Biology subjects

Blouin, C.

Publications and source records attributed to Blouin, C..

5 recordsLinked to original sources

bioRxiv2024

A mutant ASXL1-EHMT complex contributes to heterochromatin dysfunction in clonal hematopoiesis and chronic monomyelocytic leukemia

ASXL1 is one of the three most frequently mutated genes in age-related clonal hematopoiesis (CH), alongside DNMT3A and TET2. CH can progress to myeloid malignancies including chronic monomyelocytic leukemia (CMML), and is also strongly associated with inflammatory cardiovascular disease and all-cause mortality in humans. DNMT3A and TET2 regulate DNA methylation and demethylation pathways respectively, and loss-of-function mutations in these genes reduce DNA methylation in heterochromatin, allowing de-repression of silenced elements in heterochromatin. In contrast, the mechanisms that connect mutant ASXL1 and CH are not yet fully understood. CH/CMML-associated ASXL1 mutations encode C-terminally truncated proteins that enhance the deubiquitinase activity of the ASXL-BAP1 "PR-DUB" deubiquitinase complex, which removes mono-ubiquitin from H2AK119Ub. Here we show that ASXL1 mutant proteins interact with the EHMT1-EHMT2 methyltransferase complex, which generates H3K9me1 and me2, the latter a repressive modification in constitutive heterochromatin. Compared to cells from age-matched wildtype mice, we found that expanded myeloid cells from old ([≥]18-month-old) Asxl1tm/+ mice, a heterozygous knock-in mouse model of CH, display genome-wide decreases of H3K9me2, H3K9me3 and H2AK119Ub as well as an associated increase in expression of transposable elements (TEs) and satellite repeats. Increased TE expression was also observed in monocytes from ASXL1-mutant CMML patients compared to monocytes from healthy controls. Our data suggest that mutant ASXL1 proteins compromise the integrity of both constitutive and facultative heterochromatin in an age-dependent manner, by reducing the levels of H3K9me2/3 and H2AK119Ub. This increase in TE expression correlated with increased expression of nearby genes, including many interferon-inducible (inflammation-associated) genes (ISGs). Significance StatementAge-related clonal hematopoiesis (CH) is a premalignant condition associated with inflammatory cardiovascular disease. ASXL1 mutations are very frequent in CH. We show that ASXL1 interacts with EHMT1 and EHMT2, H3K9 methyltransferases that deposit H3K9me1 and me2. Using a mouse model of mutant ASXL1 to recapitulate CH, we found that old ASXL1-mutant mice showed marked expansion of myeloid cells in bone marrow, with decreased H3K9me2/3 and increased expression of transposable elements (TEs) in heterochromatin. In humans, ASXL1-mutant CH progresses to chronic monomyelocytic leukemia (CMML); CMML patient samples showed striking upregulation of many TE families, suggesting that ASXL1 mutations compromise heterochromatin integrity, hence causing derepression of TEs. Targeting heterochromatin-associated proteins and TEs might counter the progression of CH, CMML and other myeloid malignancies.

cancer biology↗

bioRxiv2019

Caveolae coupling of melanocytes signaling and mechanics is required for human skin pigmentation

Tissue homeostasis requires regulation of cell-cell communication, which relies on signaling molecules and cell contacts. In skin epidermis, keratinocytes secrete specific factors transduced by melanocytes into signaling cues to promote their pigmentation and dendrite outgrowth, while melanocytes transfer melanin pigments to keratinocytes to convey skin photoprotection. How epidermal cells integrate these functions remains poorly characterized. Here, we found that caveolae polarize in melanocytes and are particularly abundant at melanocyte-keratinocyte interface. Caveolae in melanocytes are sensitive to ultra-violet radiations and miRNAs released by keratinocytes. Preventing caveolae formation in melanocytes results in increased production of intracellular cAMP and melanin pigments, but decreases cell protrusions, cell-cell contacts, pigment transfer and epidermis pigmentation. Altogether, our data establish that, in melanocytes, caveolae serve as key molecular hubs that couple signaling outputs from keratinocytes to mechanical plasticity. This process is crucial to maintain cell-cell contacts and intercellular communication, skin pigmentation and tissue homeostasis.

cell biology↗

bioRxiv2017

Protein structures as shapes: Analysing protein structure variation using geometric morphometrics

A phenotype is defined as an organisms physical traits. In the macroscopic world, an animals shape is a phenotype. Geometric morphometrics (GM) can be used to analyze its shape. Lets pose protein structures as microscopic three dimensional shapes, and apply principles of GM to the analysis of macromolecules. In this paper we introduce a way to 1) abstract a structure as a shape; 2) align the shapes; and 3) perform statistical analysis to establish patterns of variation in the datasets. We show that general procrustes superimposition (GPS) can be replaced by multiple structure alignment without changing the outcome of the test. We also show that estimating the deformation of the shape (structure) can be informative to analyze relative residue variations. Finally, we show an application of GM for two protein structure datasets: 1) in the -amylase dataset we demonstrate the relationship between structure, function, and how the dependency of chloride has an important effect on the structure; and 2) in the Niemann-Pick disease, type C1 (NPC1) proteins molecular dynamic simulation dataset, we introduce a simple way to analyze the trajectory of the simulation by means of protein structure variation.

bioinformatics↗

bioRxiv2017

The response to selection in Glycoside Hydrolase Family 13 structures: A comparative quantitative genetics approach

The Glycoside Hydrolase Family 13 (GH13) is both evolutionary diverse and relevant to many industrial applications. Its members perform the hydrolysis of starch into smaller carbohydrates. Members of the family have been bioengineered to improve catalytic function under industrial environments. We introduce a framework to analyze the response to selection of GH13 protein structures given some phylogenetic and simulated dynamic information. We found that the TIM-barrel is not selectable since it is under purifying selection. We also show a method to rank important residues with higher inferred response to selection. These residues can be altered to effect change in properties. In this work, we define fitness as inferred thermodynamic stability. We show that under the developed framework, residues 112Y, 122K, 124D, 125W, and 126P are good candidates to increase the stability of the truncated protein 4E2O. Overall, this paper demonstrate the feasibility of a framework for the analysis of protein structures for any other fitness landscape.

bioinformatics↗

bioRxiv2017

The response to selection in Glycoside Hydrolase Family 13 structures: A comparative quantitative genetics approach

Glycoside Hydrolase Family 13 (GH13) structures are responsible for the hydrolysis of starch into smaller carbohydrates. They important in industrial applications and evolutionary studies. This family has been thoroughly documented in the the Carbohydrate-Active enZYmes Database (CAZY), and divided into subfamilies based mainly in sequence information. Here we give structural evidence into GH13 classification and evolution using structural information. Here we proposed a novel method that is sensitive enough to identify miss-classifications, or to provide evidence for further partition that can be of interests to bio-engineers and evolutionary biologists. We also introduced a method to explore the relative importance of residues with respect to the overall deformation that it causes to the overall structure in an evolutionary time scale. We found that the GH13 family can be classified into three main structural groups. There is a hierarchical structure within these clusters that can be use to inform other classification schemes. We also found that by using structural information, subtle structural shifts can be identified and that can be missed in sequence/phylogeny-only based classifications. When each structural group is explored, we found that identifying the most structurally variable sites can lead to identification of functionally (both catalytically and structurally) important residues.

bioinformatics↗