Cystathionine β-synthase is required for oocyte quality by ensuring proper meiotic spindle assembly

Poor oocyte quality is detrimental to fertilization and embryo development, which causes infertility. Cystathionine β-synthase (CBS) is one of the key enzymes modulating the metabolism of homocysteine (Hcy). Studies have shown that CBS plays an important role in female reproduction. However, the role of CBS in regulating oocyte quality during meiotic maturation still needs further investigation.

Immunohistochemistry, immunofluorescence, drug treatment, western blot, cRNA construct and in vitro transcription, microinjection of morpholino oligo and cRNA were performed for this study.

We found that CBS was expressed both in human and mouse oocytes of follicles. In mouse oocytes, CBS was distributed in the nucleus at germinal vesicle (GV) stage and localized to spindle from germinal vesicle breakdown (GVBD) to metaphase II (MII). The expression of CBS was reduced in ovaries and oocytes of aged mice. CBS depletion resulted in meiotic arrest, spindle abnormality and chromosome misalignment, disrupted kinetochore-microtubule attachments and provoked spindle assembly checkpoint (SAC). CBS was disassembled when microtubules were disrupted with nocodazole, and co-localized with the stabilized microtubules after taxol treatment. Furthermore, CBS depletion decreased the acetylation of α-tubulin.

These results reveal that CBS is required for the acetylation of α-tubulin to ensure proper spindle assembly in regulating oocyte quality during meiotic maturation.