Automated method for the isolation of collecting ducts

The structural and functional heterogeneity of the collecting duct present a tremendous experimental challenge requiring manual microdissection, which is time-consuming, labor intensive, and not amenable to high throughput. To overcome these limitations, we developed a novel approach combining the use of transgenic mice expressing green fluorescent protein (GFP) in the collecting duct with large-particle-based flow cytometry to isolate pure populations of tubular fragments from the whole collecting duct (CD), or inner medullary (IMCD), outer medullary (OMCD), or connecting segment/cortical collecting duct (CNT/CCD). Kidneys were enzymatically dispersed into tubular fragments and sorted based on tubular length and GFP intensity using large-particle-based flow cytometry or a complex object parametric analyzer and sorter (COPAS). A LIVE/DEAD assay demonstrates that the tubules were >90% viable. Tubules were collected as a function of fluorescent intensity and analyzed by epifluorescence and phase microscopy for count accuracy, GFP positivity, average tubule length, and time required to collect 100 tubules. Similarly, mRNA and protein from sorted tubules were analyzed for expression of tubule segment-specific genes using quantitative real-time RT-PCR and immunoblotting. The purity and yield of sorted tubules were related to sort stringency. Four to six replicates of 100 collecting ducts (9.68+/-0.44-14.5+/-0.66 cm or 9.2+/-0.7 mg tubular protein) were routinely obtained from a single mouse in under 1 h. In conclusion, large-particle-based flow cytometry is fast, reproducible, and generates sufficient amounts of highly pure and viable collecting ducts from single or replicate animals for gene expression and proteomic analysis.