CNGA3 mutations in hereditary cone photoreceptor disorders

We recently showed that mutations in the CNGA3 gene encoding the alpha-subunit of the cone photoreceptor cGMP-gated channel cause autosomal recessive complete achromatopsia linked to chromosome 2q11. We now report the results of a first comprehensive screening for CNGA3 mutations in a cohort of 258 additional independent families with hereditary cone photoreceptor disorders. CNGA3 mutations were detected not only in patients with the complete form of achromatopsia but also in incomplete achromats with residual cone photoreceptor function and (rarely) in patients with evidence for severe progressive cone dystrophy. In total, mutations were identified in 53 independent families comprising 38 new CNGA3 mutations, in addition to the 8 mutations reported elsewhere. Apparently, both mutant alleles were identified in 47 families, including 16 families with presumed homozygous mutations and 31 families with two heterozygous mutations. Single heterozygous mutations were identified in six additional families. The majority of all known CNGA3 mutations (39/46) are amino acid substitutions compared with only four stop-codon mutations, two 1-bp insertions and one 3-bp in-frame deletion. The missense mutations mostly affect amino acids conserved among the members of the cyclic nucleotide gated (CNG) channel family and cluster at the cytoplasmic face of transmembrane domains (TM) S1 and S2, in TM S4, and in the cGMP-binding domain. Several mutations were identified recurrently (e.g., R277C, R283W, R436W, and F547L). These four mutations account for 41.8% of all detected mutant CNGA3 alleles. Haplotype analysis suggests that the R436W and F547L mutant alleles have multiple origins, whereas we found evidence that the R283W alleles, which are particularly frequent among patients from Scandinavia and northern Italy, have a common origin.     

Free major histocompatibility complex class I heavy chain is preferentially targeted for degradation by human T-cell leukemia/lymphotropic virus type 1 p12(I) protein

Human T-cell leukemia virus type 1 (HTLV-1) establishes a persistent infection in the host despite a vigorous virus-specific immune response. Here we demonstrate that an HTLV-1-encoded protein, p12(I), resides in the endoplasmic reticulum (ER) and Golgi and physically binds to the free human major histocompatibility complex class I heavy chains (MHC-I-Hc) encoded by the HLA-A2, -B7, and -Cw4 alleles. As a result of this interaction, the newly synthesized MHC-I-Hc fails to associate with beta(2)-microglobulin and is retrotranslocated to the cytosol, where it is degraded by the proteasome complex. Targeting of the free MHC-I-Hc, and not the MHC-I-Hc-beta(2)-microglobulin complex, by p12(I) represents a novel mechanism of viral interference and disrupts the intracellular trafficking of MHC-I, which results in a significant decrease in surface levels of MHC-I on human T-cells. These findings suggest that the interaction of p12(I) with MHC-1-Hc may interfere with antigen presentation in vivo and facilitate escape of HTLV-1-infected cells from immune recognition.     

L-type Ca2+ channels and K+ channels specifically modulate the frequency and amplitude of spontaneous Ca2+ oscillations and have distinct roles in prolactin release in GH3 cells

GH3 cells showed spontaneous rhythmic oscillations in intracellular calcium concentration ([Ca2+]i) and spontaneous prolactin release. The L-type Ca2+ channel inhibitor nimodipine reduced the frequency of Ca2+ oscillations at lower concentrations (100nM-1 microM), whereas at higher concentrations (10 microM), it completely abolished them. Ca2+ oscillations persisted following exposure to thapsigargin, indicating that inositol 1,4,5-trisphosphate-sensitive intracellular Ca2+ stores were not required for spontaneous activity. The K+ channel inhibitors Ba2+, Cs+, and tetraethylammonium (TEA) had distinct effects on different K+ currents, as well as on Ca2+ oscillations and prolactin release. Cs+ inhibited the inward rectifier K+ current (KIR) and increased the frequency of Ca2+ oscillations. TEA inhibited outward K+ currents activated at voltages above -40 mV (grouped within the category of Ca2+ and voltage-activated currents, KCa,V) and increased the amplitude of Ca2+ oscillations. Ba2+ inhibited both KIR and KCa,V and increased both the amplitude and the frequency of Ca2+ oscillations. Prolactin release was increased by Ba2+ and Cs+ but not by TEA. These results indicate that L-type Ca2+ channels and KIR channels modulate the frequency of Ca2+ oscillations and prolactin release, whereas TEA-sensitive KCa,V channels modulate the amplitude of Ca2+ oscillations without altering prolactin release. Differential regulation of these channels can produce frequency or amplitude modulation of calcium signaling that stimulates specific pituitary cell functions.     

Adaptive characteristics of salt-induced myceloids of Arthrobacter globiformis

When Arthrobacter globiformis is grown in medium containing increased concentrations of NaCl or decreased levels of cations, the bacteria grow as clusters of branching myceloid cells. The sensitivities of salt-induced and citrate-induced myceloids to several environmental stresses were compared to those of normal exponential-phase bacilli and stationary-phase cocci. Salt-induced myceloids were more resistant than normal cells to ultraviolet light or heat shock at 45°C but not to osmotic upshock or pH 4.3; citrate-induced myceloids showed an intermediate rate of heat inactivation. Carbon or nitrogen starvation of myceloids in the absence of added NaCl or citrate led to their division into single cells. Both myceloids and the single cells derived from them were more resistant than normal bacteria to nitrogen starvation. Salt-induced and citrate-induced myceloids showed reduced metabolism of many different carbon compounds in Biolog GP plates. These studies suggest that the formation of multicellular structures by A. globiformis is an adaptive response which increases its potential for survival.     

Sugar meals and longevity of the sandfly Phlebotomus papatasi in an arid focus of Leishmania major in the Jordan Valley

The sugar diet and life-span of Phlebotomus papatasi were studied in a typical zoonotic focus of Leishmania major in an arid area of the Jordan Valley during 1996-1997. Plant-tissue residues (cellulose particles) were identified in the stained guts of 23% of P. papatasi and significant amounts of sugar were found in the gut of 16%. Feeding on different plants was demonstrated by using their branches, suffused with cellulose stain, as baits in the field. Ingested, stained cellulose was detected in 10% of the sandflies (6% of males, 12.5% of females) caught near bait-branches of common local plants, mostly Chenopodiaceae. The similar rates of plant and sugar feeding, with the observed absence of aphids (ruling out the availability of honeydew), implied that the sugar meals of sandflies were obtained directly from plants. The relative paucity of sugar meals in P. papatasi coincided with a short life-span, evaluated by daily growth lines in the cuticle. The age of the oldest females was estimated to be 8 days, and 6 days for males. Under local conditions, the first gonotrophic cycle can be completed in 6 days and the usual transmission of L. major is apparently afterwards, when females ingest blood to initiate another cycle. Only about 9% of P. papatasi females survived > 6 days.