| METHODS : Sections of postnatal 5 day old and adult rat , and aged human retina , and cell cultures prepared from selected cell populations of young rat retina , were immunolabeled with specific antisera to FGFR ( FGFR 1 , 2 , 3 , and 4 ) or candidate signaling molecules [ phospholipase Cg 1 ( PLCg 1 ) , son of sevenless 1 and 2 ( SOS 1 , SOS 2 ) , extracellular signal regulated kinase 1 and 2 ( ERK1 / 2 ) , protein tyrosine phosphatase ( SH PTP 2 ) and SH 2 containing protein ( Shc ) ] , and with multiple retinal cell type specific antibodies . ^^^ |