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 lysine residue 5, 8, 12, or 16 and indirect immunofluorescence microscopy to probe chromosomes from spermatogonia and spermatocytes of the desert locust, Schistocerca gregaria. The autosomes showed bright overall fluorescence, indicative of high levels of H4 acetylation. In contrast, the X chromosome, which is facultatively heterochromatic during spermatogenesis of the locust, remained completely unstained in spermatogonia and secondary spermatocytes and showed only a small terminal fluorescent band in primary spermatocytes. This band probably corresponds to centromere associated constitutive heterochromatin. Thus, underacetylation is a cytogenetic marker for facultative heterochromatin, but not necessarily constitutive heterochromatin, during spermatogenesis of the locust. Scanning electron microscopy of chromosomes from prophase spermatogonia and prophase I spermatocytes revealed that underacetylation of histone H4 in the X chromosome was not accompanied by a chromatin organization visibly different from that of the autosomes. Transmission electron microscopy of mitotic spermatogonia showed that the X chromosome is separated from the autosomes in a small nuclear compartment of its own in prophase and telophase and associated with membranes in metaphase. In prophase I spermatocytes, autosomes and the sex univalent were in the same compartment. This compartmentalization may be responsible for the underacetylation and (or) transcriptional silencing of the X chromosome in spermatogonia mitosis.