A Novel Mutation In NRL Gene Causes Autosomal Dominant Retinitis Pigmentosa

Retinitis pigmentosa（RP）is a kind of progressive and inherited retinal degeneration disease,affecting approximately 1 in 3500 to 1 in 4000 individuals in the worldwide.Patients suffering from RP usually show night blindness or impaired dark adaptation in the early stage of the disease,followed by progressive loss of visual field and finally blindness.The diagnostic criteria of RP includes night blindness,impaired vision,loss of peripheral visual field and characteristic changes in the ocular fundus.RP shows high genetic heterogeneity.It can be inherited in modes of autosomal dominant,autosomal recessive,X-linked and mitochondrial.Autosomal dominant RP（adRP）accounts for 15-25% of all RP cases.Mutations causing adRP have so far been identified in following genes: RHO、ROM1、RP1、RDS、NRL、CRX.The neural retina leucine zipper gene（NRL）encodes a basic motif-leucine zipper transcription factor that highly and specifically expressed in retinal cells.NRL is a member of the Maf transcription factor family,it is a kind of DNA binding protein with two distinct domains.The N-terminal is a transactivation（TA）domain encoded by exon 2 while the C-terminal is the DNA-binding（DB）domain contains a leucine zipper motif for dimerization encoded by exon 3.The neural retina leucine zipper（NRL）gene is the third adRP causative gene that was found following RHO and RDS.It encodes a basic motif-leucine zipper transcription factor that belongs to the Maf transcription factor family,with a N-terminal transactivation（TA）domain and a C-terminal DNA-binding（DB）domain.NRL is highly and specifically expressed in the developing and mature rod nuclei but not cones,functioning synergistically with CRX,the cone-rod homeobox transcription factor,to activate dozens of rod specific genes（such as RHO,GNAT1,PDE6 B,etc）.Accordingly,NRL plays a key role in differentiation and development of retina and is also required for maintaining the normal function of rod photoreceptors in mammalian retina.In our study,we obtained a Chinese RP family from Hubei Province with adRP diagnosed in Tongji Hospital Affilitated of Huazhong University of Science and Techonlogy.We performed the whole-exome sequencing on the proband（II:2）to get some possible causing genes.Finally we identified an NRL mutation c.147₁49del（p.S50del）by using the bioinformations analysis,Sanger sequencing and co-segregation analysis.In order to confirm the pathogenicity of this mutation,we performed the mutant’s vector construction for eukaryotic expression,immunofluorescence staining,luciferase reporter assay and phosphorylation experiment.We found that the mutation didn’t affect the subcellular localization of NRL but could accelerate the transcriptional activation ability and reduce phosphorylation level of NRL,which is consistent with the previously reported adRP-causing mutations of NRL.To sum up,we identified a novel mutation c.147₁49del（p.S50del）of NRL gene leading to adRP by means of whole-exome sequencing and investigated it’s pathogenicity by testing the mutant’s expression,transcriptional activation ability and phosphorylation modification,which expands the mutation spectrum of adRP and provides helpful cues for similar RP diagnosis,prenatal diagnosis and precise treatment.