{"created":"2023-06-20T13:20:57.624956+00:00","id":1029,"links":{},"metadata":{"_buckets":{"deposit":"ff3c79d0-cdde-4bc2-8311-a5f9b2a8fb9d"},"_deposit":{"created_by":1,"id":"1029","owners":[1],"pid":{"revision_id":0,"type":"depid","value":"1029"},"status":"published"},"_oai":{"id":"oai:ir.soken.ac.jp:00001029","sets":["2:430:20"]},"author_link":["0","0","0"],"item_1_creator_2":{"attribute_name":"著者名","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"野呂, 行彦"}],"nameIdentifiers":[{}]}]},"item_1_creator_3":{"attribute_name":"フリガナ","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"ノロ, ユキヒコ"}],"nameIdentifiers":[{}]}]},"item_1_date_granted_11":{"attribute_name":"学位授与年月日","attribute_value_mlt":[{"subitem_dategranted":"2007-03-23"}]},"item_1_degree_grantor_5":{"attribute_name":"学位授与機関","attribute_value_mlt":[{"subitem_degreegrantor":[{"subitem_degreegrantor_name":"総合研究大学院大学"}]}]},"item_1_degree_name_6":{"attribute_name":"学位名","attribute_value_mlt":[{"subitem_degreename":"博士（理学）"}]},"item_1_description_12":{"attribute_name":"要旨","attribute_value_mlt":[{"subitem_description":"&nbsp;&nbsp;&nbsp;&nbsp;The last common ancestor of bilateria and cnidaria is considered to be the first animal to obtain nervous system over 700 million years ago．After that，animals have developed their own nervous systems that are seen now．During along course of evolution traits of nervous systems in these amimals are vastly diverged and different from each other．Some of the traits，however，seem to be shared between higher animals （vertebrates and / or arthropods）and cnidaria．These seemingly similar traits can be classified into two groups：analogous traits and homologous traits．The analogous traits are defined as traits currently shared by these animals but might have been different in the past or may be different in the future．The homologous traits are long conserved among animals during their evolution．Therefore，they should shed light on what prototypical nervous system was like．The question is how to distinguish them. Generally to say，the homologous traits share common underlying mechamisms to realize them．<br />　　　This study and previous studies demonstrated interesting new aspects of <i>Hydra</i> nervous system．First，the nerve net of <i>Hydra</i> is divided into subpopulations．Second，each neuron subset expresses specific combination of neuropeptide genes．Third，each neuron subset is localized in a restricted region（s）along the oral-aboral axis．Fourth，some neighboring subsets of neurons are separated from each other with clear boundaries between them．And finally one of the possible functions of neuron subsets is local action by a localized neural neurotransmitter（s）．The last two aspects are pointed out for the first time in this study．All these features imply that the neuron subsets in <i>Hydra</i> are neural compartments and they behave as sort of functional units like those of higher orgamisms．Are these seemingly similar traits analogous or homologous？ In order to address this issue，I attempted to elucidate the mechanisms for generating neuron subsets of <i>Hydra</i> and compared them to that of neural compartments of higher animals．<br />　　A compartment is generally defined as a subdivided tissue that consists of lineage-restricted non-intermingling sets of cells between neighboring compartments．<br />According to this definition，neuron subsets in <i>Hydra</i> may not be the neural compartments equivalent to higher organisms，because there is no lineage-restriction in the formation of neuron subsets in <i>Hydra</i>．The tissue displacement in <i>Hydra</i>  continuously moves neurons in a subset into a neighboring subset．Despite this，however，each neuron subset keeps its location and size of population constant，maintaiming clear boundaries between subsets．<br />　　There are two possible mechanisms to supply neurons for balancing a loss of neurons caused by the tissue displacement：new neuron differentiation from precursors and phenotypic conversion of preexisting neurons．By comparing tissue displacement rate and labeling kinetics of BrdU in Hym-176A＋neurons in the lower peduncle of adult <i>Hydra</i>, I estimated that about 70％ of neuron turnover in the neuron subset was accounted for by new differentiation and the remaining 30％ appeared to be accounted for by phenotypic conversion．I also found another example for phenotypic conversion in the middle of this neuron subset．These results suggest that both of the two mechanisms are invoIved in the formation of neuron subsets．<br />　　New differentiation always occurred near the upper boundary of the neuron subset although neuron precursors could penetrate further down in the subset．When the situation was created where no preexisting neurons were present such as during foot regeneration or replacement of the normal foot with the nerve-free epithelial foot，essentially all the neurons produced were newly differentiated ones and distributed within the subset，not restricted at its upper boundary．These results suggest that new differentiation appears to be regulated by lateral inhibition of preexisting Hym-176A＋neurons and that more rapid new differentiation prevails in case of emergency in which new neurons are required．At the moment，the fate of neurons is not known when they leave the subset by tissue displacement．Cell death might be invoIved in addition to phenotypic conversion．Taken together，in <i>Hydra</i> although lineage-restriction may not be involved in maintaining clear boundaries and keeping the size of subsets constant，these are regulated positively by both of new differentiation and phenotypic conversion，and negatively by lateral inhibition and possibly cell death．<br />　　　Next，I addressed the issue as to what determine the position of neuron subsets in <i>Hydra</i>．Prepattern genes，pairs of mutually repressing homeobox genes，such as Otx，Pax and Hox，determine the region where neural compartments are formed in higher animals．These genes are regulated by a few secreting molecules，such as Wnts，FGFs and retinoic acid．In <i>Hydra</i>，counterparts for some of these molecules are identified but only Wnts  appear to be involved in axis formation．In this study I have shown that activation of the Wnt signaling pathway with LiCl and / or ALP，both of which inhibit GSK-3 β as their common target，altered positional information and therefore localization of neuron subsets in <i>Hydra</i>．This suggests that the Wnt signaling pathway is conserved between neural compartments and neuron subsets in determining their localization．<br />　　　How does this positional information direct region-specific differentiation of neuron subsets in <i>Hydra</i>？There must be a transcriptional control involved in it．I compared 5’-flanking genomic regions amongHym-176 paralogous genes．Some of them are expressed in different neuron subsets located in different axial regions while the others are in the same axial region．It is expected that the same or similar region-specific cis-regulatory elements may be shared by genes expressed in subsets of neurons located in the same axial region．I have found several conserved motifs．One of them was simi1ar to the STATx binding motif that was shared by subsets of paralogues expressed in the lower peduncle．Although this one might be conserved between neuron subsets and neural compartments，others showed no homology to known motifs．These results seem to indicate that the mechanism of region-specific gene regulation in neuron subsets and neural compartments is not well conserved．In other words，cnidarians might have invented cis-regulatory elements of their own．<br />　　　Comparison of the involved mechanisms between neuron subsets in <i>Hydra</i> and neural compartments in higher amimals showed both conservation and divergence．This may be taken for granted，because it has been enormously long time since they were separated from the last common ancestor．However，a crucial point was that one of the most fundamental signaling systems all through the amimal evolution，the Wnt pathway was conserved as one of the underlying mechanisms to determine the position of compartments between <i>Hydra</i> and higher organisms．Downstream genes activated by the Wnt pathway appear to be different．More evidence should be accumulated．But I would like to temporarily conclude that it is too early to give up the idea that neuron subsets in <i>Hydra</i> and neural compartments in higher animals are homologous structure reminiscent of the ancient nervous system．I would further pursue my studies along this line．","subitem_description_type":"Other"}]},"item_1_description_18":{"attribute_name":"フォーマット","attribute_value_mlt":[{"subitem_description":"application/pdf","subitem_description_type":"Other"}]},"item_1_description_7":{"attribute_name":"学位記番号","attribute_value_mlt":[{"subitem_description":"総研大甲第1058号","subitem_description_type":"Other"}]},"item_1_select_14":{"attribute_name":"所蔵","attribute_value_mlt":[{"subitem_select_item":"有"}]},"item_1_select_8":{"attribute_name":"研究科","attribute_value_mlt":[{"subitem_select_item":"生命科学研究科"}]},"item_1_select_9":{"attribute_name":"専攻","attribute_value_mlt":[{"subitem_select_item":"18 遺伝学専攻"}]},"item_1_text_10":{"attribute_name":"学位授与年度","attribute_value_mlt":[{"subitem_text_value":"2006"}]},"item_creator":{"attribute_name":"著者","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"NORO, Yukihiko","creatorNameLang":"en"}],"nameIdentifiers":[{}]}]},"item_files":{"attribute_name":"ファイル情報","attribute_type":"file","attribute_value_mlt":[{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2016-02-17"}],"displaytype":"simple","filename":"甲1058_要旨.pdf","filesize":[{"value":"374.7 kB"}],"format":"application/pdf","licensetype":"license_11","mimetype":"application/pdf","url":{"label":"要旨・審査要旨","url":"https://ir.soken.ac.jp/record/1029/files/甲1058_要旨.pdf"},"version_id":"16745aac-0745-40f8-9da9-86bd9d45ab23"},{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2016-02-17"}],"displaytype":"simple","filename":"甲1058_本文.pdf","filesize":[{"value":"21.5 MB"}],"format":"application/pdf","licensetype":"license_11","mimetype":"application/pdf","url":{"label":"本文","url":"https://ir.soken.ac.jp/record/1029/files/甲1058_本文.pdf"},"version_id":"7096b044-ce7b-4868-ba9e-eb890490919c"}]},"item_language":{"attribute_name":"言語","attribute_value_mlt":[{"subitem_language":"eng"}]},"item_resource_type":{"attribute_name":"資源タイプ","attribute_value_mlt":[{"resourcetype":"thesis","resourceuri":"http://purl.org/coar/resource_type/c_46ec"}]},"item_title":"Compartmentalized nervous system in Hydra and the mechanisms of its development","item_titles":{"attribute_name":"タイトル","attribute_value_mlt":[{"subitem_title":"Compartmentalized nervous system in Hydra and the mechanisms of its development"},{"subitem_title":"Compartmentalized nervous system in Hydra and the mechanisms of its development","subitem_title_language":"en"}]},"item_type_id":"1","owner":"1","path":["20"],"pubdate":{"attribute_name":"公開日","attribute_value":"2010-02-22"},"publish_date":"2010-02-22","publish_status":"0","recid":"1029","relation_version_is_last":true,"title":["Compartmentalized nervous system in Hydra and the mechanisms of its development"],"weko_creator_id":"1","weko_shared_id":1},"updated":"2023-06-20T15:50:06.782496+00:00"}