Interethnic genetic differentiation in Africa: HLA class I antigens in The Gambia.

A total of 752 individuals from The Gambia, west Africa who are representative of the major ethnic groups in the capital, Banjul, were serologically typed for HLA-A, -B, and -C antigens. Although all were typically "African" in their antigenic profiles, some marked frequency differences were found between the ethnic groups. Genetic distance comparisons with several other African populations showed that, although these west African populations clustered closely together, the positions of the various ethnic groups in The Gambia were consistent with historical and linguistic evidence of their affinities with one another and with other African populations. Despite the potential confounding effects both of selection by infectious diseases and of genetic drift caused by local differences in population structure, HLA frequencies appear to be of value in measuring inter- and intraregional population affinities in sub-Saharan Africa.     

Cytotoxic T cell recognition of the influenza nucleoprotein and hemagglutinin expressed in transfected mouse L cells

L cells expressing either the A/NT/60/68 nucleoprotein or the A/PR/8/34 (H1) hemagglutinin by DNA mediated gene transfer were used to investigate recognition by influenza A specific cytotoxic T lymphocytes (CTL). A subpopulation of CTL that recognized the H1 hemagglutinin was detected in mice primed with either A/PR/8/34 (H1N1) or A/JAP/305/57 (H2N2) influenza viruses. However, neither CTL from mice primed with A/NT/60/68 (H3N2) nor the recombinant virus X31 (H3N2) showed any activity on L cells expressing H1. These results showed that the majority of fully crossreactive CTL do not recognize the hemagglutinin molecule. A comparison between nucleoprotein and hemagglutinin transfected L cells reveals the nucleoprotein as the major target for CTL that are crossreactive on the three pandemic strains of human influenza A virus.     

Clones of B lymphocytes: their natural selection and expansion.

The operation of clonal selection for cells of the B-lymphocyte line is discussed with regard to: 1) The clonal repertoire determined by antigen binding to B lymphocytes, which is much larger than that determined by limiting dilution cloning assays. This quantitative difference is interpreted in terms of the multiple shared specificities of each antibody molecule. 2) Multiclonal responses and initial selection by antigen of particular clones (preferential primary selection). 3) Clonal dominance. During an immune response one clone (or a small number of clones) of B cells is preferentially selected and proliferated, apparently at random, from a heterogeneous population of cells capable of responding to the given antigen. Co-dominance of two or more clones simultaneously can be obtained by mixing selected clones. Secreted antibody is seen as playing a role in the establishment of clonal dominance. A model for clonal expansion is presented. The model attempts to explain the generation of memory and antibody secreting cells within each clonal expansion in terms of the ratio of two signals, one for proliferation and one for differentiation. The delivery of these signals is proposed to involve the receptor antibody-antigen interaction for proliferation and a self-recognition site interaction for differentiation.     

Life history of the gulf darter,Etheostoma swaini (Pisces: Percidae)

Synopsis Etheostoma swaini, the gulf darter, was collected from the Black Creek drainage in southern Mississippi (February 1978 – April 1979). The gulf darter generally inhabits small- to moderate-size creeks and occurs over a sand or sandy mud bottom, often in association with aquatic vegetation or a layer of organic debris. Larval dipterans were the most important food items, both numerically and volumetrically. Chironomids were found in 71–100% of the stomachs in all except the unusual March 16 collection. The length frequency distribution and the scale annuli analysis indicated there were three year-classes present in the population at any one time. Fifty-one percent of the specimens taken were less than 12 months old. During the mid-February to late March spawning season gulf darters were most often collected over clean gravel or gravelsand substrates. Laboratory observations suggest that the female burrows into the gravel where the demersal, adhesive eggs are deposited. Female gulf darters significantly outnumbered males at a ratio of 59:41.     

Bridging the divide between cytokinesis and cell expansion

Two of the most fundamental processes in plant development are cytokinesis, by which new cells are formed, and cell expansion, by which existing cells grow and establish their functional morphology. In this review we summarize recent progress in understanding the pathways necessary for cytokinesis and cell expansion, including the role of the cytoskeleton, cell wall biogenesis, and membrane trafficking. Here, we focus on genes and lipids that are involved in both cytokinesis and cell expansion and bridge the divide between these two processes. In addition, we discuss our understanding of and controversies surrounding the role of endocytosis in both of these processes.