Localization of tubby-like protein 1 in developing and adult human retinas

To localize tubby-like protein 1 (TULP1) in developing and adult human retinas.

TULP1 was localized by immunofluorescence microscopy in human retinas, aged 8.4 fetal weeks to adult. TULP1-positive cells were identified by double labeling with antibodies specific for cones, rods, and astrocytes.

In adult retinas, anti-TULP1 labels cone and rod inner segments, somata, and synapses; outer segments are TULP1-negative. A few inner nuclear and ganglion cells are weakly TULP1-positive. In fetal retinas, cells at the outer retinal border are TULP1-positive at 8.4 weeks. At 11 weeks, the differentiating central cones are strongly TULP1-reactive and some are positive for blue cone opsin. At 15.4 weeks, all central cones are strongly positive for TULP1 and many are reactive for red/green cone opsin. At 17.4 weeks, central rods are weakly TULP-reactive. In peripheral retina at 15.4 weeks to 1 month after birth, displaced cones in the nerve fiber layer are positive for TULP1, recoverin, and blue cone opsin. Some ganglion cells are weakly reactive for TULP1 at 11 weeks and later, but astrocytes and the optic nerve are TULP1-negative at all ages examined.

The finding of TULP1 labeling of cones before they are reactive for blue or red/green cone opsin suggests an important role for TULP1 in development. TULP1 expression in both developing and mature cones and rods is consistent with a primary photoreceptor defect in retinitis pigmentosa (RP) caused by TULP1 mutations. Weak TULP1-immunolabeling of some inner retinal neurons in developing and adult retinas suggests that optic disc changes in patients with RP who have TULP1 mutations may be primary as well as secondary to photoreceptor degeneration.