Biology subjects

Raposo, A. C.

Publications and source records attributed to Raposo, A. C..

4 recordsLinked to original sources

bioRxiv2026

A Translational Reference for Green Autofluorescence Imaging in the Rhesus Macaque Eye using the OcuMet Beacon

PurposeTo evaluate associations between green autofluorescence (GAF) and structural and functional measures relevant to retinal and optic neuropathies, and to establish normative GAF values across the optic nerve head (ONH), macula, and papillofoveal bundle (PFB) in rhesus macaques. MethodsEighty-two macaques with normal ONH morphology by spectral-domain optical coherence tomography (SD-OCT) were included with a mean {+/-} SD age of 12.76 {+/-} 7.18 (range 0.11-29.39) years. The GAF images were acquired in the ONH, macula and PFB with the OcuMet Beacon. In a subset of macaques (n=19), pattern electroretinogram (PERG) and photopic full-field ERG including the photopic negative response (PhNR) were recorded. ResultsThe GAF significantly increased with age in the ONH, macula and PFB. After adjusting by age, there were no sex differences, but IOP showed a positive association with macular GAF. At the ONH, higher GAF correlated with thinner retinal nerve fiber layer, inner and outer segment complex, and total retinal thickness. In the macula, inner nuclear layer thickness was positively associated with GAF, whereas outer plexiform layer and inner and outer segment complex were inversely associated. The PERG amplitudes inversely tracked ONH GAF. ConclusionsGAF rises with age and IOP, couples to retinal structure, and at the ONH, aligns with inner-retinal functional indices. This study provides a regional reference for GAF in rhesus macaques. Translational RelevanceNormative GAF data in healthy rhesus macaques provide a framework for interpreting this noninvasive signal in translational studies of retinal and optic nerve disease.

physiology↗

bioRxiv2024

Erosion of X-Chromosome Inactivation in female hiPSCs is heterogeneous and persists during differentiation

During culture, female human pluripotent stem cells (hPSCs), including human induced PSCs (hiPSCs) exhibit a propensity for erosion of X-chromosome inactivation (XCI). This phenomenon is characterized by the loss of XIST RNA expression and reactivation of a subset of X-linked genes from the inactive X chromosome (Xi). XCI erosion, despite its common occurrence, is often overlooked by the stem cell community, hindering a complete understanding of its impact on both fundamental and translational applications of hiPSCs. Investigating erosion dynamics in female hiPSCs, our study reveals that XCI erosion is a frequent yet heterogeneous phenomenon, resulting in the reactivation of several X-linked genes. The likelihood of a gene to erode increases for those located on the short arm of the X chromosome and within H3K27me3-enriched domains. Paradoxically, genes that typically escape XCI are hypersensitive to loss of XIST RNA and XCI erosion. This implies that XIST RNA normally restrains expression levels of these genes on the Xi. Importantly, increased X-linked gene expression upon erosion does not globally impact (hydroxy)methylation levels in hiPSCs or at imprinted regions. By exploring diverse differentiation paradigms, such as trilineage commitment and cardiac differentiation, our study reveals the persistence of abnormal XCI patterns throughout differentiation. This finding has significant implications for fundamental research, translational applications, and clinical use of stem cells. We underscore the importance of raising awareness within the stem cell community regarding XCI erosion and advocate for its inclusion in comprehensive hiPSC quality control.

molecular biology↗

bioRxiv2020

Tracking H3K27me3 and H4K20me1 dynamics during XCI reveals similarities in recruitment mechanism

During X chromosome inactivation (XCI), in female placental mammals, gene silencing is initiated by the Xist long-noncoding RNA. Xist accumulation at the X leads to enrichment of specific chromatin marks, including PRC2-dependent H3K27me3 and SETD8-dependent H4K20me1. However, the dynamics of this process in relation to Xist RNA accumulation remains unknown as is the molecular mechanism allowing for H4K20me1 enrichment. To follow XCI dynamics in living cells, we developed a genetically-encoded, H3K27me3-specific intracellular antibody, or H3K27me3-mintbody. By combining it with live-imaging of H4K20me1, the X chromosome and Xist RNA we uncover similarities in the initial accumulation dynamics of H3K27me3 and H4K20me1. Further ChIP-seq analysis confirmed concurrent accumulation of both marks during XCI albeit with distinct genomic distributions. Using a Xist B and C repeat mutant, which can silence the X but does not allow for H3K27me3 deposition, we also found a lack of H4K20me1 enrichment. Thus, these two marks accumulate at the X thanks to the same region of Xist and H4K20me1 in particular may have a role in the chromatin compaction that characterises facultative heterochromatin.

developmental biology↗

bioRxiv2018

Exploring the role of Polycomb recruitment in Xist-mediated silencing of the X chromosome in ES cells

Xist RNA has been established as the master regulator of X-chromosome inactivation (XCI) in female eutherian mammals but its mechanism of action remains unclear. By creating novel Xist mutants at the endogenous locus in mouse embryonic stem (ES) cells, we dissect the role of the conserved A-B-C-F repeats. We find that transcriptional silencing can be largely uncoupled from Polycomb repressive complex 1 and 2 (PRC1/2) recruitment, which requires repeats B and C. Xist {Delta}B+C RNA specifically loses interaction with PCGF3/5 subunits of PRC1, while binding of other Xist partners is largely unaffected. However, a slight relaxation of transcriptional silencing in Xist {Delta}B+C indicates a role for PRC1/2 proteins in early stabilization of gene repression. Distinct modules within the Xist RNA are therefore involved in the convergence of independent chromatin modification and gene repression pathways. In this context, Polycomb recruitment seems to be of moderate relevance in the initiation of silencing.

genetics↗