Y. Maheshwari et al., CHANGES IN RIBOSOMAL-PROTEIN AND RIBOSOMAL-RNA SYNTHESIS DURING RAT INTESTINAL DIFFERENTIATION, Cell growth & differentiation, 4(9), 1993, pp. 745-752
Subtraction hybridization studies, used to identify genes involved in
the control of enterocyte proliferation and/or differentiation, allowe
d detection of a clone shown to have homologies with rat, chicken, and
human acidic ribosomal phosphoprotein P1. Since increases in P1 trans
cript 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 ente
rocytes as isolated cell fractions representative of the crypt to vill
us axis of differentiation. Total RNA was extracted from pooled cell f
ractions and evaluated for mRNA and rRNA steady-state levels. Nuclei w
ere prepared from isolated enterocytes, and nuclear runoff studies wer
e performed to estimate rates of nascent transcription. The P1 complem
entary DNA from the crypt cell library detected a mRNA of 650 base pai
rs which showed approximately 8-fold greater steady-state levels in cr
ypt than in villus cells. Similar crypt specificity was also noted for
mRNAs coding for elongation factor EF-12 and for ribosomal proteins P
0, P1, and S6 (using clones from Y-L. Chan and I. G. Wool). In contras
t, 28S rRNA steady-state levels did not differ between villus and cryp
t, indicating that ribosomal content had remained constant. In situ hy
bridization studies confirmed the predominant crypt localization of P1
mRNA. Nascent transcription rate studies showed that the proportion o
f newly synthesized P1 mRNA to total RNA was the same for the villus a
nd crypt, suggesting that the lower content of villus P1 mRNA may be d
ue to increased degradation. These results suggest that the high rate
of ribosomal phosphoprotein synthesis during enterocyte proliferation
is markedly decreased upon completion of differentiation. Changes in r
ibosomal phosphoprotein synthesis may be a determinant of irreversible
differentiation.