Syntaxin3B ablation in rods and cones leads to mistrafficking a small pool of Prph2 and ROM1

Abstract

Purpose : Syntaxin3B (STX3B) is a member of the Syntaxin SNARE family and is found in photoreceptor cell bodies, inner segments (IS) and synaptic terminals (ST). Although it is known to play a part in neurotransmitter release in rod and cone synaptic terminals, its role in protein trafficking in photoreceptors is not well understood. Previously we showed that a small pool of peripherin 2 (Prph2) and rod outer segment protein 1 (ROM1) binds to STX3B and we are here addressing its potential role in their outer segment (OS) localization.

Methods : STX3B^LoxP/LoxP mice were generated and independently backcrossed into iCre75 and CRX-Cre lines to activate Cre recombinase in rods at postnatal (P) day 7 (STX3B^{f/f (iCre75)}) and in rods/cones (STX3B^{f/f (CRX-Cre)}) embryonically. Functional and structural consequences of STX3B ablation were followed by electroretinography (ERG) and histology at the light and ultrastructural levels. Immunohistochemistry (IHC) was used to assess protein distribution.

Results : STX3B^{f/f (iCre75)} exhibited a gradual photoreceptor loss starting at P30 followed by a gradual reduction in rod function (55% reduction in scotopic A and B waves) while no reductions were noted in photopic amplitudes (Fig. 1A&B). IHC showed mislocalization of Prph2 but not ROM1 to the IS and synaptic terminals (Fig. 1C&D). STX3B^{f/f (CRX-Cre)}, on the other hand, had full complement of photoreceptors at P15 while fully absent at P30 and lacked any light evoked rod and cone responses (Fig. 1A&B). ROM1 followed the same pattern of Prph2 miclocalization in STX3B^{f/f (iCre75)} (Fig. 1C&D). However, the majority of Prph2 and ROM1 were properly located to OSs in both STX3B^{f/f (iCre75)} and STX3B^{f/f (CRX-Cre)} along with other STX3B associated proteins such as rhodopsin.

Conclusions : Our data suggest that STX3B plays a role in trafficking a small pool of Prph2 and ROM1 to the OSs and hence plays a role in photoreceptor development. Our studies also show that the majority of Prph2 and ROM1 do not rely on STX3B to reach the OS. Future studies will be focused on embryonically eliminating STX3B separately in rods and postnatally in cones.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.