This disclosure provides ungulate embryonic stem cells (ESCs) derived from the inner cell mass of pre-implantation blastocysts or pluripotent cells from embryos. From an agricultural and biomedical perspectives, the derivation of stable ESCs from domestic ungulates is important for genomic testing and selection, genetic engineering, and providing an experimental tool for studying human diseases. Cattle are one of the most important domestic ungulates that are commonly used for food and bioreactors.

A method of providing a culture of oogonia stem cells comprising oogonia stem cells is provided. The method may further include culturing the oogonia stem cells with granulosa and theca cells to differentiate the oogonia stem cells into oocytes. In some embodiments, the culturing comprises including the oogonia stem cells in an in vitro follicle construct or a microcapsule comprising said granulosa and theca cells. Further described herein is a method of forming a bioengineered follicle construct capable of releasing a mature oocyte. An in vitro fertilization method using the mature oocyte is also provided.

During ageing, egg cells display a gradual loss of cohesin complexes. The cohesin loss eventually causes sister chromatids to separate prematurely, which leads to aneuploidy. The inventors engineered an artificial cohesion system, which is a complex for chromatid or chromosome tethering to reduce, for example, age-related premature separation of sister chromatids in eggs. The artificial cohesion system is a complex, which tethers chromosomes or chromatids so that e.g. the risk of aneuploidy is reduced. Said complex comprises (I) one or more first protein(s) and (II) one or more second protein(s), wherein the (I) first and the (II) second protein(s) each comprise (i) a chromatin-binding component, (ii) a protein-binding region being N-terminal of the chromatin-binding component, (Hi) a protein-binding region being C-terminal of the chromatin-binding component. The present invention also includes nucleic acid molecule(s) encoding said complex. Furthermore, several in vitro methods concerning the complex or the nucleic acid molecule(s) encoding said complex also form part of the invention.