Haploinsufficiency of GCP4 induces autophagy and leads to photoreceptor degeneration due to defective spindle assembly in retina

Retinopathy, owing to damage to the retina, often causes vision impairment, and the underlying molecular mechanisms are largely unknown. Using a gene targeting strategy, we generated mice with the essential gene Tubgcp4 knocked out. Homozygous mutation of Tubgcp4 resulted in early embryonic lethality due to abnormal spindle assembly caused by GCP4 (gamma-tubulin complex protein 4, encoded by Tubgcp4) depletion. Heterozygotes were viable through dosage compensation of one wild-type allele. However, haploinsufficiency of GCP4 affected the assembly of γ-TuRCs (γ-tubulin ring complexes) and disrupted autophagy homeostasis in retina, thus leading to photoreceptor degeneration and retinopathy. Notably, GCP4 exerted autophagy inhibition by competing with ATG3 for interaction with ATG7, thus interfering with lipidation of LC3B. Our findings justify dosage effects of essential genes that compensate for null alleles in viability of mutant mice and uncover dosage-dependent roles of GCP4 in embryo development and retinal homeostasis. These data have also clinical implications in genetic counseling on embryonic lethality and in development of potential therapeutic targets associated with retinopathy.