Oogenesis in the Apogamous Fern Pteris cretica

The events that characterize egg formation and maturation inPteris cretica were investigated using transmission electronmicroscopy and electron microscope microprobe analysis. Theydid not differ significantly from those described for sexuallyreproducing ferns. The significance of these findings is discussedin relation to current theories concerning phase change in ferns. Pteris cretica, fern, apogamy, agamospory, transmission electron microscopy, oogenesis     

Regulation of the alternative pathway of T cell activation by anti-T3 monoclonal antibody

T cell activation may be triggered either through the T3-Ti antigen receptor complex or via an alternative macrophage-independent pathway involving the 50KD T11 sheep erythrocyte-binding glycoprotein. Monoclonal antibodies anti-T11(2) and anti-T11(3), directed at distinct epitopes of the T11 molecule, trigger mature T cells to proliferate and express their functional programs, and induce expression of IL 2 receptors on both T3+ and T3- thymocytes. We now show that a non-mitogenic anti-T3 antibody blocks activation via the T11 pathway of not only peripheral blood T cells, but also T3+ thymocytes. Anti-T3 does not affect surface expression of T11 or the rapid augmentation of T11(3) expression after incubation of cells with anti-T11(2). However, anti-T3 inhibits generation of IL 2 receptors and production of IL 2 by T lineage cells cultured with anti-T11(2) plus anti-T11(3). In contrast, modulation of the T11 molecule by a non-mitogenic anti-T11 antibody does not inhibit activation of T cells by a mitogenic anti-T3 antibody. The ability of anti-T3 to block expression of IL 2 receptors on both thymocytes and mature T cells activated by the T11 pathway suggests that a regulatory interaction may be important during T cell ontogeny to provide a mechanism for inhibiting expansion of autoreactive clones.     

Clonal analysis of B cell growth and differentiation activities induced from T lymphocytes upon triggering of T3-Ti and T11 pathways

The cellular origin of B cell growth factors (BCGF) and differentiation factors (BCDF) was investigated in the present study. For this purpose, T4+ and T8+ T cell clones were obtained from human peripheral blood, activated via stimulation of either the antigen/MHC receptor (T3-Ti molecular complex) or the antigen-independent alternative pathway (T11 molecule), and subsequently examined for their capacity to induce B cell proliferation and immunoglobulin production. The results showed that 1) BCGF is produced by both T4+ and T8+ T cells at the population level as well as at the clonal level; 2) BCDF activity, in contrast, is largely but not exclusively restricted to the T4+ subset; and 3) both the T3-Ti and T11 pathways activate individual clonal T cell populations to promote B cell growth and differentiation.     

Activation of human thymocytes via the 50KD T11 sheep erythrocyte binding protein induces the expression of interleukin 2 receptors on both T3+ and T3- populations

Recent studies have demonstrated that the 50KD T11 molecule is a surface component of a macrophage-independent alternative pathway of human T cell activation that is unrelated to the T3/Ti antigen-MHC receptor complex. Given the expression of T11 on all human thymocytes, it was of interest to determine whether they could be activated via this pathway. The triggering of T11 by monoclonal antibodies anti-T112 and anti-T113, directed at two unique epitopes on the molecule, induced IL 2 receptor expression on both T3+ and T3- thymocytes but did not induce IL 2 production. Consequently, in contrast to peripheral blood T cells, thymocytes did not proliferate in response to anti-T112 and anti-T113 in the absence of exogenous IL 2. These studies suggest that IL 2 receptor gene activation precedes IL 2 gene activation in T cell development. The ability of the alternative pathway of T cell activation to induce IL 2 receptor expression on T3- thymocytes implies that the T11 molecule may have an important role in early thymocyte ontogeny.     

Ta1, a novel 105 KD human T cell activation antigen defined by a monoclonal antibody

By using a murine monoclonal antibody produced against an IL 2-dependent human T cell line, we defined a T lineage-specific molecule, termed Ta1, that is expressed strongly on activated T lymphocytes of both the T4 and T8 subsets, as well as on T cell lines and clones, but only weakly on a fraction of resting T cells. SDS-PAGE analysis of immunoprecipitates from 125I-labeled, activated T cells demonstrates a single major band of apparent m.w. 105 KD under both reducing and nonreducing conditions. Unlike anti-IL 2 receptor antibodies, anti-Ta1 does not inhibit T cell proliferative responses to mitogen, antigen, or IL 2-containing medium. Moreover, anti-Ta1 has no effect on T cell-mediated cytotoxicity. Ta1 appears to be a novel human T cell-specific activation antigen that may serve as a useful marker of T cell activation in human disease.     

Direct evidence for the existence of nominal antigen binding sites on T cell surface Ti alpha-beta heterodimers of MHC-restricted T cell clones

The binding of nominal antigen to Ti alpha-beta heterodimers on MHC-restricted human T cell clones specific for fluorescein-5-isothiocyanate (FL) was detected by flow cytometry and affinity chromatography. The FL-Ti interaction is of physiologic significance, since T cell activation is induced by cross-linked arrays of FL in the absence of the specific MHC recognition. High antigen valence is required to achieve stable binding to cells and subsequent activation, which is consistent with estimated Ti-FL association constants of less than 3 X 10(5) l/mol. In addition to providing direct evidence that the Ti alpha-beta heterodimer is the receptor for antigen, these data suggest that nominal antigen binding sites exist on the Ti molecules of at least some MHC-restricted clones.     

Genotype and phenotype associations with drought tolerance in barley tested in North Africa

A review is presented of genetic strategies deployed in a 3-yr project on drought tolerance in barley. Data were collected on genetic, physiological and agronomic traits in non-irrigated and irrigated field trials in Egypt, Morocco and Tunisia. A wide range of barley germplasm (developed from African and European cultivars, adapted landraces and wild barleys) was tested, and positive traits were found in each gene pool. The contrasting environments of the three North African countries had major effects on plant/genotype performance. Genetic effects were also detected, as were genotype × environment interactions. A range of strategies were deployed to investigate the physiology and genetics of quantitative traits associated with field performance. Quantitative trait locus (QTL) analysis was performed using backcross lines, recombinant inbred lines and doubled haploid mapping populations. A detailed genetic map was generated in the Tadmor × (ER/Apm) recombinant inbred lines, an important mapping population specifically developed by ICARDA (Centre for Agricultural Research in Dry Areas) and CIMMYT (International Maize and Wheat Improvement Center) to study drought. Quantitative trait loci (QTLs) for grain yield and other important morphological and physiological traits were also identified in a population of doubled haploids derived from F2BCj plants from a cross between a cultivar and a wild barley accession. Significantly, the wild parental line was found to contribute a number of positive alleles for yield. Effects of major developmental genes could explain many of the responses observed. QTLs were found to cluster around major genes controlling flowering time (sghI), plant stature (sdwI and arie.GP) and ear type (vrsl), and it is highly likely that the associations represent pleiotropic effects. Some QTLs were associated with candidate genes such as dehydrins and rubisco activase. One of the most significant results was the identification and generation of material that out performed the best local standards in the three participating North African countries; the selected lines have now entered local breeding programmes. The strategies adopted provided information on physiological traits, genotypes and genetic markers that could be used for marker-assisted selection. Target QTLs and their associated genetic markers may be deployed in marker assisted selection programmes to match crop phenology to the field environment.