Changes in ribosomal protein and ribosomal RNA synthesis during rat intestinal differentiation

Subtraction hybridization studies, used to identify genes involved in the control of enterocyte proliferation and/or differentiation, allowed detection of a clone shown to have homologies with rat, chicken, and human acidic ribosomal phosphoprotein P1. Since increases in P1 transcript have been associated with intestinal malignancy, we explored the relationship of P1 and other ribosomal proteins to normal intestinal proliferation and differentiation. Male rats were used to prepare enterocytes as isolated cell fractions representative of the crypt to villus axis of differentiation. Total RNA was extracted from pooled cell fractions and evaluated for mRNA and rRNA steady-state levels. Nuclei were prepared from isolated enterocytes, and nuclear runoff studies were performed to estimate rates of nascent transcription. The P1 complementary DNA from the crypt cell library detected a mRNA of 650 base pairs which showed approximately 8-fold greater steady-state levels in crypt than in villus cells. Similar crypt specificity was also noted for mRNAs coding for elongation factor EF-12 and for ribosomal proteins P0, P1, and S6 (using clones from Y-L. Chan and I. G. Wool). In contrast, 28S rRNA steady-state levels did not differ between villus and crypt, indicating that ribosomal content had remained constant. In situ hybridization studies confirmed the predominant crypt localization of P1 mRNA. Nascent transcription rate studies showed that the proportion of newly synthesized P1 mRNA to total RNA was the same for the villus and crypt, suggesting that the lower content of villus P1 mRNA may be due to increased degradation.(ABSTRACT TRUNCATED AT 250 WORDS)