Identification of a new protein essential for ovule and sperm formation

Identification of a new protein essential for ovule and sperm formation

Researchers reported that the protein RingoA is a key regulator of meiosis--the cell division process that gives rise to ovules and sperm for sexual reproduction in mammals.

In contrast to the cells in the rest of the body, sex cells hold half the number of chromosomes (they are haploid) as a result of this special kind of cell division. In meiosis, a precursor cell --primordial germ cell-- produces four spermatozoids during spermatogenesis, while only one oocyte is formed during oogenesis (the other three cells die during the process).

Mice deficient in RingoA, generated are apparently healthy but both sexes are completely sterile. The scientists have discovered that RingoA is a key activator of Cdk2, the protein kinase with which it forms a complex required for meiosis. In fact, the genetic mouse model deficient in Cdk2, which was reported 12 years ago is also viable but sterile and shows the exact same alterations in meiosis as those observed by the new work.

The study demonstrates that RingoA is active at telomeres--structures that protect the ends of chromosomes and where Cdk2 is also found. During meiosis, telomeres allow chromosomes to attach to the nuclear membrane, thus allowing them to exchange DNA fragments. This recombination of chromosomes is an essential feature of meiosis.

Without the RingoA-Cdk2 complex, the telomeres of the chromosomes do not tether to the membrane but rather float in the nucleus, leading to chaotic recombination. The breaks in DNA needed for fragment exchange are not repaired and thus meiosis is not completed. Consequently, sex cells are not formed.