The hnRNP A1 homolog Hrp36 is essential for normal development, female fecundity, omega speckle formation and stress tolerance in Drosophila melanogaster
Hrp36/Hrb87F is one of the most abundant and well-characterized hnRNP A homolog in Drosophila and is shown to have roles in regulation of alternative splicing, heterochromatin formation, neurodegeneration, etc. Yet, hrp36 null individuals were reported to be viable and without any apparent phenotype, presumably because of overlapping functions provided by Hrp38 and related proteins. Here we show that loss of both copies of hrp36 gene slows down development with significant reduction in adult life span, decreased female fecundity and high sensitivity to starvation and thermal stresses. In the absence of Hrp36, the nucleoplasmic omega speckles are nearly completely disrupted. The levels of nuclear matrix protein Megator and the chromatin remodeller ISWI are significantly elevated in principal cells of larval Malpighian tubules, which also display additional endoreplication cycles and good polytene chromosomes. We suggest that besides the non-coding hsrω-n transcripts, the Hrp36 protein is also a core constituent of omega speckles. The heat-shock-induced association of other hnRNPs at the hsrω locus is affected in hrp36 null cells, which may be one of the reasons for their high sensitivity to cell stress. Therefore, in spite of the functional redundancy provided by Hrp38, Hrp36 is essential for normal development and for survival under conditions of stress.
Keywords93D hnRNP ISWI Megator noncoding RNA omega speckles thermo-tolerance
We thank Dr Susan Hayness for the Df(3R)Hrb87F fly stock and Dr H Saumweber (Berlin, Germany) for P11, Q18, Bj6, Bx34 antibodies, Dr M B Evgen’ev (Russia) for 7Fb antibody and D Corona (Italy) for ISWI antibody. The work was supported by the Department of Science & Technology, New Delhi, through the Ramanna Fellowship and the National Facility for Confocal Microscopy grants to SCL. AKS is supported through Research Fellowship from the CSIR.
Note added in proof
Subsequent to acceptance of this paper, we have examined the effect of expression of FLAG-tagged full length Hrp36 under a leaky Hsp70 promoter (Zu et al. 1996) in otherwise hrp36 null background. The leaky expression of one copy of the FLAG-tagged full length Hrp36 in otherwise hrp36 null embryos, grown at 24°C or at 30°C, almost fully complements all the phenotypes noted in this study for the hrp36 nulls, except the elongated telomeres. These results confirm that the different phenotypes described here for the hrp36 null individuals are indeed due to absence of the Hrp36 protein.
- Lakhotia SC 2003 Integration of transcriptional and translational activities in normal and stressed cells by the noncoding hsr-omega transcripts in Drosophila. Biol. Intl. 45 30–33Google Scholar
- Lakhotia SC, Ray P, Rajendra TK and Prasanth KV 1999 The non-coding transcripts of hsr-omega gene in Drosophila: Do they regulate trafficking and availability of nuclear RNA-processing factors? Curr. Sci. 77 553–563Google Scholar
- Manita D, Toba Y, Takakusagi Y, Matsumoto Y, Kusayanagi T, Takakusagi K, Tsukuda S, Takada K, Kanai Y, Kamisuki S, Sakaguchi K and Sugawara F 2011 Camptothecin (CPT) directly binds to human heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) and inhibits the hnRNP A1/topoisomerase I interaction. Bioorg. Med. Chem. 19 7690–7697PubMedCrossRefGoogle Scholar