Artificial gametes Flashcards
Imprinted loci are a barrier to?
Cloning Mammals
Generation of oocytes in vitro
The generation of artificial gametes from somatic tissue
How was Dolly the sheep produced?
1996
She was produced by SCNT
Implantation of an adult somatic nucleus into an enucleate oocyte
The blastocyst was implanted into a surrogate ewe
She was fertile (6 offspring)
She had arthritis
She died young (lung cancer)
There was no re-setting of epigenetic marks…..
WHat is somatic cell nuclear transfer?
SCNT involves removing a donor nucleus from a non-reproductive cell (often a skin cell or mammary cell) and placing it into an egg cell that has had its nucleus removed.
WHat do clones have in regards to epigenomes?
They are abnormal epigenomes - lead to variety of problems.
First reason why epigenetic problems arise in clones
First, the donor nucleus comes from a differentiated cell with epigenetic tags already in place.
These tags keep genes switched on or off and allow the cell to perform its responsibilities.
After the donor nucleus is transferred, the egg does its best to erase the epigenetic tags.
But the process is faulty, delayed and incomplete.
Second reason why epigenetic problems arise in clones
Second, the epigenetic tags in the donor nucleus have been copied several times over.
While the machinery that copies the DNA code is faithful (it makes about one error in half a billion), the epigenetic copying machinery is sloppy.
In some cases, its error rate can be as high as 1 in 25.
Miscopied epigenetic tags on even a very small number of imprinted genes in the donor nucleus could have serious consequences during the development of the resulting embryo.
Potential applications of artificial gametes
Fertility treatment
Genetic Disorders
Research Tool
Endangered species
Describe artificial gametes
Artificial gametes are mature germ cells (sperm and eggs) generated
-in vitroby specification and maturation of their natural diploid precursors, the primordial germ cells (PGCs), or
- by directed differentiation of pluripotent cells to the germ-cell lineage.
How are artifical gametes generated?
Artificial gametes are created using advanced biotechnology techniques and aim to mimic the functions of natural gametes, such as sperm and egg cells.
The dream: Artificial Gametes as a fertility treatment
- Take somatic cell.
- Perform SCNT and induce embryo development in vitro
- Extract embryonic stem cells from blastocyst
- Induce gametogenesis in vitro
- Use functional gamete to fertilise partner’s egg or sperm
- Develop into embryo
- Implant into mother
5-7 = Normal IVF
Why is it importatn that scientists have been able to recreate the process of egg cell formation in lab using stem cells?
This is important because it allows researchers to better understand how eggs are formed and can also be used for regenerative medicine.
Man-made mouse eggs - Reconstitution in vitro of the entire cycle of the mouse female germ line.
Mature oocytes were made from
1. Embryonic stem cells
2. Induced stem cells
- Embryonic fibroblasts
- Adult tail tip fibroblast
26 fertile pups were born
Mature Oocytes then used to generate embryonic stem cells
The full-cycle in vitro
Reconstitution in vitro of the entire cycle of the mouse female germ line. - Outcome?
The scientists were able to create fully functional egg cells from both embryonic and adult stem cells and even created new stem cell lines from the eggs they produced.
This new technique can be used to study how totipotency works and could potentially be used to create eggs from other animals in the future.
How to make a mouse egg
Look at slides and listen to lecture
Oocyte production from pluripotent stem cells - To reconstitute the entire process of oogenesis in vitro, the culture period was divided into three sections in this study - describe each section
(1) in vitro differentiation (IVDi),
(2) in vitro growth (IVG)
(3) in vitro maturation (IVM), in which oogenesis would proceed to primary oocytes in the secondary follicle, fully grown germinal vesicle oocytes and metaphase II (MII) oocytes, respectively (Fig. 1a).
Hikabe 2016
WHat have researcher previously shown in regards to differentiating mouse pluripotent stem cells
The researchers previously showed that it is possible to differentiate mouse pluripotent stem cells into primordial germ-cell-like cells that can become functional oocytes.
However, the transformation from germ cell to gamete required transplantation into adult female mice.
Man-made mouse eggs
A culture system for generating fertilization-competent mouse oocytes from fibroblast-derived pluripotent stem cells in about 30 days.
Fully in vitro method, primordial germ-cell-like cells are co-cultured with female gonadal somatic cells, and hormones, inhibitors and other factors are administered at key stages to stimulate the development of a follicular environment and to coordinate stages of the egg cell’s maturation
Only 3.5% oocytes went on to make pups (compared with 60% when cells were implanted into surrogate mice to develop mature oocytes)
So not quite ready for application in humans…
What about imprinted loci?
Listen to lecture on this slide
Choose a method of generating artificial gametes
Has there been any opportunity to ‘reset’ epigenetic marks?
WHat might the impact of this approach be on imprinted loci?
What (if anything) could be done to ameliorate any deleterious effects?
Self-assessment questions
What is the imprinting status of the H19 locus in a MII oocyte made in vitro?
Describe the methylation status of a paternally-imprinted locus in an artificial gamete made via a method of your choice.
