caractérisation des enzymes bovines et étude préliminaire du rôle ...

Abstract
O-fucosylation is the addition of a fucose on serine or threonine comprised in two
types of peptidic domains, EGF and TSR. This post-translational modification depends on
two enzymes. Pofut1 is responsible for O-fucosylation of EGF repeats, whereas Pofut2 adds
fucose on TSR. We studied the evolution of Pofut1 and Pofut2 genes and demonstrated that
these genes, present in a single copy, already existed in the ancestor of Bilaterians, or even
Metazoans, probably in polyexonic form. An original situation exists for Pofut2, recovered in
a group of Protozoans, the Apicomplexa. Structures of the two bovine genes and their tissular
expression have been established. We find an original situation since it exists for each of
them, five transcript variants of which only one encodes the active enzyme, differently
expressed among bovine tissues. The Pofut1 and Pofut2 active enzymes would be present in
all analyzed tissues, except for adult skeletal muscles where atypical forms are present. The
other transcript variants, more or less truncated, probably play a role in regulating the
expression level of these genes. Pofut1 is the first fucosyltransferase to have been identified as
an endoplasmic reticulum resident. Functionally, we demonstrated for the bovine that this
glycosyltransferase, bearing two N-glycans probably of oligomannosidic type, was correctly
folded and therefore possessed an enzymatic activity, provided its first site of N-glycosylation
is occupied. The activity of the Notch receptors and their ligands, present at the surface of
numerous cells, is modulated by the state of O-fucosylation of their EGF domains.
Considering the implication of these receptors in the regulation of myogenesis, Ofucosylation
must contribute all as much there. Thus, we started a study of the repercussions
of a modulation of Pofut1 expression on the differentiation of bovine primary muscular cells
and murine cells of the C2C12 lineage. We show that the transient surexpression of the
murine Pofut1 enzyme delays the expression of myogenic transcription factors belonging to
bHLH family: Myf5, MyoD, Myogenine and MRF4. These preliminary results open new and
exciting perspectives of analysing the influence of O-fucosyltransferases during the complex
process of myogenesis.
Key words : O-fucosylation, genomic organisation, transcript variants, phylogeny, Ofucosyltransferase
activity, myogenesis, cattle