Notch Signaling Promotes Intestinal Crypt Fission in the Infant Rat

Abstract

Growth of the small intestine in the infant rat is promoted by crypt fission and later by increased crypt cell proliferation. Notch signaling could promote crypt fission. Hes-1 is a Notch target gene. We assessed the effect of Notch signaling on intestinal crypt fission and on growth of the intestine in the infant rat. Hes-1 expression was determined in the small intestine of litters of Hooded Wistar rats aged between 3 and 72days. Hes-1 RNA expression was measured by quantitative RT-PCR. Four groups of rats (n=8 or 9) were injected daily, ip, either with vehicle or with the Notch inhibitor DAPT at doses of 3, 10, and 30mg/kg, from days 9 to 13 of life, and killed on day 14. A microdissection technique was used to measure crypt fission, mitotic count, and apoptotic count. Data were analyzed by ANOVA and by use of Dunnett's F test. Hes-1 expression and crypt fission peaked on day 14. DAPT reduced Hes-1 immunostaining in proportion to dose. DAPT reduced villous area to 72% (p<0.01), 53% (p<0.001), and 38% (p<0.001) of control values for 3, 10 and 30mg/kg doses, respectively, and reduced crypt fission to 53% (p<0.001) and 38% (p<0.001) of control values, respectively, for 10 and 30mg/kg doses. Crypt mitotic count was not affected by any DAPT dose. DAPT at 10 and 30mg/kg significantly increased apoptosis in crypts, by 6.5 and 4.8-fold, respectively. We conclude that Notch signaling promotes crypt fission and growth of the intestine by maintaining low apoptosis of crypt cells.