Expression and localisation of claudin-1,-2,-3,-4,-5,-7 and-10 proteins in the normal canine mammary gland

The recently identified claudins are dominant components of tight junctions, responsible for cell adhesion, polarity and paracellular permeability. Certain claudins have been shown to have relevance in tumour development. The aim of the present study was to analyse the expression of claudin-1,-2,-3,-4,-5,-7 and-10 in normal canine mammary glands. Samples from the inguinal mammary regions of 20 non-castrated, 1–13 years old female dogs were studied. Immunohistochemical analysis was performed on conventional specimens and tissue microarrays. The results of the immunohistochemical reactions detecting claudins in tissue sections were photodocumented. The immunoreactivity of claudins was quantitatively analysed on digital images using Leica QWin morphometry software. Intense membranous immunolabelling was found for claudin-1,-3 and-7, intense membranous with non-granular cytoplasmic immunolabelling for claudin-2, moderate membranous immunolabelling for claudin-4 and-5, and weak membranous immunolabelling for claudin-10. The occurrence of tight junctions was confirmed by ultrathin section electron microscopy. The available data suggested that claudins might be proteins preserved throughout the evolution of mammals. The results of our study support the concept that they are indeed preserved, since the same type of claudins, in identical distribution, could be detected in our canine mammary tissue samples as could be found in human mammary tissue