Conditional Deletion of Cytoplasmic Dynein Heavy Chain in Postnatal Photoreceptors

PURPOSE: Cytoplasmic dynein-1 (henceforth dynein) moves cargo in conjunction with dynactin toward the minus end of microtubules. The dynein heavy chain, DYNC1H1, comprises the backbone of dynein, a retrograde motor. Deletion of Dync1h1 abrogates dynein function. The purpose of this communication is to demonstrate effects of photoreceptor dynein inactivation during late postnatal development and in adult retina. METHODS: We mated Dync1h1(F/F) mice with iCre75 and Prom1-CreER(T2) mice to generate conditional rod and tamoxifen-induced knockout in rods and cones, respectively. We documented retina degeneration with confocal microscopy at postnatal day (P) 10 to P30 for the iCre75 line and 1 to 4 weeks post tamoxifen induction (wPTI) for the Prom1-CreER(T2) line. We performed scotopic and photopic electroretinography (ERG) at P16 to P30 in the iCre75 line and at 1-week increments in the Prom1-CreER(T2) line. Results were evaluated statistically using Student's t-test, two-factor ANOVA, and Welch's ANOVA. RESULTS: Cre-induced homologous recombination of Dync1h1(F/F) mice truncated DYNC1H1 after exon 23. (rod)Dync1h1(−/−) photoreceptors degenerated after P14, reducing outer nuclear layer (ONL) thickness and combined inner segment/outer segment (IS/OS) length significantly by P18. Scotopic ERG a-wave amplitudes decreased by P16 and were extinguished at P30. Cones were stable under rod-knockout conditions until P21 but inactive at P30. In (tam)Dync1h1(−/−) photoreceptors, the IS/OS began shortening by 3wPTI and were nearly eliminated by 4wPTI. The ONL shrank significantly over this interval, indicating rapid photoreceptor degeneration following the loss of dynein. CONCLUSIONS: Our results demonstrate dynein is essential for the secretory pathway, formation of outer segments, and photoreceptor maintenance.