Biology subjects

Leonovich, I.

Publications and source records attributed to Leonovich, I..

3 recordsLinked to original sources

bioRxiv2026

Intrinsically disordered regions navigate DNA replication licensing factors to specific genomic loci.

Sites of DNA replication initiation are determined by binding of the Origin Recognition Complex (ORC, composed of Orc1-6) to specific genomic loci. Here, we determine the mechanism underlying site-specific binding of human Orc1. We find that Orc1's Bromo-Adjacent Homology (BAH) domain functions as an avidity element, whereas an intrinsically disordered region (IDR) guides genomic specificity. Deletion of the IDR abolishes chromatin binding and Orc1 chimeras with swapped IDRs are redirected to new genomic locations. Other replication factors, such as Cdt1 and Cdc6, also possess IDRs. However, despite their similar biochemical properties, we find that these IDRs are functionally non-equivalent. Like Orc1, the Cdt1 IDR guides loci-specific binding but targets distinct sites. Strikingly, the Cdt1 IDR, when swapped into Orc1, redirects Orc1 to Cdt1 binding sites. This establishes a key role for the Orc1 IDR in genome navigation and points to impressive levels of functional sophistication in licensing factor disordered regions.

cell biology↗

bioRxiv2026

Phosphorylation alters the bulk chemical properties of Orc1 to tune DNA binding, phase separation, and heterochromatin partitioning

The first step in initiating DNA replication is binding of the origin recognition complex (ORC) to chromosomes. Metazoan ORC is recruited to chromatin via the Orc1 intrinsically disordered region (IDR) whose DNA and chromatin binding activity are regulated by Cyclin Dependent Kinase (CDK) phosphorylation. ORC is also enriched in heterochromatin where it is required for the formation and maintenance of a silenced chromatin state. ORCs recruitment to heterochromatin is developmentally and cell cycle regulated but the underlying regulatory mechanism remains unknown. We hypothesized that CDK-dependent phosphorylation of the Orc1 IDR underpins regulated recruitment to heterochromatin. Using bioinformatic analyses, we find that the Drosophila Orc1 IDR (Orc1IDR) contains an exceptionally high density of CDK phospho-sites and, despite considerable sequence variation, the density of sites, but not their position, is conserved. In vitro DNA binding and phase separation experiments reveal that phosphorylation tunes Orc1IDR function in a rheostat-like fashion. Using phospho-mimetic variants, we find that constitutive phosphorylation not only weakens interphase chromatin binding but fully inhibits partitioning of Orc1IDR into heterochromatin. Finally, we use phospho-mimetic variants to probe the importance of site-specific phosphorylation and find that the precise position of sites can be changed provided the new sites are equitably distributed across the sequence. These studies demonstrate that phosphorylation tunes the biochemical properties of the Orc1 IDR to control DNA binding, phase separation, and, consequentially, heterochromatin recruitment. This work suggests that localized dephosphorylation of the DNA binding Orc1 IDR may underlie recruitment of ORC to specific genomic loci.

biochemistry↗

bioRxiv2025

Minocycline treatment affects astrocyte - microglia - neuron interaction and functional compensation of motor deficits in rat model of combined fluorocitrate and 6-OHDA lesion and early Parkinson's disease

Prolonged nervous system inflammation and glia activation are among hallmarks of Parkinsons disease. There are no therapies slowing pathology. Microglia and astrocytes are considered targets for disease modifying strategies. Nigrostriatal neurodegeneration causes locomotor dysfunction but at early stages can be compensated. Interaction between neurons, microglia and astrocytes could be essential for this functional adaptation and neuronal survival in long-term. The aim was to check how microglia activation inhibition affects neuron and astrocyte cell death caused by selective toxins and how it affects locomotion and potential for spontaneous functional compensation of motor deficits at the early stages of Parkinsons disease. In a rat model of fluorocitrate (FC)-induced astrocyte death and microglia activation combined with 6-OHDA selective dopaminergic system neurodegeneration we analyzed anti-inflammatory effect of minocycline on each of the cell type and on functional behavioral output. In result, reduced microglia activation by minocycline probably prevented part of astrocytes from FC-induced cell death. Microglia inhibition caused non-dopaminergic neurodegeneration in a group treated by both neurotoxins but still enhanced compensatory potential to functionally improve walking deficits caused by dopaminergic lesion. It seems that activation of microglia by dying astrocytes vs dying neurons induced varied mechanisms. Inhibition of strong microglia activation could be protective for astrocytes but microglia is also important for neuronal adaptation, therefore suppression of its activation perturbs structural rebuilding during progressive neurodegeneration affecting functional outcome. Understanding the relationship between neuronal death, astrocyte loss of function and microglial response could help to identify new, non-neuronal pharmacological target for healing various neurodegenerative diseases. HighlightsO_LIAstrocyte death affected neuron function but neurodegeneration did not affect astrocyte survival. C_LIO_LIMicroglia was differentially activated by death of astrocytes than by neuron degeneration. C_LIO_LIMinocycline treatment decreased morphological signs of microglia activation, probably protected some astrocytes but negatively affected astrocytes in 6-OHDA lesion group. C_LIO_LIMinocycline treatment despite inducing non-dopaminergic neurodegeneration still enhanced compensatory potential to functionally improve walking after combined 6-OHDA lesion and fluorocitrate-induced astrocyte death. C_LI

neuroscience↗