Restricted Ig variable region gene expression among Ly-1+ B cell lymphomas

The majority of the characterized Ly-1+ B cell lymphomas of B10.H-2aH-4bp/Wts origin (the CH series) bear surface Ig related by Ag specificity or idiotype or both. To determine the genetic basis for these structural similarities, we have sequenced the VH and VL region genes expressed by 10 CH lymphomas, and have compared their VH and V kappa gene rearrangements by Southern blot analysis to one another and to those of four other CH lymphomas. Sequence analysis identified only five different VH, and seven different VL genes, and indicated that these V genes are essentially unmutated. CH lymphomas which express the identical VH gene share at least one idiotope. Thus, the basis for shared idiotype and specificity is due in most cases to the use of the same V gene. This restriction in V gene expression is not due to the preferential use of V genes of any particular VH family or VL group, as the expressed V genes belong to four different VH families and four V kappa groups, and include V lambda 1 and V lambda 2. We hypothesize that Ag selection accounts for the restriction in V gene usage among CH lymphomas.     

Three classes of signalling molecules on B-cell membranes

The question of whether surface immunoglobulin and Ia molecules have a signalling function in helper T cell-dependent activation of B cells has been evaluated. Two sources of B cells have been used, one a purified population of hapten-binding B cells, the other a B-cell lymphoma, CH12, with known antigen specificity. Evidence is presented that both immunoglobulin and Ia molecules are receptors actively involved in the initial activation of resting B cells. Nevertheless, the requirements for ligand binding to either receptor can be bypassed under appropriate conditions, and the implications of this result for the function of these molecules is discussed. With respect to B-cell Ia, the authors present data that demonstrate two distinct functions of this molecule, one as a restricting element for T-cell activation, the second as a signalling receptor for B-cell excitation. On the CH12 surface, the I-A molecule fulfills the former function, but T-cell interactions with I-A fail to result in B-cell stimulation, suggesting that B-cell Ia may limit helper T cell-B cell interactions. We suggest that the binding of antigen surface immunoglobulin and binding of helper T-cell receptors to the appropriate Ia molecule(s) results in the activation of genes that encode for a third class of membrane B-cell receptors, those that bind B-cell stimulating factors.     

Antigen-induced lymphomagenesis: identification of a murine B cell lymphoma with known antigen specificity

CH12, a murine B cell lymphoma derived in B10 H-2aH-4bp/Wts mice after transfer of SRBC hyperimmunized spleen cells into an adult-thymectomized, sublethally irradiated, syngeneic recipient, is demonstrated to bear surface IgM specific for a determinant found on SRBC and ChRBC. The Ig specificity has been demonstrated by rosetting assays and complement-dependent hemolysis. The removal of CH12 surface IgM by capping with anti-mu or with anti-CH12 idiotype, but not with anti-gamma or with irrelevant anti-idiotype, eliminated the formation of rosettes between CH12 and SRBC or ChRBC. The absorption of CH12 Ig produced in vitro, with either SRBC or ChRBC but not with HRBC, removed all hemolysin activity against SRBC, demonstrating that only one CH12 product was responsible for the reactivity with both SRBC and ChRBC. CH12 has a surface phenotype of a relatively mature B cell expressing surface Ig (IgM-mu,kappa) and la antigens, but lacking Thy-1 or detectable Fc or C3 receptors. CH12 also expresses the antigen Lyt-1. Growth of CH12 in vivo or in vitro results in the generation of up to 3% direct PFC and serum hemolysin, which shows that CH12 is not irretrievably "frozen". The generation of PFC and serum hemolysin is associated with increased population density, and the rate of PFC and serum hemolysin accumulation cannot be explained by simple cell division. A continuously secreting hybridoma derived from CH12 was used to purify the CH12 IgM to facilitate studies of protein sequence and idiotype.     

Patterns of sequence variation in the mitochondrial D-loop region of shrews

Direct sequencing of the mitochondrial displacement loop (D-loop) of shrews (genus Sorex) for the region between the tRNA(Pro) and the conserved sequence block-F revealed variable numbers of 79-bp tandem repeats. These repeats were found in all 19 individuals sequenced, representing three subspecies and one closely related species of the masked shrew group (Sorex cinereus cinereus, S. c. miscix, S. c. acadicus, and S. haydeni) and an outgroup, the pygmy shrew (S. hoyi). Each specimen also possessed an adjacent 76-bp imperfect copy of the tandem repeats. One individual was heteroplasmic for length variants consisting of five and seven copies of the 79-bp tandem repeat. The sequence of the repeats is conducive to the formation of secondary structure. A termination-associated sequence is present in each of the repeats and in a unique sequence region 5' to the tandem array as well. Mean genetic distance between the masked shrew taxa and the pygmy shrew was calculated separately for the unique sequence region, one of the tandem repeats, the imperfect repeat, and these three regions combined. The unique sequence region evolved more rapidly than the tandem repeats or the imperfect repeat. The small genetic distance between pairs of tandem repeats within an individual is consistent with a model of concerted evolution. Repeats are apparently duplicated and lost at a high rate, which tends to homogenize the tandem array. The rate of D- loop sequence divergence between the masked and pygmy shrews is estimated to be 15%-20%/Myr, the highest rate observed in D-loops of mammals. Rapid sequence evolution in shrews may be due either to their high metabolic rate and short generation time or to the presence of variable numbers of tandem repeats.      

大鼠胼胝体内神经肽Y免疫反应阳性纤维的发育

本实验用免疫组织化学ＡＢＣ法研究了大鼠胼胝体内神经肽Ｙ免疫反应阳性（ＮＰＹ－ＩＲ）纤维的生后发育。结果发现,许多ＮＰＹ－ＩＲ纤维在大鼠出生时便存在于胼胝体内。ＮＰＹ－ＩＲ胼胝体纤维的密度在生后１周内继续逐渐增高,在第２周内达到最高峰。之后,ＮＰＹ－ＩＲ胼胝体纤维的密度逐渐下降,至第３周末时接近成年时的水平,即仅有少量ＮＰＹ－ＩＲ纤维存在于胼胝体内。这些结果提示在大鼠早期生后发育过程中许多ＮＰＹ－ＩＲ胼胝体纤维是暂时性的,其作用可能与大脑皮质的机能发育有关。     

Genetic control of susceptibility of mice to Rous sarcoma virus tumorigenesis

Studies with congenic resistant strains of mice indicate that susceptibility to Rous sarcoma virus tumorigenesis is influenced by a gene or genes associated with the major histocompatibility complex (H-2). These genes manifest dominant relative susceptibility. Preliminary studies indicate that the CBA/J strain harbors a gene or genes for relative susceptibility, which are recessive. These results are compared with other studies onH-2-associated genes affecting murine viral oncogenesis.     

Dedicated biomass crops can enhance biodiversity in the arable landscape

Suggestions that novel, non‐food, dedicated biomass crops used to produce bioenergy may provide opportunities to diversify and reinstate biodiversity in intensively managed farmland have not yet been fully tested at the landscape scale. Using two of the largest, currently available landscape‐scale biodiversity data sets from arable and biomass bioenergy crops, we take a taxonomic and functional trait approach to quantify and contrast the consequences for biodiversity indicators of adopting dedicated biomass crops on land previously cultivated under annual, rotational arable cropping. The abundance and community compositions of biodiversity indicators in fields of break and cereal crops changed when planted with the dedicated biomass crops, miscanthus and short rotation coppiced (SRC) willow. Weed biomass was consistently greater in the two dedicated biomass crops than in cereals, and invertebrate abundance was similarly consistently higher than in break crops. Using canonical variates analysis, we identified distinct plant and invertebrate taxa and trait‐based communities in miscanthus and SRC willows, whereas break and cereal crops tended to form a single, composite community. Seedbanks were shown to reflect the longer term effects of crop management. Our study suggests that miscanthus and SRC willows, and the management associated with perennial cropping, would support significant amounts of biodiversity when compared with annual arable crops. We recommend the strategic planting of these perennial, dedicated biomass crops in arable farmland to increase landscape heterogeneity and enhance ecosystem function, and simultaneously work towards striking a balance between energy and food security.