  Detecting the seed black holes from which quasars formed is extremely
challenging; however, those seeds that did not grow into supermassive should be
found as intermediate-mass black holes (IMBHs) of 100-10$^5$ M$_{\odot}$ in
local dwarf galaxies. The use of deep multiwavelength surveys has revealed that
a population of actively accreting IMBHs (low-mass AGN) exists in dwarf
galaxies at least out to $z\sim$3. The black hole occupation fraction of these
galaxies suggests that the early Universe seed black holes formed from direct
collapse of gas, which is reinforced by the possible flattening of the black
hole-galaxy scaling relations at the low-mass end. This scenario is however
challenged by the finding that AGN feedback can have a strong impact on dwarf
galaxies, which implies that low-mass AGN in dwarf galaxies might not be the
untouched relics of the early seed black holes. This has important implications
for seed black hole formation models.
