CORRELATION BETWEEN DEFECTS OF CHROMATIN CONDENSATION AND SPINDLE ASSEMBLY IN OOCYTES OF TWO MOUSE STRAINS

Despite the practical importance of meiotic errors, the interplay between chromatin and microtubule reorganizations in mammalian oocyte meiosis is still poorly understood, particularly with regard to the genetic background. We localized and observed chromosomes and meiotic spindles in metaphase I and mature metaphase II oocytes from two inbred mouse strains, BALB/c and C57BL. Spindles with normal morphology were most often observed together with normally condensed chromosomes and less often with long, insufficiently condensed chromosomes. Cells with degenerated chromosomes had also abnormal spindles. C57BL oocytes had slightly better chromosome condensation, while BALB/c oocytes had significantly better spindle morphology and, hence, better overall quality. All types of chromosome and spindle defects were more common in metaphase I than in metaphase II, which could indicate the action of a spindle assembly checkpoint arresting abnormal oocytes in metaphase I.