Spontaneous activity of opsin apoprotein is a cause of Leber congenital amaurosis

Mutations in Rpe65 disrupt synthesis of the opsin chromophore ligand 11-cis-retinal and cause Leber congenital amaurosis (LCA), a severe, early-onset retinal dystrophy. To test whether light-independent signaling by unliganded opsin causes the degeneration, we used Rpe65-null mice, a model of LCA. Dark-adapted Rpe65-/- mice behaved as if light adapted, exhibiting reduced circulating current, accelerated response turn-off, and diminished intracellular calcium. A genetic block of transducin signaling completely rescued degeneration irrespective of an elevated level of retinyl ester. These studies clearly show that activation of sensory transduction by unliganded opsin, and not the accumulation of retinyl esters, causes light-independent retinal degeneration in LCA. A similar mechanism may also be responsible for degeneration induced by vitamin A deprivation.     

Altered adhesive interactions with marrow stroma of haematopoietic progenitor cells in chronic myeloid leukaemia

Normal haematopoietic cell regulation involves interaction between marrow stromal cells and haematopoietic progenitor cells which may be facilitated by specific recognition and adhesion. Some leukaemogenic events might produce a selective growth advantage by altering this regulatory network, possibly by diminishing the capacities of cells to adhere to stromal elements. Using an in vitro culture system which allows investigation of adhesion to stromal layers and subsequent colony formation by blast colony-forming cells (B1-CFC) in normal marrow and Ph+ chronic myeloid leukaemic (CML) blood, we compared the adhesive properties of normal and malignant progenitor cells. We present evidence that altered adhesive interactions between primitive progenitor cells and marrow stromal cells occur in CML.     

Specific dephosphorylation of membrane proteins in Rous sarcoma virus-transformed chick embryo fibroblasts

Chick embryo fibroblasts (CEF) infected with avian sarcoma virus become rapidly transformed as a result of expression of the viral src gene in the form of a single polypeptide of molecular weight 60,000 (pp60src) with protein kinase activity and suggested preferential association with the plasma membrane. Studies with normal avian and mammalian cells have revealed the presence of an antigenically related protein which seems to have similar kinase activity, but which is present at less than 1% of the levels of virally induced src protein found in transformed cells. As dynamic phosphorylation is important in numerous regulatory processes, the phenotypic expression of transformation may arise from an imbalance in one or more regulatory mechanisms that are controlled by protein phosphorylation. The cell membrane is affected during transformation, including its phosphotransferase activity. The latter has been shown using isolated membrane fractions whose properties may be changed during preparation. Therefore, we have compared the phosphorylation state of individual membrane proteins found in intact normal and RSV-transformed cells and report here the identification of two heavily phosphorylated, acidic membrane proteins in normal CEF which are specifically dephosphorylated on transformation by wild-type and temperature-sensitive Rous sarcoma viruses.     

The DNA sequence and comparative analysis of human chromosome 5

Chromosome 5 is one of the largest human chromosomes and contains numerous intrachromosomal duplications, yet it has one of the lowest gene densities. This is partially explained by numerous gene-poor regions that display a remarkable degree of noncoding conservation with non-mammalian vertebrates, suggesting that they are functionally constrained. In total, we compiled 177.7 million base pairs of highly accurate finished sequence containing 923 manually curated protein-coding genes including the protocadherin and interleukin gene families. We also completely sequenced versions of the large chromosome-5-specific internal duplications. These duplications are very recent evolutionary events and probably have a mechanistic role in human physiological variation, as deletions in these regions are the cause of debilitating disorders including spinal muscular atrophy.     

Epitope mimics and determinant spreading: pathways to autoimmunity

Infectious microorganisms have evolved molecules which mimic the host in order to aid in their undetected propagation. In response, mammalian hosts have evolved a highly diverse immune repertoire designed to eradicate rapidly changing pathogens. The generation of diversity in the immune repertoire results in potentially damaging self cross-reactivities which require multiple regulatory controls to keep autoreactive lymphocytes in check. Here, we review how molecular mimicry at the T cell level might be important in the development of systemic autoimmunity.     

A beta peptide vaccination prevents memory loss in an animal model of Alzheimer's disease

Vaccinations with amyloid-beta peptide (A beta) can dramatically reduce amyloid deposition in a transgenic mouse model of Alzheimer's disease. To determine if the vaccinations had deleterious or beneficial functional consequences, we tested eight months of A beta vaccination in a different transgenic model for Alzheimer's disease in which mice develop learning deficits as amyloid accumulates. Here we show that vaccination with A beta protects transgenic mice from the learning and age-related memory deficits that normally occur in this mouse model for Alzheimer's disease. During testing for potential deleterious effects of the vaccine, all mice performed superbly on the radial-arm water-maze test of working memory. Later, at an age when untreated transgenic mice show memory deficits, the A beta-vaccinated transgenic mice showed cognitive performance superior to that of the control transgenic mice and, ultimately, performed as well as nontransgenic mice. The A beta-vaccinated mice also had a partial reduction in amyloid burden at the end of the study. This therapeutic approach may thus prevent and, possibly, treat Alzheimer's dementia.