Biology subjects

Bernier, G.

Publications and source records attributed to Bernier, G..

3 recordsLinked to original sources

bioRxiv2024

BMI1-mediated heterochromatinization represses G-quadruplex DNA formation to maintain genomic stability during replication

Single-stranded DNA secondary structures such as G-quadruplexes (G4s) can potentially disrupt transcription, replication, and repair. Using bio-informatic analysis, here we show that BMI1 is enriched at putative G4s flanked by heterochromatin domains, and that BMI1 knockdown in human dermal fibroblasts (HDFs) resulted in heterochromatin relaxation and G4 induction, followed by replication stress and genomic instability. In these cells, G4s co-localized with large 53BP1 and PCNA foci resembling replication catastrophes. Inhibiting transcription partly attenuated DNA damage, suggesting rescue of transcription-replication collisions at difficult-to-replicate sequences. In BMI1 knockdown or pyridostatin-exposed HDFs, the Werner helicase accumulated and co-localized with G4s. Acute WRN knockdown also resulted in G4 induction. In HDFs from Werner and Hutchinson-Gilford progeria syndromes, loss of heterochromatin and nuclear envelope anomalies were associated with G4 induction and DNA damage. Nuclear envelope anomalies were also prominent following BMI1 knockdown. These findings suggests that heterochromatin-mediated repression of G4s attenuates replication stress and genomic instability, and that this mechanism is shared across distinct progeroid models.

cell biology↗

bioRxiv2024

Epigenomic anomalies in induced pluripotent stem cells from Alzheimer disease cases

Reprogramming of adult somatic cells into induced pluripotent stem cells (iPSCs) resets the aging clock. However, primed iPSCs can retain cell-of-origin epigenomic marks, especially those linked to heterochromatin and lamina-associated regions. Here we show that iPSCs produced from dermal fibroblasts of late-onset sporadic Alzheimers disease (AD) cases retain epigenomic anomalies that supersede developmental defects and neurodegeneration. When compared to iPSCs from elderly controls, AD iPSCs show reduced BMI1 expression, lower H3K9me3 levels, and an altered DNA methylome. Gene Ontology analysis of differentially methylated DNA regions (DMRs) reveals terms linked to cell-cell adhesion and synapse, with the cognitive resilience-associated MEF2 family of transcription factors being the most enriched at DMRs. Upon noggin exposure, AD iPSCs show lesser efficient neural induction and forebrain specification, together with increased ZIC2, ZIC5 and WNT-related gene expression. Long-term AD neuronal cultures present a dedifferentiation and loss-of-cell identity phenotype. Despite these epigenomic anomalies, AD iPSCs generate cortical neurons in normal proportion and readily form cerebral organoids developing amyloid and Tau pathology. BMI1 overexpression in AD neurons mitigates amyloid and tau accumulation, heterochromatin fragmentation, and G4 DNA induction. These findings implicate reprogramming resistant epigenomic anomalies or uncharacterized genetic alterations working in trans on the epigenome in AD pathophysiology.

neuroscience↗

bioRxiv2023

Sub-retinal transplantation of human iPSC-derived retinal sheets: A promising approach for the treatment of macular degeneration

Retinal degenerative diseases affect millions of people worldwide, and legal blindness is generally associated with the loss of cone photoreceptors located in the retinas central region called the macula. Currently, there is no treatment to replace the macula. Addressing this unmet need, we employed control isogenic and hypoimmunogenic induced pluripotent stem cell (iPSC) lines to generate spontaneously polarized retinal sheets (RSs). They presented the advantage of facile customization and large-scale production, exhibiting a polarized 3D architecture within a 2D cell culture environment, thus readily adaptable for clinical applications. RSs were enriched in retinal progenitor and cone precursor cells, which could differentiate into mature S- and M/L-cones in long-term cultures. Single-cell RNA-seq analysis showed that RSs recapitulate the ontogeny of the developing human retina and are devoid of pluripotent stem cells. Isolation of neural rosettes for sub-retinal transplantation effectively eliminated unwanted cells such as RPE cells. In a porcine model of chemically induced retinal degeneration, grafts integrated the host retina and formed a new, yet immature, photoreceptor layer, exhibiting viability for up to 2 months. In one transplanted animal that met all criteria, including correct apicobasal orientation and seamless graft integration, functional and immunohistochemical assays suggest that grafts exhibited responsiveness to light stimuli and established putative synaptic connections with host bipolar neurons. This study underscores the potential and challenges of iPSC-derived RS for clinical applications while establishing the optimal methodology and conditions for RS transplantation, thus paving the path for future long-term functional investigations using RS grafts.

bioengineering↗