lrpap1 as a specific marker of proximal pronephric kidney tubuli in Xenopus laevis embryos.

LRPAP1, also known as receptor associated protein (RAP) is a small protein of 40 kDa associated with six of the seven members of the evolutionary conserved family of LDL receptors. Numerous studies showed that LRPAP1 has a dual function, initially as a chaperone insuring proper formation of intermolecular disulfide bonds during biogenesis of low density lipoprotein (LDL) receptors and later as an escort protein during trafficking through the endoplasmic reticulum and the early Golgi compartment, preventing premature interaction of receptor and ligand. Because of the general influence of LRPAP1 protein on lipid metabolism, we analyzed the temporal and spatial expression of the Xenopus laevis ortholog of lrpap1. Here, we show that lrpap1 was expressed in the developing neural system, the eye and ear anlagen, the branchial arches, the developing skin and the pronephric kidney. The very high expression level of lrpap1 specifically in the proximal tubules of the developing pronephros establishes this gene as a novel marker for the analysis of pronephros formation.