Relationship between tenascin and alpha-smooth muscle actin expression in the developing human small intestinal mucosa.

The expression of tenascin (Tn) and alpha-smooth muscle actin (alpha-SMA) was analyzed in the developing and adult human small intestine by means of double immunofluorescent staining with specific antibodies. By 7 weeks of gestation, the gut anlage has a simple tubular shape and is formed of a stratified undifferentiated epithelium surrounded by a poorly organized mesenchyme. Both Tn and alpha-SMA were found exclusively at the periphery of the tissue, corresponding to the presumptive muscularis propria. By 9 weeks, villus rudiments had formed but Tn and alpha-SMA remained restricted to the muscularis propria. Tn was first detected in the mesenchyme at 11 weeks. By 13 weeks, a preferential distribution of Tn in the subepithelial region of the mesenchyme was readily observed while alpha-SMA was still absent. From this stage to 20 weeks, Tn gradually concentrated in this region that, as determined by alpha-SMA detection, corresponded to the future muscularis mucosa area. As shown by double staining of Tn and alpha-SMA, deposition of Tn also preceded the appearance of the other alpha-SMA-expressing cells in the mucosa. These observations suggest that Tn could have a role in the differentiation of intestinal contractile cells.