Lecture 8 Fertilisation In-Vivo and In-Vitro Flashcards
How do sperm know where to go in the female reproductive tract?
Once in the uterus, sperm are attracted to the oocyte by thermotaxis (higher temperature) and chemotaxtis (oocyte-secreted factors)
Where does sperm capacitation occur and what happens during the process?
Occurs as the sperm is travelling in uterus and Fallopian tubes.
Activation of PKA causes hyperpolarisation of tyrosine residues on proteins in sperm, leading to ionic influx which causes hyperactivation of sperm motility and preparation for the acrosome reaction
What is the acrosome reaction?
Sperm releases hydrolytic enzymes from their acrosome, this degrades the cumulus cells allowing close contact with zona pellucida.
Furthermore sperm reveals protein called acrosomal process which fuses membrane with oocyte
What occurs during oocyte fusion?
Membranes of acrosomal head and oocyte fuse, entry of sperm nucleus. Cortical granules in the egg cytoplasm gets exocytosed to release proteins into space between ZP and oocyte, which solidify and prevent other sperm penetrating.
What is the mechanism of intracellular Ca2+ oscillations in the oocyte?
Sperm releases phospholipase C zeta (PLC zeta) and converts PIP2 to IP3. IP3 causes Ca2+ release from ER, leads to chromosome separation (stops block on meiosis) and cell proliferation. Ca2+ oscillations Continues until pronuclei forms
How to obtain oocytes in Assisted Reproductive Technologies via hormonal alterations?
FSH to stimulate follicle maturation. Low FSH increases chance of pregnancy and live baby, better than high FSH causing hyperstimulation of ovaries.
Also require GnRH antagonist to inhibit GnRH secretion thus prevent LH spike so no ovulation before oocyte is ready
In intracytoplasmic sperm injection, how do we ensure sperm is mature?
Need to ensure sperm has undergone capacitation and acrosome reaction, thus mature sperm in dish with Ca2+, and progesterone
What are the growth factors present in vivo acting on embryo?
Autocrine factors (embryo secretes itself, which drives cell proliferation and survival). Paracrine and endocrine factors from mother, with the same effects.
What are the disadvnatages of embryo culture in vitro compared to in vivo?
Cultured in simple media, so absence of maternal signalling molecules. Furthermore large volume dilutes embryo autocrine signalling. This suboptimal culture medium causes poor in vitro development.
How can we improve in vitro embryo culture?
Add endogenous/exogenous signalling molecules, this will increase rates of implantation and pregnancy.
