18 research outputs found
Molecular hydrogen beyond the optical edge of an isolated spiral galaxy
We know little about the outermost portions of galaxies because there is
little light coming from them. We do know that in many cases atomic hydrogen
(HI) extends well beyond the optical radius \cite{Casertano91}. In the centers
of galaxies, however, molecular hydrogen (H2) usually dominates by a large
factor, raising the question of whether H2 is abundant also in the outer
regions but hitherto unseen.Here we report the detection of emission from
carbon monoxide (CO), the most abundant tracer of H2, beyond the optical radius
of the nearby galaxy NGC 4414. The molecular clouds probably formed in the
regions of relatively high HI column density and in the absence of spiral
density waves. The relative strength of the lines from the two lowest
rotational levels indicates that both the temperature and density of the H2 are
quite low compared to conditions closer to the center. The inferred surface
density of the molecular material continues the monotonic decrease from the
inner regions. We conclude that while molecular clouds can form in the outer
region of this galaxy, there is little mass associated with them.Comment: 3 Nature page
HTLV-1 Tax Mediated Downregulation of miRNAs Associated with Chromatin Remodeling Factors in T Cells with Stably Integrated Viral Promoter
RNA interference (RNAi) is a natural cellular mechanism to silence gene expression and is predominantly mediated by microRNAs (miRNAs) that target messenger RNA. Viruses can manipulate the cellular processes necessary for their replication by targeting the host RNAi machinery. This study explores the effect of human T-cell leukemia virus type 1 (HTLV-1) transactivating protein Tax on the RNAi pathway in the context of a chromosomally integrated viral long terminal repeat (LTR) using a CD4+ T-cell line, Jurkat. Transcription factor profiling of the HTLV-1 LTR stably integrated T-cell clone transfected with Tax demonstrates increased activation of substrates and factors associated with chromatin remodeling complexes. Using a miRNA microarray and bioinformatics experimental approach, Tax was also shown to downregulate the expression of miRNAs associated with the translational regulation of factors required for chromatin remodeling. These observations were validated with selected miRNAs and an HTLV-1 infected T cells line, MT-2. miR-149 and miR-873 were found to be capable of directly targeting p300 and p/CAF, chromatin remodeling factors known to play critical role in HTLV-1 pathogenesis. Overall, these results are first in line establishing HTLV-1/Tax-miRNA-chromatin concept and open new avenues toward understanding retroviral latency and/or replication in a given cell type