Analysis of a zebrafish dync1h1 mutant reveals multiple functions for cytoplasmic dynein 1 during

: Abstract Background Photoreceptors of the retina are highly compartmentalized cells that function as the primary sensory neurons for receiving and initiating transmission of visual information. Proper morphogenesis of photoreceptor neurons is essential for their normal function and survival. We have characterized a zebrafish mutation, cannonball, that completely disrupts photoreceptor morphogenesis. Results Analysis revealed a non-sense mutation in cytoplasmic dynein heavy chain 1 (dync1h1), a critical subunit in Dynein1, to underlie the cannonball phenotypes. Dynein1 is a large minus-end directed, microtubule motor protein complex that has been implicated in multiple, essential cellular processes. In photoreceptors, Dynein1 is thought to mediate post-Golgi vesicle trafficking, while Dynein2 is thought to be responsible for outer segment maintenance. Surprisingly, cannonball embryos survive until larval stages, owing to wild-type maternal protein stores. Retinal photoreceptor Abstract Background: Photoreceptors of the retina are highly compartmentalized cells that function as the primary sensory neurons for receiving and initiating transmission of visual information. Proper morphogenesis of photoreceptor neurons is essential for their normal function and survival. We have characterized a zebrafish mutation, cannonball , that completely disrupts photoreceptor morphogenesis. Results: Analysis revealed a non-sense mutation in cytoplasmic dynein heavy chain 1 ( dync1h1 ), a critical subunit in Dynein1, to underlie the cannonball phenotypes. Dynein1 is a large minus-end directed, microtubule motor protein complex that has been implicated in multiple, essential cellular processes. In photoreceptors, Dynein1 is thought to mediate post-Golgi vesicle trafficking, while Dynein2 is thought to be responsible for outer segment maintenance. Surprisingly, cannonball embryos survive until larval stages, owing to wild-type maternal protein stores. Retinal photoreceptor neurons, however, are significantly affected by loss of Dync1h1, as transmission electron microscopy and marker analyses demonstrated defects in organelle positioning and outer segment morphogenesis and suggested defects in post-Golgi vesicle trafficking. Furthermore, dosage-dependent antisense oligonucleotide knockdown of dync1h1 revealed outer segment abnormalities in the outer segments, well organized connecting cilium and basal body, tightly packed mitochondria in the ellipsoid region, Golgi apparatus just api- cal to the nucleus in the myoid region, and numerous inputs and floating ribbons in the synaptic region. Photoreceptors of dync1h1 morphants and cnb mutants showed a spectrum of phenotypes with the most normal photoreceptors positioned in the central retina and more severely affected photoreceptors at the periphery. Cellular defects included increased incidence of outer segment vesiculation, varying degrees of organelle dispersion and depolarization, and un-der-development of the synaptic region. OS, outer segment; IS, inner segment; CB cell body; SR, synaptic region; E, ellipsoid region; M, myoid region.