Mitochondrial DNA variation and genetic structure in populations of Drosophila melanogaster

The understanding of the genetic structure of a species can be improved by considering together data from different types of genetic markers. In the past, a number of worldwide populations of Drosophila melanogaster have been extensively studied for several such markers, including allozymes, chromosomal inversions, and quantitative characters. Here we present results from a study of restriction- fragment-length polymorphisms of mitochondrial DNA (mtDNA) in 92 isofemale lines from many of the same geographic populations of D. melanogaster. Eleven restriction enzymes were used, of which four revealed restriction-site polymorphism. A total of 24 different haplotypes were observed, of which 18 were unique to single populations. In many populations, the unique haplotypes have reached high frequency without being observed in neighboring populations. A Wagner parsimony tree reveals that mutationally close variants show geographical clumping, suggesting local differentiation of mtDNA in populations. The Old-World and the New-World populations are differentiated, with the predominant Old-World haplotype being virtually absent from the New World. These results contrast with those for the nuclear genes, in which many loci show parallel clines in different continents, and suggest a common origin of D. melanogaster populations in North America.      

Isolation of metabolic cooperation-defective variants from mouse embryonal carcinoma cells

We describe the isolation from the HGPRT^? embryonal carcinoma cell line PC13TG8 of a variant, R5/3, defective in metabolic cooperation. This was achieved in two stages via an intermediate, R2/1, using a selective system in which the HGPRT^? embryonal carcinoma cells were co-cultured with HGPRT⁺ cells in 6-thioguanine. R5/3 cells show increased survival compared with PC13TG8 when retested under selection conditions, and a reduction in grain count index when tested by autoradiography as recipients of [³H]hypoxanthine-labelled nucleotides from wild-type donors and as donors of [³H]thymidine- and [³H]adenine-labelled nucleotides to suitably marked recipients. However, a low residual fraction of heavily labelled recipients is found in all autoradiographic experiments with R5/3 cells. This is not due to heterogeneity of either donor or recipient populations. We also describe the development of a colony-formation assay for metabolic cooperation based on the “kiss of life” phenomenon, in which R5/3 shows very poor survival compared with PC13TG8. R2/1 shows behaviour intermediate between PC13TG8 and R5/3 in all the tests described above. We conclude that two steps can be identified in the change of phenotype by which R5/3 is derived from PC13TG8, and that both steps modify the ability of the cells to form permeable junctions.     

中国高山ping亚属（Subgerus Alticola）的系统类与分布

高山ｐｉｎｇ亚属广布于中亚山地，即从喜马拉雅山、兴都库库会经帕米尔、天山、西茂而至图瓦、抗爱山和贝加尔湖一带。中国过去仅记录２种：银色高山ｐｉｎｇ（Ａｌｔｉｃｏｌａ ａｒｇｅｎｔａｔｃｓ Ｓｅｖｅｒｔｓｏｖ；有时定作劳氏高山ｐｉｎｇＡ．ｒｏｙｌｅｉ的一亚种）和斯氏高山ｐｉｎｇ。本文依据形态学资料和采用判别函数分析的方法，对该亚属进行了研究。我们认为中国高山ｐｉｎｇ至少有３个以上的物种存在，现概述于     

Quantitative Analysis of Actinomyces Cell Walls

Quantitative data on the amino acid composition of cell walls of five species of Actinomyces were obtained by using a Beckman-Spinco amino acid analyzer. The major amino acids in A. israelii, A. naeslundii, A. eriksonii, and A. bovis species included alanine, glutamic acid, lysine, aspartic acid, and ornithine, as reported by previous workers, whereas A. propionicus contained diaminopimelic acid. Other amino acids, including glycine, valine, leucine, proline, isoleucine, and threonine, were present in at least some of the walls in quantities equal to or slightly less than that of lysine. This raised the question of whether these may represent cross-links in the peptidoglycan or other cell wall structural components or whether the wall preparations contained nonpeptidoglycan material despite the use of electron microscopy as a standard of purity; further work is required to supply the answer. The quantitative data furnish relative molar concentrations of amino acids, which can provide definitive identification of some of the species and differentiation of Actinomyces from other members of the Actinomycetales and from morphologically similar genera such as Corynebacterium and Propionibacterium.     

Regeneration of neural crest derivatives in the <Emphasis Type="Italic">Xenopus</Emphasis>tadpole tail

Background  

After amputation of the Xenopus tadpole tail, a functionally competent new tail is regenerated. It contains spinal cord, notochord and muscle, each of which has previously been shown to derive from the corresponding tissue in the stump. The regeneration of the neural crest derivatives has not previously been examined and is described in this paper.