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発生生物学 | |
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無脊椎動物胚発生のオーガナイザー | |
環形動物貧毛類イトミミズ(Tubifex tubifex) 胚を材料にして、規則的な節構造（体節）を備えた細長い個体が丸い一個の卵（細胞）からできてくる全発生過程を明らかにすることを目指しています。私達が特に注目しているのは、胚発生の「オーガナイザー」として機能する端細胞(teloblast)のもつ目覚ましい発生能と端細胞から由来する体節形成細胞の自律分化能です。端細胞はラセン卵割動物(Spiralia)の胚発生を特徴づける割球で、胚の幹細胞(stem cell)としてふるまい、極端な不等分裂を数十回繰り返して胚の左右両側に細胞列（胚帯 germ band）を形成します。胚帯は、外胚葉組織および中胚葉組織の唯一の供給源であるばかりでなく、胚の背腹軸の確立や体節の形成（分節化）を支配する唯一の細胞集団です。これまでの私達の研究から、端細胞は誕生した時点で既に「決定」されており、それから由来する胚帯はその「決定」を受け継ぐことが示されています。私達は端細胞「決定」の分子的基盤を明らかにするとともに、イトミミズ胚発生の3つの大きな柱である、不等卵割、中胚葉形成、および体節形成（分節化）のメカニズムを解明したいと考えています。
生きものって、動物でも植物でも本当によくできていると思いませんか。どうしてこんなによくできているのだろう、と思ったが吉日、迷わず北大・理学部・生物科学科へ。
- ・「動物胚における細胞分裂パターンの制御：不等分裂を中心として」
細胞の生物学（鈴木範男・神谷律 共編）第３章 培風館 ２００７年
SHIMIZU Takashi
Developmental Biology
The oligochaete annelid Tubifex tubfex produces creamy white eggs (and embryos) that must fascinate anyone at first sight. Besides beautiful eggs, Tubifex has been providing us with an excellent system to study fundamental aspects of spiralian development, which include ooplasmic segregation, unequal spiral cleavage, D-quadrant specification, teloblastogenesis and segmentation. Embryology of Tubifex in this lab also intends to seek out the evolutionary origin of developmental mechanisms underlying specification of embryonic axes, determination of teloblasts as stem cells, and generation of a metameric body plan. Oligochaete embryology originates from Germany (20-30's), Switzerland (50's) and France (60-70's). At present, however, the Shimizu Lab at Hokkaido University is the only one for oligochaete embryology in the world. Research topics currently under investigation are: cytoskeletal mechanisms of ooplasmic segregation ; cellular and molecular basis of unequal cleavage ; D-quadrant specification via cytoplasmic determinants ; specification of teloblasts (as embryonic stem cells) ; specification of dorsoventral axis ; generation of metameric body organization ; and developmental origin of segmental identity.
Joy of Spiralian Embryology!!
Joy of Annelid Embryology!!
Joy of Tubifex Embryology!!
"That a single cell can carry the total heritage of the complex adult, that it can in the course of a few days or weeks give rise to a mollusc or a man, is one of the great marvels of nature." E. B. Wilson (1925)
- Shimizu T. (1982) Development in the freshwater oligochaete Tubifex. In Developmental Biology of Freshwater Invertebrates (F. W. Harrison and R. R. Cowden, eds.), pp. 286-316. Alan R. Liss, New York.
- Ishii R. & Shimizu T. (1995) Unequal first cleavage in the Tubifex egg: Involvement of a monastral mitotic apparatus. Development Growth & Differentiation, 37, 687-701.
- Shimizu T. (1995) Role of the Cytoskeleton in the Generation of Spatial Patterns in Tubifex Eggs. In Current Topics in Developmental Biology, Vol. 31 (D. G. Capco, ed.), pp. 197-235. Academic Press, San Diego.
- Shimizu T. (1996) Ooplasmic redistribution in Tubifex eggs with selectively impaired cortical actin cytoskeleton. Developmental Biology, 180, 54-62.
- Takahashi H. & Shimizu T. (1997) Role of intercellular contacts in generating an asymmetric mitotic apparatus in the Tubifex embryo. Development Growth & Differentiation, 39, 351-362.
- Ishii R. & Shimizu T. (1997) Equalization of unequal first cleavage in the Tubifex egg by introduction of an additional centrosome: Implications for the absence of cortical mechanisms for mitotic spindle asymmetry. Developmental Biology, 189, 49-56.
- Shimizu T., Ishii R. & Takahashi H. (1998) Unequal cleavage in the early Tubifex embryo. Development Growth & Differentiation, 40, 257-266.
- Goto A., Kitamura K., Arai A. & Shimizu T. (1999) Cell fate analysis of teloblasts in the Tubifex embryo by intracellular injection of HRP. Development Growth & Differentiation, 41, 703-713.
- Kitamura K. & Shimizu T. (2000) Analyses of segment-specific expression of alkaline phosphatase activity in the mesoderm of the oligochaete annelid Tubifex: Implications for specification of segmental identity. Developmental Biology, 219, 214-223.
- Arai A., Nakamoto A. & Shimizu T. (2001) Specification of ectodermal teloblast lineages in embryo of the oligochaete annelid Tubifex: involvement of novel cell-cell interactions. Development, 128, 1211-1219.
- Shimizu T. & Nakamoto A. (2001) Segmentation in Annelids: Cellular and Molecular basis for Metameric Body Plan. Zoological Science, 18, 285-298
- Nakamoto A., Arai A. & Shimizu T. (2004) Specification of polarity of teloblastogenesis in the oligochaete annelid Tubifex: cellular basis for bilateral symmetry in the ectoderm. Developmental Biology, 272, 248-261.
- Matsuo K., Yoshida H. & Shimizu T. (2005) Differential expression of caudal and dorsal genes in the teloblast lineages of the oligochaete annelid Tubifex tubifex. Development Genes and Evolution, 215, 238-247.
- Matsuo K. & Shimizu T. (2006) Embryonic expression of a decapentaplegic gene in the oligochaete annelid Tubifex tubifex. Gene Expression Patterns, 6, 800-806.
- Oyama A. & Shimizu T. (2007) Transient occurrence of vasa-expressing cells in non-genital segments during embryonic development in the oligochaete annelid Tubifex tubifex. Development Genes and Evolution, 217, 675-690.
- Oyama A., Yoshida H. & Shimizu T. (2008) Embryonic expression of p68, a DEAD-box RNA helicase, in the oligochaete annelid Tubifex tubifex. Gene Expression Patterns, 8, 464-470.
- Kitakoshi T. & Shimizu T. (2010) An oligochaete homologue of the Brachyury gene is expressed transiently in the third quartette of micromeres. Gene Expression Patterns, 10, 306-313.
- Nakamoto A., Nagy L.M. & Shimizu T. (2011) Secondary embryonic axis formation by transplantation of D quadrant micromeres in an oligochaete annelid. Development, 138, 283-290.
