THE PATTERN OF HISTONE H4 ACETYLATION ON THE X-CHROMOSOME DURING SPERMATOGENESIS OF THE DESERT LOCUST SCHISTOCERCA-GREGARIA

We have used antibodies directed against histone H4 acetylated at lysi ne residue 5, 8, 12, or 16 and indirect immunofluorescence microscopy to probe chromosomes from spermatogonia and spermatocytes of the deser t locust, Schistocerca gregaria. The autosomes showed bright overall f luorescence, indicative of high levels of H4 acetylation. In contrast, the X chromosome, which is facultatively heterochromatic during sperm atogenesis of the locust, remained completely unstained in spermatogon ia and secondary spermatocytes and showed only a small terminal fluore scent band in primary spermatocytes. This band probably corresponds to centromere- associated constitutive heterochromatin. Thus, underacety lation is a cytogenetic marker for facultative heterochromatin, but no t necessarily constitutive heterochromatin, during spermatogenesis of the locust. Scanning electron microscopy of chromosomes from prophase spermatogonia and prophase I spermatocytes revealed that underacetylat ion of histone H4 in the X chromosome was not accompanied by a chromat in organization visibly different from that of the autosomes. Transmis sion electron microscopy of mitotic spermatogonia showed that the X ch romosome is separated from the autosomes in a small nuclear compartmen t of its own in prophase and telophase and associated with membranes i n metaphase. In prophase I spermatocytes, autosomes and the sex unival ent were in the same compartment. This compartmentalization may be res ponsible for the underacetylation and (or) transcriptional silencing o f the X chromosome in spermatogonial mitosis.