Biology subjects

Boulard, M.

Publications and source records attributed to Boulard, M..

4 recordsLinked to original sources

bioRxiv2025

The transcription of a single olfactory receptor per neuron is enforced by epigenetic silencing of their enhancers

The ability to discriminate thousands of odors in our environment requires each olfactory neuron to express a single olfactory receptor from hundreds of available genes. The biochemical mechanism enforcing this monogenic expression remains unknown. We show that deletion of the chromatin protein TRIM66 causes individual olfactory neurons to express multiple receptors at a high level, demonstrating that monogenic expression relies on an epigenetic silencing mechanism. Moreover, TRIM66 is specifically recruited to olfactory receptor gene super-enhancers during neuronal progenitor maturation, thereby silencing nearby olfactory receptor genes. Loss of monogenic expression disrupted axonal projections to the olfactory bulb, resulting in an aberrant topographic map and impaired social odor discrimination and reproductive behaviors. These findings uncover the chromatin-based silencing of super-enhancers as the mechanism underlying the organization of the mammalian olfactory system.

molecular biology↗

bioRxiv2024

Genetic gradual reduction of OGT activity unveils the essential role of O-GlcNAc in the mouse embryo

The reversible glycosylation of nuclear and cytoplasmic proteins (O-GlcNAcylation) is catalyzed by a single enzyme, namely O-GlcNAc transferase (OGT). The mammalian Ogt gene is X-linked and it is essential for embryonic development and for the viability of proliferating cells. We perturbed OGTs function in vivo by creating a murine allelic series of four single amino acid substitutions reducing OGTs catalytic activity to a range of degrees. The severity of the embryonic lethality was proportional to the degree of impairment of OGTs catalysis, demonstrating that the O-GlcNAc modification itself is required for early development. We identified milder hypomorphic Ogt alleles that perturb O-GlcNAc homeostasis while being compatible with embryogenesis. The analysis of the transcriptomes of the mutant embryos at different stages suggested a sexually-dimorphic developmental delay caused by the decrease in O-GlcNAc. Furthermore, a mild reduction of OGTs enzymatic activity was sufficient to loosen the silencing of endogenous retroviruses in vivo.

developmental biology↗

bioRxiv2024

Trim66 paternal deficiency causes intrauterine overgrowth

The tripartite motif-containing protein 66 (TRIM66, also known as TIF1-delta) is a PHD-Bromo containing protein primarily expressed in post-meiotic male germ cells known as spermatids. Biophysical assays showed that TRIM66 PHD-Bromo domain binds to H3 N-terminus only when lysine 4 is unmethylated. We addressed TRIM66s role in reproduction by loss-of-function genetics in the mouse. Males homozygous for Trim66-null mutations produced functional spermatozoa. Round spermatids lacking TRIM66 upregulated a network of genes involved in histone acetylation and H3K4 methylation. Profiling of H3K4me3 patterns in the sperm produced by Trim66-null mutant showed minor alterations below statistical significance. Unexpectedly, Trim66-null males, but not females, sired pups overweight at birth, hence revealing that Trim66 mutations cause a paternal effect phenotype.

developmental biology↗

bioRxiv2024

Perturbing nuclear glycosylation in the mouse preimplantation embryo slows down embryonic growth

The only known form of intracellular protein glycosylation (O-GlcNAc) is reversible and has been mapped on thousands of cytoplasmic and nuclear proteins, including RNA polymerase II, transcription factors and chromatin modifiers. The O-GlcNAc modification is catalyzed by a single enzyme known as O-GlcNAc Transferase (OGT), that is required for mammalian early development. Remarkably, the regulatory function of protein O-GlcNAcylation in the embryo as well as the embryonic O-GlcNAc proteome remain unknown. Here, we devised a new method to enzymatically remove O-GlcNAc from preimplantation embryonic nuclei, where it accumulates coincidently with embryonic genome activation (EGA). Unexpectedly, the depletion of nuclear O-GlcNAc to undetectable levels has no impact on EGA, but dampens the transcriptional activation of the translational machinery, and triggers a spindle checkpoint response. These molecular alterations were phenotypically associated with a developmental delay starting from early cleavage stages and persisting after embryo implantation, establishing a novel link between nuclear glycosylation and embryonic growth.

developmental biology↗