Crim1, a transmembrane cysteine-rich repeat-containing protein that is related to chordin, plays a role in the tethering of growth factors at the cell surface. Crim1 is expressed in the developing kidney; in parietal cells, podocytes, and mesangial cells of the glomerulus; and in pericytes that surround the arterial vasculature. A gene-trap mouse line with an insertion in the Crim1 gene (Crim1 KST264/KST264 ) displayed perinatal lethality with defects in multiple organ systems. This study further analyzed the defects that are present within the kidneys of these mice. Crim1 KST264/KST264 mice displayed abnormal glomerular development, illustrated by enlarged capillary loops, podocyte effacement, and mesangiolysis. When outbred, homozygotes that reached birth displayed podocyte and glomerular endothelial cell defects and marked albuminuria. The podocytic co-expression of Crim1 with vascular endothelial growth factor-A (VEGF-A) suggested a role for Crim1 in the regulation of VEGF-A action. Crim1 and VEGF-A were shown to interact directly, providing evidence that cysteine-rich repeat-containing proteins can bind to non-TGF-␤ superfamily ligands. Crim1 KST264/KST264 mice display a mislocalization of VEGF-A within the developing glomerulus, as assessed by immunogold electron microscopy and increased activation of VEGF receptor 2 (Flk1) in the glomerular endothelial cells, suggesting that Crim1 regulates the delivery of VEGF-A by the podocytes to the endothelial cells. This is the first in vivo demonstration of regulation of VEGF-A delivery and supports the hypothesis that Crim1 functions to regulate the release of growth factors from the cell of synthesis.

Background: RGS-PX proteins are regulators of signaling and trafficking within the endosomal system. Results: A structural basis for membrane interactions of RGS-PX proteins is established. Conclusion: The four mammalian paralogues display different membrane interaction properties. Significance: RGS-PX proteins possess a conserved functional architecture in all eukaryotes.

The endocytic protein SNX27 functions to link the parathyroid hormone receptor (PTHR) to the retromer trafficking complex. Loss of SNX27 in mice leads to overactive PTHR signaling and reduced osteoblastic bone formation during postnatal bone growth. Thus SNX27 is a new modulator of PTHR signaling.

The Crim1 gene encodes a transmembrane protein containing six cysteine-rich repeats similar to those found in the BMP antagonist, chordin (chd). To investigate its physiological role, zebrafish crim1 was cloned and shown to be both maternally and zygotically expressed during zebrafish development in sites including the vasculature, intermediate cell mass, notochord, and otic vesicle. Bent or hooked tails with U-shaped somites were observed in 85% of morphants from 12 hpf. This was accompanied by a loss of muscle pioneer cells. While morpholino knockdown of crim1 showed some evidence of ventralisation, including expansion of the intermediate cell mass (ICM), reduction in head size bent tails and disruption to the somites and notochord, this did not mimic the classically ventralised phenotype, as assessed by the pattern of expression of the dorsal markers chordin, otx2 and the ventral markers eve1, pax2.1, tal1 and gata1 between 75% epiboly and six-somites. From 24 hpf, morphants displayed an expansion of the ventral mesoderm-derived ICM, as evidenced by expansion of tal1, lmo2 and crim1 itself. Analysis of the crim1 morphant phenotype in Tg(fli:EGFP) fish showed a clear reduction in the endothelial cells forming the intersegmental vessels and a loss of the dorsal longitudinal anastomotic vessel (DLAV). Hence, the primary role of zebrafish crim1 is likely to be the regulation of somitic and vascular development.

Sorting nexin 27 (SNX27) recycles PSD-95, Dlg1, ZO-1 (PDZ) domain-interacting membrane proteins and is essential to sustain adequate brain functions. Here we define a fundamental SNX27 function in T lymphocytes controlling antigen-induced transcriptional activation and metabolic reprogramming. SNX27 limits the activation of diacylglycerol (DAG)-based signals through its high affinity PDZ-interacting cargo DAG kinase ζ (DGKζ). SNX27 silencing in human T cells enhanced T cell receptor (TCR)-stimulated activator protein 1 (AP-1)- and nuclear factor κB (NF-κB)-mediated transcription. Transcription did not increase upon DGKζ silencing, suggesting that DGKζ function is dependent on SNX27. The enhanced transcriptional activation in SNX27-silenced cells contrasted with defective activation of the mammalian target of rapamycin (mTOR) pathway. The analysis of Snx27 −/− mice supported a role for SNX27 in the control of T cell growth. This study broadens our understanding of SNX27 as an integrator of lipid-based signals with the control of transcription and metabolic pathways.