Ureteric branching morphogenesis in BMP4 heterozygous mutant mice

Exogenous bone morphogenetic protein 4 (BMP4) inhibits ureteric branching morphogenesis and amplifies the already existing branching asymmetry in the developing mouse kidney in vitro. In the present study we examined ureteric branching morphogenesis in BMP4/lacZ heterozygous (BMP4(+/-)) mice in vitro under control conditions and in the presence of exogenous BMP4 using three-dimensional image analysis software. The relative expression of BMP4 mRNA was determined in BMP4(+/-) and wildtype urogenital ridges using real-time PCR. Embryonic day 12.5 (E12.5) BMP4(+/-) and wildtype mouse metanephroi were cultured for 48 h with or without 260 ng mL(-1) recombinant human BMP4 (rhBMP4) and were then wholemount immunostained in order to identify the ureteric epithelium, which was quantified in three dimensions. Despite a significant reduction in BMP4 mRNA in BMP4(+/-) mice, qualitative and quantitative studies identified no differences in ureteric branching morphogenesis between phenotypically normal BMP4(+/-) and wildtype metanephroi in either BMP4-treated or control cultures. Both BMP4(+/-) and wildtype metanephroi cultured in the presence of BMP4 showed a decrease in total ureteric length, branch number and ureteric volume, and increased average branch length compared with control cultures. A marked anterior-posterior asymmetry in both ureteric length, branch number and average branch length was observed in BMP4-treated metanephroi from both genotypes. A similar asymmetry was revealed in control metanephroi from both genotypes. This asymmetry is the result of reduced ureteric branching morphogenesis but not elongation in the posterior region of the kidney. These results suggest that despite reduced endogenous BMP4 mRNA levels, most BMP4(+/-) embryos can still facilitate normal ureteric branching morphogenesis during development. In addition, reduced endogenous levels of BMP4 do not alter the inhibitory effects of exogenous BMP4 on ureteric branching or amplification of normal renal asymmetry.