A conserved nutrient responsive axis mediates autophagic degradation of miRNA-mRNA hybrids in blood cell progenitors.

In animals, microRNAs are amongst the primary non-coding RNAs involved in regulating the gene expression of a cell. Most mRNAs in a cell are targeted by one or many miRNAs. Although several mechanisms can be attributed to the degradation of miRNA and mRNA within a cell, but the involvement of autophagy in the clearance of miRNA and its target mRNA is not known. We discover a leucine-responsive axis in blood cell progenitors that can mediate an autophagy-directed degradation of miRNA-bound mRNA in Drosophila melanogaster and Homo sapiens. This previously unknown miRNA clearance axis is activated upon amino acid deprivation that can traffic miRNA-mRNA-loaded Argonaute for autophagic degradation in a p62-dependent manner. Thus, our research not only reports a novel axis that can address the turnover of a catalytically active miRISC but also elucidates a slicer-independent mechanism through which autophagy can selectively initiate the clearance of target mRNA.

Combination of Immunofluorescence and Quantitative Fluorescence In-situ Hybridization for Analysing Differential Gene Expression in the Niche Cells of the Drosophila Lymph Gland.

The Drosophila larval haematopoietic organ or lymph gland consists of multiple cell types arranged in zones. The smallest stem cell compartment consists of 40-45 cells that constitute the haematopoietic niche. In order to analyse the haematopoietic niche, it needs to be labelled with a specific antibody to differentiate it from the other cell types. To characterise a phenotype, it is often necessary to investigate the expression of a gene in a particular stem cell compartment within the lymph gland. In such a situation, in-situ hybridization is performed, as it indicates the localization of gene expression. Although chromogenic in-situ hybridization enables us to compare the signal and tissue morphology simultaneously, it fails to harness the information related to the degree of gene expression. Dual immunofluorescence and in-situ hybridization (IF-FISH) serves as the powerful technique that helps to visualize both protein and mRNA expression within the same cell type. This technique also provides reliable quantification regarding mRNA expression levels. When dealing with a few cells within the organ, like the niche of the larval lymph gland, fluorescently labelled riboprobes allows us to localize and assess the magnitude of gene expression within the niche cells, which are also immunolabelled with a niche-specific marker, to distinguish them from the adjoining cell types.

Drosophila metamorphosis involves hemocyte mediated macroendocytosis and efferocytosis.

Drosophila hemocytes are majorly associated with immune responses, but they also undertake several non-immune functions that are crucial during various stages of development. The activity and behaviour of hemocytes are least documented during the metamorphic phase of fly development. Here we describe the activity, form and behaviour of the most abundant type of hemocyte in Drosophila melanogaster, the "plasmatocyte," throughout pupal development. Our study reveals different forms of plasmatocytes laden with varying degrees of histolyzing debris (muscle and fat) which extend beyond the size of the cell itself, highlighting the phagocytic capacity of these plasmatocytes. Interestingly, the engulfment of apoptotic debris by plasmatocytes is an actin-dependent process, and by the end of metamorphosis, clearance is achieved. The uptake of apoptotic debris consisting of muscles and lipids by the plasmatocytes provides us a model that can be employed to dissect out the relevant components of macroendocytosis and lipid-loaded phagocytosis. This understanding, by itself, is crucial for addressing the emerging role of phagocytes in physiology and pathophysiology.