Expression of galectin-7 during epithelial development coincides with the onset of stratification

Galectin-7 is a 14 KDa member of the galectin family that we have cloned fr om human, rat and mouse. Our previous studies have shown that in the adult, galectin-7 is expressed in all cell layers of epidermis and of other strat ified epithelia such as the cornea and the lining of the oesophagus. This s uggested that galectin-7 expression might be induced at a particular stage in the embryonic development of stratified epithelia. In the present study we have investigated this hypothesis by in situ hybridization of galectin-7 mRNA in mouse embryos. Starting from E13.5, weak expression of galectin-7 was detected in bilayered ectoderm, and stronger expression was found in ar eas of embryonic epidermis where stratification was more advanced. Galectin -7 expression was maintained in all living layers after epidermal developme nt was completed. Galectin-7 was also strongly and specifically expressed i n stratified regions of ectodermally-derived non-epidermal epithelia such a s the lining of the buccal cavity, the oesophagus and the ano-rectal region . In contrast, no expression of galectin-7 was found in epithelia derived f rom endoderm, such as lining of the intestine, kidney and lung. Our results demonstrate that galectin-7 is expressed ire all stratified epithelia exam ined so far, and that the onset of its expression coincides with the first visible signs of stratification. These results establish galectin-7 as the first region-independent marker of epithelial stratification.