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Fig. 4. The role of small RNAs in gene expression. (A–D) Phenotypes of small RNA-injected embryos (stage 30). (A) Control embryo. (B–D) Small RNAs in the range of 20–60 (B), 60–100 (C), and 100–120 (D) bases were injected into dorsal blastomeres of four-cell embryos. (C) Injection of small RNAs (60–100 bases) shortened the dorsal axis in all embryos (n = 56). (E) Injection of small RNAs (60–100 bases) into all blastomeres of four-cell embryos markedly reduced the expression of chordamesodermal genes but increased expression of Xfurry (stage 10). (F) Injection of small RNAs (60–100 bases) into four animal blastomeres of 32-cell embryos in solution containing cycloheximide decreased expression of chordamesodermal genes in the animal caps and slightly reduced the expression of Xfurry (stage 10). (G) Expression of enR+LZ reduced pri-mir-15, and expression of VP16+LZ slightly up-regulated pri-mir-15 in the cycloheximide-treated animal caps (stage 10). (H) Overexpression of mir-15 in the cycloheximide-treated animal caps reduced expression of chordamesodermal genes and did not alter expression of Xfurry. (I) Cycloheximide treatment from stage 7 reduced expression of pri-mir-15 in the treated animal caps (stage 10). (J) Injection of pintallavis-MO (Pint-MO) into all blastomeres of four-cell embryos increased expression of goosecoid and Xnot, did not alter the expression of chordin, and reduced the expression of pri-mir-15 (stage 10). (K) Model of the proposed Xfurry signaling pathway. Xfurry represses expression of mir-15 and microRNAs. Several chordamesodermal genes are repressed by mir-15 and microRNAs. Xfurry also is induced by goosecoid as a downstream gene. Then this feedback loop signaling pathway together with Xfurry regulates expression of chordamesodermal genes. Moreover, low protein levels of several genes activate a system that senses the low-protein condition, thereby inducing Xfurry expression and activating the function of Xfurry as a corepressor. Pin, pintallavis. Image published in: Goto T et al. (2010) Copyright © 2010. Image reproduced with permission of the publisher and the copyright holder. This is an Open Access article distributed under the terms of the Creative Commons Attribution License. Larger Image Printer Friendly View

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