To explore the function of PDEδ in vivo, we generated a
Pde6d−/− mouse by loxP/
Cre-mediated recombination.
100 Deletion of exons 2, 3, and 4 destroyed the β-sandwich structure preventing binding of prenyl side chains. The
Pde6d−/− mouse was viable, developed normally, and was fertile, but exhibited significantly reduced body size early in life.
100 Phenotypically, the
Pde6d−/− mouse exhibited transport deficiency of several prenylated membrane-associated proteins, for example, GRK1, PDE6, and Tβγ, to rod and cone OSs (
Figs. 10A–D), which correlated with anomalous physiology. In
Pde6d−/− rod single-cell recordings, sensitivity to single photons was increased.
100 Double-flash electroretinograms (ERGs) indicated a >20-minute delay in recovery to the dark state in
Pde6d−/− rods (
Fig. 10F), which is likely due to severely reduced levels of GRK1 in ROS.
100 Surprisingly, rod PDE6 trafficked nearly normally (
Fig. 10A), whereas geranylgeranylated cone PDE6α' was undetectable by immunofluorescence in
Pde6d−/− COS (
Fig. 10D).
100 Under photopic (bright light) ERG conditions, the
Pde6d−/− cone response was diminished, which is consistent with reduced PDE6α' levels in cone outer segments (COS).
100 Taken together, PDEδ deletion in photoreceptors results in defective transport of a subset of prenylated proteins (PDE6 subunits and GRK1) to the OS. Transport defects vary, suggesting presence of additional, unidentified prenyl-binding proteins or alternative trafficking pathways. Visual pigments and other TM proteins trafficked normally.
100 The
Pde6d knockout mouse phenotype resembled a slowly progressing recessive rod–cone dystrophy (retinitis pigmentosa).