Protocols using impermeable barriers to block induction events between tissues of the main body axis and flank in the chick embryo required for limb formation are described. Beads soaked in candidate inductive signals are used to overcome the effect of barrier placement and analysis of gene expression confirms this.
ニワトリ胚は、直接的な方法で発達質問を分析するために使用することができる優れた脊椎動物のモデルを提供します。外科的介入後のアクセシビリティと堅牢性が重要な実験的な強みです。マイカ板は、ニワトリ肢芽開始1を防止するために使用される最初の障壁でした。翼の芽や脚の芽の誘導およびまたは開始に不透過性障壁としてアルミ箔を使用するプロトコルが記載されています。我々は、バリアによってブロックされた外因的に供給候補内因性因子への障壁にビーズ配置横でこの技術を兼ね備えています。結果は、その後の遺伝子発現のインサイチュハイブリダイゼーションを用いて分析します。私たちの主な焦点は、誘導にレチノイン酸シグナル伝達およびニワトリ胚の前部と後肢の後に開始の役割にあります。私たちは、BMS 493(レチノイン酸受容体(RAR)の逆アゴニスト)は、バーの効果を模倣するために側板中胚葉(LPM)に移植されたビーズを浸し使用しますRIERは体節(レチノイン酸(RA)のソース)と肢芽が成長するからLPMの間に配置されました。これらのプロトコルの修正版は、誘導手がかりの起源とタイミング上の他の質問に対処するために使用することができました。ニワトリ胚の領域は、関連する発達段階でのアクセスが提供される、バリアは2つの組織の間に配置することができ、開発における必然的な変化を研究しました。例としては、肝臓や腎臓の誘導として、脳の発達、軸延長にと臓器の開発に見ることができます。
クラシック胎生学者は伝統的に胚発生を制御するメカニズムを調べるために物理的技術を採用します。 1960年代と1970年代に研究者らは、胚形成の間、誘導信号の重要性を実証するために、発生中の胚の組織の間に挿入された不透過性の障壁を使用する技術を開発しました。私たちの関心は肢芽の伸長の前にどのようなイベント脊椎動物の四肢の開発に、特にあります。例えば、バリアの挿入は、対、無操作側に正常に進行させながら、ニワトリ胚の片側に発生肢芽の成長を防止することができます。これらの障壁が変化するために使用される材料。例えば、マイカ板1とタンタル箔2。これらの障壁は、効果的に、近軸中胚葉から形成された体節から、から肢芽の形態、側板中胚葉(LPM)を分離します。外科的移植する技術は、その密接な関係のウィットを実証します肢芽の開始はLPM 3 4で発生することがある場合は時間体節が不可欠です。 80年代と90年代に発達生物学者は、発生過程の制御に不可欠である拡散性シグナル伝達分子を発見しました。これらのシグナル伝達分子に浸したビーズは、胚の特定の領域に移植し、胚発生に変化を生み出すことができます。ニワトリ胚に注入し、数字5の鏡像複製を生成することができる場合、例えば、イオン交換ビーズによって取り込まレチノイン酸(RA)は、24時間にわたって放出されます。 FGFタンパク質を含有するヘパリンアクリルビーズは、肢のLPM 6から肢芽の伸長を開始することができます。
さらに最近では、マウスや魚の遺伝学は、(7件)新たな時代に、脊椎動物の四肢開始の研究をとっています。肢芽の開始に先立って体節でRAの存在は、LPによって必要不可欠拡散信号であることを十分な証拠がありますMは、四肢の出芽を開始します。私たちは、肢芽開始の頃LPMにおける遺伝子発現に対する障壁注入の効果を分析するためにニワトリ胚のアクセシビリティと実験的な堅牢性を悪用したかったです。本手法の新規適応はバリアによってブロックされた外因的に供給候補内因性因子に対する障壁にバリアをビーズの配置、横方向と軸方向の組織からの遮断信号を組み合わせることです。次のプロトコルは、肢芽の誘導および開始のメカニズムを引き出すために開発されたものです。
肢芽の開始を研究することは、早期段階の胚を使用することを意味します。最初の皮下注射針で気嚢を通してアルブミンの一部を除去することにより、多くの研究者ウィンドウの鶏の卵。卵黄の上に位置する胚は、その後、卵の下位に位置します。これは、エレクトロポレーションのようないくつかの技術のために有利であるが、胚の外科的処置が所望される場合に不利であることができます。我々は可能な限り卵の開口部に近いが利点であるとして、胚を持つ見つけます。
質問は、脊椎動物の肢芽の誘導と開始を制御する信号についてのままであり、以下のプロトコルは、それらに対処するのに適しています。私たちは、早い段階12 8より段階でニワトリ肢芽の伸長を防止するための障壁を挿入するためのプロトコルを開発する最初のものです。これらのプロトコルの修正版もアクセス可能な誘導組織が誘導されている原基に隣接している誘導性手がかりの起源とタイミング上の他の質問に対処するために使用することができました。胚の領域は、関連する発達段階でのアクセスが設けられて、その後、バリアは2つの組織の間に配置することができ、開発における必然的な変化を研究しました。例としては、脳の発達、軸延長や、肝臓や腎臓の誘導のような可能性の臓器の開発に見ることができます。
We describe the use of impermeable barriers to prevent limb bud formation in the chick embryo. This technique has a number of critical steps. Following preliminary experiments, we found that the hinge shaped barriers used in 9, 10 remain in place in the embryo far better than straight barriers. The distal flat side of the barrier sticks to the vitelline membrane and keeps the barrier in place (Figure 2C'). Careful preparation of hinge shaped barriers from aluminum foil as described in protocol step 1.6 is essential to the success of the operation. A second important step is to ensure that eggs are not left out of the incubator for too long following windowing and staging prior to operating on the embryo. In our experience, embryos survive an operation better if they are at or near incubation temperature when the operation is carried out. Operations should therefore be carried out as quickly as possible and the eggs resealed promptly to ensure good survival rates. Many researchers add a drop of antibiotics to the embryo following microsurgery before returning the eggs to the incubator. The presence of the liquid prevented the barriers from sticking well in position. Addition of antibiotic could also dislodge beads after placement. Therefore not using antibiotics, swift operations and good cleanliness with instruments is recommended to avoid infection. Wiping instruments with 70% ethanol following every stage of an operation is essential to prevent instruments from becoming sticky from contact with the vitelline membrane which can cause both barriers or beads to adhere to forceps (see protocol step 3.1.2.2). Both varieties of beads used could fall out of place following the operation. When the barrier position was checked the next day it was not possible to see through the barrier to ascertain whether the bead remained in place or not. In cases where the bead had fallen out wing bud outgrowth was not rescued (Table 1). Avoiding transferring liquid with the bead when implanting them means that beads stick more easily to the cut face of the LPM (see protocol 2.3.2.3). Finally ensuring that embryos are fixed immediately after harvesting is critical to good subsequent gene expression analysis (see protocol step 4.2).
This protocol modifies previously published experiments that used barriers to prevent limb bud initiation, defines specific optimum widths for barriers and introduces combining barrier and bead placement followed by gene expression analysis. We found using conventional aluminum foil, which is cheap and readily available in all labs, produces outcomes equal to those that previously used tantalum foil. The foil can be left in the embryo when carrying out in situ hybridization (Figure 2C') but we usually remove it if more than one embryo is being processed to prevent the sharp edges of the foil damaging embryos. Pilot studies demonstrated that the width of leg region barriers is particularly important. Initially the barriers trialed were too short and leg bud outgrowth was not prevented. 1.2-1.3 mm is the optimum width for a barrier to block leg bud outgrowth completely. The narrowest wing barriers that one can place accurately to prevent bud outgrowth give the best survival rates. This can be as narrow as 0.5-0.7 mm. However, barriers that are a little wider are more likely to result in complete blocking of wing bud outgrowth because they allow for a little inaccuracy of placement (we used 0.7-1 mm). Avoidance of blood vessels when making the incision is critical for wing bud level barriers. Semi-permeable barriers have previously been used to bisect the chick limb bud. MacCabe and Parker, 1976 and Summerbell, 1979 both used filters 0.45 µm and 0.8 µm pore size, respectively 16, 17. They reported that diffusible signals could pass through the pores in the filters and that results gained using semi-permeable barriers were midway between a limb bud with no barrier present and one with an impermeable tantalum foil barrier. This protocol could be adapted to use semi-permeable barriers of varying pore size to differentiate candidate signals based on size or to modify the dynamics of signal diffusion.
This protocol has various limitations mainly associated with the model organism itself. Such techniques could be used to probe further questions in limb development and also other questions of vertebrate embryogenesis. A proviso is that the organ/area in question should be developing when the chick embryo is accessible to intervention. The presence of large blood vessels in the area where a barrier needs to be placed makes barrier placement later than stage 13 or 14 technically challenging. If large blood vessels are cut during barrier placement this can cause embryo mortality. Our investigation of when the transcription factors Tbx5 and Tbx4 are first induced in the LPM was limited by the earliest stage at which we could place a barrier that would later end up opposite either the wing or leg bud respectively. It could be illuminating to attempt to block Tbx gene induction at earlier stages, closer to gastrulation. The earliest a barrier could be placed in the presumptive wing region successfully was stage 8 and in the leg region stage 10. This protocol is probably not suitable for the study of gene expression beyond limb bud stages because subsequent rapid growth would displace the barrier and results would relate only to the initial position of the barrier.
Having related the limitations of the chick embryo in this context, its advantages over other vertebrate model organisms are many. The chick embryo is a very suitable animal model for this type of physical intervention in a vertebrate embryo. The embryos are relatively large and are easily accessible through the eggshell. One can return to the embryo for further experimentation (e.g., the removal of a bead 18 or even a barrier) or to check on progress by simply removing the tape window. There is possible scope to include live imaging or time lapse imaging. We describe a method of windowing chicken eggs that is particularly suited to operating on early stage embryos. In the case of limb studies it is very important and helpful that there is a contralateral control limb for every experiment that serves as an ideal internal control for each biological replicate.
The combination of using impermeable barriers to prevent limb outgrowth and beads soaked in signaling molecules has not been reported before. Our analysis of mRNA expression following such interventions is also novel. These techniques enabled us to dissect the difficult problem of when limb specific transcription factors Tbx5 and Tbx4 are induced in the LPM and also to show that later, prior to limb bud initiation, the presence of these Tbx genes in the LPM is not sufficient for the activation of Fgf10 transcription and the start of limb bud outgrowth. Figures 2G, 2D and 2E illustrate these findings well. The absence of Tbx4 expression following the insertion of a barrier at stage 10 in Figure 2G is in stark contrast to its presence in 2D and 2E following barrier insertion at stage 15, after the induction of Tbx4. The implantation of RA soaked beads facilitated the rescue of limb bud initiation following barrier insertion and so points to RA from the somites being essential in the LPM before limb bud outgrowth can begin. Such techniques could be used to solve further questions in limb development but also other questions of vertebrate embryogenesis. Areas of the brain, eye and trunk are likely to be suitable.
The authors have nothing to disclose.
This work was funded by MRC grant MC.PC_13052.
Dumont No.5 watchmakers forceps, x2 | Fine Science Tools www.finescience.de | 11251-20 | |
Dumont No.4 watchmakers forceps, x2 | Fine Science Tools www.finescience.de | 11241-30 | |
Dumont strong forceps, type AA | Fine Science Tools www.finescience.de | 11210-10 | |
Curved scissors with blades 2.5 cm long | Fine Science Tools www.finescience.de | 14061-11 | |
Blunt ended curved forceps, | Fine Science Tools www.finescience.de | 11065-07 | |
ends approx 0.5 cm long | |||
Steel pin, 0.2 mm wide | Fine Science Tools www.finescience.de | 26002-20 | |
Sharpening stone, square | Fine Science Tools www.finescience.de | 29008-01 | |
Mineral oil | |||
Needle holder | Fine Science Tools www.finescience.de | 26016-12 | |
Clear tape, 50 mm x 66 m | www.5staroffice.com | 295985 | |
FGF4 protein | A gift from Cliff Tabin. | ||
all-trans-retinoic acid | Sigma www.sigmaaldrich.com | R2625-50MG | Remember to protect from light. |
BMS 493 | Sigma www.sigmaaldrich.com | B6688-5MG | |
Scalpel blade No. 15 | www.swann-morton.com | cat no. 0105 | |
Affi-Gel Blue, affinity chromatography gel | Bio-Rad www.bio-rad.com | 153-7301 | Beads for delivering protein. |
AG1-X2 Ion exchange resin | Bio-Rad www.bio-rad.com | 140-1251 | Beads for delivering RA or BMS 493. |
Incubator for eggs | Memmert www.hce-uk.com | LAB128 | |
Paraformaldehyde (PFA) | Sigma www.sigmaaldrich.com | P6148-1KG | Harmful, irritant, corrosive. Handle powder in fumehood with full protective clothing. |
Ethanol | Sigma www.sigmaaldrich.com | 32221-2.5L | |
DMEM, high glucose | Gibco www.thermofisher.com | 41965-039 | 500ml |
Dimethyl sulfoxide (DMSO) | Fisher Scientific webshop.fishersci.com | D/4121/PB08 | 500ml |
Binocular Microscope | Leica www.leica-microsystems.com | MZ6 | Replaced by M60 |
Chicken eggs | Henry Stewart & Co Ltd sales@medeggs.com | Brown Eggs |