Huitema, L.F., Renn, J., Logister, I., Gray, J.K., Waltz, S.E., Flik, G., and Schulte-Merker, S. (2012) Macrophage-stimulating protein and calcium homeostasis in zebrafish. FASEB journal : official publication of the Federation of American Societies for Experimental Biology. 26(10):4092-4101.
To systematically identify novel gene functions essential for osteogenesis and skeletal mineralization, we performed a forward
genetic mutagenesis screen in zebrafish and isolated a mutant that showed delayed skeletal mineralization. Analysis of the
mutant phenotype in an osterix:nuclear-GFP transgenic background demonstrated that mutants contain osterix-expressing osteoblasts comparable to wild-type embryos. Positional cloning revealed a premature stop mutation in the macrophage-stimulating
protein (msp) gene, predicted to result in a biologically inactive protein. Analysis of the embryonic expression pattern for the receptor
for Msp, Ron, shows specific expression in the corpuscles of Stannius, a teleost-specific organ that produces stanniocalcin,
a pivotal hormone in fish calcium homeostasis. Knockdown of Ron resulted in identical phenotypes as observed in msp mutants. Msp mutant embryos could be rescued by excess calcium. Consistent with a role for Msp/Ron in calcium homeostasis, calcium-regulating
factors, such as pth1, pth2, stc1l, and trpv5/6 were significantly affected in msp mutant larvae. While Msp and Ron have previously been shown to play a critical role in a wide variety of biological processes,
we introduce here the Msp/Ron signaling axis as a previously unappreciated player in calcium homeostasis and embryonic skeletal
mineralization.