Abstracts

PLASMID PROFILE AND ANTIBIOTIC RESISTANCE OF BACTERIAL ISOLATES OF A RECREATIONAL LAKE
Jennifer Rayner, Melvin Oputa, Goldie Byrd, and Jonathan Ladapo.  North Carolina Central University, Durham, NC

    Eight bacterial isolates were obtained from water samples of a local recreational lake after a prolonged cultivation and successive transfers.  The isolated bacteria were screened for the presence of plasmid DNA by agarose gel electrophoresis and tested for susceptibility to 10 common antibiotics.  The cultural, morphological, biochemical, and molecular characterization of these isolates is summarized in this report.  Eight pure isolates, which stained gram negative were isolated from this flood controlled lake water.  By using a combination of non-selective plating techniques, the isolates were tentatively identifies as four strains of Enterobacter sp. and for strains of Acinetobacter sp. based on biochemical, morphological, and molecular characterization.  Their morphology varied from gram negative rods to gram negative coccobacilli of about 1.5 to 3.0 u.  Their susceptibility to antibiotics was evaluated by the disc diffusion method.  Some of the isolates were as resistant to common antibiotics as isolations of clinical origin.  All the isolates were inhibited by 10 ug ampicillin while 50% of the isolates were resistant to 30 ug chloramphenicol.  Eighty seven and a half percent of the isolates are resistant to both nalidixic acid and streptomycin.  All the Acinetobacter sp. are resistant to tetracycline.  Plasmids of about 4.5 and 9.0 kb were found in two of the eight isolates (25%).  The finding of such a high percentage of resistance suggests that freshwater environment may represent a reservoir for the spread and evolution of resistance bacterial strains.

COMPARISON OF XFRZB ACTIVITIES IN XENOPUS laevis EMBRYOS
Jennifer Rayner, Leila Bradley, Hazel Sive, Massachusetts Institute of Technology, North Carolina Central University

    The Wnt signal transduction pathway is an important component of many key developmental processes, including dorso-ventral axis specification in vertebrate embryos.  The frzb gene family encodes a potentially important component of these Wnt pathways.  Frzbs are secreted proteins closely related to the ligand binding domain of Wnt receptors, Frizzled, that are expressed during early stages of embryogenesis.  In Xenopus embryos, frzb1 has been shown to antagonize Wnt activities as well as to dorsalize whole embryos (Leyens et al., 1997; Wang et al., 1997).  Two additional genes, Xfrzb2 and Xfrb3, have also been isolated (Bradley et al., 1999).  It is expected that frzb2 and frzb3 might have similar activities- antagonizing Wnt function and influencing early embryonic patterning.  In an effort to understand the normal role of frzb2 and frzb3 in early development, several functional assays have been performed using frzb1 for a comparison.  A morphological assay showed that frzb1 and frzb3 have similar dorsalizing capabilities, and that conversely, frzb2 inhibits head formation.  Investigations into frzb activity levels showed that frzb1 and frzb2 are able to antagonize Xwnt8-RNA axis duplication activity.  Experiments to determine if the Xenopus frzbs block muscle induction are ongoing.

A model system for studying the tumor suppressor adenomatous polyposis coli (APC) in Drosophila
Jennifer Rayner, Brooke McCartney, Mark Peifer; University of North Carolina-Chapel Hill; SPGRE Program

    The Wnt signaling pathway plays an integral part in the development of organisms.  It directs cell fates and regulates cell proliferation in diverse tissues.  Through mutations, Wnt signaling can be turned on inappropriately.  When this occurs, cells proliferate without regulation and cancer can be the result.  In familial adenomatous polyposis coli, an inherited form of colon cancer, patients inherit a germline mutation in the gene encoding the tumor suppressor adenomatous polyposis coli (APC).  APC is a protein that negatively regulates the Wnt signaling pathway preventing signaling when Wnts are not present.  However, APC may also have other functions.  The Drosophila homologue dAPC2 regulates Wingless (Wg)/Wnt signaling in the embryonic epidermis, which is consistent with vertebrate APC function.  It has been suggested that it may also play a role in mitotic spindle positioning as well as in regulating the actin and microtubule cytoskeletons.
    Our previous analysis focused on the larval epidermis, where Wg signaling regulates cell fates.  We have been investigating whether dAPC2 may also regulate Wg signaling in other tissues, focusing on larval muscle development.  dAPC2 mutants show a muscle phenotype different from that of wild-type.  This may be due to its role in Wg signaling, because Wg is necessary for the formation of muscle precursors.  Alternatively, the muscle phenotype found in dAPC2 mutants may be due to defects in cytoskeletal organization.  To distinguish between these possibilities, the muscle phenotypes of several mutants, including zeste-white3 (zw3)—another negative regulator of the Wg signaling pathway—were examined.  From these assays, we hope to determine if the phenotype is the result of dAPC2 negatively regulating the Wg signaling pathway in the muscles, or if the phenotype is a result of defects during cytoskeletal organization. Tests to examine the effect of dAPC2 mutants in other tissues including the nervous system are ongoing.