New factors and signaling pathways for developmental regulation.

The developmental process is a highly complicated process for building multicellular organisms. JMCB has published several research works in recent collections on this topic (Wu, 2013, 2014). In the present issue, five more articles report new biological factors and cell signaling pathways that are discovered controlling the developmental process. These findings might provide new insights into the intricate developmental regulation. Dr Wu's group and collaborators reported in this issue that a microRNA, miR-181, is essential for the onset of embryo implantation. The authors showed that the upregulation of exogenous miR-181 expression resulted in impaired embryo implantation of mice. They further showed that Emx2-mediated miR-181 expression could directly downregulate the expression of leukemia inhibitory factor (LIF), which is required for embryo implantation. These results indicate the involvement of non-coding RNAs, in addition to proteins, in the regulation of embryo implantation. It has been known that epigenetic regulations, such as DNA methylation and histone methylation, are involved in a variety of physiological and pathological processes. Dr Chen's group analyzed the function of JMJD3, an H3K27me3 demethylase, during bone formation in mice. They found that JMJD3 was highly expressed in prehypertrophic and hypertrophic chondrocytes during endochondral ossification. Furthermore, Jmjd3-deficient mice showed severely suppressed proliferation and delayed hypertrophy of chondrocytes, implying retardation of endochondral ossification. This study demonstrates that JMJD3 is an important epigenetic regulator in the process of bone formation. Hippo/Yap signaling pathway is reported to regulate proliferation and differentiation of stem/progeni-tor cells. By knocking out Hippo kinases, Mst1 and Mst2, in epithelial cells of the embryonic or mature mouse lung, Dr Whitsett's laboratory demonstrated that Mst1/2 deletion promoted proliferation and suppressed differentiation of epithelial cells in the fetal lung, but altered differentiation of bronchiolar epithelial cells in the adult lung. In addition, Mst1/2 deletion downregulated the inhibitory Yap phosphor-ylation, but upregulated Yap nuclear localization and transcriptional targets. The authors conclude that Hippo/Yap signaling regulates proliferation and differentiation of lung epithelial progenitor cells. The zebrafish sensory posterior lateral line (pLL) has been used as a model for studying developmental regulation. In this issue, Dr Meng and Jia's laboratory reported that TGFb signaling pathway participated in regulating cell morphogenesis during pLL development. The authors showed that the tgfb1a gene was abundantly expressed in the pLL primordium (pLLP), and the tgfb1a depletion resulted in aberrant morphogenesis of pLLP. They further showed that exogenous Smad5 expression could rescue the defects in tgfb1a-knockdown embryos, suggesting that Smad5 …