Glycosylation of cell surface proteins is important in thymocyte maturation. In particular, the level of sialylation of key glycoproteins such as C
D45 is believe
d to play a major role in regulating TCR signaling, a
dhesion an
d apoptosis of
developing thymocytes. We show here that transgenic expression of human
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der="0">1–2 fucosyltransferase (
hFUT1) in mice resulte
d in a marke
d shift from sialylation to fucosylation of thymocyte glycoproteins. This was associate
d with a significant re
duction in thymocyte number, an increase
d rate of apoptosis in
double positive an
d single positive thymocytes, an
d a maturation arrest at TCR-
depen
dent
developmental transitions reminiscent of CD45
deficiency. In
dee
d, CD45RB
dimerization was elevate
d in
hFUT1 thymocytes, consistent with its hyposialylation, an
d there was a correspon
ding increase in phosphorylation of the TCR-associate
d protein Lck. However, contrary to the re
duce
d TCR signaling in CD45 null mice, basal an
d stimulate
d TCR signaling was higher in
hFUT1 thymocytes than in wil
d type thymocytes. Our results therefore
demonstrate that aberrant expression of a single glycosyltransferase can profoun
dly affect thymopoiesis, although the relative involvement of CD45-
depen
dent an
d -in
depen
dent mechanisms is yet to be
determine
d.