Gene expression profiles of the collecting duct in the mouse renal inner medulla.
Background: Gene expression profiles, constructed from 1000 to 2000 cloned cDNA sequences, depict their relative abundance of expression in a tissue. Establishing such a profile for mouse inner renal medullary collecting ducts (IMCDs), we compared expression patterns with those in other tissues including proximal tubule.
Methods: A nonbiased 3'-end cDNA library was prepared from microdissected mouse IMCDs. Single-pass sequencing of 2000 randomly selected cDNA clones collected short sequences (approximate length, 250 bp) following poly (A), called gene signatures (GS). Identical sequences were considered a single GS. GS occurrence was quantitated to yield a list of expressed genes indicating their abundance.
Results: Among 2000 clones, 1613 types of transcripts were found in IMCDs; 155 were identical or homologous to reported genes. The gene most expressed in IMCDs was alphaB-crystallin, a small stress (heat-shock) protein that is also a major structural protein in the ocular lens. According to Northern analysis, renal expression of this mRNA was induced by dehydration, presumably via tissue hypertonicity. However, expression did not change with acute NaCl loading. Also, a new member of the glutathione-S-transferase family was identified by comparing the IMCD expression profile with those of other tissues.
Conclusion: With our database of genes expressed in mouse IMCDs, we are devising an IMCD-specific microarray to study gene-expression responses to various physiologic alterations.