supports the recent study which compared the tumor incidence in ApcMin/+ mice and APCloxP/+ mice crossed with CDX2P-NLS Cre or Villin-Cre transgenic mice [37]. Their data indicate that the small intestinal tumor burden may inhibit, via an unknown mechanism, the development and/or progression of colorectal tumors in the mouse. In contrast to human cases, APC mutations in mice usually develop far fewer tumors in the colon than the small intestine, for as yet unknown reasons. Further studies will hopefully solve the riddle which underlies gut tumors of the human and the mouse. In summary, miR-143 and miR-145 likely work together to inhibit at least two signaling pathways involving ERK5/c-Myc and p68/p72/b-catenin in the intestine tumors of ApcMin/+ mice, and thereby suppress their common downstream effectors. Although further studies remain to be investigated, the signaling circuit between miR-143/miR-145 and their modulators p68/p72 might also act as a guardian to arrest the overproduction of the miRNAs (Figure 6). The present study may shed new light on the network between cancer-related signaling molecules and miRNAs, which would be more diverged than expected. Repression of Tumors in miR-143 Transgenic Mice Materials and Methods Mice and Ethics Statement BCF1 (C57BL/6NRx BALB/c=) females were mated with BCF1 males the night before injection and the eggs were prepared for injection as described previously [38]. Injected eggs were implanted into the oviducts of the pseudo-pregnant ICR mice. Transgenic progeny were backcrossed to C57BL/6J mice. C57BL/6J- ApcMin/+/J mice were purchased from The Jackson Laboratory. Primers for genotyping are shown in Table S1.This study was performed in strict accordance with the recommendations in Fundamental Guidelines for Proper Conduct of Animal Experiment and Related Activities in Academic Research Institutions under the jurisdiction of the Ministry of Education, Culture, Sports, Science and Technology, Japan. The protocol was approved by the Committee on the Ethics of Animal Experiments and the Institutional Animal Care and Use of Chubu University (Permit Number: 2210029). All surgery was performed under sodium pentobarbital anesthesia, and every effort was made to minimize suffering. Figure 6. Schematic model of the regulation of APC signaling by miR-143 in the small intestine tumors. The complex of p53, p68 and p72 with DGCR8 and Drosha reinforces the processing of pri-miR-143/pri-miR-145. miR-143 downregulates the expression of c-Myc, cyclin D1 and c- jun through inhibiting ERK5 expression, and upregulates miR-145, probably by elevating the common transcript of endogenous pri-miR-143/pri-miR- 145. Downregulation of c-Myc may contribute to this transcriptional augmentation of pri-miRNA. Effect of miR-143 and miR-145 converge on the repression of c-Myc, leading to the decrease of p68 expression, while miR-145 directly inhibits p72 expression. Repression of p68/p72 may impair b- catenin signaling to repress the expression of c-Myc, cyclin D1 and c-jun, and concurrently retard the processing of pri-miR-143/miR-145 to prevent the overproduction of miR-143 and miR-145. Red lines indicate the pathways which were found or confirmed in this study. doi:10.1371/journal.pone.0042137.g006 PLoS ONE | www.plosone.org 9 August 2012 | Volume 7 | Issue 8 | e42137