PEX , a phosphate-regulating gene with homology to endopeptidases on the X chromosome, was recently identified as the candidate gene for X-linked hypophosphatemia. In the present study, we cloned mouse and human Pex/PEX cDNAs encoding part of the 5 Ј untranslated region, the protein coding region, and the entire 3 Ј untranslated region, determined the tissue distribution of Pex/PEX mRNA, and characterized the Pex mutation in the murine Hyp homologue of the human disease. Using the reverse transcriptase/polymerase chain reaction (RT/PCR) and ribonuclease protection assays, we found that Pex/PEX mRNA is expressed predominantly in human fetal and adult mouse calvaria and long bone. With RNA from Hyp mouse bone, an RT/PCR product was generated with 5 Ј but not 3 Ј Pex primer pairs and a protected Pex mRNA fragment was detected with 5 Ј but not 3 Ј Pex riboprobes by ribonuclease protection assay. Analysis of the RT/ PCR product derived from Hyp bone RNA revealed an aberrant Pex transcript with retention of intron sequence downstream from nucleotide 1302 of the Pex cDNA. Pex mRNA was not detected on Northern blots of poly (A) ϩ RNA from Hyp bone, while a low-abundance Pex transcript of Ϸ 7 kb was apparent in normal bone. Southern analysis of genomic DNA from Hyp mice revealed the absence of hybridizing bands with cDNA probes from the 3 Ј region of the Pex cDNA. We conclude that Pex/PEX is a low-abundance transcript that is expressed predominantly in bone of mice and humans and that a large deletion in the 3 Ј region of the Pex gene is present in the murine Hyp homologue of X-linked hypophosphatemia. ( J. Clin. Invest . 1997. 99:1200-1209.)

Coordinated development of excitatory and inhibitory synapses is essential for higher brain function, and impairment in this development is associated with neuropsychiatric disorders. In contrast to the large body of accumulated evidence regarding excitatory synapse development, little is known about synaptic adhesion and organization mechanisms underlying inhibitory synapse development. Through unbiased expression screens and proteomics, we identified immunoglobulin superfamily member 21 (IgSF21) as a neurexin2α-interacting membrane protein that selectively induces inhibitory presynaptic differentiation. IgSF21 localizes postsynaptically and recruits axonal neurexin2α in a trans-interaction manner. Deleting IgSF21 in mice impairs inhibitory presynaptic organization, especially in the hippocampal CA1 stratum radiatum, and also diminishes GABA-mediated synaptic transmission in hippocampal CA1 neurons without affecting their excitatory synapses. Finally, mice lacking IgSF21 show a sensorimotor gating deficit. These findings suggest that IgSF21 selectively regulates inhibitory presynaptic differentiation through interacting with presynaptic neurexin2α and plays a crucial role in synaptic inhibition in the brain.

Na+-phosphate (Pi) cotransport across the renal brush border membrane is the rate limiting step in the overall reabsorption of filtered Pi. Murine and human renalspecific cDNAs (NaPi-7 and NaPi-3, respectively) related to this cotransporter activity (type II Na+-Pi cotransporter) have been cloned. We now report the cloning and characterization of the corresponding mouse (Npt2) and human (NPT2)

4-1BB is a member of the TNFR superfamily, which contributes to the activation of signaling pathways required for the survival of activated and memory T cells. We have shown previously that TRAF1, an adaptor protein recruited to 4-1BB, is required for 4-1BB-mediated CD8 T cell survival in vivo. With the use of a proteomics approach in primary T cells, we have identified LSP1 as a novel protein recruited to the 4-1BB signaling complex in a TRAF1-dependent manner. Further characterization of the interaction between TRAF1 and LSP1 revealed that LSP1 requires the TRAF-N domain of TRAF1 for direct association. Similarly to TRAF1(-/-) T cells, LSP1(-/-) T cells exhibit impaired ERK activation following stimulation through 4-1BB and consequently, are unable to down-modulate expression of the proapoptotic Bcl-2 family member Bim. Moreover, we demonstrate that the absence of LSP1 expression leads to defective expansion and survival of T cells in response to 4-1BB stimulation. Thus, we have identified LSP1 as a new mediator involved in 4-1BB signaling and T cell survival. Collectively, our work shows that TRAF1 and LSP1 cooperate downstream of 4-1BB to activate ERK signaling and down-modulate the levels of Bim leading to enhanced T cell survival.

The N-terminal P1 protein of tumip mosaic potyvirus (TuMV) polyprotein was overexpressed in Escherichia coli, purified by metal chelation chromatography under denaturing conditions and renatured. U.v. cross-linking experiments indicated that the recombinant protein interacted with RNA, and gel retardation electrophoresis demonstrated that more than one molecule of P1 bound one molecule of RNA. Formation of the protein-RNA complexes was dependent on the conformational state of P1 and was stable at relatively high concentrations of NaCI. P1 had the ability to bind ssRNA and ssDNA, with similar affinity, but was not able to bind to dsDNA. The TuMV protein had the additional characteristic of binding dsRNA with affinity similar to that observed with single-stranded nucleic acids.