INTRODUCTION AND OBJECTIVES: An important step in the development of the permanent mammalian kidney (metanephros) is the outgrowth of the ureteric bud (UB) from the Wolffian duct (WD). This occurs on day 30 of human gestation or mouse embryonic day (E) 10.5. The UB grows into the surrounding metanephric mesenchyme (MM) which induces the ureteric bud epithelium to elongate and branch to form the collecting duct system of the kidney. This process is called branching morphogenesis.

Ureteric budding and branching morphogenesis are tightly controlled by the competing actions of two major Transforming Growth Factor-Superfamily signalling pathways: the BMP4 and glial cell line-derived neurotrophic factor (GDNF)/Ret pathways. BMP4 is a protein expressed in the MM where it inhibits ectopic budding and branching of the UB, whereas GDNF promotes both of these events. This signalling interplay allows emergence of the UB at precisely the right site from the WD.

Gastrin-Releasing Peptide is a 10 amino acid peptide processed from a 125 amino acid prohormone, proGRP, and plays a role in metabolism, organ development, behaviour, and carcinogenesis. Amidated GRP (GRP18-27) and fragments from the C-terminal of proGRP (such as proGRP47-68)are both biologically active products of proGRP. mRNA for GRP and GRP-R has been detected in foetal whole kidneys of the sheep and rat as well as in the human embryonic kidney cell line HEK293 suggesting that it plays an important role in kidney development. However, the function of GRP in the foetal kidney has not to date been investigated.

METHODS: Metanephroi were removed with the aid of a dissecting microscope from E12.5 mouse embryos and cultured for 3 days in media with or without GRP, GRP antagonist, or proGRP47-68. Metanephroi were fixed and incubated with a monoclonal anticalbindin antibody. The degree of branching morphogenesis was accurately quantitated using three-dimensional image analysis software. Branch points and tips were viewed and counted with an Olympus Provis epifluorescence microscope and images were obtained using a Leica DC digital camera.

RESULTS: There was no statistical difference in the number of ureteric branch points or tips in mouse metanephroi grown in the presence of GRP, GRP antagonist, or proGRP47-68 compared with control.

CONCLUSIONS: While GRP is present in the developing human and rat kidney, it does not appear to be involved in branching morphogenesis of the ureter. The presence of GRP in the embryological kidney is yet to be explained and its role is open to speculation based on the numerous functions of GRP in other tissues.

Source of Funding: J Ischia: Royal Australasian College of Surgeons Scholarship