Abstract
Purpose :
Mutations in TMEM216, a ciliary transition zone tetraspan transmembrane protein, are linked to Joubert Syndrome (JBTS) and Meckel Syndrome (MKS). Photoreceptor degeneration is a prominent phenotype in Joubert Syndrome. How TMEM216 contributes to photoreceptor health is poorly understood.
Methods :
We have generated TMEM216 mutant zebrafish by CRISPR genome editing. The impact of TMEM216 deletion on photoreceptors was evaluated by immunofluorescence staining and electron microscopy.
Results :
Homozygous TMEM216 mutant zebrafish died before 21-days post fertilization. Their retina exhibited reduced immunoreactivity to rod photoreceptor outer segment marker 4D2, and cone photoreceptor outer segment marker G protein subunit alpha transducin 2 (GNAT2). Terminal deoxynucleotidyl transferase dUTP Nick-End Labeling (TUNEL) revealed an increase in TUNEL-positive nuclei in the mutant retina, indicating photoreceptor degeneration. TMEM216 mutation resulted in shortened photoreceptor ciliary axoneme, as revealed by acetylated α-tubulin immunostaining. Photoreceptors in mutant zebrafish exhibited mislocalization of outer segment proteins such as rhodopsin, GNAT2, and red opsin to the inner segment and cell bodies. Additionally, electron microscopy revealed that the mutant photoreceptors elaborated outer segment with abnormal disc morphology such as shortened discs and vesicles/vacuoles within the outer segment.
Conclusions :
Our results indicate that TMEM216 is essential for normal genesis of outer segment disc structures, transport of outer segment materials, and survival of photoreceptors in zebrafish. These TMEM216 mutant zebrafish will be useful in studying how transition zone proteins regulate photoreceptor outer segment formation and maintenance.
This is a 2020 ARVO Annual Meeting abstract.