Age- and caste-independent piRNAs in the germline and miRNA profiles linked to caste and fecundity in the ant Temnothorax rugatulus.

Social insects are models for studies of phenotypic plasticity. Ant queens and workers vary in fecundity and lifespan, which are enhanced and extended in queens. Yet, the regulatory mechanisms underlying this variation are not well understood. Ant queens live and reproduce for years, so that they need to protect their germline from transposable element (TE) activity, which may be redundant in short-lived, often sterile workers. We analysed the expression of two protective classes of small RNAs, microRNAs (miRNAs) and Piwi-interacting RNAs (piRNAs), in various tissues, castes and age classes of the ant Temnothorax rugatulus. In queens, piRNAs were highly abundant in ovaries with TEs being their clear targets, with reduced but still detectable piRNA-specific ping-pong signatures in thorax and brains. piRNA pathway activity varied little with age in queens. Moreover, the reduced ovaries of workers also exhibited similar piRNA activity and this not only in young, fertile workers, but also in older foragers with regressed ovaries. Therefore, these ants protect their germline through piRNA activity, regardless of ovarian development, age or caste, even in sterile workers often considered the soma of the superorganism. Our tissue-specific miRNA analysis detected the expression of 304 miRNAs, of which 105 were expressed in all tissues, 10 enriched in the brain, three in the thorax, whereas 83 were ovarian-specific. We identified ovarian miRNAs whose expression was related to caste, fecundity and age, and which likely regulate group-specific gene expression. sRNA shifts in young- to middle-aged queens were minor, suggesting delayed senescence in this reproductive caste.

Conditional down-regulation of GreA impacts expression of rRNA and transcription factors, affecting Mycobacterium smegmatis survival.

Gre, one of the conserved transcription factors in bacteria, modulates RNA polymerase (RNAP) activity to ensure processivity and fidelity of RNA synthesis. Gre factors regulate transcription by inducing the intrinsic-endonucleolytic activity of RNAP, allowing the enzyme to resume transcription from the paused and arrested sites. While Escherichia coli and a number of eubacteria harbor GreA and GreB, genus mycobacteria has a single Gre (GreA). To address the importance of the GreA in growth, physiology and gene expression of Mycobacterium smegmatis, we have constructed a conditional knock-down strain of GreA. The GreA depleted strain exhibited slow growth, drastic changes in cell surface phenotype, cell death, and increased susceptibility to front-line anti-tubercular drugs. Transcripts and 2D-gel electrophoresis (2D-PAGE) analysis of the GreA conditional knock-down strain showed altered expression of the genes involved in transcription regulation. Among the genes analysed, expression of RNAP subunits (ß, ß' and ω), carD, hupB, lsr2, and nusA were affected to a large extent. Severe reduction in the expression of genes of rRNA operon in the knock-down strain reveal a role for GreA in regulating the core components of the translation process.