A POPULATION MEMETICS APPROACH TO CULTURAL EVOLUTION IN CHAFFINCH SONG: DIFFERENTIATION AMONG POPULATIONS

We investigated cultural evolution in populations of common chaffinches (Fringilla coelebs) in the Atlantic islands (Azores, Madeira, and Canaries) and neighboring continental regions (Morocco and Iberia) by employing a population-memetic approach. To quantify differentiation, we used the concept of a song meme, defined as a single syllable or a series of linked syllables capable of being transmitted. The levels of cultural differentiation are higher among the Canaries populations than among the Azorean ones, even though the islands are on average closer to each other geographically. This is likely the result of reduced levels of migration, lower population sizes, and bottlenecks (possibly during the colonization of these populations) in the Canaries; all these factors produce a smaller effective population size and therefore accentuate the effects of differentiation by random drift. Significant levels of among-population differentiation in the Azores, in spite of substantial levels of migration, attest to the differentiating effects of high mutation rates of memes, which allow the accumulation of new mutants in different populations before migration can disperse them throughout the entire region.     

Allozyme differentiation within and between red drum (Sciaenops ocellatus) from the Gulf of Mexico and Atlantic Ocean

Nine polymorphic nuclear-gene (allozyme) loci were surveyed among 491 red drum ( Sciaenops ocellatus ) sampled in 1988 and 1989 from nearshore localities in the northern Gulf of Mexico (Gulf) and the Atlantic coast of the southeastern United States (Atlantic). Data were combined with those from a previous study to generate a data set of 762 individuals representing 11 sample localities in the Gulf and 175 individuals representing five sample localities in the Atlantic. The combined data set included individuals from the 1986 and 1987 year classes and permitted rigorous testing of both temporal and spatial genetic heterogeneity. Average heterozygosity-per-locus values (estimated using 33 assumed monomorphic loci) were 0·048 (Gulf red drum) and 0·046 (Atlantic red drum). Tests of heterogeneity in allele frequencies between year classes at individual localities and across regions (Gulf and Atlantic) were non-significant. Tests of spatial (geographic) heterogeneity indicated that red drum are weakly subdivided: genetically-differentiated subpopulations occur in the northern Gulf and along the south-eastern Atlantic coast. Genetic data were consistent with the hypothesis that red drum within the Gulf and along the Atlantic coast comprise singie subpopulalions. Genetic differences between Gulf and Atlantic red drum seem likeiy to stem from historical or recent interactions between dispersal and impediments to gene flow.     

A simple derivation of the partitioning of genetic differentiation within subdivided populations

The genetic differentiation within a subdivided population can be partitioned into two proportions, one due to differentiation within sub-populations and the other due to differentiation among subpopulations. A simple mathematical derivation of this procedure, known as Nei's G _ST -statistics, is presented. The significance of considering the differing relative sizes of subpopulations is stressed. Possible fields of applications for breeders and conservationists who are concerned with the establishment of genetically diverse populations are mentioned.     

Tumor Necrosis Factor-α (TNF-α), Interferon-γ, and Interleukin-6 but Not TNF-β Induce Differentiation of Neuroblastoma Cells: The Role of Nitric Oxide

Abstract: Tumor necrosis factor-a (TNF-α), interferon-γ (IFN-7), and interleukin-6 (IL-6), but not TNF-β, can induce the in vitro differentiation of the neuroblastoma cell line N103 in a dose-dependent manner. Differentiation of N103 was accompanied by the arrest of cell growth and neurite formation. The induction of neuroblastoma cell differentiation by TNF-α and IFN-γ can be specifically inhibited by a nitric oxide (NO) synthase inhibitor, l -N^G-monomethylarginine. In contrast, the differentiation of N103 cells by IL-6 was not affected by l -N^G-monomethylarginine. These results indicate that TNF-α and IFN-γ, but not IL-6, induce the differentiation of neuroblastoma cells via NO. This is confirmed by the finding that the culture super- natants of N103 cells induced by TNF-α and IFN-γ, but not that by IL-6, contained high levels of NO₂⁻, the production of which was inhibited by l - N ^G-monomethylarginine. Furthermore, the differentiation of N103 cells can be induced directly in a dose-dependent manner by the addition of nitroprusside, a generator of NO, into the culture medium. These data therefore indicate that NO may be an important mediator in the induction of neuronal cell differentiation by certain cytokines such as TNF-α and IFN-γ and that neuronal cells, in addition to the macrophagelike brain cells, can be induced by immunological stimuli to produce large quantities of NO.     

Genetic analysis of populations of threatened snake species using RAPD markers

Snakes are a particularly threatened vertebrate taxon, with distributions of many species and populations becoming increasingly fragmented. At present, little is known about the degree of genetic differentiation that exists between isolated populations even though such information may be critical to their survival and conservation. As an example of how recently developed RAPD genetic markers can be used in conservation genetics, we present preliminary results from a study which used these DNA-based markers to assess population divergence in two threatened Canadian snakes, the black rat snake ( Elaphe o. obsoleta ) and the eastern massasauga rattlesnake ( Sistrurus c. catenatus ). We present information on the levels of variation and reliability of amplification for fragments generated from five primers. We then use a recently developed analytical technique to estimate levels of nucleotide diversity within populations and sequence divergence between populations. Our results show that intrapopulation levels of divergence as estimated by the methods of Clark & Lanigan ( Molecular Biology and Evolution 1993, 10 , 1096–1111) approximate those found for mtDNA in vertebrates and that diversity between snake populations is small and non-significant when tested using randomization procedures. Thus, our study provides an example of how RAPDs can be applied to conservation genetic studies of vertebrates and suggest that the snake populations we examined have only recently become isolated and maybe considered genetically equivalent from a conservation perspective, although this conclusion needs to be confirmed with other DNA-based markers.     

Efficient generation of chimaeric mice using embryonic stem cells after long-term culture in the presence of ciliary neurotrophic factor

The aim of our study was to evaluate whether ciliary neurotrophic factor (CNTF) can substitute for leukaemia inhibitory factor (LIF) in maintaining pluripotential embryonic stem (ES) cells in culture. Two subclones of D3 ES cells were used to assess cell proliferation and differentiation in the presence of CNTF, LIF or Buffalo rat liver (BRL) cell-conditioned medium, or in the absence of exogenous differentiation inhibiting factors. ES cells maintained in medium supplemented with CNTF for up to four weeks were injected into blastocysts to investigate theirin vivo pluripotency in terms of chimaera formation. CNTF inhibited ES cell differentiation in a dose-dependent manner. The most effective concentration was 10 ng CNTF per ml of medium. The effects of CNTF on ES cell differentiation and proliferation were comparable to those of LIF at the same concentration. BRL cell-conditioned medium was less effective at preventing ES cell differentiation but induced their proliferation very markedly. Both ES cell clones efficiently formed chimaeras after long-term culture with CNTF as the only differentiation inhibiting agent. The ability of these ES cells to colonize the germ-line is the ultimate proof that CNTF can preserve the pluripotency of ES cells.     

密码结构域及其功能表现

能组织成超级结构的各种序列组块,因其具有特定一级序列、或者具有某种卷曲的螺旋构象和某种非β螺旋结构,可以作为有特异功能的结构域、被特异的结合蛋白质识别和结合,因而可称为密码结构域,密码结构域作为特异的分子相互作用和过程的遗传指令,参与细胞周期的各种事件乃至发育和分化过程中基因有区别的表达.     

Genome size and restriction fragment length polymorphism analysis of Vibrio cholerae strains belonging to different serovars and biotypes

Abstract The genome size of Vibrio cholerae has been determined by pulsed field gel electrophoresis following digestion of chromosomal DNA with endonucleases. The genome size of all the classical strains examined was about 3000 kb and that of El Tor biotype was 2500 kb. The Not I and S fi I digestion patterns of the genomes of several V. cholerae straimns belonging to different serovars and biotypes showed distinct restriction fragment length polymorphism (RFLP). RFLP analysis together with the genome size can be used to differentiate strains of different serovars and biotypes of V. cholerae .     

Towards and understanding of nuclear morphogenesis

In the age of “virtual reality,” the imperfect microscopic silhouettes of cells and organelles are gradually being replaced by calligraphic computer drawings. In this context, textbooks and introductory slides often depict the cell nucleus as a smooth-shaped, featureless object. However, in reality, the nuclei of different cells possess distinct sizes and morphological features which develop in a programmed fashion as each cell differentiates. To dissect this complex morphogenetic process, we need to identify the basic elements that determine nuclear architecture and the regulatory factors involved. Recently, clues about the identity of these components have been obtained both by systematic analysis and by serendipity. This review summarizes a few recent findings and ideas that may serve as a first forum for future discussions and, I hope, for further work on this topic. © 1994 Wiley-Liss, Inc.