The Function Of ARL2 In Mammalian Retinas

The retinal degeneration are a group of diseases that lead to the loss of functional vision and often progressing to blindness.In human retinopathy,numerous mutated genes were screen out to find that they lead to death of photoreceptor mostly via mistrafficking of proteins in photoreceptors.Up to now,there is still no effective treatment and no cure.Thus,the new causative genes and molecular basis of the pathogenesis are still awaiting further investigation.Arl2,which encodes a 20 kDa GTPase ARL2,known as a member of the Arl gene family,is highly conserved and ubiquitously expressed in eukaryotes.ARL2 participated in regulating tubulin folding,mitochondrial mobility and might maintaining vision function in photoreceptors.This study aimed to identify the phenotype of Arl2 conditioned knockout mice to study whether ARL2 was involved in the transport of membrane proteins,as well as the influences on mitochondria and tubulins.In our study,we developed eye-specific Arl2 knockout mice using Cre / Loxp and Frt / Flp recombination system and using conditional gene knockout technique to study the function of ARL2 in photoreceptors.Immunohistochemstry method,laser confocal scanning microscopy,and transmission electron microscopy were used to identify the phenotype of the knockout mice,including expression level of membrane proteins,and to verify whether the morphology and function of retina are affected.Compared with WT mice,Arl2-/-mice were significantly smaller in both body size and eyeballs at P12.In P30,a large amount of photoreceptors might die via apoptosis,while thickness of retina,and number of cells were significantly reduced.The expression of TM(rhodopsin,ML-opsins,GC1,CNGA1/3)and PM(T?,GRK1,PDE6)were slightly down-regulated,and the immuno staining of Rhodopsin and INPP5 E proteins exhibited obvious mistrafficking,while others are not.The ultrastructure of the Arl2-/-mice not significantly different from the normal mice.Additionally,loss of ARL2 resulted in down-regulation level of mitochondrial and tubulin;we surprisedly found that knockout mice could not generate a complete vascular structure in retina.Based on the results,ARL2 is critical for maintaining the survival of photoreceptors and the integrity of structure and function of retina in mice,and is of significance to the development of outer segment.ARL2 is not essential for transport of most membrane proteins but it can make fine adjustment to Rhodopsin and INPP5 E,namely,ARL2 might be a release factor of Rhodopsin and INPP5 E.In addition,ARL2 may play an important role in retinal vascular development.The molecular mechanism of retinal degeneration casused by knockout of Arl2 gene in eyes might be apoptosis,microtubules depolymerization,mitochondria reduction,and mistrafficking of membrane proteins.