Transformation of the interlamellar epithelium of the gills of the anadromous sea lamprey, Petromyzon marinus L., during metamorphosis

The interlamellar areas of the gills of the anadromous sea lamprey, Petromyzon marinus, undergo structural modification during the process of metamorphosis of larvae to young adults. The initial changes involve a degeneration of presumed ion-absorptive superficial cells of the larvae and this is followed by a differentiation of adult-type chloride cells presumably from intermediate cells. Adult-type chloride cells are characterized primarily by the presence of an extensive tubular reticulum, which is continuous with lateral and basal plasma membranes. The tubules first appear in peripheral regions of intermediate cells and subsequent development involves a proliferation of the tubules toward the interior of the cell. Autoradiography with [3H]thymidine indicates that extensive DNA synthesis occurs synchronously in the interlamellar basal cells throughout the gill filaments. This DNA synthesis and division of both basal and intermediate cells is most common immediately preceding the first appearance of immature chloride cells. This suggests that cells are produced in apparent anticipation of a requirement for adult-type chloride cells and that they subsequently differentiate. The timing of differentiation of chloride cells is well correlated with developmental changes in other organs during metamorphosis.