vitelline layer becomes fertilisation membrane Chemically transformed by the enzymes released © 2016 Paul Billiet ODWS

Ovulation to implantation morula blastocyst zygote ovulation fertilisation implantation © 2016 Paul Billiet ODWS