Morphogenesis and growth of the definitive opisthonephros during metamorphosis of anadromous sea lamprey, Petromyzon marinus L.

Abstract

The definitive opisthonephros of the adult lamprey, Pertomyzon marinus L., develops during metamorphosis from the nephrogenic cord confined within a nephric fold and extending from the posterior tip of the larval opisthonephros to the cloaca. This development is initiated prior to the first signs of external metamorphosis and begins with the simultaneous appearance of clusters of cells scattered along the entire length of the cord. Proliferation of the cell clusters and their elongation to connect to the closely associated archinephric duct results in the formation of rudimentary nephron units. Subsequent development involves the formation of tubular lumina, branching of the tubules, and the participation of the proximal ends of the newly formed tubules in the formation of the single renal corpuscle, Growth in size of the kidney is the result of lengthening of the existing tubules through cell proliferation rather than through the addition of new nephrons. This growth appears to be at the expense of adipose tissue within the nephric fold. During later stages of metamorphosis, cell proliferation is more relevant in the ventral part of the nephric fold where a parallel system of tubules develops. The development of the definitive opisthonephros during metamorphosis of lamprey may prove to be a useful model for further studies of tissue differentiation and interaction during kidney development in vertebrates.