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Method Article
This paper introduces the method of developing, characterizing, and tracking in real-time the tumor metastasis in zebrafish model of neuroblastoma, specifically in the transgenic zebrafish line with overexpression of MYCN and LMO1, which develops metastasis spontaneously.
Zebrafish has emerged as an important animal model to study human diseases, especially cancer. Along with the robust transgenic and genome editing technologies applied in zebrafish modeling, the ease of maintenance, high-yield productivity, and powerful live imaging altogether make the zebrafish a valuable model system to study metastasis and cellular and molecular bases underlying this process in vivo. The first zebrafish neuroblastoma (NB) model of metastasis was developed by overexpressing two oncogenes, MYCN and LMO1, under control of the dopamine-beta-hydroxylase (dβh) promoter. Co-overexpressed MYCN and LMO1 led to the reduced latency and increased penetrance of neuroblastomagenesis, as well as accelerated distant metastasis of tumor cells. This new model reliably reiterates many key features of human metastatic NB, including involvement of clinically relevant and metastasis-associated genetic alterations; natural and spontaneous development of metastasis in vivo; and conserved sites of metastases. Therefore, the zebrafish model possesses unique advantages to dissect the complex process of tumor metastasis in vivo.
Zebrafish has been widely used and applied to several areas of research, especially in cancer. This model provides many advantages-such as its robust reproduction, cost-effective maintenance, and versatile visualization of tumor growth and metastasis-all of which make zebrafish a powerful tool to study and investigate the cellular and molecular bases of tumorigenesis and metastasis. New techniques for large-scale genome mapping, transgenesis, genes overexpression or knockout, cell transplantation, and chemical screens have immensely augmented the power of the zebrafish model1. During the past few years, many zebrafish lines have been developed to study tumorigenesis and metastasis of a variety of human cancers, including but not limited to leukemia, melanoma, rhabdomyosarcoma, and hepatocellular carcinoma2,3,4,5. Additionally, the first zebrafish model of neuroblastoma (NB) was generated by overexpressing MYCN, an oncogene, in the peripheral sympathetic nervous system (PSNS) under control of the dopamine-beta-hydroxylase (dβh) promoter. With this model, it was further demonstrated that activated ALK can synergize with MYCN to accelerate tumor onset and increase tumor penetrance in vivo6.
NB is derived from the sympathoadrenal lineage of the neural crest cells, and is a highly metastatic cancer in children7. It is responsible for 10% of pediatric cancer-related deaths8. Widely metastasized at diagnosis, NB can be clinically presented as tumors primarily originating along the chain of the sympathetic ganglia and the adrenal medulla of PSNS9,10. MYCN amplification is commonly associated with poor outcomes in NB patients11,12. Moreover, LMO1 has been identified as a critical NB susceptibility gene in high-risk cases13,14. Studies found that the transgenic coexpression of MYCN and LMO1 in the PSNS of the zebrafish model not only promotes earlier onset of NB, but also induces widespread metastasis to the tissues and organs that are similar to sites commonly seen in patients with high-risk NB13. Very recently, another metastatic phenotype of NB has also been observed in a newer zebrafish model of NB, in which both MYCN and Lin28B, encoding an RNA binding protein, are overexpressed under control of the dβh promoter16.
The stable transgenic approach in zebrafish is often used to study whether overexpression of a gene of interest could contribute to the normal development and disease pathogenesis14,15. This technique has been successfully used to demonstrate the importance of multiple genes and pathways to NB tumorigenesis6,16,17,18,19,20. This paper will introduce how the transgenic fish line that overexpresses both MYCN and LMO1 in the PSNS was created and how it was demonstrated that the cooperation of these two oncogenes accelerate the onset of NB tumorigenesis and metastasis13. First, the transgenic line that overexpresses EGFP-MYCN under control of the dβh promoter (designated MYCN line) was developed by injecting the dβh-EGFP-MYCN construct into one-cell stage of wild-type (WT) AB embryos, as previously described6,17. A separate transgenic line that overexpresses LMO1 in the PSNS (designated LMO1 line) was developed by coinjecting two DNA constructs, dβh-LMO1 and dβh-mCherry, into WT embryos at the one-cell stage13. It has been previously demonstrated that coinjected double DNA constructs can be cointegrated into the fish genome; therefore, LMO1 and mCherry are coexpressed in the PSNS cells of the transgenic animals. Once the injected F0 embryos reached sexual maturity, they were then out-crossed with WT fish for the identification of positive fish with transgene(s) integration. Briefly, the F1 offspring were first screened by fluorescent microscopy for mCherry expression in the PSNS cells. The germline integration of LMO1 in mCherry-positive fish was further confirmed by genomic PCR and sequencing. After successful identification of each transgenic line, the progeny of heterozygous MYCN and LMO1 transgenic fish were interbred to generate a compound fish line expressing both MYCN and LMO1 (designated MYCN;LMO1 line). Tumor-bearing MYCN;LMO1 fish were monitored by fluorescent microscopy biweekly for the evidence of metastatic tumors in the regions distant to the primary site, interrenal gland region (IRG, zebrafish equivalent of human adrenal gland)13. To confirm the metastasis of tumors in MYCN;LMO1 fish, histological and immunohistochemical analyses were applied.
All research methods using zebrafish and animal care/maintenance were performed in compliance with the institutional guidelines at Mayo Clinic.
1. Preparation and microinjection of transgene constructs for the development of LMO1 transgenic zebrafish line with overexpression in PSNS
2. Screen and verify LMO1 transgenic fish line for germline transmission of LMO1 and mCherry
3. Outcross of LMO1 and MYCN transgenic lines to create metastatic model
4. Visualizing tumor burden in transgenic zebrafish lines
5. Tissue processing and paraffin sectioning of tumor-bearing fish
NOTE: Perform this step to characterize the spontaneously developed primary and/or metastatic tumors in MYCN and MYCN;LMO1 transgenic fish.
6. Hematoxylin and eosin (H&E) staining of paraffin sections for pathology review
7. Immunohistochemical Analysis (IHC) with antibodies against NB marker and overexpressed transgenes to further confirm the spread of tumor and their sympathoadrenal lineage property
8. Picrosirius red staining of paraffin slides for collagen accumulation in tumors as mechanism study
To determine whether LMO1 synergizes with MYCN to affect NB pathogenesis, transgenic constructs that drive expression of either LMO1 (dβh:LMO1 and dβh:mCherry) or MYCN (dβh:EGFP-MYCN) in the PSNS cells under control of the dβh promoter were injected into zebrafish embryos13. As illustrated in Figure 1A, after the development of stable transgenic lines and validation of their ge...
Zebrafish has been commonly used in research for the past few decades, especially in cancer research, for obvious reasons, such as its ease of maintenance, robust reproduction, and clear advantages for in vivo imaging1,28. The zebrafish model can be easily manipulated embryonically due to their external fertilization and development, which complements well to mammalian model organisms, such as rats and mice, for large-scale genetic studies
The authors declare that they have no competing financial interests.
This work was supported by a grant R01 CA240323 (S.Z.) from the National Cancer Institute; a grant W81XWH-17-1-0498 (S.Z.) from the United States Department of Defense (DoD); a V Scholar award from the V Foundation for Cancer Research (S.Z.) and a Platform Grant from the Mayo Center for Biomedical Discovery (S.Z.); and supports from the Mayo Clinic Cancer Center and Center for Individualized Medicine (S.Z.).
Name | Company | Catalog Number | Comments |
3,3’-Diaminobenzidine (DAB) Vector Kit | Vector | SK-4100 | |
Acetic Acid | Fisher Scientific / Acros Organic | 64-19-7 | |
Agarose GP2 | Midwest Scientific | 009012-36-6 | |
Anti-Tyrosine Hydroxylase (TH) Antibody | Pel-Freez | P40101 | |
Avidin/Biotin Blocking Kit | Vector | SP-2001 | |
BOND Intense R Detection | Leica Biosystems | DS9263 | |
BOND primary antibody diluent | Leica Biosystems Newcastle, Ltd. | AR9352 | |
BOND-MAX IHC instrument | Leica Biosystems Newcastle, Ltd. | N/A | fully automated IHC staining system |
CH211-270H11 BAC clone | BACPAC resources center (BRFC) | N/A | |
Compound microscope equipped with DP71 camera | Olympus | AX70 | |
Cytoseal XYL (xylene based mounting medium) | Richard-Allan Scientific | 8312-4 | |
Eosin | Leica | 3801601 | ready-to-use (no preparation needed) |
Ethanol | Carolina | 86-1263 | |
Expand Long Template PCR System | Roche Applied Science, IN | 11681834001 | |
Gateway BP Clonase II enzyme mix | Invitrogen, CA | 11789-020 | |
Gateway LR Clonase II enzyme mix | Invitrogen, CA | 11791-100 | |
Goat anti-Rb secondary antibody (Biotinylated) | Dako | E0432 | |
Hematoxylin Solution, Harris Modified | Sigma Aldrich Chemical Company Inc. / SAFC | HHS-32-1L | |
HRP Avidin D | Vector | A-2004 | |
Hydrochloric Acid | Aqua Solutions | 4360-1L | |
Hydrogen Peroxide, 3% | Fisher Scientific | H324-500 | |
I-SceI enzyme | New England Biolabs, MA | R0694L | |
Kanamycin sulfate | Teknova, Inc. | K2150 | |
Kimberly-Clark Professional Kimtech Science Kimwipes | Fisher Scientific | 34133 | |
Lithium Carbonate | Sigma Aldrich Chemical Company Inc. / SAFC | 554-13-2 | |
Microtome for sectioning | Leica Biosystems | RM2255 | |
One Shot TOP10 Chemically Competent E. coli | Invitrogen | C404006 | |
p3E-polyA | Dr. Chi-Bin Chien, Univ. of Utah | N/A | a generous gift (Please refer to webpage http://tol2kit.genetics.utah.edu/index.php/Main_Page to obtain material, which is freely distrubted as described.) |
Parafin wax | Surgipath Paraplast | 39603002 | Parrafin to parafin |
Paraformaldehyde | Alfa Aesar | A11313 | |
pDEST vector (modified destination vector containing I-SceI recognition sites) | Dr. C. Grabher, Karlsruhe Institute of Technology, Karlsruhe, Germany | N/A | a generous gift |
pDONR 221 gateway donor vector | Thermo Fisher Scientific | 12536-017 | |
pDONRP4-P1R donor vector | Dr. Chi-Bin Chien, Univ. of Utah | N/A | a generous gift |
Phenol red, 0.5% | Sigma Aldrich | P0290 | |
Phosphate Buffered Saline (PBS), 10X | BioRad | 1610780 | |
Picrosirrius red stain kit | Polysciences | 24901-250 | |
pME-mCherry | Addgene | 26028 | |
Proteinase K, recombinant, PCR Grade | Roche | 21712520 | |
QIAprep Spin MiniPrep Kit | Qiagen | 27104 | |
RDO Rapid Decalcifier | Apex Enginerring | RDO04 | |
Sodium Azide (NaN3) | Sigma Aldrich | 26628-22-8 | |
Stereo fluorescence microscope | Leica | MZ10F | |
Stereoscopic fluorescence microscope equipped with a digital sight DS-U1 camera for imaging | Nikon | SMZ-1500 | |
Taq DNA Polymerase | New England Biolabs, MA | M0273L | |
Tissue-Tek VIP® 6 AI Vacuum Infiltration Processor | Sakura | N/A | Model #: VIP-6-A1 |
Tricaine-S | Western Chemical Incorporated | 20513 | |
Xylene | Thermo Fisher Scientific | X3P1GAL |
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