元谋古猿下颌臼齿三维立体特征

采用欧氏距离矩阵分析（EDMA）方法对72枚元谋古猿及作为对比样本的10枚禄丰古猿、现生大猿类和人类下颌臼齿齿冠13个测量标志点三维测量数据的统计分析显示：元谋古猿在下颌臼齿齿冠三维形态测量特征上与禄丰古猿最为接近。与现生大猿类及人类相比,元谋古猿和禄丰古猿均与人类之间呈现出非常显著的差异,而与猿类较为接近。它们两者及生大猿类均与人类之间具有许多共同的差异表现特点。元谋古猿在下颌臼齿三维测量特征方面与三种现生大猿类各自之间的差别表现相似。其中,元谋古猿与猩猩之间的牙齿形态特征上似乎更为接近。但目前对这些特征相似差异的含义尚难以确定。     

中枢ACTH受体研究进展

除垂体以外,中枢神经系统也含有促肾上腺皮质激素（ＡＣＴＨ）能神经元,其神经纤维在中枢具有较广泛的投射。ＡＣＴＨ相关肽类在中枢发挥着多种生理功能。近年来对于中枢ＡＣＴＨ受体的研究取得很大的进展,现已确认ＡＣＴＨ结合位点在中枢具有广泛的分布。新近克隆出的四种ＡＣＴＨ受体中,有两种是中枢神经系统占优势的受体亚型。     

Mutations in the M1 region of the nicotinic acetylcholine receptor alter the sensitivity to inhibition by quinacrine

Summary 1. Site directed mutagenesis was used to alter the structure ofTorpedo californica nicotinic acetylcholine receptor (nAChR) and to identify amino acid residues which contribute to noncompetitive inhibition by quinacrine. Mutant receptors were expressed inXenopus laevis oocytes injected within vitro synthesized mRNA and the whole cell currents induced by acetylcholine (ACh) were recorded by two electrode voltage clamp.2. A series of mutations of a highly conserved Arg at position 209 of the subunit ofTorpedo californica nAChR revealed that positively charged amino acids are required for functional receptor expression. Mutation of Arg to Lys (R209K) or His (R209H) at position 209 shifted the EC₅₀ for ACh slightly from 5µM to 12µM and increased the normalized maximal channel activity 8.5-and 3.2-fold, respectively.3. These mutations altered the sensitivity of nAChR to noncompetitive inhibition by quinacrine. The extent of inhibition of ion channel function by quinacrine was decreased as pH increased in both wild type and mutant nAChR suggesting that the doubly charged form of quinacrine was responsible for the inhibition.4. Further mutations at different positions of the subunit suggest the contribution of Pro and Tyr residues at positions 211 and 213 to quinacrine inhibition whereas mutationsI210A andL212A did not have any effects. None of these mutations changed the sensitivity of nAChR to inhibition by a different noncompetitive inhibitor, chlorpromazine.5. These findings support a hypothesis that the quinacrine binding site is located in the lumen of the ion channel. In addition, the quantitative effect of point mutations at alternate positions on the sensitivity of quinacrine inhibition suggests that the secondary structure at the beginning of M1 region might be sheet structure.     

Polarity of meiotic gene conversion is 5′ to 3′ within the niaD gene of Aspergillus nidulans

We have examined polarity of meiotic gene conversion in the niiA-niaD gene cluster of Aspergillus nidulans in two-point crosses. The type and position of the mutations represented by the niaD alleles and the correlation between the relative frequency of gene conversion and the physical position of these mutations were determined. We show that polarity of meiotic gene conversion is 5 to 3 (transcribed strand) within the niaD gene. Additional crosses involving a niiA allele and a niaD allele show little polarity of gene conversion, which suggests that the recombination events leading to restoration of the niaD gene are initiated upstream of the coding region of the niaD gene but within the niiA-niaD gene cluster, possibly within the intergenic promoter region.     

Population structure in Mediterranean islands and risk of genetic invasion in Culexpipiens L. (Diptera: Culicidae)

The mosquito Culex pipiens is subjected to organophosphate treatments in both Corsica and southern Sardinia, but the resistance gene A2-B2, which is currently in a worldwide expansion, has only reached Sardinia. In order to understand this situation, the genetic structure of populations sampled in Sardinia and Corsica was assessed using 15 isozymes. Two loci (HK1 and HK2) were not taken into account because of the possibility of selection. For trie other loci, statistical independence was not rejected for all possible pairs, and no deviation from Hardy-Weinberg expectations was apparent. Low but significant genie differentiation was present between Corsica and Sardinia, as well as between northern and southern Sardinia, despite a large number of effective migrants per generation. These results are discussed in the context of the high probability of extinction/recolonization of breeding sites, the flight migration ability of this mosquito, and the pleiotropic cost of insecticide resistances genes. It is concluded that A2-B2 resistance is unlikely to reach Corsica from southern Sardinia, unless accidental human transportation occurs.     

Temperature Dependence of Muscarinic Acetylcholine Receptor Activation, Desensitization, and Resensitization

Abstract: The effects of temperature on muscarinic acetylcholine receptor activation, desensitization, and resensitization were studied with the use of intact mouse neuroblastoma cells (clone N1E-115), which have muscarinic receptors that mediate cyclic GMP synthesis. Below 15-20°C, activation or desensitization of muscarinic receptors by carbamylcholine and recovery from desensitization (caused by carbamylcholine at 37°C) did not occur. Above these temperatures, the apparent rates of receptor-mediated cyclic GMP synthesis, desensitization, and recovery of sensitivity increased as the incubation temperature was increased. Arrhenius plots of the data yielded activation energies of 25, 14, and 23 kcal.mol⁻¹ for activation, desensitization, and resensitization, respectively. These data suggest that a certain degree of membrane phospholipid fluidity is required for these processes to occur.     

Stretch activated ion channels in ventricular myocytes

Patch-clamp recordings from ventricular myocytes of neonatal rats identified ionic channels that open in response to membrane stretch caused by negative pressures (1 to 6 cm Hg) in the electrode. The stretch response, consisting of markedly increased channel opening frequency, was maintained, with some variability, during long (>40 seconds) stretch applications. The channels have a conductance averaging 120 pS in isotonic KCl, have a mean reversal potential 31 mV depolarized from resting membrane potential, and do not require external Ca⁺⁺ for activation. The channels appear to be relatively non-selective for cations. Since they are gated by physiological levels of tension, stretch-activated channels may represent, a cellular control system wherein beat-to-beat tension and/or osmotic balance modulate a portion of membrane conductance.Abbreviations SACs stretch-activated channels - HEPES 4-(2-hydroxyethyl)-1-piperazine-ethanesulfonic acid     

Organisation and expression of a wound/ripening-related small multigene family from tomato

cDNA clones derived from a ripe tomato fruit cDNA library were used to investigate changes in the abundance of specific mRNAs in ripening fruit and wounded leaves. mRNAs related to one cDNA clone (pTOM 13) were expressed in both situations. This clone was used to identify homologous sequences in a tomato genomic library. Three groups of related clones that hybridised to the pTOM 13 cDNA insert were identified and subcloned into plasmid vectors. Genomic Southern analysis of tomato DNA using gene-specific DNA fragments isolated from the subcloned DNAs indicated that all pTOM 13 closely related genes had been isolated. RNA dot blot analysis with these DNA fragments as probes indicated differential expression of this small multigene family in leaves and fruit.