It is known that some matrix integrals over U(n) satisfy an sl(2,R)-algebra
of Virasoro constraints. Acting with these Virasoro generators on 2-dimensional
Schur function expansions leads to difference relations on the coefficients of
this expansions. These difference relations, set equal to zero, are precisely
the backward and forward equations for non-intersecting random walks. The
transition probabilities for these random walks appear as the coefficients of
an expansion of U(n)-matrix integrals (of the type above), by inserting in the
integral the product of two Schur polynomials associated with two partitions;
the latter are specified by the initial and final positions of the
non-intersecting random walk. An essential ingredient in this work is the
generalization of the Murnaghan-Nakayama rule to the action of Virasoro on
Schur polynomials.