The excurrent ducts of the testis of the emu (Dromaius novaehollandiae) and ostrich (Struthio camelus): Microstereology of the epididymis and immunohistochemistry of its cytoskeletal systems.

The volumetric proportion of the various ducts of the epididymis of the emu and ostrich and the immunohistochemistry of actin microfilaments, as well as cytokeratin, desmin and vimentin intermediate filaments, were studied in the various ducts of the epididymis of the emu and ostrich. The volumetric proportions of various ducts, which are remarkably different from those of members of the Galloanserae monophyly, are as follows: the rete testis, 5.2 +/- 1.4% for the emu and 2.4 +/- 1.8% for the ostrich; efferent ducts, 14.2 +/- 2.3% (emu) and 11.8 +/- 1.8% (ostrich); epididymal duct unit, 25.8 +/- 5.8% (emu) and 26.1 +/- 4.1% (ostrich) and connective tissue and its content, 54.7 +/- 5.8% (emu) and 60.0 +/- 4.9% (ostrich). Unlike in mammals and members of the Galloanserae monophyly, only vimentin was immunohistochemically demonstrated in the rete testis epithelium of the emu, and none of the cytoskeletal protein elements in the ostrich rete testis. The epithelium of the efferent ducts of the emu co-expressed actin, cytokeratin and desmin in the non-ciliated type I cells, and vimentin in the ciliated cell component. The ostrich demonstrated only cytokeratin in this epithelium. The ratite epididymal duct unit is different from that of mammals in lacking actin (only weaky expression in the ostrich), desmin and cytokeratin, and a moderate/strong immunoexpression of vimentin in the basal cells and basal parts of the NC type III cell in the epididymal duct unit. Immunoexpression of the microfilaments and intermediate filaments varied between the two ratite birds, as has been demonstrated previously in birds of the Galloanserae monophyly, and in mammals.