The developing nephron of the sea lamprey during metamorphosis

Abstract

The definitive opisthonephric kidneys of lamprey each contains a single renal corpuscle with multiple nephric capsules surrounding a single compound glomerulus (glomus), which extends the length of the kidney. Each nephric capsule possesses a visceral layer of podocytes and a parietal layer continuous with the tubular epithelium. The development of these renal corpuscles and proximal portions of the tubules in the sea lamprey, Petromyzon marinus L., during metamorphosis was studied using electron microscopy.The nephron rudiments of the definitive opisthonephros arose as condensations of undifferentiated cell mass (Fig. 1) closely associated with the peritoneum. The differentiation of nephron rudiments along the entire nephrogenic cord was initiated synchronously at the onset of metamorphosis resulting in a series of rudimentary nephron units (RNU) which formed connections with the archinephric duct. The branching of RNU gave rise to secondary and tertiary rudimentary nephrons which radiated semicircularly from the original point of attachment to the peritoneum.