KOSEN 한인과학기술자네트워크

>beta tubulin gene이 종간의 관계를 밝히는데 >특이적인 역할을 하는가요?? >ITS같은 경우에는 길이도 짧고, 종.속 분류에 적합한 5.8S 부위를 포함하고 있기때문에 >각 종간의 비교가 가능하다고 알고 있습니다. > >하지만 beta tubulin의 dimer 형태가 microtubule라고 하는데, >이것이 종,속의 분류에 적합한가요?? >적합하다면 왜 그런지 궁금합니다. 모든 eukaryotes에서 기본적인 구조적 기능을 가지는 단백질들을 코딩하는 유전자중에 beta-tubulin에 대해 highly conserved 및 functionally essential gene이 광범위의 진핵세포내에 phylogenies의 reconstruction하는데 이용되고 있습니다. 이것을 위해서는 fungi (Fungi)나 animals (Animalia) 및 green plants (Planta)같은 모든 주용한 eukaryotic kingdoms가운데 beta-bubulin gene들의 재현성 있는 amplication을 가능케하는 universally applicable한 primers을 만들어야 합니다. 광범위 진핵세포들에 대해서 재현성 있는 amplication이 deep level phylogenies와 beta-tubulin gene trees에 근거한 complex species groups에 대한 정보를 줄 수 있습니다.

최근에 생물의 종 분류 및 동정에 많이 사용하는 유전자 marker로는 single copy gene인 nuclear DNA와 multi-copy gene인 mitochondrial DNA와 ribosomal DNA를 대표로 들 수 있습니다. 그 중 가장 많이 활용되는 유전자는 ribosomal DNA (rDNA)로서 18S, 5.8S, 28S의 coding part와 intergenic region에 속해 있는 ITS (ITS-1 & ITS-2)의 두 부분으로 나눌 수 있습니다. 또한, 이에 추가하여 일반적으로 생명체 (진핵세포)를 구성하며 뼈대를 이루는 구조 단백질인 actin, alpha-tubulin, beta-tubulin 등의 유전자는 보존성이 높기 때문에 비교 분석에 예전부터 많이 사용되어 왔습니다. >beta tubulin gene이 종간의 관계를 밝히는데 >특이적인 역할을 하는가요?? >ITS같은 경우에는 길이도 짧고, 종.속 분류에 적합한 5.8S 부위를 포함하고 있기때문에 >각 종간의 비교가 가능하다고 알고 있습니다. > >하지만 beta tubulin의 dimer 형태가 microtubule라고 하는데, >이것이 종,속의 분류에 적합한가요?? >적합하다면 왜 그런지 궁금합니다.

>beta tubulin gene이 종간의 관계를 밝히는데 >특이적인 역할을 하는가요?? >ITS같은 경우에는 길이도 짧고, 종.속 분류에 적합한 5.8S 부위를 포함하고 있기때문에 >각 종간의 비교가 가능하다고 알고 있습니다. > >하지만 beta tubulin의 dimer 형태가 microtubule라고 하는데, >이것이 종,속의 분류에 적합한가요?? >적합하다면 왜 그런지 궁금합니다. http://tolweb.org/Eukaryotes/3/2000.09.08#titlefigcaption 아주 좋은 설명이 있는 것 같습니다. 윗분 설명가 유사하듯 동물, 식물, 균류 등 진핵 생물들은 세포막안에는 고유으 단백질을 가지고 있어 예를 들면 tubulin (microtubules 형성), actin (microfilaments)등이 있는데 이들 구조 및 단백질 서열은 종별로 오랜동안 잘 유지 되어 비교함을 통해 분류할 수 있는 도구가 되는 것 같습니다. Animals, plants, fungi, and protists are eukaryotes (IPA: /juːkært/ or IPA: /-ot/), organisms whose cells are organized into complex structures enclosed within membranes. The defining membrane-bound structure that differentiates eukaryotic cells... What makes a eukaryote a eukaryote? The eukaryotes are distinguished from prokaryotes by the structural complexity of the cells - characterized by having many functions segregated into semi-autonomous regions of the cells (organelles), and by the cytoskeleton. The most evident organelle in most cells is the nucleus, and it is from the presence of this organelle that the eukaryotes get their name. Most cells have a single nucleus, some have more (some have thousands) and others like red blood cells of ourselves have none - but they can be shown to derive from cells with nuclei. Nuclei contain most of the genetic material of a cell - with other elements of the genome located in mitchondria and plastids (if those organelles are also present). The nucleus is bounded by a membranous envelope. The nuclear envelope is part of the endomembrane system that extends to include the endoplasmic reticulum, dictyosomes (Golgi apparatus) and the cell or plasma membrane that encloses the cell. The envelope is perforated by nuclear pores which allow compounds to pass between the nucleus and the surrounding cytoplasm. Some protists have more than one kind of nucleus - using one to retain a copy of the genome for purposes of reproduction, and another in which some genes have been greatly amplified, to regulate activities. Within the nucleus, the genes are located on a number of chromosomes. The total amount of DNA in a nucleus measuring less than one hundredth of a millimetre across may stretch to over a metre. When not in use this is kept within a nucleus measuring only a few microns across by being bundled up in superhelical arrays. The cytoskeleton is comprised of a rich array of proteins. The major ones are tubulin (which forms microtubules) and actin (forming microfilaments) and a myriad of interacting proteins which effect movement or create the skeletal architecture of cells. The cytoskeleton provides shape for the cell and support for membranous organelles. It also provides anchorage for motility proteins which transport materials within the cell and cause deformations which bring about the movements of the entire cell - or organism. General relationships among eukaryotes Our understanding of the phylogenetic relationships among the eukaryotes is not yet resolved nor stable. Two large bodies of data have contributed most to our current understanding of the diversity and interrelationships of eukaryotic lineages. Information derived from electron microscopy on the structure of the cells has revealed consistent patterns among groups for which the monophyly is not doubted (such as the ciliates or the red algae). The same approach has then been applied to many protists, and has revealed that there are about 80 patterns of organization (Patterson, 1999). These have now been clustered into about 60 lineages. Molecular analyses, when available, usually confirm these groupings. The second body of data derives from comparative molecular data - initially focussing on the genes which code for small subunit ribosomal RNA. As it became evident that the insights might be distorted by problems in the methods of phylogenetic inference, and that our emerging insights (trees) were imprecise, so an increasing number of genes have been called upon to identify which elements of our understanding are secure and which are unrealiable. The position now is less confident than a decade earlier, and the means of resolving conflict among molecular insights has yet to be agreed upon (Philippe & Adoutte, 1998; Katz, 1999). The most comprehensive molecular trees are still those based on analysis of 16S ribosomal RNA (e.g. Cavalier-Smith, 1993; Sogin & Silberman, 1998). The early molecular trees indicated that the earliest branches of eukaryote evolution are represented by microsporidia, trichomonads and diplomonads. These organisms lack dictyosomes, peroxisomes and conventional mitochondria. In addition, the organization of their cytoskeleton was simple and they had a relatively small number of membranous organelles when compared to more recently evolved taxa such as plants, animals and fungi. Organisms located higher in the tree had more organellar diversity, including the presence of dictyosomes, various membranous compartments and mitochondria and chloroplasts. The consistency of the molecular and structural insights led to models that these taxa were primitively amitochondriate, had derived early in eukaryote evolution, and could reveal to us the sequence in which the eukaryotic cell was assembled. Early trees included an unresolved polytomy for the early-branching amitochondriate protists (Leipe et al., 1993). It was followed by the separation of the Euglenozoa (Euglena + other euglenids, trypanosomes + other kinetoplastids), a few other taxa such as the Heterolobosea (acrasid slime moulds, and the agents of amoebic meningitis - Naegleria), and a variety of amoeboid organisms (Sogin et al., 1996). The remaining organisms formed a cluster that was referred to as the eukaryotic crown and was interpreted as the nearly simultaneous separation of animals, plants, fungi and several complex protist assemblages (Knoll, 1992). Within the last decade, it became increasingly evident that this understanding was not accurate (Roger, 1999). There is a problem that lineages which have shown rapid rates of evolution (have long branch lengths) are drawn together at the base of dendrograms created by programs that sought to interpret molecular data as evolutionary trees. Secondly, a variety of the 'amitochondriate' organisms have been shown to have genes for mitochondrial proteins suggesting that they are not primitively amitochondriate but secondarily amitochondriate. The presence of small membranous organelles in a number of these taxa suggests that they contain pre-mitochondria or reduced mitochondria. Enhanced molecular data provided evidence of different associations - the microsporidia were not organisms at the base of the tree but were a specialised kind of fungus and derived late in eukaryotic evolution, their structural simplicity being attributed to regression (Edlind et al., 1996; Keeling & Doolittle, 1996; Li et al., 1996; Germot et al., 1997; Edlind, 1998; Fast et al. 1999; Hirt et al., 1999; Keeling et al., 2000; Van de Peer et al., 2000). Molecular data also identified new candidates for the most primitive eukaryotes - Reclinomonas (an excavate flagellate) has a mitochondrial genome more replete with genes than any other and may be related to one of the first eukaryotes to acquire mitochondria (Lang et al., 1997). Yet molecular trees do not concur with each other (Katz, 1999). The consequence of these insights has been to demolish the model of the 1990's, but not to replace it with something better. Yet, the intervening period has seen progress. At the beginning of the 1990's, we could recognise about 80 different types of eukaryotes (Patterson, 1994). In the intervening period, perhaps 10 further types of protists were being or have been added - either through the efforts of bioprospectors or through more detailed study of many of the underdescribed genera of protists. Yet only about 60 lineages are currently recognised. That is - about half of the lineages have found homes. We have now agreed that the sister group to the Metazoa are the collar-flagellates (choanoflagellates), and that these, together with the fungi and chytrids form a lineage (the opisthokonts), and that the opisthokonts contain two types of spore-forming organisms (Microsporidia and Myxozoa) that used to be considered as protists but are now seen as derived from multicellular organisms (Microsporidia from fungi, Myxozoa from coelenterates or bilateria); the ciliates, apicomplexan sporozoa and dinoflagellates are regarded as forming a lineage (the alveolates), the stramenopiles is now home to the brown algae, diatoms, chrysophytes, opalines, Blastocystis, some heliozoa, some heterotrophic flagellates and so on), and new groups - such as the excavates (including Giardia and the other diplomonads, retortamonads, and various heterotrophic flagellates such as Carpediemonas and the quadriflagellated Trimastix) - continue to be promoted. The resolution to the interrelationships of all eukaryotes looks as if it will reside in the piece by piece assembly of the jig-saw puzzle, rather than in the broad sweep approach which gave us so much confidence a decade ago. Phylogenetic relationships among the opisthokonts The term 'opisthokont' was introduced by Copeland (Copeland, 1956) for the chytrids - a small group of parasitic protists, now commonly included within the fungi. The name refers to the posterior (opistho) location of the flagellum (kont) in swimming cells. As comparative molecular biology indicated that the fungi and animals were related, so the term was applied to the (animals + fungi) clade (Cavalier-Smith & Chao, 1995). This is not entirely satisfactory, but an alternative name for the (animals + fungi) clade has yet to emerge. The argument that the choanoflagellates gave rise to sponges and these in turn to the diploblastic and triploblastic animals is one with a long history, but an understanding of the origins of animals was impeded by spurious arguments based on reference to mythical ancestors (Hanson, 1977; Willmer, 1990). The relatedness of the collar flagellates (choanoflagellates) to the Metazoa was confirmed by comparative analyses of ribosomal RNA (Kim et al., 1999; Wainright et al., 1993), and the basal status of the sponges within Metazoa is widely accepted (Jenner & Schram 1999). The relatedness of extended animal and fungal clades was not suggested by comparative morphology, but was revealed by comparative molecular biology (Baldauf & Palmer, 1993; Wainright et al., 1993; Sogin & Silberman, 1998; Baldauf, 1999). Subsequently, similarities in the anchorage systems of flagella of chytrid fungi and choanoflagellates have been identified, corroborating the molecular perspective (Moestrup, unpublished). Microsporidian and myxosporan protists as members of the opisthokonts Microsporidia are mostly unicellular intracellular parasites and have traditionally been classified within the protozoan group 'Sporozoa'. With the advent of molecular phylogeny, they were placed at the base of the tree of eukaryotes because of their gene structure and comparisons of small subunit ribosomal RNA. They also have a very simple cellular organization which corroborated this insight. The extension of comparative molecular biology to embrace more genes has led to the view that the microsporidia are a derived type of fungus, an argument supported by the presence of a distinctive signature sequence (Kamaishi et al., 1996; Keeling et al., 2000). There are no structural synapomorphies tying the microsporidia to the fungi or to a subset of the fungi. Myxozoa (= Myxosporidia) were traditionally regarded as a type of protist which produces multicellular spores. The spore contains 'cells' which could eject filaments. In the 1970's it became evident that the appearance and development of the filaments co-incided with that of the nematocysts of the coelenterates (Metazoa). Molecular evidence has confirmed that Myxozoa are allied to the Metazoa, but molecular approaches are as yet unable to resolve particular relationships (Siddall et al., 1995; Smothers et al., 1994). Symbioses, Endosymbioses and the Origin of the Eukaryotic State Symbiosis is the process in which unrelated organisms come together

>beta tubulin gene이 종간의 관계를 밝히는데 >특이적인 역할을 하는가요?? >ITS같은 경우에는 길이도 짧고, 종.속 분류에 적합한 5.8S 부위를 포함하고 있기때문에 >각 종간의 비교가 가능하다고 알고 있습니다. > >하지만 beta tubulin의 dimer 형태가 microtubule라고 하는데, >이것이 종,속의 분류에 적합한가요?? >적합하다면 왜 그런지 궁금합니다.

>beta tubulin gene이 종간의 관계를 밝히는데 >특이적인 역할을 하는가요?? >ITS같은 경우에는 길이도 짧고, 종.속 분류에 적합한 5.8S 부위를 포함하고 있기때문에 >각 종간의 비교가 가능하다고 알고 있습니다. > >하지만 beta tubulin의 dimer 형태가 microtubule라고 하는데, >이것이 종,속의 분류에 적합한가요?? >적합하다면 왜 그런지 궁금합니다. 첨부자료