The asynaptic chromatin in spermatocytes of translocation carriers contains the histone variant gamma-H2AX and associates with the XY body.

<bold>Background: </bold>The close apposition of multivalents with the XY body has been repeatedly described in heterozygous carriers of chromosomal rearrangements. Because in many of these carriers spermatogenesis is deeply disturbed at the spermatocyte level, the association of autosomal chromatin with the XY body may impair the spermatocyte life.<bold>Methods: </bold>Testicular biopsies from three men carriers of three different chromosomal rearrangements have been analysed by electron microscopy (EM) and immunolocalization of meiotic proteins.<bold>Results: </bold>There is an ordered transition from isolated multivalents at early pachytene to XY body association in late pachytene, as shown in a carrier of a rob t(13;14) translocation by EM and in a reciprocal translocation t(9;14) carrier by immunofluorescence. The non-synapsed ends of the quadrivalent show BRCA1 located on the axes and the variant histone gamma-H2AX located on the chromatin. The area covered by gamma-H2AX increases with the association of the asynaptic ends with the XY body in the t(9;14) carrier, and the area covered with gamma-H2AX in the t(Y;15) carrier is larger than that of the XY body of controls.<bold>Conclusions: </bold>The affinity between the inactive XY body and asynaptic regions of multivalents is given a material basis, and transcriptional inactivation is probably shared by these two chromatin types. [ABSTRACT FROM AUTHOR]