研究者詳細 - 佐藤　伸

論文 - 佐藤　伸

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Blastema induction in aneurogenic state and Prrx-1 regulation by MMPs and FGFs in Ambystoma mexicanum limb regeneration 査読

Akira Satoh, Aki Makanae, Ayako Hirata, Yutaka Satou

DEVELOPMENTAL BIOLOGY 355 ( 2 ) 263 - 274 2011年7月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE

Urodele amphibians can regenerate amputated limbs. It has been considered that differentiated dermal tissues generate multipotent and undifferentiated cells called blastema cells during limb regeneration. In early phases of limb regeneration, blastema cells are induced by nerves and the apical epithelial cap (AEC). We had previously investigated the role of neurotrophic factors in blastema or blastema-like formation consisting of Prrx-1 positive cells. A new system suitable for investigating early phases of limb regeneration, called the accessory limb model (ALM), was recently developed. In this study, we performed a comparative transcriptome analysis between a blastema and wound using ALM. Matrix metalloproteinase (MMP) and fibroblast growth factor (FGF) signaling components were observed to be predominantly expressed in ALM blastema cells. Furthermore, we found that MMP activity induced a blastema marker gene, Prrx-1, in vitro, and FGF signaling pathways worked in coordination to maintain Prrx-1 expression and ALM blastema formation. Furthermore, we demonstrated that these two activities were sufficient to induce an ALM blastema in the absence of a nerve in vivo. (C) 2011 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.ydbio.2011.04.017

Regulation of proximal-distal intercalation during limb regeneration in the axolotl (Ambystoma mexicanum) 査読

Akira Satoh, Gillian M. C. Cummings, Susan V. Bryant, David M. Gardiner

DEVELOPMENT GROWTH & DIFFERENTIATION 52 ( 9 ) 785 - 798 2010年12月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY-BLACKWELL

Intercalation is the process whereby cells located at the boundary of a wound interact to stimulate proliferation and the restoration of the structures between the boundaries that were lost during wounding. Thus, intercalation is widely considered to be the mechanism of regeneration. When a salamander limb is amputated, the entire cascade of regeneration events is activated, and the missing limb segments and their boundaries (joints) as well as the structures within each segment are regenerated. Therefore, in an amputated limb it is not possible to distinguish between intersegmental regeneration (formation of new segments/joints) and intrasegmental regeneration (formation of structures within a given segment), and it is not possible to study the differential regulation of these two processes. We have used two models for regeneration that allow us to study these two processes independently, and report that inter- and intrasegmental regeneration are different processes regulated by different signaling pathways. New limb segments/joints can be regenerated from cells that dedifferentiate to form blastema cells in response to signaling that is mediated in part by fibroblast growth factor.

DOI： 10.1111/j.1440-169X.2010.01214.x

Ex vivo generation of a functional and regenerative wound epithelium from axolotl (Ambystoma mexicanum) skin 査読

Donald R. Ferris, Akira Satoh, Berhan Mandefro, Gillian M. Cummings, David M. Gardiner, Elizabeth L. Rugg

DEVELOPMENT GROWTH & DIFFERENTIATION 52 ( 8 ) 715 - 724 2010年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY-BLACKWELL

Urodele amphibians (salamanders) are unique among adult vertebrates in their ability to regenerate structurally complete and fully functional limbs. Regeneration is a stepwise process that requires interactions between keratinocytes, nerves and fibroblasts. The formation of a wound epithelium covering the amputation site is an early and necessary event in the process but the molecular mechanisms that underlie the role of the wound epithelium in regeneration remain unclear. We have developed an ex vivo model that recapitulates many features of in vivo wound healing. The model comprises a circular explant of axolotl (Ambystoma mexicanum) limb skin with a central circular, full thickness wound. Re-epithelialization of the wound area is rapid (typically < 11 h) and is dependent on metalloproteinase activity. The ex vivo wound epithelium is viable, responds to neuronal signals and is able to participate in ectopic blastema formation and limb regeneration. This ex vivo model provides a reproducible and tractable system in which to study the cellular and molecular events that underlie wound healing and regeneration.

DOI： 10.1111/j.1440-169X.2010.01208.x

The apical ectodermal ridge (AER) can be re-induced by wounding, wnt-2b, and fgf-10 in the chicken limb bud 査読

Akira Satoh, Aki Makanae, Naoyuki Wada

DEVELOPMENTAL BIOLOGY 342 ( 2 ) 157 - 168 2010年6月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE

Little effort has been made to apply the insights gained from studies of amphibian limb regeneration to higher vertebrates. During amphibian limb regeneration, a functional epithelium called the apical ectodermal cap (AEC) triggers a regenerative response. As long as the AEC is induced, limb regeneration will take place. Interestingly, similar responses have been observed in chicken embryos. The AEC is an equivalent structure to the apical ectodermal ridge (AER) in higher vertebrates. When a limb bud is amputated it does not regenerate; however, if the AER is grafted onto the amputation surface, damage to the amputated limb bud can be repaired. Thus, the AER/AEC is able to induce regenerative responses in both amphibians and higher vertebrates. It is difficult, however, to induce limb regeneration in higher vertebrates. One reason for this is that re-induction of the AER after amputation in higher vertebrates is challenging. Here, we evaluated whether AER re-induction was possible in higher vertebrates. First, we assessed the sequence of events following limb amputation in chick embryos and compared the features of limb development and regeneration in amphibians and chicks. Based on our findings, we attempted to re-induce the AER. When wnt-2b/fgf-10-expressing cells were inserted concurrently with wounding, successful re-induction of the AER occurred. These results open up new possibilities for limb regeneration in higher vertebrates since AER re-induction, which is considered a key factor in limb regeneration, is now possible. (C) 2010 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.ydbio.2010.03.018

Dermal fibroblasts contribute to multiple tissues in the accessory limb model 査読

Ayako Hirata, David M. Gardiner, Akira Satoh

DEVELOPMENT GROWTH & DIFFERENTIATION 52 ( 4 ) 343 - 350 2010年5月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY-BLACKWELL

The accessory limb model has become an alternative model for performing investigations of limb regeneration in an amputated limb. In the accessory limb model, a complete patterned limb can be induced as a result of an interaction between the wound epithelium, a nerve and dermal fibroblasts in the skin. Studies should therefore focus on examining these tissues. To date, however, a study of cellular contributions in the accessory limb model has not been reported. By using green fluorescent protein (GFP) transgenic axolotl tissues, we can trace cell fate at the tissue level. Therefore, in the present study, we transgrafted GFP skin onto the limb of a non-GFP host and induced an accessory limb to investigate cellular contributions. Previous studies of cell contribution to amputation-induced blastemas have demonstrated that dermal cells are the progenitors of many of the early blastema cells, and that these cells contribute to regeneration of the connective tissues, including cartilage. In the present study, we have determined that this same population of progenitor cells responds to signaling from the nerve and wound epithelium in the absence of limb amputation to form an ectopic blastema and regenerate the connective tissues of an ectopic limb. Blastema cells from dermal fibroblasts, however, did not differentiate into either muscle or neural cells, and we conclude that dermal fibroblasts are dedifferentiated along its developmental lineage.

DOI： 10.1111/j.1440-169X.2009.01165.x

Analysis of hoxa11 and hoxa13 expression during patternless limb regeneration in Xenopus 査読

Shiro Ohgo, Akari Itoh, Makoto Suzuki, Akira Satoh, Hitoshi Yokoyama, Koji Tamura

DEVELOPMENTAL BIOLOGY 338 ( 2 ) 148 - 157 2010年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE

During limb regeneration, anuran tadpoles and urodele amphibians generate pattern-organizing, multipotent, mesenchymal blastema cells, which give rise to a replica of the lost limb including patterning in three dimensions. To facilitate the regeneration of nonregenerative limbs in other vertebrates, it is important to elucidate the molecular differences between blastema cells that can regenerate the pattern of limbs and those that cannot. In Xenopus froglet (soon after metamorphosis), an amputated limb generates blastema cells that do not produce proper patterning, resulting in a patternless regenerate, a spike, regardless of the amputation level. We found that re-expression of hoxa11 and hoxa13 in the froglet blastema is initiated although the subsequent proximal-distal patterning, including separation of the hoxa11 and hoxa13 expression domains, is disrupted. We also observed an absence of EphA4 gene expression in the froglet blastema and a failure of position-dependent cell sorting, which correlated with the altered hoxa11 and hoxa13 expression. Quantitative analysis of hoxa11 and hoxa13 expression revealed that hoxa13 transcript levels were reduced in the froglet blastema compared with the tadpole blastema. Moreover, the expression of sox9, an important regulator of chondrogenic differentiation, was detected earlier in patternless blastemas than in tadpole blastemas. These results suggest that appropriate spatial, temporal, and quantitative gene expression is necessary for pattern regeneration by blastema cells. (C) 2009 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.ydbio.2009.11.026

Neurotrophic regulation of fibroblast dedifferentiation during limb skeletal regeneration in the axolotl (Ambystoma mexicanum) 査読

Akira Satoh, Gillian M. C. Cummings, Susan V. Bryant, David M. Gardiner

DEVELOPMENTAL BIOLOGY 337 ( 2 ) 444 - 457 2010年1月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE

The ability of animals to repair tissue damage is widespread and impressive. Among tissues, the repair and remodeling of bone occurs during growth and in response to injury; however, loss of bone above a threshold amount is not regenerated, resulting in a "critical-size defect" (CSD). The development of therapies to replace or regenerate a CSD is a major focus of research in regenerative medicine and tissue engineering. Adult urodeles (salamanders) are unique in their ability to regenerate complex tissues perfectly, yet like mammals do not regenerate a CSD. We report on an experimental model for the regeneration of a CSD in the axolotl (the Excisional Regeneration Model) that allows for the identification of signals to induce fibroblast dedifferentiation and skeletal regeneration. This regenerative response is mediated in part by BMP signaling, as is the case in mammals; however, a complete regenerative response requires the induction of a population of undifferentiated, regeneration-competent cells. These cells can be induced by signaling from limb amputation to generate blastema cells that can be grafted to the wound, as well as by signaling from a nerve and a wound epithelium to induce blastema cells from fibroblasts within the wound environment. (C) 2009 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.ydbio.2009.11.023

Effects of Activation of Hedgehog Signaling on Patterning, Growth, and Differentiation in Xenopus Froglet Limb Regeneration 査読

Nayuta Yakushiji, Makoto Suzuki, Akira Satoh, Hiroyuki Ide, Koji Tamura

DEVELOPMENTAL DYNAMICS 238 ( 8 ) 1887 - 1896 2009年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY-LISS

Regenerating limbs of urodele amphibians and Xenopus tadpole are reconstructed along proximal-distal, anterior-posterior (AP), and dorsal-ventral axes. In contrast, a regenerated limb of the Xenopus froglet does not have digits, and only a simple cartilaginous structure referred to as a "spike" is formed. This suggests that repatterning along the AP axis is absent in the froglet blastema. Previous studies have shown that Shh and its target genes are not expressed in the froglet blastema. In this study, we activated Hedgehog signaling in the froglet blastema and found that target genes of Shh were inducible in the mesenchyme of limb blastema. Furthermore, we found that activation of the signaling had effects on blastema cell proliferation and chondrogenesis and resulted in the formation of multiple cartilaginous structures. These findings indicate that activation of signaling that is absent in the froglet blastema is effective for improvement of limb regeneration ability in the Xenopus froglet. Developmental Dynamics 238:1887-1896, 2009. (C) 2009 Wiley-Liss, Inc.

DOI： 10.1002/dvdy.22011

The Role of Nerve Signaling in Limb Genesis and Agenesis During Axolotl Limb Regeneration 査読

Akira Satoh, Michelle A. James, David M. Gardiner

JOURNAL OF BONE AND JOINT SURGERY-AMERICAN VOLUME 91A 90 - 98 2009年7月

Regulation of dermal fibroblast dedifferentiation and redifferentiation during wound healing and limb regeneration in the Axolotl 査読

Akira Satoh, Susan V. Bryant, David M. Gardiner

DEVELOPMENT GROWTH & DIFFERENTIATION 50 ( 9 ) 743 - 754 2008年12月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY

Adult urodeles (salamanders) are unique in their ability to regenerate complex organs perfectly. The Accessory Limb Model (ALM) in the axolotl allows for the identification of signals from the wound epidermis, nerves and dermal fibroblasts that interact to regenerate a limb. In the present study, we have used the ALM to identity the axolotl (Ambystoma mexicanum) orthologue of Twist (AmTwist), a basic helix-loop-helix transcription factor that is involved in the regeneration of the dermis during limb regeneration. AmTwist is expressed during the blastema stages in regeneration, but is inhibited by signals from the nerve during the early stages when dermal fibroblasts dedifferentiate to form blastema cells. As the dermis regenerates, AmTwist is expressed in association with the synthesis of type I collagen in the proximal region of the blastema. Exogenous bone morphogenetic protein-2 leads to an increase in AmTwist expression, and therefore may function as an endogenous regulator of AmTwist expression and dermis regeneration. The nerve appears to have a dual function in regeneration by coordinately regulating dedifferentiation and redifferentiation of dermal fibroblasts.

DOI： 10.1111/j.1440-169X.2008.01072.x

Neurotrophic regulation of epidermal dedifferentiation during wound healing and limb regeneration in the axolotl (Ambystoma mexicanum) 査読

A. Satoh, G. M. C. Graham, S. V. Bryant, D. M. Gardiner

DEVELOPMENTAL BIOLOGY 319 ( 2 ) 321 - 335 2008年7月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE

Adult urodeles (salamanders) are unique in their ability to regenerate complex organs perfectly. The recently developed Accessory Limb Model (ALM) in the axolotl provides an opportunity to identify and characterize the essential signaling events that control the early steps in limb regeneration. The ALM demonstrates that limb regeneration progresses in a stepwise fashion that is dependent on signals from the wound epidermis, nerves and dermal fibroblasts from opposite sides of the limb. When all the signals are present, a limb is formed de novo. The ALM thus provides an opportunity to identify and characterize the signaling pathways that control blastema morphogenesis and limb regeneration. In the present study, we have utilized the ALM to identity the buttonhead-like zinc-finger transcription factor, Sp9, as being involved in the formation of the regeneration epithelium. Sp9 expression is induced in basal keratinocytes of the apical blastema epithelium in a pattern that is comparable to its expression in developing limb buds, and it thus is an important marker for dedifferentiation of the epidermis. Induction of Sp9 expression is nerve-dependent, and we have identified KGF as an endogenous nerve factor that induces expression of Sp9 in the regeneration epithelium. (c) 2008 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.ydbio.2008.04.030

Mitf contributes to melanosome distribution and melanophore dendricity 査読

Akiha Kawasaki, Mayuko Kumasaka, Akira Satoh, Makoto Suzuki, Koji Tamura, Toshiyasu Goto, Makoto Asashima, Hiroaki Yamamoto

PIGMENT CELL & MELANOMA RESEARCH 21 ( 1 ) 56 - 62 2008年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：BLACKWELL PUBLISHING

Mitf is a transcription factor of the basic/helix-loop-helix/leucine-zipper family which is indispensable for development of melanocytes and the retinal pigment epithelium. Our previous work using Xenopus laevis as a model system suggested that Mitf regulates melanosome dispersal in vivo though whether this was via melanosome transport or melanophore dendricity was not obvious. To better understand the role of Mitf, we have now characterized neural tube cultures from wild-type Mitf-injected or a dominant-negative Mitf-injected embryos and compared them with controls. In vitro, lower levels of Mitf activity induced less dendritic melanophores with aggregated melanosomes, whereas melanophores overexpressing Mitf had an extensive dendritic morphology with dispersed melanosomes. Moreover, immunorfluoresence assays reveal that expression of a dominant-negative Mitf leads to decreased Rab27a expression. These results suggest that Mitf is involved in the regulation of melanosome transport and the level of dendricity in melanophores.

DOI： 10.1111/j.1755-148X.2007.00420.x

Nerve-induced ectopic limb blastemas in the axolotl are equivalent to amputation-induced blastemas 査読

Akira Satoh, David M. Gardiner, Susan V. Bryant, Tetsuya Endo

DEVELOPMENTAL BIOLOGY 312 ( 1 ) 231 - 244 2007年12月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE

Adult urodeles (salamanders) are unique in their ability to regenerate complex organs perfectly. The recently developed Accessory Limb Model (ALM) in the axolotl provides an opportunity to identify and characterize the essential signaling events that control the early steps in limb regeneration. The ALM demonstrates that limb regeneration progresses in a stepwise fashion that is dependent on signals from the wound epidermis, nerves and dermal fibroblasts from opposite sides of the limb. When all the signals are present, a limb is formed de novo. The ALM thus provides an opportunity to identify and characterize the signaling pathways that control blastema morphogenesis and limb regeneration. Our previous study provided data on cell contribution, cell migration and nerve dependency indicating that an ectopic blastema is equivalent to an amputation-induced blastema. In the present study, we have determined that formation of both ectopic blastemas and amputation -induced blastemas is regulated by the same molecular mechanisms, and that both types of blastema cells exhibit the same functions in controlling growth and pattern formation. We have identified and validated five marker genes for the early stages of wound healing, dedifferentiation and blastema formation, and have discovered that the expression of each of these markers is the same for both ectopic and amputation-induced blastemas. In addition, ectopic blastema cells interact coordinately with amputation-induced blasterna, cells to form a regenerated limb. Therefore, the ALM is appropriate for identifying the signaling pathways regulating the early events of tetrapod limb regeneration. (C) 2007 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.ydbio.2007.09.021

Correlation between Shh expression and DNA methylation status of the limb-specific Shh enhancer region during limb regeneration in amphibians 査読

Nayuta Yakushiji, Makoto Suzuki, Akira Satoh, Tomoko Sagai, Toshihiko Shiroishi, Hisato Kobayashi, Hiroyuki Sasaki, Hiroyuki Ide, Koji Tamura

DEVELOPMENTAL BIOLOGY 312 ( 1 ) 171 - 182 2007年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE

The Xenopus adult limb has very limited regeneration ability, and only a simple cartilaginous spike structure without digits is formed after limb amputation. We found that expression of Shh and its downstream genes is absent from the regenerating blastema of the Xenopus froglet limb. Moreover, we found that a limb enhancer region of the Shh gene is highly methylated in the froglet, although the sequence is hypomethylated in the Xenopus tadpole, which has complete limb regeneration ability. These findings, together with the fact that the promoter region of Shh is hardly methylated in Xenopus, suggest that regenerative failure (deficiency in repatteming) in the Xenopus adult limb is associated with methylation status of the enhancer region of Shh and that a target-specific epigenetic regulation is involved in gene re-activation for repatteming during the Xenopus limb regeneration process. Because the methylation level of the enhancer region was low in other amphibians that have Shh expression in the blastemas, a low methylation status may be the basic condition under which transcriptional regulation of Shh expression can progress during the limb regeneration process. These findings provide the first evidence for a relationship between epigenetic regulation and pattern formation during organ regeneration in vertebrates. (C) 2007 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.ydbio.2007.09.022

Transgenic Xenopus with prx1 limb enhancer reveals crucial contribution of MEK/ERK and PI3K/AKT pathways in blastema formation during limb regeneration 査読

Makoto Suzuki, Akira Satoh, Hiroyuki Ide, Koji Tamura

DEVELOPMENTAL BIOLOGY 304 ( 2 ) 675 - 686 2007年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE

Understanding the mechanisms that control amphibian limb regeneration should allow us to decipher the critical differences between amphibians and humans, which have the limited ability of organ regeneration. However, many issues at the cellular and molecular levels still remain unresolved. We have generated a transgenic Xenopus laevis line that expresses green fluorescent protein (GFP) under the control of mouse prxI limb enhancer, which directs reporter gene expression in limb mesenchyme in mice, and found that GFP accumulated in blastemal mesenchymal cells of the transgenic froglets after limb amputation. Thus, this transgenic line should provide a new approach to gain insights into the cellular dynamics and signaling pathways involved in limb blastema formation. We have also developed a culture system for forelimb explants of froglets and found that treatment with inhibitors of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated protein kinase (ERK) kinase 1/2 (MEK1/2) and phosphatidylinositol 3-kinase (PI3K) repressed GFP expression. These effects were partially reversible, and down-regulation of GFP was associated with inhibition of cell-cycle progression and induction of ectopic apoptosis. In addition, we found that ERK1/2 and AKT, downstream mediators of MEK1/2 and PI3K pathways, were activated in amputated forelimb stumps. These results demonstrate that MEK/ERK and PI3K/AKT pathways regulate limb blastema formation in the X laevis froglet. (c) 2007 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.ydbio.2007.01.019

Limb regeneration in Xenopus laevis froglet 査読

Makoto Suzuki, Nayuta Yakushiji, Yasuaki Nakada, Akira Satoh, Hiroyuki Ide, Koji Tamura

THESCIENTIFICWORLDJOURNAL 6 26 - 37 2006年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：THESCIENTIFICWORLD LTD

Limb regeneration in amphibians is a representative process of epimorphosis. This type of organ regeneration, in which a mass of undifferentiated cells referred to as the "blastema" proliferate to restore the lost part of the amputated organ, is distinct from morphallaxis as observed, for instance, in Hydra, in which rearrangement of pre-existing cells and tissues mainly contribute to regeneration. In contrast to complete limb regeneration in urodele amphibians, limb regeneration in Xenopus, an anuran amphibian, is restricted. In this review of some aspects regarding adult limb regeneration in Xenopus laevis, we suggest that limb regeneration in adult Xenopus, which is pattern/tissue deficient, also represents epimorphosis.

DOI： 10.1100/tsw.2006.325

Characterization of Xenopus digits and regenerated limbs of the froglet 査読

Akira Satoh, Tetsuya Endo, Masahiro Abe, Nayuta Yakushiji, Shiro Ohgo, Koji Tamura, Hiroyuki Ide

DEVELOPMENTAL DYNAMICS 235 ( 12 ) 3316 - 3326 2006年12月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY-LISS

Xenopus has 4 and 5 digits in a forelimb and hindlimb, respectively. It is thought that their limbs and digits develop in Xenopus by mechanisms that are almost conserved from amphibians to higher vertebrates. This is supported by some molecular evidence. The 5'hoxd genes are convenient marker genes for characterizing digits in the chick and mouse. The anteriormost digit is characterized by being hoxd13-positive and hoxd12 (hoxd11)-negative in the chick and mouse. In this study, we revealed that the anteriormost digit of the Xenopus forelimb is hoxd13-positive and hoxd11-positive, that is, a more posterior character than digit I. The order of formation of digit cartilages also suggested that Xenopus forelimb digit identity is 11 to V, not I to IV. We have also been interested in the relationship between digit identity and shh. The anteriormost digit develops in a shh-independent way. A limb treated with cyclopamine (a shh inhibitor) has a gene expression pattern (hoxd11-negative) similar to that in shh-deficient mice, suggesting that a hindlimb treated with cyclopamine has a digit I character. However, a Xenopus froglet regenerate (spike), which lacks shh expression during its regeneration process, does not have such an expression pattern, being hoxd11-positive. We investigated hoxd11 transcriptions in blastemas that formed in the anteriormost and posteriormost digits, and we found that the blastemas have different hoxd11 expression levels. These findings suggest that the froglet limb blastema does not have a mere digit I character in spite of shh defectiveness and that the froglet limb blastema recognizes its positional differences along the anterior-posterior axis.

DOI： 10.1002/dvdy.20985

Limb regeneration in Xenopus laevis froglet. 査読

Suzuki M, Yakushiji N, Nakada Y, Satoh A, Ide H, Tamura K

TheScientificWorldJournal 6 Suppl 1 26 - 37 2006年5月

Analysis of scleraxis and dermo-1 genes in a regenerating limb of Xenopus laevis 査読

A Satoh, Y Nakada, M Suzuki, K Tamura, H Ide

DEVELOPMENTAL DYNAMICS 235 ( 4 ) 1065 - 1073 2006年4月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY-LISS

Xenopus laevis larvae can regenerate an exact replica of the missing part of a limb after amputation at an early limb bud stage. However, this regenerative capacity gradually decreases during metamorphosis, and a froglet is only able to regenerate hypomorphic cartilage, resulting in a spike-like structure (spike). It has been reported that the spike has tissue deformities, e.g., a muscleless structure. However, our previous study demonstrated that the muscleless feature of the spike can be improved. The existence of other kinds of tissue, such as tendon, has not been clarified. In this study, we focused on the tendon and dermis, and we isolated the scleraxis and dermo-1 genes, which are known to be marker genes for the tendon and dermis, respectively. The expressions of these genes were investigated in both the developmental and regenerating processes of a Xenopus limb. Although muscle was needed to maintain scleraxis expression, scleraxis transcription was detectable in the muscleless spike. Additionally, although grafting of matured skin, including dermal tissue, inhibited limb regeneration, the expression of dermo-1, a dermal marker gene, was detected from the early stage of the froglet blastema. These results indicate that tendon precursor cells and dermal cells exist in the regenerating froglet blastema. Our results support the idea that spike formation in postmetamorphic Xenopus limbs is epimorphic regeneration.

DOI： 10.1002/dvdy.20701

Characteristics of initiation and early events for muscle development in the Xenopus limb bud 査読

A Satoh, K Sakamaki, H Ide, K Tamura

DEVELOPMENTAL DYNAMICS 234 ( 4 ) 846 - 857 2005年12月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY-LISS

In Xenopus laevis, limb buds start to develop at a later point of the larval stage, prior to metamorphosis. This onset of limb development in Xenopus is totally different from that in amniotes such as birds and mammals, in which limb buds emerge at an early stage of embryogenesis, in parallel with other organogenesis. We investigated limb myogenesis in Xenopus, focusing on myogenic gene expression, myogenic ability of limb bud cells in the early stage, and the origin of myogenic precursor cells in the limb bud. The Xenopus early limb bud contains myoD/cardiac actin-positive and pax3/pax7-negative cells. Interestingly, results of transplantation experiments have revealed that this early limb bud contains myogenic precursor cells. In order to know the contribution of myogenic cells in somites to myogenic precursor cells in the early limb bud, we used a Cre-LoxP system for tracing over a long period. The results of fate tracing for myogenic cells in somites of the Xenopus embryo suggested that early-specified myogenic cells in somites do not contribute to limb muscle in Xenopus. Taken together, the results suggest that limb muscle development in Xenopus has characteristics of initiation and early events distinct from those of other vertebrate clades.

DOI： 10.1002/dvdy.20573

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