CELL BIOLOGY, GENETICS, AND BIOCHEMISTRY OF GIARDIA

描述(由申请人提供)：蓝氏贾第鞭毛虫是一种无线粒体、双核原生生物，在美国和发展中国家引起腹泻。我们的初步研究结果对了解羊肚菌的细胞生物学、遗传学和生物化学有重要的贡献。细胞生物学：核膜在细胞分裂过程中保持完好。贾第鞭毛虫在粘附盘的平面上以镜像对称性分裂。一对对分裂的贾第鞭毛虫的核由微管阵列连接在一起。贾第鞭毛虫[2Fe-2S]铁氧还蛋白具有细胞器靶向序列。遗传学：被用来证明科赫假设的GS菌株具有对称的核，每个核都是二倍体。目前正在进行测序的WB菌株具有不对称的核，这些核是单体和三体染色体的混合体。每个贾第虫基因的四个副本都有相同的序列。贾第虫缺乏性行为的大部分机制。贾第虫有一个剪接体内含子。生物化学：编码大部分贾第虫发酵酶的基因是从厌氧原核生物横向转移过来的。贾第虫含有编码硝基还原酶的基因，这种基因类似于细菌中激活甲硝唑的基因。贾第鞭毛虫有一种铁氢酶。这些结果提出了多个假设，这些假设将在三个具体目标中进行检验。目标1(细胞生物学)的主要假设：核周微管将分裂贾第鞭毛虫的核对捆绑在一起，因此细胞核正确地分配给母亲和女儿贾第鞭毛虫。目标2(遗传学)的主要假设：贾第鞭毛虫是四倍体，但序列类似单倍体；对称的枝状核是每条染色体的二倍体(如GS)；而不对称的枝状核具有单体和三体的混合染色体(如WB)。次要假设：贾第虫能够剪接异源内含子。目标3(生物化学)的主要假设：贾第虫对甲硝唑和呋喃唑酮敏感，因为存在硝基还原酶，如厌氧细菌的硝基还原酶，减少和激活这些药物。

DESCRIPTION (provided by the applicant): Giardia lamblia is an amitochondriate, binucleate protist that causes diarrhea in the U.S. and the developing world. Our preliminary results make numerous important contributions to the understanding of the cell biology, genetics, and biochemistry of G. iamblia. Cell biology: Nuclear membranes remain intact during cell division. Giardia divides with mirror image symmetry in the plane of the adherence disc. Pairs of nuclei of dividing giardia are tethered together by arrays of microtubules. The Giardia [2Fe-2S] ferredoxin has an organelle-targeting sequence. Genetics: The GS strain, which was used to prove Koch's postulates, has symmetric nuclei that are each diploid. The WB strain, which is presently being sequenced, has asymmetric nuclei that are a mixture of monosomic and trisomic chromosomes. Four copies of each Giardia gene all have the same sequence. Giardia lack most of the machinery for sex. Giardia have a spliceosomal intron. Biochemistry: Genes encoding the majority of Giardia fermentation enzymes were laterally transferred from anaerobic prokaryotes. Giardia contain genes encoding nitroreductases, which are similar to those that activate metronidazole in bacteria. Giardia have an Fe-hydrogenase. These results suggest multiple hypotheses that will be tested in three Specific Aims. Major hypothesis for Aim 1 (cell biology): Perinuclear microtubules tether together pairs of nuclei of dividing Giardia, so nuclei are correctly distributed to mother and daughter Giardia. Major hypotheses for Aim 2 (genetics): Giardia are tetraploid but sequence like haploids; symmetric diplomonad nuclei are diploid for each chromosome (like GS); while asymmetric diplomonad nuclei have a mixture of monosomic and trisomic chromosomes (like WB). Minor hypothesis: Giardia are capable of splicing heterologous introns. Major hypothesis for Aim 3 (biochemistry): Giardia is sensitive to metronidazole and furazolidone, because of the presence of nitroreductases, like those of anaerobic bacteria, which reduce and activate these drugs.