Published: August 31st, 2016
A novel technique for the detection of low abundance endogenous receptors present in zebrafish embryos is described. We have named it AFLIP because it consists of affinity labeling of the receptor by its ligand linked to immunoprecipitation.
By combining the powers of Affinity Labeling and Immunoprecipitation (AFLIP), a technique for the detection of low abundance receptors in zebrafish embryos has been implemented. This technique takes advantage of the selectivity and sensitivity conferred by affinity labeling of a given receptor by its ligand with the specificity of the immunoprecipitation. We have used AFLIP to detect the type III TGF-β receptor (TGFBR3), also know as betaglycan, during early zebrafish development. AFLIP was instrumental in validating the efficacy of a TGFBR3 morphant zebrafish phenotype. In the first step, embryo protein extracts are prepared and used to generate 125I-TGF-β2-TGFBR3 complexes that are purified by immunoprecipitation. Later, these complexes are covalently cross-linked and revealed using SDS-PAGE separation and autoradiography detection. This technique requires the availability of a labeled ligand for, and a specific antibody against, the receptor to be detected, and shall be easily adapted to identify any growth factor or cytokine receptor that meets these requirements.
Specific detection of proteins expressed during embryonic development is required to validate expression profiles obtained by measuring their cognate mRNAs with RT-PCR or in situ hybridization (ISH). This is commonly achieved by a western blot of embryo extracts followed by detection with specific antibodies. However, this approach is hard to apply to proteins that are in very low abundance, or that have properties that hamper their quantitative transfer during their blotting. Betaglycan, also known as the type III transforming growth factor β (TGF-β) receptor (TGFBR3), is an example of these difficulties. TGFBR3 is a part time membrane proteoglycan....
All experiments carried out in animals were approved by the Committee for Laboratory Animal Care and Use of the Autonomous National University of México (UNAM), under the CICUAL-Protocol number: FLC40-14. (CICUAL: "Comité Institucional para el Cuidado y Uso de los Animales de Laboratorio del Instituto de Fisiologìa Celular, Universidad Nacional Autònoma de México").
1. Preparation of Embryo Protein Extract
Figure 1 shows a representative result obtained with AFLIP. Signals in Lane 1 come from the 125I-ligand covalently linked to either the zebrafish betaglycan core protein (BG core, below the 150 kDa marker) or the BG core that has been processed to its proteoglycan form by attachment of glycosaminoglycans (GAG, smear ranging from 170 kDa to the top of the gel). This pattern of migration, a sharp core protein plus a smeared proteoglycan (due to heterogeneity in t.......
The use of Western blots with a specific antibody against a protein of interest is a valuable tool to study its expression7 during embryogenesis. However, immunoblotting of highly-glycosylated proteins has not been very successful due to their inefficient transfer and weak binding to nitrocellulose or PVDF membranes8,9.
Proteoglycans are a good example of this shortcoming, because of their covalently attached glycosaminoglycan chains (GAG) that are negatively charged and .......
The authors thank Gilberto Morales for fish care and maintenance, and Drs. Claudia Rivera and Hector Malagòn (IFC-UNAM Animal Facility) for their help in rabbit immunization. This work was supported by grants from CONACYT 131226 and PAPIIT-DGAPA-UNAM IN204916.....
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