The zebrafish floating head mutant demonstrates podocytes play an important role in directing glomerular differentiation.

In zebrafish, the pronephric glomerulus occupies a midline position underneath the notochord and is vascularized through angiogenic capillary ingrowth from the dorsal aorta. The midline mutants floating head (flh), sonic you (syu), and you-too (yot) provide the opportunity to study glomerular differentiation in the absence of the notochord and vascularization from the dorsal aorta. In flh, syu, and yot mutants, glomeruli differentiate at ectopic lateral positions within the embryo and contain morphologically identifiable podocyte and endothelial cell types. In the absence of the dorsal aorta, endothelia from an alternate source are recruited by podocytes during glomerular vascularization to make functional glomeruli. Our results suggest that midline signals are required for proper glomerular morphogenesis but not for the differentiation of podocytes. Podocytes appear to play an important role in directing cellular recruitment events leading to glomerular differentiation. Furthermore, we find defects in sclerotomal development that correlate with defects in glomerular morphogenesis suggesting a possible link between the formation of these embryonic structures.