We describe a method of generating a possible zebrafish model of polycystic kidney disease. We used Tg(wt1b:GFP) fish to visualize kidney structure. Knockdown of wnt5a was by morpholino injection. Pronephric cyst formation after wnt5a knockdown was observed in this GFP transgenic zebrafish.
Polycystic kidney disease (PKD) is one of the most common causes of end-stage kidney disease, a devastating disease for which there is no cure. The molecular mechanisms leading to cyst formation in PKD remain somewhat unclear, but many genes are thought to be involved. Wnt5a is a non-canonical glycoprotein that regulates a wide range of developmental processes. Wnt5a works through the planar cell polarity (PCP) pathway that regulates oriented cell division during renal tubular cell elongation. Defects of the PCP pathway have been found to cause kidney cyst formation. Our paper describes a method for developing a zebrafish cystic kidney disease model by knockdown of the wnt5a gene with wnt5a antisense morpholino (MO) oligonucleotides. Tg(wt1b:GFP) transgenic zebrafish were used to visualize kidney structure and kidney cysts following wnt5a knockdown. Two distinct antisense MOs (AUG – and splice-site) were used and both resulted in curly tail down phenotype and cyst formation after wnt5a knockdown. Injection of mouse Wnt5a mRNA, resistant to the MOs due to a difference in primary base pair structure, rescued the abnormal phenotype, demonstrating that the phenotype was not due to “off-target” effects of the morpholino. This work supports the validity of using a zebrafish model to study wnt5a function in the kidney.
Zebrafish (Danio rerio) embryos have been widely used as a model for studying kidney development and polycystic kidney disease. There are many advantages to using zebrafish as an animal model: the feasibility of studying genetic interactions, the ability to use antisense morpholinos (MO) for protein knockdown, the opportunity to quickly assay large numbers of embryos, and the ease of viewing organ phenotypes in living larvae 1. The pronephros is the first kidney to develop in vertebrates and is functional in larval zebrafish 2. The structure of the zebrafish pronephros is relatively simple compared to the mammalian metanephros, the third and final kidney to develop in mammals. The nephron is the working unit of the kidney, with each human kidney containing between 500,000-1,000,000 nephrons3,4 and each mouse kidney having approximately 13,000 nephrons5, making it difficult to observe single nephron structure in human or mouse kidneys. The zebrafish has only two nephrons, and each zebrafish nephron contains all the major components found in the glomerulus and tubules of mice and humans6and similar specialized renal cell types. Compared to other vertebrate models such as Xenopus, the zebrafish nephron more closely resembles the mammalian nephron because it has a closed system7.
In recent years, the zebrafish genome has been sequenced, allowing the wide introduction of genetic tools, extensive mutant resources, and collections of transgenic reporter lines in zebrafish models. The zebrafish pronephros forms between 12-72 hr post fertilization (hpf) and can be visualized easily in the transparent embryos. The Wilm’s tumor protein WT1 is an essential factor for kidney development. Transgenic zebrafish lines expressing green fluorescent protein (GFP) under the control of the wt1b promoter Tg(wt1b:GFP) show GFP expression specifically located in pronephric regions in zebrafish embryos, starting from 17 hpf 8. Nephronophthisis (NPHP), an autosomal recessive cystic kidney disease, is caused by mutations of NPHP genes 9. NPHP4 knockdown by morpholino caused cyst formation in the Tg(wt1b:GFP) fish. 10 Therefore, this transgenic fish is a suitable model for observing kidney structures and cyst formation during kidney development. Importantly, the influence of modulators of kidney development can be studied using this strain in a time and labor efficient manner.
Our paper describes the use of Tg(wt1b:GFP) fish as a model to visualize kidney cyst formation after gene modulation. We used start- and splice-site anti-sense MOs to knock down the wnt5a gene in zebrafish. Wnt5a is a non-canonical secreted glycoprotein of the Wnt family that plays an important role in the development of various organs and postnatal cellular function11. Wnt5a works through non-canonical Wnt pathways, including the planar cell polarity (PCP) pathway, which has been found to play a role in oriented cell division during renal tubular elongation. Wnt5a regulates the Wnt/PCP pathway by forming a complex with the receptor like tyrosine kinase (Ryk), which further transduces Wnt5a signaling by forming a complex with the VANGL planar cell polarity protein 2 (Vangl2), thereby promoting Vangl2 stability 12. Defects in the PCP pathway can result in random cell division and cause renal cyst formation. We used the Tg(wt1b:GFP) zebrafish line to observe kidney cyst formation following wnt5a knockdown. The Tg(wt1b:GFP) zebrafish model allows live imaging and timely observation of kidney structure. After wnt5a knockdown, kidney cyst formation was found beginning at 24 hpf; at 72 hpf, cysts could be found in the glomeruli and the proximal tubules. This method could also be used to screen other genes that might cause kidney cyst formation.
Polycystic kidney disease (PKD) is one of the leading causes of end-stage renal disease in humans and is characterized by progressive cyst formation, renal enlargement, and abnormal tubule development 14. Autosomal dominant PKD (ADPKD) is a genetic disease in which mutation of either PKD1, encoding polycystin-1 (PC1), or PKD2, encoding polycystin-2 (PC2), results in polycystic kidneys. Many other genes, especially those encoding proteins found in the primary cilium, are thought to be involved in the developmen…
The authors have nothing to disclose.
This work was supported by the NIH (DK093625 to L.H., and DK069909 and DK047757 to J.H.L.) and the VA (Merit Award I01BX000820 to J.H.L.). We would like to thank Dr. Michael Pack and Dr. Jie He at the University of Pennsylvania Zebrafish Core for providing essential support.
0.5% Phenol-Red | Sigma | P0290 | Color indicator for injection |
Morpholino | Genn Tools, LLC | (customized) | Customized designed to the gene of interest |
Pre-pulled needle | Tritech Research | MINJ-PP | If large amount of needle is required, you can also purchase a needle puller and prepare the needle in the lab |
T7 mMessage Kit | Ambion | 1344 | For in vitro transcription to make capped mRNA for rescue experiment |
N-Phenylthiourea | Sigma | P7629 | For prevention of melanization |
Tricaine | Sigma | A5040 | Also called ethyl 3-aminobenzoate, for zebrafish anesthesia |
Methyl Cellulose | Sigma | M-0387 | For position of zebrafish |
QIAquick PCR Purification Kit | Qiagen | 28104 | For purification of PCR product for cap RNA synthesis. |
dNTP mix | Promega | U1511 | For PCR |
Tag DNA Polymerase | Invitrogen | 10342-053 | For PCR |
Equipment | |||
NanoDrop sepctrophotometer | Thermo Scientific | ND-1000 | For measure morpholino and RNA concentration |
Air Compressor | Werther International, Inc. | Panther Compact 106 | Air source for injection |
Pico micro-injection pump | World Precision Instruments Inc | PV830 Pnematic PicoPump | Other types of microinjection system can be used. |
Micro-manuplator | World Precision Instruments Inc | MMJR | Right-handed (MMJL for left handed) |
Needle holder | World Precision Instruments Inc | 5430-ALL | To hold needle for micromanipulation |
Dumont Tweezers | Fine Surgical Tools | 11253-20 | For breaking off the needle tip |
Dissecting microscope | Leica M205C | For observing and imaging zebrafish embryos | |
Fluorscence microscope | Zeiss Axio Obserer D1m | For imaging zebrafish pronephros | |
Capillary tube (I.D 0.15 mm) | VitroCom | CV1525Q-100 | For measure the volume of each injected drop |