Cellular autonomy of hyperactivity in segmentalXchromosomal aneuploids ofDrosophilaand dosage compensation

Abstract

Transcription in 9A-11A aneuploid mosaic female larvae of Drosophila melanogaster has been assessed autoradiographically. Eleven larvae were found to exhibit mosaicism out of sixty-six larvae scanned and the percentage of XO and XX nuclei varied from approximately 9 to 100. Irrespective of the number of XX nuclei present the XO nuclei (duplicated for 9A-11A) invariably showed hyperactivity for both the segments. The XX nucleus exhibited a dosage effect for all the three segments of 9A-11 A. Results support the transcriptional constancy of the entire X chromosome, as proposed by Maroni and Lucchesi. Cellular autonomy of hyperactivity of the single X chromosome even at the level of segments of the X is thus evident from the present results. Autonomy

A different level ofX-chromosomal transcription in an In(1)BM2(reinverted) strain and in its hyperploid derivatives resolves anX-coded regulatory activity for dosage compensation inDrosophila

“…We are working on this possibility. In all of the rv hyperploids examined, each of the diplo-Z segments involved in the hyperploidy showed a morphology characteristic of that shown by the equivalent segment in a normal male (a dosage effect for hyperactivity) (Prasad, Duttagupta & Mukherjee, 1981;Prasad-Sinha & Mukherjee, 1985). The remaining part of the X containing only one homologue also showed uniformly normal male-like puffiness, being neither flabby nor at the lower level characteristic of a female (Fig.…”

“…They attributed this lower activity for haplo segments in the hyperploid male as resulting from a pre-disposed constancy in the overall level of A'-chromosome transcription. While Prasad et al (1981) could not verify this, Prasad-Sinha & Mukherjee (1985) substantiated this finding in cellular mosaics for the aneuploid segment 9A-11 A. The finding is not substantiated, however, in aneuploids containing such duplications which also include 16A-20F (PrasadSinha, unpublished).…”