Cone Specific -Transducin Rescues Rod Function in the Rod -Transducin Knockout Mice

Abstract

Purpose: : The cone photoreceptor function loss 3 (Gnat2^cpfl3) mouse carries a missense mutation in the cone α-transducin Gnat2 gene, and the rod α-transducin knockout mouse has a targeted deletion of rod α-transducin Gnat1 gene. The Gnat2^cpfl3 mouse has an undetectable cone electroretinogram (ERG) and a normal rod ERG, whereas rod α-transducin knockout mouse has an undetectable rod ERG but a normal cone ERG. We have shown previously that AAV vector-mediated expression and cone-targeted delivery of rod GNAT1 in cones restored cone ERG function in the Gnat2^cpfl3 mice. Here we investigate whether rod function in the rod α-transducin mice can be rescued by rod-targeted delivery of the cone α-transducin GNAT2. In each vector treated mouse, localization of GNAT1 and GNAT2 in dark- and light-adapted conditions were also examined to study cone protein translocation in rods and rod protein translocation in cones when exogenously expressed.

Methods: : A murine GNAT2 cDNA was cloned into an AAV vector backbone under the control of a mouse opsin promoter (pTR-mops500-GNAT2) and packaged into serotype 5 capsids. 1ul of AAV5-mops500-GNAT2 virus (5X10¹³ particles/ml) was injected subretinally into the right eyes of nine rod α-transducin mice at postnatal day 23. ERG analysis was performed one month after injection. Immunostaining and confocal microscope were used to study the localization of GNAT1 and GNAT2.

Results: : Six of nine GNAT2 treated rod α-transducin knockout eyes responded to the therapy and rod ERG amplitudes were corrected to within the normal range. In GNAT1 treated Gnat2^cpfl3 mice, preliminary immunostaining results indicated that GNAT1 is localized in the outer segment (OS) of cones and does not translocate in either or dark environments although more analysis is underway to confirm this observation. The localization of GNAT2 in rod under light and dark-adapted conditions is also under investigation in Gnat1 knockout mice.

Conclusions: : The results demonstrate that GNAT1 is able to substitute for GNAT2 and restore cone ERG in Gnat2^cpfl3 mice, and visa versa, GNAT2 can substitute GNAT1 and rescue rod ERG in rod α-transducin knockout mice.

Keywords: photoreceptors • protein structure/function • gene transfer/gene therapy