Molecular cloning and characterization of NKT, a gene product related to the organic cation transporter family that is almost exclusively expressed in the kidney.

We have identified a gene product (NKT) encoding an apparently novel transcript that appears to be related to the organic ion transporter family and is expressed almost exclusively in the kidney. Analysis of the deduced 546-amino acid protein sequence indicates that NKT is a unique gene product which shares a similar transmembrane domain hydropathy profile as well as transporter-specific amino acid motifs with a variety of bacterial and mammalian nutrient transporters. Nevertheless, the overall homology of NKT to two recently cloned organic ion transport proteins (NLT and OCT-1) is significantly greater; together these three gene products may represent a new subgroup of transporters. The NKT was characterized further with respect to its tissue distribution and its expression during kidney development. A 2.5-kilobase transcript was found in kidney and at much lower levels in brain, but not in a number of other tissues. Studies on the embryonic kidney indicate that the NKT transcript is developmentally regulated with significant expression beginning at mouse gestational day 18 and rising just before birth, consistent with a role in differentiated kidney function. Moreover, in situ hybridization detected specific signals in mouse renal proximal tubules. NKT was mapped by linkage disequilibrium to mouse chromosome 19, the same site to which several mouse mutations localize, including that for osteochondrodystrophy (ocd). Although initial experiments in a Xenopus oocyte expression system failed to demonstrate transport of known substrates for OCT-1, the homology to OCT-1 and other transporters, along with the proximal tubule localization, raise the possibility that this gene may play a role in organic solute transport or drug elimination by the kidney.

Selective amplification of protein-coding regions of large sets of genes using statistically designed primer sets.

We describe a novel approach to design a set of primers selective for large groups of genes. This method is based on the distribution frequency of all nucleotide combinations (octa- to decanucleotides), and the combined ability of primer pairs, based on these oligonucleotides, to detect genes. By analyzing 1000 human mRNAs, we found that a surprisingly small subset of octanucleotides is shared by a high proportion of human protein-coding region sense strands. By computer simulation of polymerase chain reactions, a set based on only 30 primers was able to detect approximately 75% of known (and presumably unknown) human protein-coding regions. To validate the method and provide experimental support for the feasibility of the more ambitious goal of targeting human protein-coding regions, we sought to apply the technique to a large protein family: G-protein coupled receptors (GPCRs). Our results indicate that there is sufficient low level homology among human coding regions to allow design of a limited set of primer pairs that can selectively target coding regions in general, as well as genomic subsets (e.g., GPCRs). The approach should be generally applicable to human coding regions, and thus provide an efficient method for analyzing much of the transcriptionally active human genome.

Dry eye in Waldenström's macroglobulinemia. Improvement after systemic chemotherapy.

Waldenström's macroglobulinemia is an uncommon cause of dry eye. We describe a case of dry eye associated with Waldenström's macroglobulinemia that responded poorly to substitutive topical treatment but improved spectacularly in response to systemic chemotherapy. As far as we know, no similar case has been reported.

[Retinal involvement in Gaucher's disease]. / La participation rétinienne dans la maladie de Gaucher.

Gaucher's disease, a storage disease, causes storage of the sphingolipid glucosylceramide in the reticulo endothelial system. The manifestations of such deposits within the retina consist of the appearance of numerous whitish spots, such as preretinian infiltrates. Several authors have noticed the higher frequency of appearance of such spots in splenectomized patients, with marked extrasplenic infiltration. In our case, the systemic infiltration was massive at the time of the ophthalmoscopic examination, as confirmed by the bone-marrow biopsy and computerized axial tomography study, in spite of the fact that the spleen had not been removed. Our hypothesis is that the appearance of the whitish preretinian deposits in the course of the disease is connected with the degree of systemic infiltration, stressing the importance of examination of the eye fundus in Gaucher's disease.