Abstract
Purpose :
Infantile nystagmus syndrome (INS) is a gaze-holding disorder characterized by conjugate, uncontrolled oscillation of the eyes that can result in significant loss of visual acuity. However, a large number of INS patients have no known cause in the absence of known sensory afferent defects or previously identified genetic mutations. Using the albino mouse as a model for nystagmus, we tested the optokinetic nystagmus reflexes (OKN) of a mouse strain developed from C57BL6 mice with a mutation in the tyr gene making them phenotypically albino. We performed RNAseq on the extraocular muscles (EOM) and abducens (CN6) and oculomotor (CN3) neurons from B6(CG)-Tyr(c-2J)/J and C57BL6 mice in an attempt to discover molecular differences that may account for nystagmus.
Methods :
OKN was measured in C57BL6 and the B6(CG)-Tyr(c-2J)/J mice using an iSCAN system. EOM, tibialis anterior (TA), neuronal populations from CN3 and CN6 isolated en block were dissected from the C57BL6 and B6(CG)-Tyr(c-2J)/J mouse strains. RNA was isolated using a Qiagen kit, and RNAseq analyses were performed. RNA expression levels were compared between the strains to determine genes that were over or under-expressed in the normal compared to the nystagmus mice. We validated candidate genes with a 2-fold difference using PCR and immunohistochemical staining of mouse and surgical waste tissues in children with INS.
Results :
All the B6(CG)-Tyr(c-2J)/J mice tested had a nystagmus phenotype when measured with OKN, while the C57BL6 mice had normal OKN. Differential expression analysis from the RNA isolated from the B6(CG)-Tyr(c-2J)/J mice compared to the C57BL6 showed 286 genes differentially expressed in the EOM, 11 genes differentially expressed in the CNs, and 2 genes differentially expressed in all four tissue types: wdfy1 and nnt. Wdfy1 showed decreased immunostaining in rectus muscle samples from human nystagmus subjects compared to controls.
Conclusions :
The B6(CG)-Tyr(c-2J)/J mice have nystagmus but, except for the mutation in the tyr gene, are genetically very similar to the C57BL6 mice. Wdfy1 and nnt have been implicated in mitochondrial dysfunction and in maintenance of stem cells in other systems, but their function in the extraocular muscles is unknown. These studies suggest that this mouse model of nystagmus makes them a prime candidate for studying differentially expressed genes between normal and nystagmus mouse groups.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.