Interleukin 1 increases collagen type IV production by murine mammary epithelial cells

The effects of human interleukin 1 (IL 1) on collagen type IV production by normal mouse mammary epithelial cells were examined. Human IL 1 was derived from the culture media of peripheral blood monocytes or placental cells that were stimulated with silica. Although crude culture media of silica-stimulated monocytes or placental cells had no enhancing activity for type IV collagen production, IL 1-containing fractions obtained by Sephacryl S-200 gel chromatography and isoelectrofocusing from such media possessed considerable activity. To confirm the effects of IL 1 on collagen production, human monocyte-derived IL 1 was highly purified by sequential isoelectrofocusing, anion-exchange (AX 300), high-performance liquid chromatography (HPLC), and HPLC gel filtration (TSK 3000). The same HPLC gel filtration fractions contained both an activity that stimulated collagen synthesis by mammary cells and thymocyte growth-promoting activity. These activities of IL 1 differed from a number of other factors, such as epidermal growth factor and another factor produced by placental cells that stimulated type IV collagen production but not thymocyte proliferation. In fact, IL 1 induced 100-fold less collagen type IV production by mammary epithelial cells than was needed to induce thymocyte proliferation. Our data suggest that IL 1-like molecules, which reportedly are produced by many tissue cell types, may therefore play a role in promoting a basement membrane formation at stromal-epithelial boundaries.     

Two locus models of selection and mutation within and among full-sib lines

Summary General models for continued full-sib mating with two diallelic autosomal loci taking account of linkage, mutation and selection within and among lines are considered. The problems are first approached by deriving the full probability transition matrix, taking account of linkage, mutation and within-line selection. Exact solutions to the equilibrium system are possible, but the computational effort is prohibitive, and this is exacerbated by the introduction of between-line selection. A second approach is based on decomposing the transition matrix into blocks whose properties suggest approximations that lead to a rapid iterative solution of the equilibrium system. Extensive numerical analysis of models of within-line selection and of combined within- and between-line selection were made. The results show that equilibrium values are essentially independent of the degree of linkage under models of within-line selection. This is because mutation plays a dominant role in determining equilibrium structure. Results from models of combined within- and between-line selection show that between-line selection has the dominant influence on gene frequency equilibrium. Both within-line and between-line selection produce appreciable linkage disequilibrium only when selection is disruptive. The results also suggest that much of the twolocus equilibrium structure can be predicted from a knowledge of single-locus equilibria.     

Horizontal transfer

Eukaryotic transposable elements provide some of the best documented examples of the occasional horizontal transfer of DNA sequences between both closely and distantly related species. Although the mechanisms involved in such a transfer remain a puzzle, new ideas are beginning to emerge. The rapidly expanding number of reports of transposable elements that may have been transferred horizontally raises questions both about whether these elements are more prone to this mode of transfer than non-mobile genes, and about the possible evolutionary significance if such a difference is real.