Aggregate community properties and the strength of species' interactions

Although humanity depends on the continued, aggregate functioning of natural ecosystems, few studies have explored the impact of community structure on the stability of aggregate community properties. Here we derive the stability of the aggregate property of community biomass as a function of species' competition coefficients for a two-species model. The model predicts that the stability of community biomass is relatively independent of the magnitude of the interaction strengths. Instead, the degree of asymmetry of the interactions appears to be key to community stability.     

Characterization of lineage restricted forms of a Xenopus CD45 homologue

The leukocyte common antigen, also known as CD45, is a structurally heterogenous molecule ranging in molecular weight from 180 to 220 kDa. CD45 belongs to a family of high molecular weight, cell surface glycoproteins expressed on all hematopoietic lineages with the exception of mature erythrocytes. In higher vertebrates, the highly conserved cytoplasmic domain of CD45 exhibits protein tyrosine phosphatase activity and has been implicated in lymphocyte activation through dephosphorylation of critical tyrosine residues on substrates associated with signal transduction pathways. The monoclonal antibody CL21 recognizes a high molecular weight determinant expressed on the surface of Xenopus leukocytes which was postulated to be a CD45 homologue. In order to determine if lymphocyte subpopulations expressed different molecular weight variants, splenic B cells were identified and isolated on the basis of surface IgM and the CL21 determinant expressed by these cells was compared to the determinant expressed by thymocytes. Immunoprecipitation revealed that IgM + B cells expressed a 220 kDa molecular weight variant whereas thymocytes and IgM-cells expressed a 180 kDa variant. Bone marrow myeloid cells, isolated on the basis of light scatter properties, expressed a determinant which ranged from 150 to 160 kDa. Dephosphorylation experiments utilizing p-nitrophenyl phosphate, 32P-labeled Raytide [tyr(P)], or Kemptide [ser(P)] as substrates demonstrated that immunoprecipitated CL21 antigen exhibited tyrosine specific phosphatase activity which was inhibited by sodium orthovanadate. Thus, data based on the presence of enzymatic activity and lineage restricted molecular weight variants support the hypothesis that the CL21 determinant is the amphibian homologue of mammalian CD45, and suggest that both structural and functional elements of CD45 have been conserved during vertebrate evolution.     

Localization of ROMK channels in the rat kidney

Renal potassium secretion occurs in the distal segments of the nephron through apically located secretory potassium (SK) channels. SK may correspond to the ROMK channels cloned from rat kidney. In this study, the localization of ROMK at the cellular level in the rat kidney was examined using an affinity-purified polyclonal antibody raised against a C-terminal peptide of ROMK. The specificity of the antibody was demonstrated by immunoblots of membranes of Xenopus oocytes expressing ROMK2. Immunoblots of homogenates from rat renal outer medulla and cortex revealed predominant bands of 70 to 75 kD, which were ablated by preadsorption with an excess of peptide. These bands were specific for the rat kidney. Immunolocalization studies revealed that ROMK is expressed in specific nephron segments in both the cortex and medulla. In the cortex, ROMK was found in the apical domain of the thick ascending limb of Henle's loop, the connecting tubule, and in some, but not all, cells of cortical collecting tubules. In the medulla, expression in the apical membrane of the thick ascending limbs of Henle's loop was strong, whereas outer medullary collecting ducts were weakly stained. Expression in the thick ascending limb was also heterogeneous; some cells that expressed the Na-K-Cl cotransporter were weakly stained with the anti-ROMK antibody. No staining of glomeruli, proximal tubules, or inner medullary collecting ducts was found. The localization of ROMK agrees well with the findings of SK in patch-clamp studies and supports the view that ROMK is the SK channel of the distal segments of the nephron.     

Paraneoplastic syndromes

Paraneoplastic syndromes (i.e. organ/tissue disorders associated with cancer) affecting the nervous system are thought to be the result of an autoimmune response triggered by specific cancer antigens. Several of these antigens have recently been identified and include the Hu, Yo and Ri proteins, with the Hu antigens being the best studied. Immunization of animals with HuD has been shown to retard the growth of HuD-positive neuroblastomas. In addition, the presence of anti-HuD antibody in humans with small-cell lung cancer predicts the slow growth of the tumor. The associated neurological disorders, however, limit the use of these and other antigens with similar characteristics in cancer vaccines.