Pronephric Development

Developmental stages in pronephros formation. Request reprint >>



A One to eight somite stage (10-13 hpf): Expression patterns of pax2.1 and lim-1 define the posterior regions of the intermediate mesoderm (im) and suggest that a nephrogenic field is established early in development.

B Early somitogenesis to Prim-5 stage (12- 24 hpf): Growth of the pronephric duct (pnd) follows behind somitogenesis and is complete by 24 hpf. Nephron primordia form at the anterior tips of the pronephric ducts by 24 hpf.

C Prim-5 to High-Pec stage (24 - 42 hpf ): Nephron primordia (np) ventral to somite three separate from the coelom and undergo integrated morphogenesis, giving rise to pronephric glomeruli and tubules.

D High-Pec stage to Hatching (42-48 hpf): Vascularization of the pronephros by ingrowth of capillaries from the dorsal aorta (da) starts at 40-42 hpf and continues over the next 24 h and correlates with the onset of glomerular filtration. Stages of zebrafish development refer to Kimmel et al. (Kimmel et al., 1995).

Following the caudal growth of the pronehric duct, the pronephric nephron develops beneath somite three.

At 24 hpf a nephron primordium is present ventral to the third somite (top). The primordium at this stage appears as an infolding of the coelomic lining and a clear opening to the coelom is apparent (top). This opening to the coelom could be considered the equivalent of a nephrostome observed in other fish species and in mature amphibian pronephroi.

By 32 - 33 hpf the separation of the nephron primordium from the coelom is complete and it appears as a distinct and separate group of cells with no connection to the body cavity (middle). In cross section a central lumen or nephrocoele is seen and the nephron primordium consists of a flattened vesicle of cells.

At 40 hpf a clear morphological distinction is apparent between midline cells and cells lying more laterally, adjacent to the anterior tip of the pronephric duct (bottom). In cross section, midline cells appear to be enclosed by a basement membrane or capsule, while lateral cells are beginning to take on the appearance of the pronephric tubule (bottom).

Histological analysis suggests that after the separation of the paired nephron primordia from the coelom, each pronephric nephron differentiates as an integrated group of cells to form a closed pronephric system with the bilaterally paired tubules directly connected to midline fused glomeruli.

In sagital view the pronephric nephron primordium appears as a disk shaped group of cells.

At 24 hpf, no distinct tubules or glomeruli ate seen (top).The anterior tips of the pronephric ducts lie directly adjacent to the lateral edges of the nephron primordia.

Sagital sections at 32-33 hpf (middle) reveal the first signs of pronephric nephron morphogenesis. The primordium at this stage appears to be partitioned into lateral and medial domains in the regions of the future tubules and glomeruli respectively.

The morphological distinction between tubule and glomerulus is also apparent in sagital section where paired oval masses of presumptive glomerular cells are observed at the midline and pronephric tubules are seen emanating from the lateral aspect of the forming glomerulus (bottom).