Cold-induced alteration in the global structure of the male sex chromosome of In1BM2(reinverted) of Drosophila melanogaster is associated with increased acetylation of histone 4 at lysine 16.

In Drosophila melanogaster, dosage compensation occurs through hypertranscription of sex-linked genes in males. The hypertranscription involves acetylation of histone 4 at lysine 16 (H4K16) on amale X-chromosome, brought about by a histone acetyltransferase encoded by the dosage compensation gene, males absent on the first (mof). We report a phenomenon in the strain In(1)B(M2)(reinverted) of D. melanogaster where the global structure of the male X-chromosome can be altered at the third instar larval stage through a 4-h cold shock at 12+/-1 degrees C. We show that the cold shock results in a transient hyperacetylation of H4K16 and an increased expression of MOF. Control proteins H4 acetylated at lysine 5, and the dosage compensation gene msl-2, do not show any change in expression after cold shock. Cytology of the male X-chromosome at different time points during cold shock and recovery, suggests that the hyperacetylation of H4 at lysine 16 causes the X-chromosome to corkscrew into itself, thereby achieving the cold-induced change in the higher order structure of the male polytene X-chromosome. Our studies suggest a role for H4K16 in maintaining the structure of the male X-chromosome in Drosophila.

Binding affinity of leucine-containing chromatin proteins to the polytene X chromosome of Drosophila hydei and its significance.

Association of newly synthesised non-histone chromosomal protein to the polytene X chromosome of larval salivary glands of D. hydei has been examined by autoradiographic procedure using 3H-leucine. It has been observed that 3H-leucine labelling pattern is inhibited in presence of puromycin. Results further reveal that there is a reasonable concordance between the binding affinity of newly synthesized protein on the single X chromosome of the male and paired X's of the female. A sitewise analysis of 3H-leucine labelling reveals that although 3H-leucine incorporation pattern are not strictly comparable with 3H-RNA synthesis pattern observed under in vivo transcription condition, the labelling pattern with 3H-leucine are not merely the reflection of mass distribution of protein in the polytene chromosomes. Certain aspects of regulation in the organisation of male and female X chromosome in Drosophila by de novo synthesis of protein are discussed.

Mosaic pattern of X-chromosomal transcription in a strain of Drosophila melanogaster with aneuploid X chromosome.

Organisation and template activity pattern of salivary gland chromosomes of a segmental male aneuploid of D. melanogaster, carrying duplication for the segment 8C-20F of X chromosome, have been examined by in situ transcription. In an earlier study [Chatterjee, Chromosoma 91 (1985) 259], it was suggested that in male aneuploids, up to an additional length of 8C-20F, the template activity of X chromosome tends to remain at a male level and beyond that level shifts towards female level. A large scale search of the template activity pattern of the aneuploid carrying dp.(8C-20F) clearly indicates that presence of the duplication fragment to X in the normal karyotype (1X2A) lead to a varying degree of condensation of euchromatic regions of entire X chromosome (X + X fragment 8C-20F) starting from 'male' level, over a wide range of 'intermediate' level to a normal 'female' level. In this study, the individual cells of the aneuploid appeared to display their own state of X condensation and transcription. Although in the aneuploid, X chromosomal activity is not determined by a purely quantitative effect of X vs. autosomal material (X:A ratio = 0.81), the 8C-20F segment of X chromosome must contain some major elements concerned with the signal given by X:A ratio for X chromosome differentiation.