Articles written in Journal of Genetics

    • TheHsp60C gene in the 25F cytogenetic region inDrosophila melanogaster is essential for tracheal development and fertility

      Surajit Sarkar Subhash C. Lakhotia

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      Earlier studies have shown that of the four genes (Hsp60A, Hsp60B, Hsp60C, Hsp60D genes) predicted to encode the conserved Hsp60 family chaperones inDrosophila melanogaster, theHsp60A gene (at the 10A polytene region) is expressed in all cell types of the organism and is essential from early embryonic stages, while theHsp60B gene (at 21D region) is expressed only in testis, being essential for sperm individualization. In the present study, we characterized theHsp60C gene (at 25F region), which shows high sequence homology with the other threeHsp60 genes ofD. melanogaster. In situ hybridization of Hsp60C-specific riboprobe shows that expression of this gene begins in late embryonic stages (stage 14 onwards), particularly in the developing tracheal system and salivary glands; during larval and adult stages, it is widely expressed in many cell types but much more strongly in tracheae and in developing and differentiating germ cells. A P-insertion mutant (Hsp60C1) allele with the P transposon inserted at -251 position of theHsp60C gene promoter was generated. This early larval recessive lethal mutation significantly reduces levels ofHsp60C transcripts in developing tracheae and this is associated with a variety of defects in the tracheal system, including lack of liquid clearance. About 10% of the homozygotes survive as weak, shortlived and completely sterile adults. Testes of the surviving mutant males are significantly smaller, with fewer spermatocytes, most of which do not develop beyond the round spermatid stage.In situ and Northern hybridizations show significantly reduced levels of theHsp60C transcripts inHsp60C1 homozygous adult males. The absence of early meiotic stages in theHsp60C1 homozygous testes contrasts with the effect of testis-specificHsp60B (21D) gene, whose mutation affects individualization of sperm bundles later in spermiogenesis. In view of the specific effects in tracheal development and in early stages of spermatogenesis, it is likely that, besides its functions as a chaperone, Hsp60C may have signalling functions and may also be involved in cation transport across the developing tracheal epithelial cells.

    • The commonly used eye-specific sev-GAL4 and GMR-GAL4 drivers in Drosophila melanogaster are expressed in tissues other than eyes also

      Mukulika Ray Subhash C. Lakhotia

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      The binary GAL4-UAS system of conditional gene expression is widely used by Drosophila geneticists to target expression of the desired transgene in tissue of interest. In many studies, a preferred target tissue is the Drosophila eye, for which the sev-GAL4 and GMR-GAL4 drivers are most widely used since they are believed to be expressed exclusively in the developing eye cells. However, several reports have noted lethality following expression of certain transgenes under these GAL4 drivers notwithstanding the fact that eye is not essential for survival of the fly. Therefore, to explore the possibility that these drivers may also be active in tissues other than eye, we examined the expression of UAS-GFP reporter driven by the sev-GAL4 or GMR-GAL4 drivers. We found that both these drivers are indeed expressed in additional tissues, including a common set of specific neuronal cells in larval and pupal ventral and cerebral ganglia. Neither sev nor glass gene has so far been reported to be expressed in these neuronal cells. Expression pattern of sev-GAL4 driver parallels that of the endogenous Sevenless protein. In addition to cells in which sev-GAL4 is expressed, the GMR-GAL4 is expressed in several other larval cell types also. Further, two different GMR-GAL4 lines also show some specific differences in their expression domains outside the eye discs. These findings emphasize the need for a careful confirmation of the expression domains of a GAL4 driver being used in a given study, rather than relying only on the empirically claimed expression domains.

    • Divergent actions of long noncoding RNAs on X-chromosome remodelling in mammals and Drosophila achieve the same end result: dosage compensation

      Subhash C. Lakhotia

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      Organisms with heterochromatic sex chromosomes need to compensate for differences in dosages of the sex chromosome-linked genes that have somatic functions. In-depth cytological and subsequent biochemical and molecular studies on dosage compensation started with Mary F. Lyon’s proposal in early 1960s that the Barr body in female mammalian somatic cells represented one of the randomly inactivated and heterochromatinized X chromosomes. In contrast, Drosophila was soon shown to achieve dosage compensation through hypertranscription of single X in male whose chromatin remains more open. Identification of proteins that remodel chromatin either to cause one of the two X chromosomes in somatic cells of very early female mammalian embryos to become condensed and inactive or to remodel the single X in male Drosophila embryos to a more open state for hypertranscription provided important insights into the underlying cellular epigenetic processes. However, the most striking and unexpected discoveries were the identification of long noncoding RNAs (lncRNAs), X- inactive specific transcript (Xist) in mammals and roX1/2 in Drosophila, which were essential for achieving the contrasting chromatin organizations but leading to similar end result in terms of dosage compensation of X-linked genes in females and males. An overview of the processes of X inactivation or hyperactivation in mammals and Drosophila, respectively, and the roles played by Xist, roX1/2 and other lncRNAs in these events is presented.

    • Dosage compensation in Drosophila in the 1960s: a personal historical perspective


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    • Delayed discovery of Hsp60 and subsequent characterization of moonlighting functions of multiple Hsp60 genes in Drosophila: a personal historical perspective


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      The pioneering studies carried out on heat shock-induced synthesis of specific proteins in the early 1970s did not identify any Hsp60 family protein in Drosophila. By the early 1980s, although the members of Hsp60 family of heat shock proteins (Hsp) were identified in a wide range of eukaryotes as homologs of the bacterial GroEL, none was known in Drosophila. The existence of the Hsp60 family protein was serendipitously revealed in Drosophila in my laboratory in 1989. Contrary to the earlier reports that all tissues in flies display the canonical heat shock response, the larval Malpighian tubules (MT) did not show induction of any of the major Hsps but synthesis of a putative Hsp60 family protein was found to be the most abundant in this tissue. A few years later, we identified this MTspecific heat shock-induced protein to indeed be a member of the Hsp60/chaperonin family. The Drosophila genome sequence projectssubsequently revealed four putative Hsp60 gene sequences in the D. melanogaster genome. The present historical perspective chroniclescontributions from my and other laboratories that unraveled several aspects of intriguing biology of the multiple Hsp60 genes in D. melanogaster, and highlights challenging questions awaiting future studies.

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