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

by Sara Formichetti, Agnieszka Sadowska, Michela Ascolani, Julia Hansen, Kerstin Ganter, Christophe Lancrin, Neil Humphreys, Mathieu Boulard

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 OGT’s function in vivo by creating a murine allelic series of four single amino acid substitutions, reducing OGT’s catalytic activity to a range of degrees. The severity of the embryonic lethality was proportional to the extent of impairment of OGT’s catalysis, demonstrating that the O-GlcNAc modification itself is required for early development. We identified hypomorphic Ogt alleles that perturb O-GlcNAc homeostasis while being compatible with embryogenesis. The analysis of the transcriptomes of the mutant embryos at different developmental stages suggested a sexually-dimorphic developmental delay caused by the decrease in O-GlcNAc. Furthermore, a mild reduction of OGT’s enzymatic activity was sufficient to loosen the silencing of endogenous retroviruses in vivo.