PITPNM1 and retinal degeneration: Dendritic retraction of second order neurons, typically observed in faster forms of retinal degeneration (Jones et al., 2003; Marc et al., 2003; Gargini et al., 2007; Strettoi, 2015), is never observed in rd9 mutants, reinforcing the notion that only major photoreceptor death can drive synaptic deafferentation in the outer retina and major regressive remodeling of inner retinal neurons and suggesting the existence of a photoreceptor loss threshold for initiating this remodeling.