Dissociation of the X chromosome from the synaptonemal complex in the XY body of the rodent Galea musteloides

Abstract

The XY body from spermatocy tes of the rodent Galea musteloides shows progressiv e changes of the sy naptonemal complex (SC) axes and the X-chromatin during pachy nema. There is a gross thickening of the X-axis and the f ormation of a large X chromosome loop at mid and late pachy tene stages. The SC proteins sy naptonemal complex protein 3 (SY CP3), sy naptonemal complex protein 1, and sy naptonemal complex central element protein 3 and the proteins breast cancer 1, MutL homolog 1 (MLH1), and radiation-repair 51 (related to meiotic processes), the cohesin structural maintenance of chromosome 3, the centromeric protein (with CREST antibody), and the silenced chromatin (with phosphory lated (Ser139) histone 2, A.X (γ-H2A.X) antibody) were analy zed in this XY body . The thick X-axis, including the interstitial loop, becomes f ormed by f our to six laminae showing a cross-striation with a periodicity of about 20 nm. The whole length of the gross X-axis shows no signif icant changes during pachy nema, but the interstitial chromatin of the X chromosome and the X centromere are included in the large loop, and it becomes separated f rom the SC. A conv entional SC f ormed by the Y -axis, a central region and a thin lateral element originally corresponding to the X-axis, remains undisturbed up to the end of pachy nema. A single MLH1 f ocus dev elops either at the distal or the proximal region of the loop end attached to the conv entional SC. The chromatin surrounding the thickened axis is labeled with γ-H2A.X. It is shown that most of the SY CP3 protein associated with the X chromosome loop is not inv olv ed in the SC maintenance, but it is located with the cohesin axis separated f rom the SC proper.