Biology subjects

Joshi, R. L.

Publications and source records attributed to Joshi, R. L..

3 recordsLinked to original sources

bioRxiv2025

Interactions of the LINE-1 encoded ORF1p with proteins and chromatin converge on a role in neuronal physiology

Retrotransposons are emerging as novel regulators of embryonic and brain development. We recently demonstrated that the LINE-1-encoded protein ORF1p is abundantly expressed in adult mouse and human neurons, although its function remains unclear. Here, we characterize the ORF1p interactome in differentiated mouse and human neurons using mass spectrometry and identify novel partners implicated in gene regulation and neuron-specific processes. ORF1p localizes not only to neuronal nuclei, where it associates with chromatin under steady-state conditions, but also to neurites, supporting a role in neuronal physiology. To further explore its nuclear functions, we sorted human post-mortem neurons with high or low nuclear ORF1p levels and performed ORF1p knockdown in cultured human neurons, followed by chromatin accessibility assays. Both approaches revealed consistent patterns of differential chromatin accessibility dependent on ORF1p. Loss of ORF1p also led to the downregulation of long, neuron-specific genes and altered neurite morphology. Together, these findings point to a physiological role of ORF1p in post-mitotic neurons, mediated through converging interactions with proteins and chromatin.

neuroscience↗

bioRxiv2020

Perturbed DNA methylation by sustained overexpression of Gadd45b induces chromatin disorganization, DNA strand breaks and dopaminergic neuron death in mice

Heterochromatin disorganization is a key hallmark of aging and DNA methylation state is currently the main molecular predictor of chronological age. The most frequent neurodegenerative diseases like Parkinson disease and Alzheimers disease are age-related but how the aging process and chromatin alterations are linked to neurodegeneration is unknown. Here, we investigated the consequences of viral overexpression of Gadd45b, a multifactorial protein involved in active DNA demethylation, in the midbrain of wild-type mice. Gadd45b overexpression induces global and stable changes in DNA methylation, particularly on gene bodies of genes related to neuronal functions. DNA methylation changes were accompanied by perturbed H3K9me3-marked heterochromatin and increased DNA damage. Prolonged Gadd45b expression resulted in dopaminergic neuron degeneration accompanied by altered expression of candidate genes related to heterochromatin maintenance, DNA methylation or Parkinson disease. Gadd45b overexpression rendered midbrain dopaminergic neurons more vulnerable to acute oxidative stress. Heterochromatin disorganization and DNA demethylation resulted in derepression of mostly young LINE-1 transposable elements, a potential source of DNA damage, prior to Gadd45b-induced neurodegeneration. Our data implicate that alterations in DNA methylation and heterochromatin organization, LINE-1 derepression and DNA damage can represent important contributors in the pathogenic mechanisms of dopaminergic neuron degeneration with potential implications for Parkinson disease.

neuroscience↗

bioRxiv2017

LINE-1 repression attenuates degeneration in adult dopaminergic neurons

LINE-1 mobile genetic elements have shaped the mammalian genome during evolution. A minority of them have escaped fossilization which, when activated, can threaten genome integrity. We report that LINE-1 are expressed in substantia nigra ventral midbrain dopaminergic neurons, a class of neurons that degenerate in Parkinson disease. In Engrailed-1 heterozygotes, these neurons show a progressive degeneration that starts at 6 weeks of age, coinciding with an increase in LINE-1 expression. Similarly, DNA damage and cell death, induced by an acute oxidative stress applied to embryonic midbrain neurons in culture or to adult midbrain dopaminergic neurons in vivo, are accompanied by enhanced LINE-1 expression. Reduction of LINE-1 activity through (i) direct transcriptional repression by Engrailed, (ii) a siRNA directed against LINE-1, (iii) the nucleoside-analogue reverse transcriptase inhibitor stavudine and (iv) viral Piwil1 expression, protects against oxidative stress in vitro and in vivo. We thus propose that LINE-1 overexpression triggers oxidative stress-induced DNA strand breaks and that an Engrailed adult function is to protect mesencephalic dopaminergic neurons through the repression of LINE-1 expression.

neuroscience↗