Epidermal growth factor-like immunoreactivity in the buccopharyngeal mucous glands of Xenopus laevis tadpoles.

We report epidermal growth factor (EGF)-like and epidermal growth factor receptor (EGFR)-like immunoreactivity in the buccopharyngeal mucous glands of Xenopus laevis larvae. EGF-like immunostaining was heaviest at the apices of the secretory cells of these glands. Immunostaining for EGFR-like protein was also observed in the mucosal lining of the alimentary tract. This staining was heaviest in cells lining the foregut but was almost absent in cells from the hindgut. A potential role for an orally secreted EGF homologue in anuran amphibians is discussed. Wassersug (1986) hypothesized the existence of a metamorphic inhibitory agent, produced by larval buccopharyngeal mucous glands, which could indirectly link food ingestion to the endocrine control of metamorphosis. The presence of EGF-like immunoreactivity in the oral mucous glands of X. laevis larvae, as well as the presence of EGFR-like immunoreactivity in the gut wall of this tadpole, satisfies many of the criteria for Wassersug's regulatory agent. It remains to be shown that EGF (or an anuran EGF homologue) has a direct inhibitory effect on anuran metamorphosis when administered via an orogastric route.