In Vitro Gametogenesis Flashcards
(16 cards)
What is In Vitro Gametogenesis?
- Recreating germ cell development in a lab using induced pluripotent stem cells (iPSCs)
- Cells are cultured to become primordial germ-cell-like cells (PGCLCs) which can then differentiate into immature oocytes or spermatogonia
Who can IVG help?
- Same-sex couples
- Infertile cancer patients
- Theoretically anyone
What are some other potential applications of IVG?
- Understanding germ cell development (ethical, no preg women)
- Endangered species preservation
- Medical advancements (potential ART development + infertility treatments)
- Infertility research (explore why IVG-derived gametes may differ from natural ones)
How has IVG been looked at in Mice?
- Reconstitution of the entire female germ line cycle in vitro, resulting in fertile mouse eggs produced from ESCs and iPSCs
- From the mature oocytes, 26 fertile pups were born and the oocytes were used to generate new ESCs, completing the cycle
What was the process for IVG in mice?
- Pluripotent stem cells → Cultured to form primordial germ-cell-like cells (PGCLCs)
- Co-culture with ovarian somatic cells → Required to induce secondary follicle development
- Maturation into tertiary follicles and mature oocytes
- Fertilization and implantation into a foster mother
What is the challenge of the IVG process in mice?
- The process required an oocyte from another mouse.
- Scientists aimed to develop a fully synthetic approach without biological surrogates.
How was the need for surrogate mice for IVG solved?
The process was refined into three key stages:
- ESCs/iPSCs cultured into PGCLCs
- PGCLCs co-cultured with gonadal somatic cells from a 12.5-day-old embryo, forming a reconstituted ovary (R-ovary)
- In vitro differentiation:
After 11 days → Germinal vesicle-stage oocyte
Followed by in vitro maturation (IVM) → Metaphase II oocyte
What is the flaw of the removed-surrogate IVG mice study?
- Only 3.5% of embryos developed into pups compared to 60% when implanted into a foster mother
What were the Genetic and Epigenetic Concerns of this study?
- Some mice exhibited differences in DNA methylation at key imprinting genes (H19 and IGF2r) though no deaths were observed
(overall though imprinting was sufficiently maintained)
What is the current timeline for IVG in humans?
- 2014: Immature human eggs successfully grown from stem cells.
- 2018: Complete in vitro development of human oocytes from primordial follicles taken from adult women.
- However, primordial follicle formation still occurred in vivo, limiting full artificial gametogenesis.
This could help women who produce primordial follicles but struggle to reach mature oocytes.
What xenogenic approach was taken to culture human PGCLCs?
2018- mouse embryonic ovary cells used to culture human {GCLCs
- The IVG-derived human oogonia exhibited the key maturation indicators such as:
1. Genome wide DNA demethylation
2. Imprint erasure and partial demethylation
3. Reactivation of the inactive X chromosome
What is the difference in time frames between oocyte development in vivo/in vitro?
In vitro = 120 weeks
In vivo = 11 weeks
What IVG studies have been conducted in primates?
- Mouse embryos have been used to create a reconstituted ovary supporting cynomolgus monkey PGCLC development.
- However, progress in primates lags behind mouse studies.
Why is there less focus on spermatogenesis?
- Generally no shortage of sperm so demand for in vitro sperm production is lower
What were the findings of a study which did look at spermatogenesis?
**2015 study showed that mouse germline stem cell-like cells (GSCLCs) could:
1. Colonize adult testes
2. Contribute to spermatogenesis
3. Produce fertile offspring
BUT exhibited aberrant DNA methylation at critical regulatory sites
What are the ethical considerations of IVG?
- Safety and offspring normality - primates before humans
- Genetic and epigenetic integrity
- Could ‘redefine’ reproductive norms requiring broad discussions
- ‘Designer baby hysteria’ - selecting specific traits in children
- Ableism seen with IVG combined with gene editing - could eradicate heath conditions
