The identification of genes specifically expressed in epithelial cells of the rat intestinal crypts

Abstract

Abstract Undifferentiated embryonic and dedifferentiated tumor cells express genes that are down-regulated or not expressed in differentiated tissue. The progenitor cells of the intestinal crypt are undifferentiated cells that, similarly, should express genes that are not evident in the more differentiated villus cells. Some of these genes may be related to the control of differentiation. We attempted to define crypt-associated genes by constructing a cDNA library from isolated rat intestinal crypt cells and screening for messages that remained after subtractive hybridization using > 20-fold more mRNA from villus than from the crypt cells. This process identified about two percent of the colonies containing transcripts expressed by the crypt cell. Northern blot analysis showed hybridization to messages in a range from 700 to 12,000 base pairs. Six clones out of 136 initial isolates were shown to hybridize to crypt mRNAs at levels four to tenfold greater than to villus mRNAs. Three of these clones showed greater hybridization to mRNA of the distal (ileum) when compared to the proximal end of the adult small bowel. Increased expression in fetal rat intestine was seen for five mRNAs and in fetal liver for four mRNAs when compared to adult. Most of the crypt associated gene probes preferentially bound mRNA from ovary, kidney, and spleen but did not bind mRNA derived from testis, muscle and brain. Cultured mouse teratocarcinoma cells (F9) showed high levels of three of these transcripts. Portions of each insert were sequenced and examined for homology to entries in national computer banks. The genes, with one exception, did not match any reported nucleotide or peptide sequence. These probes may detect mRNAs that are critical to normal differentiation.