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* These authors contributed equally
Corals create biodiverse ecosystems important for both humans and marine organisms. However, we still do not understand the full potential and function of many coral cells. Here, we present a protocol developed for the isolation, labeling, and separation of stony coral cell populations.
Coral reefs are under threat due to anthropogenic stressors. The biological response of coral to these stressors may occur at a cellular level, but the mechanisms are not well understood. To investigate coral response to stressors, we need tools for analyzing cellular responses. In particular, we need tools that facilitate the application of functional assays to better understand how cell populations are reacting to stress. In the current study, we use fluorescence-activated cell sorting (FACS) to isolate and separate different cell populations in stony corals. This protocol includes: (1) the separation of coral tissues from the skeleton, (2) creation of a single cell suspension, (3) labeling the coral cells using various markers for flow cytometry, and (4) gating and cell sorting strategies. This method will enable researchers to work on corals at the cellular level for analysis, functional assays, and gene expression studies of different cell populations.
Coral reefs are one of the most important ecosystems on Earth. They facilitate biodiversity by providing critical habitats for fish and invertebrates and are crucial for sustaining anthropogenic communities by providing food and economic livelihood through tourism1. As the key builder of coral reefs, the coral animal (Phylum: Cnidaria) also aids coastal communities by creating large calcium carbonate frameworks that mitigate wave and storm damage2.
Corals as adults are sessile animals that host a wide array of endosymbiotic partners, including viruses, archaea, bacteria, protists, fungi, and most notably, members of the algal dinoflagellate family Symbiodiniaceae3. Changes in the environment can cause imbalances in this community, often leading to disease outbreaks and coral bleaching in which the symbiotic Symbiodiniaceae are expelled from the coral colony, thus eliminating the major source of nutrition for the coral. Both of these scenarios often cause death of the coral host4,5,6. Effects of anthropogenic-induced stressors, such as rapid climate change, are accelerating mass coral death events, leading to a global decline of coral reefs7.
Recently, many different methods have been developedto help mitigate coral reef loss. These methods includeoutplanting of corals on existing reefs, genetic crossing using thermally tolerant genotypes, and cellular manipulation of the microbial and symbiotic communities hosted within the coral8,9. Despite these efforts, much remains unknown about coral cell diversity and cell function10,11,12,13. A thorough understanding of coral cell type diversity and cell function is necessary to understand how the coral organism behaves under normative and stressful conditions. Efforts to maximize restoration and preservation efficiency will benefit from an enhanced understanding of how cell diversity and gene function are coupled.
Previous work on cell diversity and function has primarily focused on histological studies and whole-tissue RNA sampling14,15,16,17. To obtain greater detail on specific cell type function in corals, there need to be methods for the isolation of specific populations of live coral cells. This has been done successfully in nonclassical model organisms by means of fluorescence-activated cell sorting (FACS) flow cytometry technology18. FACS utilizes a combination of lasers tuned to varying wavelengths to measure different endogenous cellular properties at the single cell level such as relative cell size, cell granularity, and autofluorescence. Additionally, the cells may be marked by fluorescently labeled compounds to measure specific, desired properties18,19.
Thus far, the application of flow cytometry to coral cells has mainly been for the analysis of symbiotic Symbiodiniaceae and other bacterial populations by utilizing their strong, natural autofluorescence20,21,22. FACS has also been used to estimate coral genome size by using fluorescent DNA marker signal compared against reference model organism cells23,24. The efficient application of FACS provides three distinct tools that are useful for cell biology studies: 1) morphological and functional description of single cells; 2) identification, separation, and isolation of specific cell populations for downstream studies; and 3) the analysis of functional assays at the single cell level.
The development and application of various exogenous fluorescent markers for the study of coral cells remains almost unexplored. Such markers may include tagged proteins, tagged substrates for enzymes, or fluorescent responses to other compounds. These markers can be used to identify cell types that have unique properties, such as highlighting cells that produce varying amounts of a specific cellular compartment feature, like lysosomes. An additional example is the use of fluorescently labeled beads to functionally identify cells competent for phagocytosis, or the engulfment of a targeted pathogen25. Populations of cells active in immunity responses can be easily identified by FACS after engulfment of these exogenously applied beads. While traditional histological methods require preserved tissue and many hours to approximate the percentage of cells positive for bead engulfment, a FACS-based functional assay for pathogen engulfment can be performed relatively quickly on isolated live cells. In addition to studying cell-specific responses to stress, this technology has the potential to clarify gene-specific expression and illuminate the evolutionary and developmental history of cell types entirely unique to cnidarians, such as calicoblasts and cnidocytes.
Recently, we performed an intensive screening of over 30 cellular markers that resulted in identifying 24 that are capable of labeling coral cells, 16 of which are useful for distinguishing unique populations18, making them clusters of differentiation (CD). Here we describe the process of coral cell isolation in Pocillopora damicornis from removing cells from the calcium carbonate skeleton to the identification and isolation of specific cell populations with FACS (Figure 1).
1. Dissociation of tissues from coral skeleton via airbrush and compressor
NOTE: Perform steps on ice and protect hands with gloves.
2. Dissociation of cells from coral tissue
NOTE: Perform all steps on ice and protect hands with gloves.
3. Cell staining
NOTE: Perform all steps on ice and protect hands with gloves. Stains featured in this protocol are for representation purposes. Alternative stains will require different concentrations and incubation times.
4. FACS startup
NOTE: The steps may vary according to the make and model of the cytometer due to differences in the lasers and channels. For this protocol, a cytometer with 405, 488, 535, and 640 nm wavelength lasers was used. Filters featured in this protocol are for representation purposes. Alternative cell stains may require a different set of filters and lasers.
5. FACS gating setup
NOTE: Steps may vary according to make and model of the cytometer and the acquisition program coupled with the cytometer.
6. FACS analysis and cell isolation
NOTE: Steps may vary according to the make and model of the cytometer and the coupled acquisition program.
7. FACS sorting and collection
NOTE: Steps may vary according to make and model of the cytometer and the acquisition program coupled with the cytometer.
Overall, this protocol is useful because it facilitates the identification and collection of live coral cell populations that can be used for functional analyses. The workflow started with the mechanical separation of coral tissues from the underlying calcium carbonate skeleton (Figure 1). This is one of the most important initial steps because improper technique results in high cell mortality and can create large amounts of debris. Enzymatic separation is no...
This protocol was adapted from Rosental et al.18 and developed for the identification and isolation of P. damicornis cells. The methodology focuses on the process of filtering samples to remove debris, nonviable cells, and Symbiodiniaceae-hosted cells through the examination of cell intrinsic factors, including relative cell size, relative cell granularity, cell autofluorescence, and the presence of intact cellular membranes. These techniques can be applied to other coral species. However...
The authors have nothing to disclose.
NTK would like to acknowledge the University of Miami Research Awards in Natural Sciences and Engineering for funding this research. BR would like to thank Alex and Ann Lauterbach for funding the Comparative and Evolutionary Immunology Laboratory. The work of BR was supported by Israel Science Foundation (ISF) numbers: 1416/19 and 2841/19, and HFSP Research Grant, RGY0085/2019. We would like to thank Zhanna Kozhekbaeva and Mike Connelly for technical assistance. We would also like to thank the University of Miami, Miller School of Medicine’s Flow Cytometry Shared Resource at the Sylvester Comprehensive Cancer Center for access to the FACS cytometer and to Shannon Saigh for technical support.
Name | Company | Catalog Number | Comments |
Airbrush Kit & Compressor | TCP Global | ABD KIT-H-SET | Paasche H Series Single-Action Siphon Feed Airbrush Kit with Master TC-20 Compressor & Air Hose |
BD FACSAria II | BD | 644832 | |
Bone Cutters | Bulk Reef Supply | 205357 | Oceans Wonders Coral Stony Bone Cutter |
Cell Strainer | Corning | 352340 | 40 um; BD Falcon; individually wrapped; sterile; nylon |
CellRox Green | Life Technologies | C10444 | 2.5 mM in DMSO; Excitation/Emission: 485/520 nm |
Collection bag | Grainger | 38UV35 | Reloc Zippit 6"L x 4"W Standard Reclosable Poly Bag with Zip Seal Closure, Clear; 2 mil Thickness |
DAPI | Invitrogen | D1306 | 10mg in H2O; Excitation/Emission: 358/461 nm |
Fetal Calf Serum | Sigma-Aldrich | F2442-100ML | Heat-inactivated at 57 °C for 30 minutes |
Hemacytometer | Sigma-Aldrich | Z359629 | Bright-Line Hemacytometer |
HEPES Buffer | Sigma-Aldrich | H0887 | |
LysoTracker Deep Red | Life Technologies | L12492 | 1mM in DMSO; Absorption/Emission: 647/668 nm |
Microcentrifuge tubes | VWR | 87003-294 | 1.7 mL |
Phophate Buffered Saline (PBS) | Gibco | 70011-044 | pH 7.4; 10X |
Round-bottom tubes | VWR | 352063 | 5 mL Polypropylene Round-Bottom Tube |
Syringe | BD | 309628 | 1 mL BD Luer-Lok Syringe sterile, singe use polycarbonate |
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