Eur Arch Otorhinolaryngol (1990) 247 : 182-188 European Archives of Oto-Rhino- Laryngology @ Spnnger-Verlag 1990 Regional variations in the expression of cytokeratin proteins in the adult human cochlea* M. Anniko 1, W. Arnold 2, L.-E. Thornell 3, I. Virtanen 4, F. C. S. Ramaekers 5, and C. R. Pfaltz 6 1 Department of Oto-Rhino-Laryngology and Head and Neck Surgery, University Hospital, S-901 85 Ume&, Sweden 2Department of Oto-Rhino-Laryngology Head and Neck Surgery, Kantonsspital, Lucerne, Switzerland 3Department of Anatomy, University of Ume~t, Ume~t, Sweden 4Department of Anatomy, University of Helsinki, Helsinki, Finland 5Department of Pathology, University of Nijmegen, Nijmegen, The Netherlands 6Department of Oto-Rhino-Laryngology, University of Basle, Basle, Switzerland Received May 2, 1989 / Accepted August 16, 1989 Summary. In the adult human cochlea, a cytokeratin (Ck) network exists along the entire surface of the organ of Corti, enclosing it like a shell. Only the surfaces of the outer and inner hair cells are not integrated in this net- work. In temporal bone specimens, Ck filaments in Hen- sen's cells were found to be arranged parallel with and closely apposed to the plasma membrane. In the stria vascularis, Cks were identified only in the marginal cells. Cells in Reissner's membrane and spiral prominence showed varying degrees of immunoreactivity to different monoclonal antibodies directed against Cks. A distinct positivity for Cks was found in most spiral ganglion cells, indicating their presence in all cells. The principal pattern of immunoreactivity was the same in the organ of Corti of the entire cochlea. However, a quantitative gradient in the expression of Cks was observed, with more Cks at the apex than at the base. This was correlated to a differ- ence in the number of Hensen's cells between the two re- gions. The distinct shell configuration of the Ck network in Corti's organ gives it a tonotopically related difference in rigidity which must be of considerable importance for the perception of sound in the cochlea. The absence of Cks in inner and outer sulcus cells gives them cyto- skeletal characteristics of mesenchymal cells with a pos- sible regenerative potential. Key words: Human cochlea - Intermediate filaments - Cytokeratins - Cytoskeleton - Immunomorphology * Supported by grants from the SwedishMedical Research Council (M. A.: 12X-7305; L.-E. T.: 12X-3934), the Ragnar and Torsten S6derberg Foundation (M.A.), the Foundation Tysta Skolan (M. A.), the Swiss National Funds (W. A., C. R. P.: 3.997-1.86), the Finnish Cancer Research Fund (I.V.), the Sigrid Juselius Foundation (I. V.), the Dutch Cancer Foundation (K. W. F.) and the Medical Faculty University of Ume~ Offprint requests to: M. Anniko Introduction The cytoskeleton in all eukaryotic cells consists of three types of filamentous structure: microfilaments (actin; 4- 6 nm in diameter), intermediate filaments (IFs; 8-11 nm in diameter) and microtubules (22-25 nm in diameter). The protein organization of the cytoskeleton has specific features in each cell type. IFs have been only relatively recently established as a separate class of major fibrous cellular structures. Ac- cording to their morphology and solubility properties, IFs are a fairly homogeneous class of filaments. On the basis of biochemical and immunological criteria, they can be subdivided into five classes: vimentin, desmin, neurofilament triplet proteins, cytokeratins (Cks) and glial fibrillary acidic proteins [18]. All five classes display striking similarities in amino acid sequence, antigenicity, assembly proteins, subunit structure, and gene organiza- tion. This suggests that all IFs belong to a chemically heterogeneous, yet evolution-related, homologous group of proteins. Whereas vimentin, desmin and glial fibrillary acidic proteins (GFAP) consist of identical subunits of a single polypeptide chain, the Ck filaments of both ectodermal and endodermal epithelial cells are formed from several different subunits in the molecular weight range 40- 70kDa [8]. In the human, 19 subclasses of Cks have been identified [12]. By comparison, the neurofilament (NF) fibers comprise three polypeptides of 200kDa, 150 kDa, and 68 kDa. The presence of IFs in the inner ear was first reported by our group in 1986 [2]. Since then, the human fetal labyrinth has been investigated in detail and also com- pared with the normal and pathologically altered inner ear in various animal species [3-5]. In the present study, the first of its kind, the expression of Cks has been