Characterization of tubulin post-translational modifications and their enzymes during human oocyte meiosis

Research question: What are the profiles of tubulin post-translational modifications (PTM) in the meiotic spindles of oocytes with different developmental competence: in-vivo matured MII oocytes (IVO) versus cumulus-free in-vitro matured germinal vesicles (IVM)? Design: Cumulus-free germinal vesicles were matured in vitro and compared with IVO in terms of their tubulin PTM, characterizing tubulin PTM patterns (acetylation, tyrosination, detyrosination, D2-tubulin formation and polyglutamylation) of their meiotic spindles by immunofluorescence and by evaluation of the expression levels of the enzymes involved by quantitative reverse transcription polymerase chain reaction. Results: Levels of D2-tubulin, tyrosination and polyglutamylation were similar in IVO and IVM oocytes; acetylation displayed different patterns in both groups, whereas detyrosination was detected only in MII oocytes matured in vivo. The PTM enzyme RNA expression levels in germinal vesicles, IVO and IVM were analysed, as well as in oocytes that failed to mature. Of the 24 PTM enzyme transcripts tested, 17 were present in at least one of the groups under study (aTAT1, NAA50, HDAC6, SIRT2, TTL, TTLL1, TTLL2, TTLL4, TTLL5, TTLL6, TTLL9, TTLL11, TTLL12, CCP1, CCP5, CCP6, VASH1), of which three were differentially expressed (NAA50, TTLL12, CCP1). Conclusion: All modifications studied were present in human oocytes regardless of whether their meiotic maturation occurred in vivo or in vitro, except for detyrosination, which was found at low levels in the IVO group, but not in the IVM group. This suggests that the presence of tubulin PTMs may play a role in human oocyte maturation, completion of meiosis and developmental competence.