METHODS

Total RNA isolation: Total RNA from tissues possessing a high content of collagen and/or adipose (eg, optic nerve) was extracted using the Tri-Pure isolation Reagent kit (Roche Molecular Biochemicals, Laval, Quebec, Canada). RNA extraction from all other tissues utilized the RNeasy Midi Kit (QIAGEN Inc., Mississauga, Ontario, Canada). Manufacturer’s instructions were followed for all procedures [20]. Methods optimized for dealing with pigmented tissues were adopted to insure isolation of high quality RNA [20, 21]. The concentration and purity of total RNA was determined by UV light absorption using a GeneQuant pro RNA/DNA calculator (Biochrom Ltd.; Cambridge, UK). Preparations were discarded if they had a ratio of optical densities at 260 nm/280 nm lower than 1.6 [21]. Furthermore, the presence of intact RNA was determined by loading it on 1% agarose-formalde-