We present a protocol for capturing the dynamics of zebrafish larval tail fin regeneration on a whole-tissue scale using brightfield-based stereomicroscopy. This technique enables capturing the regeneration dynamics with single cell resolution. This methodology can be adapted to any stereomicroscope equipped with a CCD camera and time-lapse software.
The zebrafish larval tail fin is ideal for studying tissue regeneration due to the simple architecture of the larval fin-fold, which comprises of two layers of skin that enclose undifferentiated mesenchyme, and because the larval tail fin regenerates rapidly within 2-3 days. Using this system, we demonstrate a method for capturing the repair dynamics of the amputated tail fin with time-lapse video brightfield stereomicroscopy. We demonstrate that fin amputation triggers a contraction of the amputation wound and extrusion of cells around the wound margin, leading to their subsequent clearance. Fin regeneration proceeds from proximal to distal direction after a short delay. In addition, developmental growth of the larva can be observed during all stages. The presented method provides an opportunity for observing and analyzing whole tissue-scale behaviors such as fin development and growth in a simple microscope setting, which is easily adaptable to any stereomicroscope with time-lapse capabilities.
The ability of an organism to orchestrate tissue repair processes after injury is crucial for its survival 1. While all animals have the capacity to heal their wounds, the extent to which tissues regenerate differs greatly among species. Vertebrate species such as zebrafish, salamanders and frog tadpoles have the remarkable ability to regenerate lost tissues, including their appendages, portions of their eyes, heart, and central nervous system 2-4. Mammalian species, such as the African spiny mouse and rabbits, are capable of regenerating holes in their pinnae 5-7, and humans and mice regenerate portions of their liver as well as their digit tips during fetal and juvenile stages 8-12. Although it is not well understood yet why and how certain species regenerate tissues more effectively than others, the presence of similar genetic pathways suggests that these mechanisms may lie dormant in species without great regeneration potential 13,14. Thus elucidating tissue repair and regeneration mechanisms in species with satisfactory regeneration outcomes will benefit regeneration in humans.
We have chosen the larval zebrafish tail fin as a paradigm to demonstrate its regeneration with time-lapse brightfield stereomicroscopy. The zebrafish larval tail fin is anatomically simple as compared to the more complex adult structures, consisting of a two-layered, infolded epithelium with somatosensory axons innervating the skin that surrounds medially located mesenchymal cells 15. Despite the anatomical differences, larval tail fin regeneration is somewhat comparable to adult fin regeneration in terms of the molecular signatures and the outgrowth responses 16,17. As compared to the adult fin, imaging larval tail fin regeneration has however several advantages: 1) larval fin regeneration is completed within just 2-3 days 16, 2) larvae can be mounted in low-melt agarose, and 3) larvae do not require feeding until ~ 5 days post fertilization (dpf) due to the presence of the yolk sac. This makes zebrafish larvae ideal for observing tissue repair dynamics in vivo.
The presented method enables the capture of detailed dynamics underlying the early processes of fin regeneration. Many studies have utilized fluorescence-based confocal microscopy to study cellular and subcellular biological processes in embryonic and larval zebrafish. Sophisticated confocal imaging setups are however often not accessible to everyone and highly expensive as compared to other imaging techniques. In contrast, the presented methodology utilizes a Discovery V12 stereomicroscope equipped with Axiovision software and a time-lapse module, thus providing a more affordable alternative to expensive imaging equipment to examine tissue behaviors. We demonstrate that this method can be utilized for imaging tissue regeneration with high temporal resolution at a minimal cost. The implications for this method could extend beyond basic biology to advance mammalian regeneration studies using organ cultures, for therapeutic development through pharmacological and genetic screens, and it can serve as a teaching tool in a classroom setting.
所提出的方法允许观察伤口愈合和组织再生中在明视显微镜活斑马鱼幼虫体内延时成像,使用相对简单的设置。这个过程需要我们已经测试过的某些重要方面,这将优化结果:1)低浓度琼脂糖(〜0.5%)将减少不断增长的幼虫斑马鱼的生长障碍,2)清除周围的散热片的琼脂糖重要的是不要模糊愈合过程,3)捕获在一个塑料网状琼脂糖保留在整个手术过程中稳定的位置琼脂糖和动物,以及4)一个适当的温度控制的环境中,这是幼虫存活必不可少的。我们已经适应加热的孵育室23,24,其利用正在录音到纸板泡沫包装,以及有线圆顶加热器来控制温度和适当的空气流通用在最小的波动成像过程。这个简单的和有成本效益室可以制备以适应任何显微镜。类似的温水孵化室也已用于成像老鼠和小鸡发展24,29。
我们建议预截去的幼虫被安装为一个预截肢图像,拆下截肢,和重新安装用于延时成像。虽然它是在最终的成像室中的单个步骤执行这些步骤是可行的,在我们的经验,我们发现,截肢尾鳍在玻璃盖玻片不是最佳的,因为它泪组织并且不会导致在一个干净的切口。用注射器针头琼脂糖为基础的截肢方法最初是由川和他的同事(2004)16中描述,也是在我们的经验,非常适合进行截肢。因此,在相当复杂的一系列步骤,我们介绍的是有充分理由的,并确保最佳的再生效果。
我们发现,larv人斑马鱼在2 DPF可以被成像到在琼脂糖和三卡因溶液1.5天。我们使用制备即时海洋盐,其不与试样的健康干扰对所呈现的成像期间的pH优化的三卡因(pH7的)解决方案。我们先前然而还证明了在Danieau介质使用三卡因允许在共聚焦显微镜对至少2天30 2.5延时成像DPF幼虫斑马鱼。因此,最佳的缓冲液条件可以延长幼虫健康和成像的长度。或者,可用于麻醉,或2-苯氧基乙醇,我们发现在幼虫和成虫阶段的耐受性良好,在28℃下进行至少60小时下三卡因的浓度。
为了避免在散热片再生的缺陷,我们删除从之前的成像尾鳍琼脂糖。我们的数据表明,在1.5天鳍已再生至约60%。这种再生率与以前的研究定义3天一致s的平均时间尾鳍再生的斑马鱼幼虫多达6 DPF 16。替代方法琼脂糖却可能被用来装鱼的成像。例如,等离子体细凝块31或氟化乙烯丙烯(FEP)管涂覆有甲基纤维素和填充有非常低的琼脂糖浓度(0.1%),已被建议用于光片镜32和可适合于我们提出的方法。然而,我们不推荐甲基纤维素和0.1%琼脂糖,因为它们需要该样品被安装在所述腔室的底部,由于缺乏这些介质的凝固。非常高浓度的甲基纤维素将另外产生根据我们的经验气穴,并且这些可以与成像过程产生干扰。如果这些媒体是优选使用的底腔,重要的是,在物镜和试样之间的适当的工作距离是否存在。应当注意的是,米乙基纤维素作为安装介质,建议只为1天,因为它可能与幼虫健康干预32。
安装在盖的检体可能会导致缓慢的引力向下漂移。因此,在每一个时间点,这可以被投影成一个单一的平面或仅是在焦平面可以提取用于组装最终电影图像推荐图像的多个部分。成像试样在底部室可以是一种替代方法,以避免潜在的向下漂移。血浆凝块可能是有用的,以避免漂移,作为等离子体会粘到外层包封层(EVL,周皮)31,因此,可以稳定的样品。然而,这需要进行测试,以及多久幼虫斑马鱼可以保持在血浆凝块而不与健康幼虫或鳍再生的干扰。
我们的电影是利用组装各个部分(26微米)的一个记录,Z堆叠,其覆盖所述鳍(〜10微米),并且在成像过程期间占鳍的潜在的z漂移的整个厚度。为了保留的3-D信息,但也可以突出的z栈成单个图像。因为这可能会导致在图像的模糊程度,明去卷积可以期望。软件,如反卷积或Autoquant X3可以被用于此目的。或者,数学算法(在Tadrous 33描述的)可被用于获得高的信号-噪声比(SNR)的点扩散函数。获得高信噪比表示在明解卷积的主要障碍之一。虽然这种方法需要高对比度和细样品的厚度,这将是适当的尾鳍的成像,由于其宽度减小。
所提出的成像方法的一个明显的优点是,它是快速适应装备有CCD照相机的任何立体显微镜ð时间推移软件,并提供一种低成本的替代更昂贵的共焦成像系统。虽然这种方法不使用荧光进行小区检测,它可以扩展为这样的应用,利用一种自动系统,用于快门控制和后摄像卷积软件34。这将使用户能够进一步的观察与单细胞或亚细胞分辨率创面的修复和再生过程在更长的时间段。
光学清晰度和缓解与胚胎和幼虫的斑马鱼可以处理了,这种方法对任何立体的适应能力使得它适合于教学的基本脊椎动物生物学课堂上。这种方法可以为学生提供一个更好地了解组织修复和再生背后的基本生物过程。已经捕获用类似的方法等生物学过程是斑马鱼胚胎发育23,34和心函数(未公布的)。这种方法还提供了可能性监测伤口修复和再生中的幼虫已进行遗传和药理学上操纵。
The authors have nothing to disclose.
We thank the MDI Biological Laboratory animal core service facility for zebrafish maintenance. Research reported in this publication was supported by Institutional Development Awards (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under grant numbers P20GM104318 (for COBRE) and P20GM103423 (INBRE) and Department of Defense – USAMRAA (W81XWH-BAA-1) grant.
Reagents | |||
Bullseye Agarose (MidSci, Cat. No. BE-GCA500) | |||
Low-melt agarose (Fisher BioReagents, Cat No. BP1360-100) | |||
1-phenyl-2-thiourea [Alfa Aesar, Cat No. L06690] | |||
Instant Ocean Aquarium Salt (Pet store) | |||
Methylene Blue (0.1% solution) (Sigma, Cat. No. M9140) | |||
Tricaine (Ethyl 3-aminobenzoate methanesulfonate, Sigma-Aldrich, Cat. No. E10505) | |||
2-Phenoxyethanol (Sigma-Aldrich, Cat. No. 77699) | |||
Petri Dish 35 x 15 mm (BD Falcon, Cat. No 351008) | |||
Petri Dish 60 x 15 mm (BD Falcon, Cat. No 351007) | |||
Petri Dish 100 x 25 mm (BD Falcon, Cat. No 351013) | |||
5.75 inch boroschillate glass pipets (Fisher) | |||
35 mm Glass Top Glass Bottom Dish (MatTek Corporation, Cat No. D35-20-0-TOP) Glass: 0.085-0.115mm | |||
Superfrost/Plus microscope slides (Fisherbrand, Cat No. 12-550-15) | |||
Glass coverslips (Electron Microscopy Services, Cat No. 72191-75) | |||
Glass coverslips (Warner Instruments, Cat. No. CS-18R15) | |||
Phifer Phiferglass Insect Screen Charcoal – 48" (Home Depot) | |||
DOW CORNING® HIGH VACUUM GREASE | |||
Microloader pipette tips 20 µl (Eppendorf, Cat. No. 930001007) | |||
Fine Scissors – Sharply Angled Up (Fine Science Tools, Cat. No. 14037-10) | |||
3 mL Luer-Lok™ disposable syringe (BD, Cat. No. 309657) | |||
60 mL Luer-Lok™ disposable syringe (BD, Cat. No. 309653) | |||
23-gauge syringe needles (BD, Cat. No. 305145) | |||
Dumont #5 Forceps (Fine Science Tools, Cat. No. 11295-00) | |||
Equipment | |||
LabDoctor Mini Dry Bath (MidSci) | |||
Zeiss Discovery.V12 compound microscope | |||
Zeiss Plan Apo S 3.5X objective | |||
Zeiss AxioCam MRm | |||
Zeiss Axiovision software, Release 4.8.2SP1 (12-2011) |