BMP4とマウスの発生

 

 

  1. Temporal BMP4 effects on mouse embryonic and extraembryonic development　Nature volume 634, pages652–661 (2024)　Published: 18 September 2024 https://www.nature.com/articles/s41586-024-07937-5　figure 1

神経誘導に必要なシグナル経路：BMP、FGF、WNT

神経誘導に必要なシグナル経路はBMP、FGF、WNTのどれでしょうか？カエルやマウスやニワトリの論文をバラバラに読むと、いろいろなシグナルの重要性が報告されており、どれが本当のところ重要なのか整理がつきにくくなってきます。

動物種による違い

The molecular mechanism that initiates the formation of the vertebrate central nervous system has long been debated. Studies in Xenopus and mouse demonstrate that inhibition of BMP signaling is sufficient to induce neural tissue in explants or ES cells respectively, whereas studies in chick argue that instructive FGF signaling is also required for the expression of neural genes.

The response of early neural genes to FGF signaling or inhibition of BMP indicate the absence of a conserved neural induction module　BMC Developmental Biology volume 11, Article number: 74 (2011)https://bmcdevbiol.biomedcentral.com/articles/10.1186/1471-213X-11-74

ニワトリ胚の神経誘導はカエルほど単純ではないようです。

In Xenopus, the release from the inhibitory, epidermal inducing signal bone morphogenetic protein-4 (BMP-4) by antagonizing secreted factors such as chordin, noggin, and follistatin, or by simple cell dissociation, seems to be sufficient to make ectodermal cells develop into neural tissue. Several lines of evidence in amniotes suggest a much higher degree of complexity. In the chick, inhibition of the BMP signaling pathway does not lead to neural differentiation, nor can BMPs prevent initial induction. However, antagonism between BMP-4 and chordin seems to play a role in controlling the extent of the neural plate once it is formed.

Cell Lineage and Fate Determination 1999, Pages 437-449 29 – More to Neural Induction Than Inhibition of BMPs Andrea Streit , Claudio D. Stern https://www.sciencedirect.com/science/article/abs/pii/B9780125052559500304?via%3Dihub

Consensus.aiに訊いてみました。

神経誘導に必要なシグナル：BMPかFGFか

神経誘導は、胚の外胚葉から脊椎動物の神経系を生成する最初のステップです。この過程において、BMP（骨形成タンパク質）とFGF（線維芽細胞成長因子）のシグナルがどのように関与しているかについて、多くの研究が行われています。

主要な知見

  • BMPの抑制が必要だが不十分

    • BMPシグナルの抑制は神経誘導に必要だが、それだけでは不十分であることが示されています。BMPの抑制は神経誘導の遅い段階で必要であり、他のシグナルも関与している可能性があります。

  • FGFシグナルの重要性

    • FGFシグナルは神経誘導において重要な役割を果たしており、BMPの抑制と組み合わせることで神経運命の指定が行われます。FGFシグナルは、BMPシグナルの抑制だけでなく、独自の役割を持っています。

  • BMPとFGFの相互作用

    • BMPの抑制とFGFシグナルは、Smad1のリン酸化を通じて相互作用し、神経誘導を促進します。これにより、BMPシグナルの抑制とFGFシグナルの活性化が統合され、神経誘導が行われます。

  • モデル生物間の違い

    • Xenopus（アフリカツメガエル）やマウス、ヒヨコなどの異なるモデル生物において、BMPとFGFの役割が異なることが示されています。特に、XenopusではBMPの抑制が神経誘導に十分である一方、他のモデルではFGFシグナルが必要とされています。

結論

神経誘導にはBMPシグナルの抑制が必要ですが、それだけでは不十分であり、FGFシグナルも重要な役割を果たします。これらのシグナルは相互に作用し、神経運命の指定を促進します。したがって、神経誘導にはBMPの抑制とFGFシグナルの両方が必要です。

  1. Neural induction requires BMP inhibition only as a late step, and involves signals other than FGF and Wnt antagonists BMP 阻害は神経誘導の最終段階でのみ必要であり、FGF および Wnt 拮抗薬以外のシグナルが関与します。 C. Linker et al.
  2. Neural induction in Xenopus requires early FGF signalling in addition to BMP inhibition アフリカツメガエルにおける神経誘導には BMP 阻害が必要ですが、それだけでは十分ではありません。神経運命の出現には前胚 FGF シグナル伝達が必要です。 Emilie A Delaune et al.
  3. Integration of IGF, FGF, and anti-BMP signals via Smad1 phosphorylation in neural induction. 神経誘導は、Smad1 リン酸化を介した抗 BMP、FGF8、および IGF2 シグナルの統合によって生じます。 Genes & development E. Pera et al.
  4. BMP inhibition initiates neural induction via FGF signaling and Zic genes BMP 阻害は、FGF シグナル伝達と Zic 遺伝子を介して神経誘導を開始します。 Proceedings of the National Academy of Sciences Leslie Marchal et al. 127 Citations 2009 Info Highly Cited Ask this paper icon button Study snapshot Save Cite Share
  5. BMP antagonists and FGF signaling contribute to different domains of the neural plate in Xenopus. BMP シグナル伝達の阻害は、アフリカツメガエル胚の外胚葉組織片における神経誘導には十分ですが、結論には sox 遺伝子発現の解釈によって若干の矛盾が生じます。 Developmental biology A. Wills et al. 46 Citations 2010 icon button Study snapshot Save Cite Share
  6. BMP signalling inhibits premature neural differentiation in the mouse embryo BMP シグナル伝達は哺乳類の神経誘導において中心的な役割を果たしますが、FGF は着床後のマウス胚において神経誘導因子として作用しません。 Aida Di-Gregorio et al. 188 Citations 2007 Info In Vitro Trial Info Highly Cited icon button Study snapshot Save Cite Share
  7. An early requirement for FGF signalling in the acquisition of neural cell fate in the chick embryo FGF シグナル伝達は、ニワトリ胚における BMP 発現の抑制と神経運命の獲得に必要です。 Current Biology S. Wilson et al. 342 Citations 2000 Info In Vitro Trial Info Highly Cited icon button Study snapshot Save Cite Share
  8. FGF/MAPK signaling is required in the gastrula epiblast for avian neural crest induction 鳥類の神経堤誘導には、胚葉形成中の神経堤上胚葉予定層内での FGF/MAPK シグナル伝達が必要である。 Development T. Stuhlmiller et al. 83 Citations 2012 Info In Vitro Trial Info Highly Cited icon button Study snapshot Save Cite Share
  9. The response of early neural genes to FGF signaling or inhibition of BMP indicate the absence of a conserved neural induction module BMP 阻害と FGF シグナル伝達は、それぞれの遺伝子の発現に異なるシグナル伝達要件を伴い、互いに独立して神経遺伝子を誘導します。 BMC Developmental Biology C. Rogers et al. 19 Citations 2011 Info In Vitro Trial icon button Study snapshot Save Cite Share
  10. Regulation of Neural Specification from Human Embryonic Stem Cells by BMP and FGF FGF は、神経誘導のための BMP シグナル伝達とは独立して、ヒトの神経の特異性を強化します。 STEM CELLS T. Lavaute et al. 97 Citations 2009 Info In Vitro Trial Info Highly Cited

カエル

  1. 15 November 2012 BMP, Wnt and FGF signals are integrated through evolutionarily conserved enhancers to achieve robust expression of Pax3 and Zic genes at the zebrafish neural plate border Development (2012) 139 (22): 4220–4231.　https://journals.biologists.com/dev/article/139/22/4220/45624/BMP-Wnt-and-FGF-signals-are-integrated-through
  2. Development . 1996 Jun;122(6):1711-21. doi: 10.1242/dev.122.6.1711. Regulation of dorsal-ventral patterning: the ventralizing effects of the novel Xenopus homeobox gene Vox https://journals.biologists.com/dev/article/122/6/1711/39169/Regulation-of-dorsal-ventral-patterning-the

ニワトリ

  1. The acquisition of neural fate in the chick　Mechanisms of Development Volume 121, Issue 9, September 2004, Pages 1031-1042 Mechanisms of Development Review https://www.sciencedirect.com/science/article/pii/S0925477304001303　
  2. Reciprocal Repression between Sox3 and Snail Transcription Factors Defines Embryonic Territories at Gastrulation Developmnetal Cell Volume 21, Issue 3, 13 September 2011, Pages 546-558
  3. Mechanisms of Development Volume 82, Issues 1–2, 1 April 1999, Pages 51-66 Mechanisms of Development Establishment and maintenance of the border of the neural plate in the chick: involvement of FGF and BMP activity　https://www.sciencedirect.com/science/article/pii/S0925477399000131

ゼブラフィッシュ

  1. Development . 2012 Nov;139(22):4220-31. doi: 10.1242/dev.081497. Epub 2012 Oct 3. BMP, Wnt and FGF signals are integrated through evolutionarily conserved enhancers to achieve robust expression of Pax3 and Zic genes at the zebrafish neural plate border Aaron T Garnett 1, Tyler A Square,　https://pubmed.ncbi.nlm.nih.gov/23034628/

神経堤細胞の誘導

　Post-transcriptional tuning of FGF signaling mediates neural crest induction Jacqueline Copeland and Marcos Simoes-Costa simoescosta@cornell.eduAuthors Info & Affiliations　PNAS　December 21, 2020 117 (52) 33305-33316https://www.pnas.org/doi/10.1073/pnas.2009997117

Brachuryとは？ブラキューリ？

カエルでの発現パターン

Comparison of Xbra reporter gene expression with that of the endogenous gene. (A) Time course of Xbra-2.1 expression compared with that of endogenous Xbra. Dorsal is upwards in all panels, except wild-type stage 9.5 (dorsal to the right). The colour reaction to detect reporter gene expression took 24 to 48 hours compared with 5 hours to detect endogenous Xbra. Reporter gene expression was restricted to the marginal zone in approximately 80% (n>150) of transgenic embryos. (B) Expression of endogenous Xbra RNA at stage 9.0. Left panel: animal pole view; right panel: side view. Embryos were cleared to visualise internal staining. Nuclear staining indicates newly transcribed zygotic RNA. Non-transgenic embryos stained for GFP RNA for the same time showed no expression (not shown). Weaker staining in the vegetal pole may be due to poor probe diffusion, but see the sectioned in situ hybridisations of Panitz et al. (1998). (C) GFP fluorescence of an embryo transgenic for Xbra-4.1. Note slightly weaker expression in the dorsal marginal zone (top right).

15 June 2000 Region-specific activation of the Xenopus Brachyury promoter involves active repression in ectoderm and endoderm: a study using transgenic frog embryos Walter Lerchner, Branko V. Latinkic, Jacques E. Remacle, Danny Huylebroeck, James C. Smit

Brachyury Knockdown Phenotype in Xenopus

Brachyury (Xbra) is a crucial gene involved in mesoderm formation and notochord differentiation in vertebrates, including Xenopus. The following synthesis presents the key findings from multiple research papers on the phenotype observed when Brachyury is knocked down in Xenopus.

Key Insights

  • Failure in Gastrulation Movements:
    • Knockdown of Brachyury in Xenopus embryos results in the failure to complete gastrulation due to the loss of convergent extension movements, which are essential for proper morphogenetic movements .
  • Down-Regulation of Downstream Genes:
    • Brachyury knockdown leads to the down-regulation of its downstream genes, including Xwnt11, which is crucial for regulating gastrulation movements via the Dishevelled pathway, but not through the canonical Wnt pathway .
  • Morphological Defects:
    • Both genetic knockout (KO) and morpholino-mediated knockdown (KD) of Brachyury in Xenopus result in virtually identical morphological defects, indicating the critical role of Brachyury in early development.
  • Off-Target Effects and Immune Response:
    • Morpholino-mediated knockdown of Brachyury can induce off-target splicing defects and a systemic immune response, which can be mitigated but not entirely eliminated by optimizing morpholino dosage and incubation conditions.

Conclusion

Knockdown of Brachyury in Xenopus leads to significant developmental issues, primarily characterized by the failure of gastrulation movements due to disrupted convergent extension. This is accompanied by the down-regulation of key downstream genes like Xwnt11. While both genetic knockout and morpholino-mediated knockdown produce similar morphological defects, the latter can also cause off-target effects and immune responses. These findings underscore the essential role of Brachyury in early vertebrate development and the complexities involved in gene knockdown studies.

(consensus.ai)

  1. Highly conserved functions of the Brachyury gene on morphogenetic movements: insight from the early-diverging phylum Ctenophora. アフリカツメガエルの胚における Brachyury のノックダウンは、収束伸展運動の喪失により胚葉形成の完了に失敗する結果となる。Developmental biology A. Yamada et al. 49 Citations 2010
  2. Innate Immune Response and Off-Target Mis-splicing Are Common Morpholino-Induced Side Effects in Xenopus 対照または標的 MO を注入された胚は、全身の GC 含有量依存性免疫応答と多くのオフターゲットスプライシング欠陥を示します。 Developmental Cell George E. Gentsch et al. 41 Citations 2018
  3. Xwnt11 is a target of Xenopus Brachyury: regulation of gastrulation movements via Dishevelled, but not through the canonical Wnt pathway. Xbra の転写活性化の妨害は、胚葉形成中の形態形成運動の阻害につながります。 Development M. Tada et al. 742 Citations 2000
  4. Cooperative non-cell and cell autonomous regulation of Nodal gene expression and signaling by Lefty/Antivin and Brachyury in Xenopus. アフリカツメガエルにおけるブラキュリ媒介転写抑制は、オーガナイザーおよび中内胚葉組織のさらなる拡大につながり、背側の特異性に影響を及ぼします。 Developmental biology Y. R. Cha et al. 33 Citations 2006
  5. The Brachyury gene encodes a novel DNA binding protein. Brachyury 変異胚は中胚葉形成が不十分で、体軸の発達が完了せず、脊索が最も影響を受けます。 The EMBO Journal A. Kispert et al. 364 Citations 1993
  6. In vivo knockdown of Brachyury results in skeletal defects and urorectal malformations resembling caudal regression syndrome. Brachyury の体内でのノックダウンは、胎児の尾部退縮症候群に似た骨格異常および尿直腸奇形を引き起こします。 Developmental biology T. Pennimpede et al. 50 Citations 2012
  7. Goosecoid and mix.1 repress Brachyury expression and are required for head formation in Xenopus. goosecoid または mix.1 の機能が阻害されると、Xbra が一時的に異所的に発現し、背前部異常や心臓および腸管の形成異常が生じます。 Development Branko V. Latinkić et al. 116 Citations 1999
  8. Expression of a xenopus homolog of Brachyury (T) is an immediate-early response to mesoderm induction Brachyury のアフリカツメガエル相同遺伝子である Xbra は、胚葉口周囲の予定中胚葉細胞で発現し、その後脊索で発現します。 Cell James C. Smith et al. 1,030 Citations 1991 本文有料

原始結節nodeを移植すると二次の体軸が形成されるという実験報告論文

Consensus.aiによるまとめ。

Introduction

The transplantation of the node, a critical embryonic structure, has been studied for its ability to induce ectopic body axes in both mice and chicks. This research explores the node’s role in axis formation and its potential to organize and pattern embryonic development when transplanted to non-native locations.

Key Insights

  • Induction of Ectopic Neural Axis in Mice:
    • Transplanting the mouse node to a posterolateral location in a host embryo induces a second neural axis and ectopic somites. The graft predominantly forms notochord and endoderm, while the host contributes to neurectoderm and somites.
  • Induction of Ectopic Axis in Chicks:
    • Hensen’s node in chick embryos can induce a complete embryonic axis, including a fully patterned central nervous system, when transplanted to an ectopic site. This includes host-derived neural tissue.
  • Role of Node in Axis Formation:
    • The mouse node is crucial for the formation of the notochord, floor plate, and gut endoderm. Its ablation leads to the recruitment of surrounding tissues to restore the neural tube and paraxial mesoderm, although the body axis may be foreshortened and somite formation delayed.
  • Synergistic Activity in Axis Induction:
    • In mice, the combination of the early gastrula organizer (posterior epiblast), anterior visceral endoderm, and anterior epiblast is necessary to induce anterior neural structures and form an ectopic axis. The anterior germ layer tissues alone do not act as a classical organizer.
  • Molecular Mechanisms in Chicks:
    • The protein Tsukushi (TSK) in chicks inhibits BMP signaling, which is essential for the formation of Hensen’s node and the induction of an ectopic node when combined with the middle primitive streak.

Conclusion

The transplantation of the node in both mice and chicks can induce the formation of ectopic body axes, demonstrating its critical role in embryonic patterning. In mice, the node primarily contributes to the notochord and endoderm, while（全然対比になっていない。。） in chicks, Hensen’s node can induce a complete axis including neural tissues. The induction of anterior neural structures in mice requires a combination of specific germ layer tissues, highlighting the complexity of axis formation. Molecular mechanisms, such as BMP inhibition by Tsukushi in chicks, further elucidate the processes involved in node-induced axis formation.

名前が似ているけどnorrin とnogginは全く別の遺伝子

nogginは有名ですがnorrinは初めて知りました。まさかミスプリじゃないよねと思ってChatGPTで確認したところ、もちろん別の遺伝子でした。

質問：norrinとnogginは同じものですか？

No, Norrin and Noggin are different genes with distinct functions and roles in development.

Key Differences between Norrin and Noggin:

  1. Noggin:
    • Gene Symbol: NOG
    • Function: Noggin is a secreted protein that acts as an antagonist of BMP (Bone Morphogenetic Protein) signaling. It binds to BMPs and prevents them from interacting with their receptors, which helps to regulate dorsal-ventral patterning during early embryonic development.
    • Role in Development: Noggin is crucial for neural induction and dorsalization of mesoderm, particularly in the context of vertebrate development. It is one of the organizer molecules discovered in studies on Spemann’s organizer.
    • Pathways: It primarily modulates TGF-β family signaling, including BMPs.
  2. Norrin:
    • Gene Symbol: NDP (stands for Norrie Disease Protein)
    • Function: Norrin is a secreted signaling molecule that functions as a ligand for the Frizzled-4 (FZD4) receptor in the Wnt/β-catenin signaling pathway.
    • Role in Development: Norrin is primarily involved in the development of the retina and inner ear. It plays a critical role in vascular development, especially in the retina and blood-brain barrier. Mutations in the NDP gene are associated with Norrie disease, which leads to blindness and other developmental issues.
    • Pathways: Norrin functions through the Wnt signaling pathway, specifically by binding to Frizzled-4 and LRP5/6 to activate β-catenin signaling.

Summary:

  • Noggin is involved in BMP inhibition and dorsal-ventral patterning during embryonic development.
  • Norrin is involved in Wnt signaling, particularly in the context of vascularization and retinal development.

They are distinct genes with different roles and mechanisms in development, even though their names sound similar.

体軸上で、四肢の出る位置はどのようにして決まるのか？

 

 

 

Patterning mechanisms controlling vertebrate limb development. J. Capdevila, J. C. I. Belmonte · 2001　脊椎動物の四肢芽では、シグナル伝達経路間の複雑な相互作用により、四肢の位置決め、成長、パターン形成が制御されます。　https://www.annualreviews.org/content/journals/10.1146/annurev.cellbio.17.1.87　本文有料 総説論文

 

Analysis of Hox gene expression in the chick limb bud. C. Nelson, Bruce A. Morgan, Ann C. Burke+7 more · 1996年5月1日　肢芽における Hox 遺伝子の発現は、肢の近位遠位節 (上腕、下腕、手) の指定とパターン形成に関連して、最大 3 つの独立した段階で制御されます。https://journals.biologists.com/dev/article/122/5/1449/39007/Analysis-of-Hox-gene-expression-in-the-chick-limb　Expression of the Hoxa genes during normal chick limb development. Whole mount in situ hybridizations to wings (upper row) and legs (lower row) for the genes: Hoxa-9 (A), Hoxa-10 (B), Hoxa-11 (C) and Hoxa-13 (D). Approximate stages are: stage 19/20, stage 23, stage 25 and stage 28 (from left to right). All panels are dorsal views with anterior to the top and distal to the right. (A) Hoxa-9 is expressed uniformly in limb mesenchyme at the earliest stages of limb bud outgrowth. By stage 19, there is a region in the anterior/proximal region of the wing bud that does not express Hoxa-9. This region, which does not express Hoxa-9, persists and expands through subsequent stages of development. Expression throughout the rest of the bud is strong through stage 23 and then fades slowly throughout the limb bud. By stage 25, only low levels of transcript are detected. By stage 28 expression is no longer detected in the limb. In the leg bud, Hoxa-9 expression parallels that in the wing, but there is no region of non-expressing tissue in the anterior/proximal region. (B) By stage 19 Hoxa-10 is expressed in the wing bud, but it is largely excluded from the marginal mesenchyme. By stage 22 Hoxa-10 is expressed at moderate levels throughout the wing mesenchyme with the exception of a region in the anterior/proximal portion of the wing. In the leg bud Hoxa-10 is expressed uniformly by stage 19 and never appears to be excluded from the anterior/proximal region seen in the wing. As development proceeds, progressively lower levels of transcript are detected throughout both limbs. At late stages, Hoxa-10 expression is still detectable in the upper arm/leg and lower arm/leg, but is largely absent from the hand/foot. (C) At early stages a region of expression is detected in the medial region of the wing bud, where scattered punctate staining is also observed. In late stage 19, a separate domain of expression along the distal margin of the wing is also observed. At stage 22, Hoxa-11 expression is observed in the distal half of the wing bud across the A/P axis of the limb. By stage 25, expression is restricted to the presumptive lower arm and is largely absent from the upper arm and hand. This pattern of expression persists through stage 28. By stage 19 Hoxa-11 expression in the distal margin of the leg bud is strong and uniform. Expression is also detected in more proximal regions, but in a less uniform, punctate pattern with higher levels observed in the posterior two thirds of the limb. By stage 22, expression is strong and uniform through most of the leg bud, although Hoxa-11 is not expressed in the proximal anterior region. At later stages, expression persists in the lower leg but is greatly reduced or absent in the upper leg and foot. This pattern persists through stage 28. Like many of the Hox genes, Hoxa-11 expression becomes excluded from regions of condensing cartilage. (D) Hoxa-13 is first expressed in the hind limb at stage 19 in the posterior distal mesenchyme. Expression in the fore limb begins shortly thereafter at the posterior distal margin (data not shown). Later, Hoxa-13 is expressed at high levels in a crescent along the distal margin of both limbs. By stage 25 expression is strong throughout the hand/foot with no obvious bias in expression level along the anterior/posterior axis; no Hoxa-13 expression is detected in the proximal segments of the limb. High levels of expression persist in the hand/foot through at least stage 28.

分子生物学とは？生化学との違い

大雑把にいうと、分子生物学はDNAの科学、生化学はタンパク質の科学と捉えてよいものでしょうか？ChatGPTに訊いてみました。

分子生物学とは？

  • 分子生物学は、DNA、RNA、タンパク質の相互作用を中心に、生物の遺伝情報の伝達と機能を探る学問です。
  • 遺伝子の複製（DNAのコピー）、転写（DNAからRNAへの変換）、翻訳（RNAからタンパク質への変換）など、遺伝情報がどのようにして細胞内で利用されるかを研究します。
  • たとえば、遺伝子の発現調節、遺伝子変異、シグナル伝達などが分子生物学の対象となります。

生化学とは？

  • 生化学は、生物を構成する化学的な物質やその化学反応を研究する学問です。
  • タンパク質に関する研究は生化学の大きな部分を占めますが、それだけではなく、脂質、糖、核酸、代謝経路（例えばエネルギーの生成や利用）、酵素反応など、生物のあらゆる化学反応が対象です。
  • 酵素の機能や、細胞の代謝過程における化学反応の詳細なども生化学の主要な研究テーマです。

まとめ：

  • 分子生物学＝「DNAや遺伝子の科学」に近いが、実際にはRNAやタンパク質も含む遺伝情報の流れ全体を研究する。
  • 生化学＝「生体内の化学反応」や「タンパク質を含む生体分子の機能」を広く研究する。

したがって、「分子生物学がDNAの科学、生化学がタンパク質の科学」という理解は、分子生物学と生化学の一部を反映していますが、全体の範囲や対象を理解するにはもう少し幅広く捉える必要があります。

(ChatGPT 4o）

カエルとマウスの発生学から得られた知見の統合：wnt, BMP, nordal, オーガナイザー、神経誘導などについて

 

Segregation of brain and organizer precursors is differentially regulated by Nodal signaling at blastula stage　https://www.biorxiv.org/content/10.1101/2020.07.16.167320v1.full

 

Developmental Cell Volume 1, Issue 5, November 2001, Pages 605-617 Journal home page for Developmental Cell Review Nodal Signaling in Early Vertebrate Embryos: Themes and Variations　https://www.sciencedirect.com/science/article/pii/S1534580701000764

TGF-b family signaling gradients during gastrulation. (A ...

TGF-β Family Signaling in Early Vertebrate Development June 2017Cold Spring Harbor Perspectives in Biology 10(6):a033274 DOI:10.1101/cshperspect.a033274　https://www.researchgate.net/figure/TGF-b-family-signaling-gradients-during-gastrulation-A-Embryonic-tissues-patterned-by_fig1_317494952

上肢や下肢が出る位置はどのようにして決まるのか？

上肢や下肢が出る位置はどのようにして決まるのでしょうか？体軸の位置はHOXコードで決まるのだとすれば、ある特定のHOX遺伝子産物が転写制御因子となって上肢や下肢の肢芽で発現するTbx5やTbx4の発現を直接制御するのでしょうか（エンハンサーかプロモーターに特異的に結合するなどして）？

下の総説によれば、HOX遺伝子が活性化や抑制に働くようです。

A Combination of Activation and Repression by a Colinear Hox Code Controls Forelimb-Restricted Expression of Tbx5 and Reveals Hox Protein Specificity Satoko Nishimoto,Carolina Minguillon,Sophie Wood,Malcolm P. O. Logan Published: March 20, 2014 https://doi.org/10.1371/journal.pgen.1004245

最近の総説論文を読むと, HOXコードで前肢の出る位置は決まるようですが、そう単純ではなさそうです。ただTbx5はFgf10遺伝子のプロモーターに直接結合して発現を誘導するそうです。下肢については、前肢ほどには研究がなされておらず、HOXコードで位置が規定されるのか、FGF10を発現させるものが何なのかについては報告がなさそうです。

  1. Current research on mechanisms of limb bud development, and challenges for the next decade Takayuki Suzuki　Genes & Genetic Systems/Volume 99 (2024)　https://www.jstage.jst.go.jp/article/ggs/99/0/99_23-00287/_html/-char/en　

 

  1. Tbx5 is essential for forelimb bud initiation following patterning of the limb field in the mouse embryo　Development (2003) 130 (3): 623–633.　https://journals.biologists.com/dev/article/130/3/623/42069/Tbx5-is-essential-for-forelimb-bud-initiation
    1. mouse embryos lacking Tbx5 do not form forelimb buds
    2. Tbx5 directly activates the Fgf10 gene via a conserved binding site, providing a simple and direct mechanism for limb bud initiation
  2. Tbx5 is required for forelimb bud formation and continued outgrowth　Development . 2003 Jun;130(12):2741-51. doi: 10.1242/dev.00473.

Fig. 3. Antero-posterior limb polarity. (A) Major regulatory interactions involved in the specification of forelimb field antero-posterior polarity. Retinoic acid (RA) signalling is implicated in the defined anterior to posterior order of expression of Hox5-Hox9 paralogous group (PG) genes in presumptive forelimb regions of the lateral plate mesoderm (LPM). Hox5 PG proteins repress anterior Shh expression indirectly through activation of Plzf. Gata4 and Gata6 proteins transcriptionally inhibit Shh and attenuate Shh signal transduction by promoting the repressor form of Gli3. RA stimulates the posterior expression of Hand2, the product of which both represses Gli3 in the posterior part of the limb bud and stimulates Shh expression at the posterior margin. Gli3 also represses Hand2. Sall4 is expressed in the presumptive forelimb and its protein product contributes to the expression of Gli3. (B) Major regulatory interactions involved in the specification of hindlimb field antero-posterior polarity. Gata6 directly represses anterior expression of Shh. Sall4, Irx3 and Irx5 regulate Gli3 expression anteriorly. Isl1 indirectly promotes the posterior expression of Shh in the hindlimb by inducing Hand2, which represses Gli3 in the posterior part of the hindlimb. A, anterior; P, posterior.

https://journals.biologists.com/dev/article/147/17/dev177956/225797/Establishing-the-pattern-of-the-vertebrate-limb

notchは原始線条nodeのmotile ciliaをもつ細胞でnodal遺伝子発現を誘導するか

左右差を生み出す最初の仕組みは、マウスの場合は原始結節（2層の細胞層）の下側（中胚葉由来である脊索が脊索板になって内胚葉の層と一体化している）の細胞がもつ線毛の回転により左向きの水流が生じて、それを原始結節の両側に存在する動かない線毛を持つ細胞が感知して、左側に特異的な遺伝子発現を始めるというものでした。

動かない線毛を持つ細胞は左右両側にありますが、その線毛に存在するカルシウムチャンネルPkd2は正中線側に偏って存在しているため、左向きの水流で曲げられた線毛の正中線側の部分は、左側の細胞では引っ張られ、右側の細胞では表面が縮まることになります。張力によって開くカルシウムチャネルPkd2は、左側でのみ開くので、Ca濃度上昇に依存した細胞内の変化が、特異的な遺伝子発現につながるわけです。その細胞内変化とはどのようなものでしょうか。

notchは原始線条nodeのmotile ciliaをもつ細胞でnodal遺伝子発現を誘導するのでしょうか？

  1. Notch signaling regulates left–right asymmetry determination by inducing Nodal expression Luke T Krebs 1,4, Naomi Iwai 2,3,4, Shigenori Nonaka 2,3, Ian C Welsh 1, Yu Lan 1,5, Rulang Jiang 1,5, Yukio Saijoh 2, Timothy P O’Brien 1, Hiroshi Hamada 2,3,6, Thomas Gridley 1,7　Genes Dev. 2003 May 15;17(10):1207–1212. doi: 10.1101/gad.1084703 https://pmc.ncbi.nlm.nih.gov/articles/PMC196059/
  2. Notch activity acts as a sensor for extracellular calcium during vertebrate left–right determination Ángel Raya, Yasuhiko Kawakami, Concepción Rodríguez-Esteban, Marta Ibañes, Diego Rasskin-Gutman, Joaquín Rodríguez-León, Dirk Büscher, José A. Feijó & Juan Carlos Izpisúa Belmonte Nature volume 427, pages121–128 (2004) figure 1
  3. Notch activity induces Nodal expression and mediates the establishment of left–right asymmetry in vertebrate embryos　Genes Dev. 2003 May 15;17(10):1213–1218. doi: 10.1101/gad.1084403 https://pmc.ncbi.nlm.nih.gov/articles/PMC196060/
  4. Developmental Biology Asymmetric distribution of dynamic calcium signals in the node of mouse embryo during left–right axis formation Developmental Biology Volume 376, Issue 1, 1 April 2013, Pages 23-30  https://www.sciencedirect.com/science/article/pii/S0012160613000365?via%3Dihub