A Whole Mount In Situ Hybridization Method for the Gastropod Mollusc Lymnaea stagnalis
Summary
The goal of this protocol is to provide users with a set of methods for the high-throughput decapsulation of Lymnaea stagnalis embryos and larvae in preparation for whole mount in situ hybridization, and for subsequent pre- and post-hybridization treatments.
Abstract
Whole mount in situ hybridization (WMISH) is a technique that allows for the spatial resolution of nucleic acid molecules (often mRNAs) within a 'whole mount' tissue preparation, or developmental stage (such as an embryo or larva) of interest. WMISH is extremely powerful because it can significantly contribute to the functional characterization of complex metazoan genomes, a challenge that is becoming more of a bottleneck with the deluge of next generation sequence data. Despite the conceptual simplicity of the technique much time is often needed to optimize the various parameters inherent to WMISH experiments for novel model systems; subtle differences in the cellular and biochemical properties between tissue types and developmental stages mean that a single WMISH method may not be appropriate for all situations. We have developed a set of WMISH methods for the re-emerging gastropod model Lymnaea stagnalis that generate consistent and clear WMISH signals for a range of genes, and across all developmental stages. These methods include the assignment of larvae of unknown chronological age to an ontogenetic window, the efficient removal of embryos and larvae from their egg capsules, the application of an appropriate Proteinase-K treatment for each ontogenetic window, and hybridization, post-hybridization and immunodetection steps. These methods provide a foundation from which the resulting signal for a given RNA transcript can be further refined with probe specific adjustments (primarily probe concentration and hybridization temperature).
Introduction
Molluscs are a group of animals that hold the interest of a broad diversity of scientific disciplines. Despite their morphological diversity1, species richness (second only to the Arthropods in terms of species number2) and relevance to a wide range of commercial3, medical4 and scientific issues5-8, there are relatively few molluscan species that can claim to be both well-equipped scientific models and easy to maintain in a laboratory environment. One mollusc that is much used by disciplines such as neurobiology9, ecotoxicology10 and more recently evolutionary biology11,12, is Lymnaea stagnalis, primarily because of its widespread distribution and extreme ease of maintenance. Despite its popularity as a 'model' organism and its long history of use by developmental biologists13-19, the range and power of molecular tools available to the L. stagnalis scientific community lies far behind that of more traditional animal models (Drosophila, mouse, sea urchin, nematodes).
Our desire to develop Lymnaea as a molecular model stems from an interest in the molecular mechanisms that guide shell formation. This motivated us to refine a set of techniques that would allow for the efficient, consistent and sensitive visualization of gene expression during Lymnaea's development. Whole mount in situ hybridization (WMISH) is widely employed for a variety of model organisms and has been in use for more than 40 years 20. In its different guises, ISH can be employed to spatially localize specific loci on chromosomes, rRNA, mRNA and micro-RNAs.
One of the challenges we needed to address prior to refining a WMISH method for L. stagnalis was the issue of gently and efficiently extracting embryos and larvae of varying stages from the egg capsules in which they are deposited. This extraction, or 'decapsulation', needs to be achieved efficiently in order to collect adequate material for a given in situ experiment, while at the same time maintaining morphological and cellular integrity. While other model organisms also undergo encapsulated development, in our hands none of the methods reported for those species could be successfully employed in L. stagnalis.
The overall goals of this method are therefore: to extract L. stagnalis embryos and larvae from their capsules in a high-throughput fashion, to apply pre-hybridization treatments that optimize the WMISH signal, to prepare embryos and larvae with satisfactory WMISHsignals for imaging.
Protocol
Representative Results
Discussion
The method described here allows for the efficient visualization of RNA transcripts with presumably varying expression levels within all developmental stages of Lymnaea stagnalis. To remove embryos and larvae from their capsules we trialed a variety of chemical, osmotic shock and physical treatments reported for other encapsulated-developing model organisms. However, in our hands the method we describe here is the only high-throughput technique that removes the tough capsular membrane without damaging the embryo…
Divulgations
The authors have nothing to disclose.
Acknowledgements
This work was supported by funding to DJJ through DFG project #JA2108/2-1.
Materials
| Featherweight forceps | Ehlert & Partner | #4181119 | |
| Silicon tubing | Glasgerätebau OCHS GmbH | 760070 | |
| Glass capillaries | Hilgenberg | 1403547 | |
| 12 well tissue culture dishes | Carl Roth | CE55.1 | |
| 37% Formaldehyde | Carl Roth | P733.1 | CAUTION – May cause cancer. Toxic by inhalation, in contact with skin and if swallowed. Toxic: danger of very serious irreversible effects through inhalation, in contact with skin and if swallowed. |
| Ethylenediamine tetraacetic acid | Carl Roth | CN06.3 | CAUTION – CAUSES EYE IRRITATION. MAY CAUSE RESPIRATORY TRACT AND SKIN IRRITATION. Avoid breathing dust. Avoid contact with eyes, skin and clothing. Use only with adequate ventilation |
| Magnesium Chloride | Carl Roth | 2189.1 | |
| Tween-20 | Carl Roth | 9127.1 | CAUTION – May be harmful if inhaled. May cause respiratory tract irritation. May be harmful if absorbed through skin. May cause skin irritation. May cause eye irritation. May be harmful if swallowed. |
| Sodium Chloride | Carl Roth | 3957.1 | |
| Ficoll type 400 | Carl Roth | CN90.1 | |
| polyvinylpyrrolidone K30 (MW 40) | Carl Roth | 4607.1 | CAUTION – May be harmful if inhaled. May cause respiratory tract irritation. May be harmful if absorbed through skin. May cause skin irritation. May cause eye irritation. May be harmful if swallowed. |
| Nuclease freeBovine Serum Albumin | Carl Roth | 8895.1 | |
| Salmon sperm | Carl Roth | 5434.2 | |
| Heparin | Carl Roth | 7692.1 | CAUTION – ADVERSE EFFECTS INCLUDE HEMORRHAGE, LOCAL IRRITATION. POSSIBLE ALLERGIC REACTION IF INHALED, INGESTED/CONTACTED. EYES/SKIN/RESPIRATORY TRACT IRRITANT. POSSIBLE HYPERSENSITIZATION. DURING PREGNANCY HAS BEEN REPORTED TO INCREASE RISK OF STILLBIRTH |
| Proteinase-K | Carl Roth | 7528.1 | |
| Glycine | Carl Roth | 3790.2 | |
| Deionised formamide | Carl Roth | P040.1 | CAUTION – Irritating to eyes and skin. May be harmful by inhalation, in contact with skin and if swallowed. May cause harm to the unborn child. Hygroscopic. |
| Standard formamide | Carl Roth | 6749.3 | CAUTION – Irritating to eyes and skin. May be harmful by inhalation, in contact with skin and if swallowed. May cause harm to the unborn child. Hygroscopic. |
| Triethanolamine | Carl Roth | 6300.1 | CAUTION – Avoid breathing vapor or mist. Avoid contact with eyes. Avoid prolonged or repeated contact with skin. Wash thoroughly after handling. |
| Acetic anhydride | Carl Roth | 4483.1 | CAUTION – CAUSES SEVERE SKIN AND EYE BURNS. REACTS VIOLENTLY WITH WATER. HARMFUL IF SWALLOWED. VAPOR IRRITATING TO THE EYES AND RESPIRATORY TRACT |
| Maleic acid | Carl Roth | K304.2 | CAUTION – Very hazardous in case of eye contact (irritant), of ingestion, . Hazardous in case of skin contact (irritant), of inhalation (lung irritant). Slightly hazardous in case of skin contact (permeator). Corrosive to eyes and skin. |
| Benzyl benzoate | Sigma | B6630-250ML | CAUTION – May be harmful if inhaled. May cause respiratory tract irritation. May be harmful if absorbed through skin. May cause skin irritation. May cause eye irritation. Harmful if swallowed. |
| Benzyl alcohol | Sigma | 10,800-6 | CAUTION – Harmful if swallowed. Harmful if inhaled. Causes serious eye irritation. |
| Glycerol | Carl Roth | 3783.1 | |
| Blocking powder | Roche | 11096176001 | |
| Anti DIG Fab fragments AP conjugated | Roche | 11093274910 | |
| Tris-HCl | Carl Roth | 9090.3 | |
| 4-Nitro blue tetrazolium chloride in dimethylformamide | Carl Roth | 4421.3 | CAUTION – May cause harm to the unborn child. Harmful by inhalation and in contact with skin. Irritating to eyes. |
| 5-bromo-4-chloro-3-indolyl-phosphate | Carl Roth | A155.3 | CAUTION – Potentially harmful if ingested. Do not get on skin, in eyes, or on clothing. Potential skin and eye irritant. |
| N-acetyl cysteine | Carl Roth | 4126.1 | |
| Dithiothreitol | Carl Roth | 6908.1 | CAUTION – May cause eye and skin irritation. May cause respiratory and digestive tract irritation. The toxicological properties of this material have not been fully investigated. |
| Tergitol | Sigma | NP40S | CAUTION – May be harmful if inhaled. May cause respiratory tract irritation. May be harmful if absorbed through skin. May cause skin irritation. May cause eye irritation. May be harmful if swallowed. |
| Sodium dodecyl sulphate | Carl Roth | CN30.3 | CAUTION – Harmful if swallowed. Toxic in contact with skin. Causes skin irritation. Causes serious eye damage. May cause respiratory irritation. |
| Potassium Chloride | Carl Roth | 6781.1 | |
| di-Sodium hydrogen phosphate dihydrate (Na2HPO4.2H2O) | Carl Roth | 4984.1 | |
| Potassium dihydrogen phosphate (KH2PO4) | Carl Roth | 3904.1 | |
| Tri sodium citrate dihydrate (C6H5Na3O7.2H2O) | Carl Roth | 3580.1 | CAUTION – May cause eye, skin, and respiratory tract irritation. The toxicological properties of this material have not been fully investigated. |
| Mineral oil | Carl Roth | HP50.2 | |
| InSituPro-Vsi | Intavis | www.intavis.de/products/automated-ish-and-ihc |
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