Cell Biology, Genetics, and Biochemistry of Giardia

描述（由申请人提供）：贾第鞭毛虫是一种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为了解G. iamblia的细胞生物学、遗传学和生物化学做出了许多重要贡献。细胞生物学：核膜在细胞分裂过程中保持完整。贾第鞭毛虫在附着盘的平面上以镜像对称分裂。正在分裂的贾第鞭毛虫核对被微管阵列拴在一起。贾第鞭毛虫[2Fe-2S]铁氧还蛋白具有细胞器靶向序列。遗传学：用于证明科赫假设的GS菌株具有对称的细胞核，每个细胞核都是二倍体。目前正在测序的WB菌株具有不对称细胞核，是单体和三体染色体的混合物。每个贾第鞭毛虫基因的四个拷贝都有相同的序列。贾第虫缺乏大多数的性机制。贾第虫有一个剪接体内含子。生物化学：编码大多数贾第虫发酵酶的基因是从厌氧原核生物中横向转移过来的。贾第鞭毛虫含有编码硝基还原酶的基因，这种基因与细菌中激活甲硝唑的基因相似。贾第虫有铁氢化酶。这些结果提出了多种假设，将在三个具体目标中进行测试。Aim 1（细胞生物学）的主要假设：核周微管将正在分裂的贾第鞭毛虫的细胞核对系在一起，因此细胞核正确地分布到贾第鞭毛虫的母株和子株上。Aim 2（遗传学）的主要假设：贾第鞭毛虫是四倍体，但序列像单倍体；对称双核每条染色体为二倍体（如GS）；而非对称双核则是单体和三体染色体的混合物（如WB）。次要假设：贾第鞭毛虫能够剪接异源内含子。Aim 3（生物化学）的主要假设：贾第鞭毛虫对甲硝唑和呋喃唑酮敏感，因为硝基还原酶的存在，就像厌氧菌一样，可以还原和激活这些药物。

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.