  A large fraction of bulgeless disk galaxies contain young compact stellar
systems at their centers, in spite of the local gravitational stability of
these disks. We evaluate two contrasting hypotheses for the origin of the
nuclear star clusters in late-type disk galaxies. The clusters could not have
migrated from distant eccentric locations in the disk. Instead they must have
formed in situ, requiring radial transport of gas toward the center of the
disk. This transport could be a consequence of the development of the
magnetorotational instability in the differentially rotating warm neutral
medium. We evaluate the rate of gas transport into the disk center and find
that it is sufficient to support continuous star formation in that location.
Enhanced stellar surface brightness in the inner few hundred parsecs and the
formation of a compact stellar system in the central few parsecs are
unavoidable in dark matter halos with divergent density profiles. We illustrate
our conclusions on a model of the nearest late-type disk galaxy M33.
