Intraspecific nuclear DNA variation in Drosophila

We have summarized and analyzed all available nuclear DNA sequence polymorphism studies for three species of Drosophila, D. melanogaster (24 loci), D. simulans (12 loci), and D. pseudoobscura (5 loci). Our major findings are: (1) The average nucleotide heterozygosity ranges from about 0.4% to 2% depending upon species and function of the region, i.e., coding or noncoding. (2) Compared to D. simulans and D. pseudoobscura (which are about equally variable), D. melanogaster displays a low degree of DNA polymorphism. (3) Noncoding introns and 3' and 5' flanking DNA shows less polymorphism than silent sites within coding DNA. (4) X-linked genes are less variable than autosomal genes. (5) Transition (Ts) and transversion (Tv) polymorphisms are about equally frequent in non-coding DNA and at fourfold degenerate sites in coding DNA while Ts polymorphisms outnumber Tv polymorphisms by about 2:1 in total coding DNA. The increased Ts polymorphism in coding regions is likely due to the structure of the genetic code: silent changes are more often Ts's than are replacement substitutions. (6) The proportion of replacement polymorphisms is significantly higher in D. melanogaster than in D. simulans. (7) The level of variation in coding DNA and the adjacent noncoding DNA is significantly correlated indicating regional effects, most notably recombination. (8) Surprisingly, the level of polymorphism at silent coding sites in D. melanogaster is positively correlated with degree of codon usage bias. (9) Three proposed tests of the neutral theory of DNA polymorphisms have been performed on the data: Tajima's test, the HKA test, and the McDonald-Kreitman test. About half of the loci fail to conform to the expectations of neutral theory by one of the tests. We conclude that many variables are affecting levels of DNA polymorphism in Drosophila, from properties of nucleotides to population history and, perhaps, mating structure. No simple, all encompassing explanation satisfactorily accounts for the data.      

A molecular phylogeny for the Drosophila melanogaster subgroup and the problem of polymorphism data

Drosophila melanogaster belongs to a closely related group of eight species collectively known as the melanogaster subgroup; all are native to sub-Saharan Africa and islands off the east coast of Africa. The phylogenetic relationships of most species in this subgroup have been well documented; however, the three most closely related species, D. simulans, D. sechellia, and D. mauritiana, have remained problematic from a phylogenetic standpoint as no data set has unambiguously resolved them. We present new DNA sequence data on the nullo and Serendipity-alpha genes and combine them with all available nuclear DNA sequence data; the total data encompass 12 genes and the ITS of rDNA. A methodological problem arose because nine of the genes had information on intraspecific polymorphisms in at least one species. We explored the effect of inclusion/exclusion of polymorphic sites and found that it had very little effect on phylogenetic inferences, due largely to the fact that 82% of polymorphisms are autapomorphies (unique to one species). We have also reanalyzed our previous DNA-DNA hybridization data with a bootstrap procedure. The combined sequence data set and the DNA-DNA hybridization data strongly support the sister status of the two island species, D. sechellia and D. mauritiana. This at least partially resolves what had been a paradox of parallel evolution in these two species.      

Temporal fluctuation in shrub species preferences of two native rodents: The effect of infection status on habitat use

Small mammals use plant species for gathering food resources and for shelter. Preferences for certain plant species are related to nutritional restrictions and behavioural patterns, which could be altered in the presence of an infectious disease. Several native small mammals are part of the wild cycle of the protozoan Trypanosoma cruzi, responsible for Chagas disease in humans. This is a vector‐borne disease transmitted by insects of the subfamily Triatominae. We examined the effect of T. cruzi infection status on the use and preference patterns of shrub species by two native rodent species: Octodon degus and Phyllotis darwini. This study was conducted during four sampling years (2010–2013) in a hyper‐endemic zone of Chagas disease located in a semiarid Mediterranean ecosystem. We captured individuals of 599 O. degus and 575 P. darwini (89% of the total captures), which were related to nine shrub species and examined for T. cruzi infection. In a community‐level analysis, infected and non‐infected O. degus used individual shrub species within the shrub community significantly non‐randomly relative to their availability; the same pattern was detected for non‐infected P. darwini individuals, whereas infected individuals used the shrub community according to the abundance of each shrub species. Examining individual preferences, both rodents showed a strong preference for Flourensia thurifera and Colliguaja odorifera regardless of their infection status. Preferences for specific shrub species were variable among years, showing a ‘core’ of preferred shrub species and variable levels of use of the remaining ones. Our results show that T. cruzi infection in wild small mammals can modify habitat use patterns and preferences for certain shrub species, probably affecting processes acting at community level.     

用抗性筛选法选育γ—亚麻酸（GLA）高产菌株

以深黄被孢霉（Mortierella isabellina）为出发菌株,经紫外线诱变处理,采用抗性筛选法,直接在梯度平板上挑选取抗脂肪酸脱氢酶抑制物抑芽丹（maleic hydrazide）的菌株进行初筛,然后经摇瓶发酵法测定相关性能指标进行得筛,获得一株生产性能比出发菌株显提高的突变株M80,其菌体收率达25.10g/L、油脂产率达12.35g/L、γ-亚麻酸（GLA）产率达771.88mg/L。     

Cloning of the mouse homolog of the 126-kDa human C1q/MBL/SP-A receptor, C1qRp

Binding of C1q to cell surfaces has been shown to mediate a number of biological activities including enhancement of phagocytosis and stimulation of superoxide production. Several C1q binding proteins have been proposed as candidate receptors for these functions. The 126-kDa human C1q membrane receptor, termed C1qR_p, has recently been cloned. This molecule is believed to play a role in the enhancement of phagocytosis in monocytes and macrophages, and its expression has been shown to be restricted to cells of the myeloid lineage, endothelial cells, and platelets. Here we report the isolation and genomic characterization of the murine homolog of C1qR_p. Degenerate oligonucleotide primers based on the published human sequence were used to amplify a region of the murine homolog spanning from the carbohydrate recognition domain to the fourth epidermal growth factor (EGF) domain. This fragment was used as a probe to isolate the murine gene from a 129/Sv genomic λ library. The predicted primary protein sequence displayed 68.1% identity with the human homolog. All the major structural domains were conserved between the two molecules. The coding sequence of the murine gene was contained within two exons separated by a small intron of approximately 250 bp. The structure of the human gene was found to be similar, with the position of the intron conserved. Cloning of the murine C1qR_p will facilitate further investigation of the physiological function of this molecule. Received: 9 November 1998 / Accepted: 28 March 1999     

A novel mechanism for complement activation at the surface of B cells following antigen binding

Coligation of CD21 with BCR on the surface of B cells provides a costimulatory signal essential for efficient Ab responses to T-dependent Ags. To achieve this, Ag must be directly linked to C3 fragments, but how this occurs in vivo is not fully understood. Using BCR transgenic mice, we demonstrated that C3 was deposited on the surface of B cells following both high- and moderate-affinity Ag binding. This was dependent on the specific binding of IgM to the BCR-bound Ag and can occur independently of soluble immune complex formation. Based on these data, we propose a novel model in which immune complexes can form directly on the surface of the B cell following Ag binding. This model has implications for our understanding of B lymphocyte activation.