Microtubule-associated protein tau in bovine retinal photoreceptor rod outer segments: Comparison with brain tau

Abstract

Recent studies have suggested a possible involvement of abnormal tau in some retinal degenerative diseases. The common view in these studies is that these retinal diseases share the mechanism of tau-mediated degenerative diseases in brain and that information about these brain diseases may be directly applied to explain these retinal diseases. Here we collectively examine this view by revealing three basic characteristics of tau in the rod outer segment (ROS) of bovine retinal photoreceptors, i.e., its isoforms, its phosphorylation mode and its interaction with microtubules, and by comparing them with those of brain tau. We find that ROS contains at least four isoforms: three are identical to those in brain and one is unique in ROS. All ROS isoforms, like brain isoforms, are modified with multiple phosphate molecules; however, ROS isoforms show their own specific phosphorylation pattern, and these phosphorylation patterns appear not to be identical to those of brain tau. Interestingly, some ROS isoforms, under the normal conditions, are phosphorylated at the sites identical to those in Alzheimer’s patient isoforms. Surprisingly, a large portion of ROS isoforms tightly associates with a membranous component(s) other than microtubules, and this association is independent of their phosphorylation states. These observations strongly suggest that tau plays various roles in ROS and that some of these functions may not be comparable to those of brain tau. We believe that knowledge about tau in the entire retinal network and/or its individual cells are also essential for elucidation of tau-mediated retinal diseases, if any.

Is Angiostatin Involved in Physiological Foveal Avascularity?

“…Colabeling with angiostatin and Tau-1, which is expressed in the telodendrons of terminal photoreceptor axons, 35,36 revealed a strong association between the proteins in the OPL. Weaker angiostatin/Tau-1 colabeling was found in the INL (Figs.…”

Microtubule‐associated protein tau promotes neuronal class II β‐tubulin microtubule formation and axon elongation in embryonic Xenopus laevis

“…The human peripheral nervous system contains two additional ‘big’ tau isoforms, which are distinguished from the shorter isoforms by inclusion of exon 4a. In addition to these eight distinct isoforms, still other, less common ones may exist in various populations of neurons and at earlier developmental stages, as suggested by studies of bovine tau isoforms (Himmler, ; Hanes et al ., ; Yamazaki et al ., ).…”

“…Scale bars: 100 lm for all panels; (B1 and 2) are at the same magnification, as are (C1 and 2). by studies of bovine tau isoforms (Himmler, 1989;Hanes et al, 2009;Yamazaki et al, 2013). With regard to exon structure, Xenopus and mammalian mapt were very similar, especially between exons 4a and 13.…”

Neurodegenerative Proteinopathies in the Proteoform Spectrum—Tools and Challenges

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