Small nuclear ribonucleoprotein polypeptide N (SNRPN), an expressed gene in the Prader-Willi syndrome critical region.

Prader-Willi syndrome (PWS) is associated with paternally derived chromosomal deletions in region 15q11-13 or with maternal disomy for chromosome 15. Therefore, loss of the expressed paternal alleles of maternally imprinted genes must be responsible for the PWS phenotype. We have mapped the gene encoding the small nuclear RNA associated polypeptide SmN (SNRPN) to human chromosome 15q12 and a processed pseudogene SNRPNP1 to chromosome region 6pter-p21. Furthermore, SNRPN was mapped to the minimal deletion interval that is critical for PWS. The fact that the mouse Snrpn gene is maternally imprinted in brain suggests that loss of the paternally derived SNRPN allele may be involved in the PWS phenotype.     

Specific low-affinity recognition of major histocompatibility complex plus peptide by soluble T-cell receptor.

The T-cell receptor is necessary and sufficient for recognition of peptides presented by major histocompatibility complex molecules. Other adhesion molecules, like CD4 or CD8, play an auxiliary role in antigen recognition by T cells. Here we analyse T-cell receptor (TCR) binding using a soluble rather than a cell-bound receptor molecule. A TCR-immunoglobulin chimaera is constructed with the variable and the first constant regions of both the TCR alpha- and beta-chains linked to the immunoglobulin light-chain constant regions. This soluble TCR is expressed, assembled and secreted as an alpha beta heterodimer by a myeloma cell line transfected with the recombinant genes. Furthermore, the soluble TCR is biologically active: it specifically inhibits antigen-dependent activation of the relevant T-cell clones and thus discriminates between proper and irrelevant peptides presented by major histocompatibility complex molecules.     

Retinoic acid alters hindbrain Hox code and induces transformation of rhombomeres 2/3 into a 4/5 identity.

It has been suggested that Hox genes play an important part in the patterning of limbs, vertebrae and craniofacial structures by providing an ordered molecular system of positional values, termed the Hox code. Little is known about the nature of the signals that govern the establishment and regulation of Hox genes, but retinoic acid can affect the expression of these genes in cell lines and in embryonic tissues. On the basis of experimental and clinical evidence, the hindbrain and branchial region of the head are particularly sensitive to the effects of retinoic acid but the phenotypes are complex and hard to interpret, and how and if they relate to Hox expression has not been clear. Here we follow the changes induced by retinoic acid to hindbrain segmentation and the branchial arches using transgenic mice which contain lacZ reporter genes that reveal the endogenous segment-restricted expression of the Hox-B1 (Hox-2.9), Hox-B2(Hox-2.8) and Krox-20 genes. Our results show that these genes rapidly respond to exposure to retinoic acid at preheadfold stages and undergo a progressive series of changes in segmental expression that are associated with specific phenotypes in hindbrain of first branchial arch. Together the molecular and anatomical alterations indicate that retinoic acid has induced changes in the hindbrain Hox code which result in the homeotic transformation of rhombomeres (r) 2/3 to an r4/5 identity. A main feature of this rhombomeric phenotype is that the trigeminal motor nerve is transformed to a facial identity. Furthermore, in support of this change in rhombomeric identity, neural crest cells derived from r2/3 also express posterior Hox markers suggesting that the retinoic acid-induced transformation extends to multiple components of the first branchial arch.     

Mapping of the protein import machinery in the mitochondrial outer membrane by crosslinking of translocation intermediates.

Mitochondria contain a complex machinery for the import of nuclear-encoded proteins. Receptor proteins exposed on the outer membrane surface are required for the specific binding of precursor proteins to mitochondria, either by binding of cytosolic signal recognition factors or by direct recognition of the precursor polypeptides. Subsequently, the precursors are inserted into the outer membrane at the general insertion site GIP (general insertion protein). Here we report the analysis of receptors and GIP by crosslinking of translocation intermediates and by coimmunoprecipitation. Surface-accumulated precursors were crosslinked to the receptors MOM19 and MOM72, suggesting a direct interaction of preproteins with surface receptors. We identified three novel mitochondrial outer membrane proteins, MOM7, MOM8, and MOM30 that, together with the previously identified MOM38, seem to form the GIP site and are present in the mitochondrial receptor complex.     

Close linkage of glucokinase locus on chromosome 7p to early-onset non-insulin-dependent diabetes mellitus.

Non-insulin-dependent diabetes mellitus (NIDDM) is a major health problem, affecting 5% of the world population. Genetic factors are important in NIDDM, but the mechanisms leading to glucose intolerance are unknown. Genetic linkage has been investigated in multigeneration families to localize, and ultimately identify, the gene(s) predisposing to NIDDM. Here we report linkage between the glucokinase locus on chromosome 7p and diabetes in 16 French families with maturity-onset diabetes of the young, a form of NIDDM characterized by monogenic autosomal dominant transmission and early age of onset. Statistical evidence of genetic heterogeneity was significant, with an estimated 45-95% of the 16 families showing linkage to glucokinase. Because glucokinase is a key enzyme of blood glucose homeostasis, these results are evidence that a gene involved in glucose metabolism could be implicated in the pathogenesis of NIDDM.     

A human recombinant haemoglobin designed for use as a blood substitute.

The need to develop a blood substitute is now urgent because of the increasing concern over blood-transmitted viral and bacterial pathogens. Cell-free haemoglobin solutions and human haemoglobin synthesized in Escherichia coli and Saccharomyces cerevisiae have been investigated as potential oxygen-carrying substitutes for red blood cells. But these haemoglobins cannot be used as a blood substitute because (1) the oxygen affinity in the absence of 2,3-bisphosphoglycerate is too high to allow unloading of enough oxygen in the tissues, and (2) they dissociate into alpha beta dimers that are cleared rapidly by renal filtration, which can result in long-term kidney damage. We have produced a human haemoglobin using an expression vector containing one gene encoding a mutant beta-globin with decreased oxygen affinity and one duplicated, tandemly fused alpha-globin gene. Fusion of the two alpha-globin subunits increases the half-life of this haemoglobin molecule in vivo by preventing its dissociation into alpha beta dimers and therefore also eliminates renal toxicity.     

Superantigen implicated in dependence of HIV-1 replication in T cells on TCR V beta expression.

In the pathogenesis of AIDS it is not yet understood whether the small fraction of CD4+ T cells (approximately 1%) infected with the human immunodeficiency virus (HIV) are randomly targeted or not. Here we present evidence that human CD4 T-cell lines expressing selected T-cell antigen receptor V beta gene products can all be infected in vitro with HIV-1, but give markedly different titres of HIV-1 virion production. For example, V beta 12 T-cell lines from several unrelated donors reproducibly yielded up to 100-fold more gag gene product (p24gag antigen) than V beta 6.7a lines. This is consistent with a superantigen effect, because the V beta selectivity was observed with several divergent HIV-1 isolates, was dependent on antigen-presenting cells and on major histocompatibility complex (MHC) class II but was not MHC class II-restricted. The in vivo significance of these findings is supported by the preferential stimulation of V beta 12+ T cells by freshly obtained irradiated antigen-presenting cells from some HIV-1-seropositive but not HIV-1-negative donors. Moreover, cells from patients positive for viral antigen (gp120) were enriched in the V beta 12 subpopulation. V beta 12+ T cells were not deleted in AIDS patients, however, raising the possibility that a variety of mechanisms contribute to T-cell depletion. Our results indicate that a superantigen targets a subpopulation of CD4+ cells for viral replication.