Changes in mRNA levels of the Myoc/Tigr gene in the rat eye after experimental elevation of intraocular pressure or optic nerve transection.

PURPOSE: To isolate the rat Myoc/Tigr gene and investigate changes in its expression pattern in normal eyes and in eyes with either pressure-induced optic nerve damage or optic nerve transection.
METHODS: Expression pattern of the rat Myoc/Tigr gene was investigated by Northern blot hybridization. Optic nerve damage and death of ganglion cells in the retina were induced unilaterally, by injection of hypertonic saline solution, episcleral vein cauterization, or optic nerve transection. The levels of mRNA for Myoc/Tigr were compared between several tissues of the control and surgically altered eyes, by using semiquantitative RT-PCR, real-time PCR, and Northern blot analysis.
RESULTS: The rat Myoc/Tigr gene is 10 kb long and contains three exons. Among the eye tissues analyzed, Myoc/Tigr mRNA was detected in the combined tissues of the eye angle, sclera, cornea, retina, and optic nerve head. With pressure-induced optic nerve degeneration, the level of Myoc/Tigr mRNA decreased in the retina and the combined tissues of the eye angle, but increased in the optic nerve head. After optic nerve transection, the level of Myoc/Tigr mRNA increased in the retina, but did not change in the combined tissues of the eye angle.
CONCLUSIONS: The decreased level of Myoc/Tigr mRNA in the retina after induction of elevated intraocular pressure compared with that in the control retina cannot be explained by ganglion cell death alone. Differences in Myoc/Tigr mRNA levels in eye tissues after elevation of intraocular pressure or optic nerve transection may reflect the activation of different signaling pathways involved in regulation of this gene.