Photoreceptors are highly polarized, compartmentalized cells. Protein synthesis initiates in the inner segment and then transport proceeds in the apical direction toward the outer segment or basally toward the synapse. In recent years, several investigators have made seminal discoveries about the mechanism(s) of transport to the outer segment. In contrast, very little is known about the transport of proteins destined for the synapse or the sorting within the inner segment of proteins destined for different cellular compartments. Phosphoinositides are known to be key regulators in membrane trafficking and are involved in signaling, specification and protein recruitment in a wide variety of cell types. A key regulator of cellular phosphoinositides is the lipid phosphatase, synaptojanin I (SynJ1), whose primary intracellular target is PI(4,5)P2. We have established zebrafish as a model system in which to evaluate both phosphoinositide signaling and SynJ1 function in the process of protein sorting in cone photoreceptors. Our current work finds a role for SynJ1 in the inner segment. We find that SynJ1 concentrates in the cone inner segment and that large vesicles abnormally accrue and/or the Golgi architecture is disrupted in nrc mutants lacking this protein. We hypothesize that the inner segment phenotype reflects a disruption of transport and sorting of proteins destined for the synapse. We propose a series of experiments that test this hypothesis and define precisely the abnormal vesicular structures we detect in nrc inner segments, their content and derivation. The specific expected outcome of our proposal is a detailed understanding of the inner segment defect detected in nrc when the balance of polyphosphoinositides within the photoreceptor is disrupted due to the loss of the critical PI(4,5)P2 phosphatase, SynJ1. In addition, our studies will provide fundamental information about the cellular distribution of polyphosphoinositides in both wild-type and nrc cone photoreceptors. Finally, our studies will define the importance of different structural domains of SynJ1. The critical, fundamental information we discover from the studies outlined in this proposal will help open this field to many additional important investigations.
Proper phosphoinositide homeostasis is essential for normal photoreceptor function. Loss of the critical PI(4,5)P2 phosphatase synaptojanin 1 causes dramatic inner segment and synaptic vesicle transporting defects in cone photoreceptors. The findings from our proposed studies will yield novel and fundamental information that will deepen our understanding of phosphoinositide signaling in cones.
|George, Ashley A; Hayden, Sara; Stanton, Gail R et al. (2016) Arf6 and the 5'phosphatase of synaptojanin 1 regulate autophagy in cone photoreceptors. Bioessays 38 Suppl 1:S119-35|
|George, Ashley A; Hayden, Sara; Stanton, Gail R et al. (2016) Arf6 and the 5'phosphatase of Synaptojanin 1 regulate autophagy in cone photoreceptors. Inside Cell 1:117-133|
|Lewis, Alaron A; Mahoney, Joseph T; Wilson, Neil et al. (2015) Identification of amacrine subtypes that express the atypical cadherin celsr3. Exp Eye Res 130:51-7|
|Decker, Amanda R; McNeill, Matthew S; Lambert, Aaron M et al. (2014) Abnormal differentiation of dopaminergic neurons in zebrafish trpm7 mutant larvae impairs development of the motor pattern. Dev Biol 386:428-39|
|George, Ashley A; Hayden, Sara; Holzhausen, Lars C et al. (2014) Synaptojanin 1 is required for endolysosomal trafficking of synaptic proteins in cone photoreceptor inner segments. PLoS One 9:e84394|
|Lewis, Alaron; Wilson, Neil; Stearns, George et al. (2011) Celsr3 is required for normal development of GABA circuits in the inner retina. PLoS Genet 7:e1002239|
|Brockerhoff, Susan E (2011) Phosphoinositides and photoreceptors. Mol Neurobiol 44:420-5|
|Ile, Kristina E; Kassen, Sean; Cao, Canhong et al. (2010) Zebrafish class 1 phosphatidylinositol transfer proteins: PITPbeta and double cone cell outer segment integrity in retina. Traffic 11:1151-67|
|Holzhausen, Lars C; Lewis, Alaron A; Cheong, Kimberly K et al. (2009) Differential role for synaptojanin 1 in rod and cone photoreceptors. J Comp Neurol 517:633-44|
|Trapani, Josef G; Obholzer, Nikolaus; Mo, Weike et al. (2009) Synaptojanin1 is required for temporal fidelity of synaptic transmission in hair cells. PLoS Genet 5:e1000480|
Showing the most recent 10 out of 13 publications