Specific expression of annexin A8 in adult murine stratified epithelia

Annexin A8 is a member of the annexin family of calcium-regulated membrane-binding proteins. In this report, we investigated the expression of annexin A8 in adult mouse organs. Northern blot analysis of adult mouse organs showed that a single annexin A8 transcript of 1.9 kb is expressed most strongly in skin, eye and tongue. In situ hybridisations using annexin A8-specific probes revealed that in the stratified epithelia of the tongue and the early postnatal epidermis, annexin A8 transcription could be detected in basal and suprabasal layers of these stratified epithelia. Western blot analyses using a murine ANXA8-specific antiserum showed, that the 36 kD ANXA8 protein was most abundant in the skin and tongue. The abundance of ANXA8 protein in the skin increased during postnatal days 1-18 and was immunohistochemically localised in suprabasal layers of the epidermis. In the tongue epithelium as well, ANXA8 protein was found in suprabasal layers. ANXA8 immunoreactivity was also found in suprabasal layers of the stratified epithelia of the oesophagus and the forestomach, while it was detected in all layers of the cornea epithelium and in the cornea endothelium of the eye. We also investigated the expression of retinoic acid receptor alpha protein (RARA) and ANXA8 in the epidermis immunohistochemically. While RARA immunoreactivity was exclusively detected in the basal layer, ANXA8 immunoreactivity was restricted to suprabasal layers of the epidermis. Thus, ANXA8 protein is most abundant in stratified epithelia of the postnatal mouse. Its location in the suprabasal layers suggests that ANXA8 may be associated with the terminal differentiation of epithelial cells in these tissues.