97th DOG Annual Meeting 1999
LOCALIZATION OF DIFFERENT ISOFORMS OF THE CYTOSKELETAL PROTEIN ANKYRIN IN HUMAN RETINA
A. Mantel1, B. Püschel2
Introduction: Ankyrins represent a widely distributed family of proteins connecting integral membrane proteins to the fodrin/spectrin-based cytoskeleton of the cell. In many polarized cells a colocalization of integral membrane proteins with ankyrins is observed. In those cells ankyrins might play a key role in the generation and/or maintenance of polarized membrane domains. Up to now three different ankyrin genes and a number of splice variants are known. In this study we analysed the occurence and the cellular localization of different ankyrin isoforms in human retina.
Materials and Methods: Semithin sections of human retina were analysed immunohistochemically. For this purpose rabbit polyclonal antisera as well as affinity-purified antisera directed against human ankyrin 1, the 440 kD isoform and against both isoforms (220 kD and 440 kD isoform) of human ankyrin 2 were used.
Results: The 440 kD isoform of ankyrin 2 mainly localizes at the membrane of photoreceptor terminals. Moreover, this isoform can be found at the membran of photoreceptors from the terminals to the outer limiting membrane as well as at the neuropil of horizontal and/or bipolar cells in the inner and outer plexiform layer. Interestingly, this isoform localizes at structures that might correspond to synaptic invaginations of the cone pedicles. The 220 kD isoform of ankyrin 2 can mainly be found in the neuropil of the outer plexiform layer and also localizes at the membrane of ganglial cells including axons and dendrites. At these sites this isoform colocalizes with ankyrin 1. Ankyrin 1 can also be found at the membrane of the cone terminals.
Conclusions: These results demonstrate the expression of different isoforms of ankyrin in the human neuroretina. The ankyrin isoforms are localized only in certain defined cell types and in some cases they are restricted to certain membrane domains. Furthermore the results show that even in a single cell type probably functionally different ankyrin isoforms can be found. The functional importance of the different isoforms of ankyrin is subject to further investigations.
1Augenklinik der Julius-Maximilians-Universität, Josef-Schneider Str. 11, 97080 Würzburg
2Anatomisches Institut der Julius-Maximilians-Universität, Koellikerstr. 6, 97070 Würzburg