Stage-specific polypeptide and villin expression during thyroid-hormone-induced substitution of the amphibian intestinal epithelium.

Treatment of anuran tadpoles with 5 nM 3,3',5-triiodo-L-thyronine (T3) results in the complete substitution of the intestinal epithelium. We have examined the developmental pattern of protein synthesis in Alytes obstetricans intestinal epithelium using two-dimensional gel electrophoresis. Four different types of changes have been observed. The group I polypeptides (Mr: 41,500; 44,500; 51,500; 55,000 and 101,000) are only synthesized during the first week of hormonal treatment. They are specific of the primary (larval) epithelium. On the other hand, polypeptides referred to as Group II (Mr: 47,000; 48,000; 58,000; 66,500, pl 5.2; 99,500 and 102,000) are not detected until day 8. They are characteristic of the secondary tissue. Polypeptides of Group III (Mr: 42,000, pl 5.15 and 5.25; 42,500, 47,500, pl 5.25 and 5.55) expressed between the 6th and 8th day of T3 treatment, are specific of growing stem cells. During this critical period, Group IV polypeptides (Mr: 63,500; 66,500, pl 6.35; 105,000, pl 5.5 and 5.55) are not synthesized. The protein of Mr 105,000 (pI 5.5 and 5.55) is immunologically related to villin, a core protein of intestinal microvilli. Expression of this protein has been analyzed by immunoreplica and immunocytochemical procedures during differentiation of basal stem cells into secondary absorptive epithelial cells. The results have been compared to that obtained during spontaneous metamorphosis.