• Satish Kumar

      Articles written in Journal of Biosciences

    • Interaction of twoLAC repressor protein segments with polynucleotides

      M V R Rao M Atreyi G Suresh Kumar Satish Kumar V S Chauhan

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      The interaction of the oligopeptides Ala-Gln-GIn-Leu-Ala-Gly-OH and Gln-Leu-Ala-Gly-OMe corresponding, respectively, to the sequence 53–58 and 55–58 oflac repressor protein with four polynucleotides was studied. The two peptides did not interact with poly dA. poly dT, poly d(A-T)·poly d(A-T) or poly d(A-G)·poly d(C-T). But they interacted in a characteristic way with poly d(A-C). poly d (G-T), the sequences of which are in abundance in thelac operator region. Both the peptides stabilised the melting of poly d (A-C). poly d (G-T) at a peptide to nucleotide ratio (P/N) of 4; at lower ratios, they destabilised the DNA slightly. The circular dichroism of the alternating polynucleotide with CAC/GTG sequences was perturbed by both the oligopeptides. The hexapeptide at a P/N of 4 caused the transformation of the B-form circular dichroism spectrum to a new state, characterised by strong 220 and 240 nm bands, and a rather weak long wavelength spectrum.

    • Argonaute-2-null embryonic stem cells are retarded in self-renewal and differentiation

      P Chandra Shekar Adnan Naim D Partha Sarathi Satish Kumar

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      RNA interference (RNAi) pathways regulate self-renewal and differentiation of embryonic stem (ES) cells. Argonaute 2 (Ago2) is a vital component of RNA-induced silencing complex (RISC) and the only Ago protein with slicer activity. We generated Ago2-deficient ES cells by conditional gene targeting. Ago2-deficient ES cells are defective in the small-RNA-mediated gene silencing and are significantly compromised in biogenesis of mature microRNA. The self-renewal rate of Ago2-deficient ES cells is affected due to failure of silencing of Cdkn1a by ES-cell-specific microRNAs (miRNA) in the absence of Ago2. Interestingly, unlike Dicer- and Dgcr8-deficient ES cells, they differentiate to all three germ layers both in vivo and in vitro. However, early differentiation of Ago2-deficient ES cells is delayed by 2–4 days as indicated by persistence of higher levels of self-renewal/ pluripotency markers during differentiation. Further, appearance of morphological and differentiation markers is also delayed during the differentiation. In this study we show that Ago2 is essential for normal self-renewal and differentiation. Also, our data suggest that self-renewal and differentiation of ES cells are regulated by both siRNA and miRNA pathways.

    • Mammary gland stem cells: More puzzles than explanations

      Suneesh Kaimala Suneesh Kaimala Satish Kumar

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      Mammary gland stem cells (MaSC) have not been identified in spite of extensive research spanning over several decades. This has been primarily due to the complexity of mammary gland structure and its development, cell heterogeneity in the mammary gland and the insufficient knowledge about MaSC markers. At present, LinCD29hiCD49fhiCD24+/modSca-1 cells of the mammary gland have been reported to be enriched with MaSCs. We suggest that the inclusion of stem cell markers like Oct4, Sox2, Nanog and the mammary gland differentiation marker BRCA-1 may further narrow down the search for MaSCs. In addition, we have discussed some of the other unresolved puzzles on the mammary gland stem cells, such as their similarities and/or differences with mammary cancer stem cells, use of milk as source of mammary stem cells and the possibility of in vitro differentiation of embryonic stem (ES) cells into functional mammary gland structures in this review. Nevertheless, it is the lack of identity for a MaSC that is curtailing the advances in some of the above and other related areas.

    • Commentary: Monotremes and marsupials: Comparative models to better understand the function of milk

      Sanjana Kuruppath Swathi Bisana Julie A Sharp Christophe Lefevre Satish Kumar Kevin R Nicholas

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