Retinal anatomy and function of the transthyretin null mouse

Vitamin A (retinol) is vital for the normal development and function of many tissues in the body including the eye. The purpose of this project was to characterize the retinal anatomy and function of the transthyretin (TTR) null mouse. Mice lacking TTR have been constructed by homologous recombination. Immunocytochemistry was performed to localize short and mid-long wavelength cone opsins as well as morphological examination of the entire retina in wild-type and TTR null mice. Visual function was assessed using the electroretinogram (ERG) and resulting waveforms were analysed in terms of receptoral and postreceptoral components. Retinal morphology of the TTR null mouse was normal. In addition, short and mid-long wavelength cone opsins were localized normally in both TTR null and wild-type retinae. Consistent with these findings, TTR null mice show no anomalies of receptoral (P3) nor post-receptoral (b-wave) ERG components compared with wild-type mice. The results suggest that although circulating plasma levels of retinol and retinol binding protein (RBP) are extremely low, this reduction has little effect on the retinal structure or function of the TTR null mouse. These data are consistent with the existence of mechanisms for the transport of retinol to the retina independent of the classical retinol-RBP-TTR complex.