Embryo transfer and stem cells Flashcards
What is embryo transfer?
Transfer of an embryo, derived from the mating of
genetically proven, valuable parents, into a fertile
but less valuable recipient (host) female who carries
the pregnancy to term & offspring to weaning.
Neither AI nor ET are permitted in Thoroughbred
horses
What are the steps in embryo transfer?
- Selection of genetically superior male and
female donors - Superovulation of donor female (not horse)
- Insemination of donor female with semen
- Recovery and identification of viable
embryo(s) from donor female - Synchronisation of recipients with donor
female - Transfer of embryos into synchronised
recipient(s)
What are the advantages and applications of embryo transfer?
- Maximises reproductive efficiency of high quality animals.
- Circumvents female infertility due to uterine tract abnormalities.
- Enables breeding from injured or old animals.
- Enables athletic females to remain working e.g. showjumping mare.
Ideally where should the recipient be in their cycle compared to the donor?
The recipient is a few days behind the donor’s cycle
— ideal
— means embryo is transferred into a similar uterine
environment
— gives the embryo time to “settle in” and release its
maternal recognition of pregnancy signal
— prevents lysis of CL
Remember you can always chill and freeze the embryo and wait for the recipient to be at a suitable time in their cycle for implantation.
Outline the method for synchronising donor and recipient cycles?
Administration of progesterone followed by Withdrawal of progesterone OR Lysis of CL with PGF2a Causes a Reduction in progesterone which Allows follicle development to begin
How does giving progesterone then withdrawal of progesterone cause follicle development?
Progesterone suppresses hypothalamus / pituitary axis and therefore LH and FSH, its withdrawal allows a rebound effect, stimulating follicular development and eventually ovulation.
Methods of synchronising donor &
recipient cycles*
Progesterone withdrawal
— Mimicks lysis of CL and decline of progesterone
— gonadotrophins released, leading to follicular
development
— withdrawal in recipients happens a few days behind donor
— results in the recipient cycle being a few days behind the donors cycle
What is the disadvantage of using prostaglandins over progesterone to synchronise donor and recipient cycles?
Reliant on knowing where the animals are in their cycle so close monitoring required.
What is superovulation and in what species is it possible?
Superovulation results in the stimulation (FSH) & ovulation of multiple oocytes
. in the cow it’s a common procedure
. in the horse it’s not currently possible
What gonadotrophins are used to super ovulate cows?
*Equine chorionic gonadotrophin (eCG) or pregnant mare serum gonadotrophin (PMSG) *Pituitary follicle stimulating hormone (FSH) porcine, equine, ovine *Human menopausal gonadotrophin (hMG)
Why must you be gentle when manipulating the cervix during ET?
— Rough handling results in PGF2a release which lyses
corpus luteum
— CL lysis leads to decline in progesterone
— recipient returns to oestrus & uterine environment
becomes hostile
— pregnancy is lost
What are stem cells?
Unspecialised cells with capacity to self-renew for long periods. . Self-renewal: ability of stem cells to divide and maintain an undifferentiated state . They have the capacity to differentiate into specialised cell types (e.g: muscle cells, neural cells, haematopoietic cells, etc)
What does totipotent mean?
Able to form entire organism. e.g zygote
What does pluripotent mean?
Able to form all body cell lineages including germ cells.
e.g. embryonic stem cells
What does multipotent mean?
Can form multiple lineages that constitute an entire tissue or tissues.
e.g. haematopoietic stem cells
What are embryonic stem cells?
Embryonic Stem cells come from the embryo. They have the ability to form virtually any type of cell found in the body, but are not capable of developing into a whole new organism.
