Biology subjects

Rao, B. J.

Publications and source records attributed to Rao, B. J..

3 recordsLinked to original sources

bioRxiv2018

Modulation of TOR kinase activity in Chlamydomonas reinhardtii: Effect of N-starvation and changing carbon pool

Target Of Rapamycin (TOR) kinase is a sensor as well as a central integrator of internal and external metabolic cues. The upstream and downstream signals of this kinase are very well characterized in animals. However, in algae, higher plants and other photosynthetic organisms, the components of the TOR kinase-signaling are yet to be characterized. Here, we establish an assay system to study TOR kinase activity in C.reinhardtii using the phosphorylation status of its downstream target, CrS6K. We further use this assay to monitor TOR kinase activity under various physiological states such as photoautotrophy, heterotrophy, mixotrophy and nitrogen starvation. We observe that autotrophy in light (and not in dark) leads to TOR kinase attenuation during N starvation while the same is not observed in mixotrophy. Importantly, we show that the external carbon source glucose is sensed and uptaken by C.reinhardtii cells only in the presence of light and not in the dark. And such exogenously added glucose, as the photoassimilate carbon mimic, results in enhanced production of ROS, induction of autophagy and concomitant drop in TOR kinase activity, creating N-starvation-like cellular state even in N+ conditions. Interestingly, dose dependent addition of glucose revealed TOR kinase activation in low glucose regime (ROS independent) followed by attenuation of TOR kinase (ROS dependent) at high glucose levels.\n\nSummaryTOR kinase activity in C.reinhardtii is modulated by available carbon source especially glucose, where low levels of glucose cause an increase whereas high levels cause a reduction in TOR kinase activity.

plant biology↗

bioRxiv2017

Somatic developmental defects in dmrad51/spnA mutant show low temperature sensitivity with enhanced genomic damages and cell death

Homologous Recombination (HR) is one of the key pathways to repair Double Strand Breaks (DSBs). Rad51 serves an important function of catalysing strand exchange between two homologous chromosomes in the HR pathway. In higher organisms, Rad51 function is indispensable with its absence leading to early embryonic lethality, thus precluding any mechanistic probing of the system. In contrast, absence of Drosophila rad51 (Dmrad51/spnA) has been associated with defects in female germline causing ventralization of the egg, without any reported detrimental consequences to Drosophila somatic tissues. In this study, we have performed a systematic analysis of somatic development of dmrad51 null mutant flies by using genetic complementation between multiple dmrad51 alleles. Our current study, for the first time, uncovers the requirement of Dmrad51 in somatic tissue maintenance at both larval and pupal stages. Also, we show that dmrad51 mutant exhibit patterning defects in abdominal cuticle in the stripes and bristles, while there appears to be only subtle defects in the adult wing and eye. Interestingly, dmrad51 null mutant and other alleles show discernible phenotype of low temperature sensitivity, suggesting a role for Dmrad51 in temperature sensitive cellular processes, which thus presents an elegant system for probing temperature sensitive cellular/tissue responses that ensue when a mutation leads to the loss of protein expression (null mutant) rather than its altered protein structure.

developmental biology↗

bioRxiv2016

Genome-level parameters describe the pan-nuclear fractal nature of eukaryotic interphase chromosomal arrangement

Long-range inter-chromosomal interactions in the interphase nucleus subsume critical genome-level regulatory functions such as transcription and gene expression. To decipher the physical basis of diverse pan-nuclear patterns of chromosomal arrangement that facilitates these processes, we investigate the scaling effects within disparate genomes and compared their total number of genes with chromosome size. First, we derived the pan-nuclear average fractal dimension of inter-chromosomal arrangement in interphase nuclei of different species and corroborated our predictions with independently reported results. Then, we described the different patterns across disparate unicellular and multicellular eukaryotes. We report that, unicellular lower eukaryotes have inter-chromosomal fractal dimension = 1 at the pan-nuclear scales, which is analogous to the multi-polymer crumpled globule model. Multi-fractal dimensions, corresponding to different inter-chromosomal arrangements emerged from multicellular eukaryotes, such that closely related species have relatively similar patterns. Using this theoretical approach, we could distinguish fractal patterns from human acrocentric versus metacentric chromosomes, implying that the multi-fractal nature of inter-chromosomal geometry facilitates viable large-scale chromosomal aberrations, such as Robertsonian translocations. We report that the nature of such an average multi-fractal dimension for nocturnal mammals is very different in diurnal mammals, which suggests a greatly enhanced plasticity in arrangement across different cell types, for example retinal versus dermal fibroblasts. Altogether, our results substantiate that genome-level constraints have also co-evolved with the average pan-nuclear fractal dimension of inter-chromosomal folding during eukaryotic evolution.

evolutionary biology↗