Abstract
The glomerulus of the vertebrate kidney links the vasculature to the excretory system and produces the primary urine. It is a component of every single nephron in the complex mammalian metanephros and also in the primitive pronephros of fish and amphibian larvae. This systematic work highlights the benefits of using teleost models to understand the pronephric glomerulus development. The morphological processes forming the pronephric glomerulus are astoundingly different between medaka and zebrafish. (1) The glomerular primordium of medaka - unlike the one of zebrafish - exhibits a C-shaped epithelial layer. (2) The C-shaped primordium contains a characteristic balloon-like capillary, which is subsequently divided into several smaller capillaries. (3) In zebrafish, the bilateral pair of pronephric glomeruli is fused at the midline to form a glomerulus, while in medaka the two parts remain unmerged due to the interposition of the interglomerular mesangium. (4) Throughout pronephric development the interglomerular mesangial cells exhibit numerous cytoplasmic granules, which are reminiscent of renin-producing (juxtaglomerular) cells in the mammalian afferent arterioles. Our systematic analysis of medaka and zebrafish demonstrates that in fish, the morphogenesis of the pronephric glomerulus is not stereotypical. These differences need be taken into account in future analyses of medaka mutants with glomerulus defects.
Highlights
During vertebrate ontogeny and phylogeny, three types of kidney are distinguishable on the basis of their localization and developmental process [1,2]
Teleost fishes generally possess a pair of functional pronephroi, which consist of three anatomical subunits [5]
The most medial portion of the vesicle invaginated into the lumen to form the glomerular primordium at 3 dpf (Fig. 1A1)
Summary
During vertebrate ontogeny and phylogeny, three types of kidney are distinguishable on the basis of their localization and developmental process [1,2]. The pronephros is the first kidney that forms and functions as a primary osmoregulatory organ in the larvae of teleost fishes and amphibians [3,4]. Teleost fishes generally possess a pair of functional pronephroi, which consist of three anatomical subunits (glomerulus, pronephric tubule, and pronephric duct) [5]. The pronephros is the first kidney to form and is succeeded by the mesonephros, which is the adult kidney in fishes and amphibians. The pronephros is formed, but remains non-functional; the mesonephros serves as the embryonic kidney and the metanephros as the adult kidney. The progression to the more advanced kidney form is always accompanied by the degeneration of the previous kind [6]
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