Mandibular patterning information initially resides in the epithelium during development. However, how transcriptional regulation of epithelium-derived signaling controls morphogenesis of the mandible remains elusive. Using Shh Cre to target the mandibular epithelium, we ablated transcription factor Islet1, resulting in a distally truncated mandible via unbalanced cell apoptosis and decreased cell proliferation in the distal mesenchyme. Loss of Islet1 caused a lack of cartilage at the distal tip, leading the fusion of two growing mandibular elements surrounding the rostral process of Meckel's cartilage. Loss of Islet1 results in dysregulation of mesenchymal genes important for morphogenesis of the mandibular arch. We revealed that Islet1 is required for the activation of epithelial ␤-catenin signaling via repression of Wnt antagonists. Reactivation of ␤-catenin in the epithelium of the Islet1 mutant rescued mandibular morphogenesis through sonic hedgehog (SHH) signaling to the mesenchyme. Furthermore, overexpression of a transgenic hedgehog ligand in the epithelium also partially restored outgrowth of the mandible. These data reveal functional roles for an ISLET1-dependent network integrating ␤-catenin/SHH signals in mesenchymal cell survival and outgrowth of the mandible during development.

The current study investigated the regulation and the spatiotemporal expression pattern of Errfi1 and Ifrd1, genex encoding factors that regulate differentiation and cessation of cell division, in the rat ovary during the periovulatory period. Immature female rats (22-23 days old) were injected with pregnant-mare serum gonadotropin to stimulate folliculogenesis, followed by human chorionic gonadotropin (hCG) to induce ovulation. Ovaries, granulosa cells, theca-interstitial cells, or cumulus oocyte complexes (COCs) were collected at various times after hCG administration (n = 3 per time point). Expression analysis revealed that Errfi1 and Ifrd1 were highly induced in the ovary, although their spatiotemporal expression differed: In situ hybridization analysis demonstrated that Errfi1 mRNA expression was initially induced in theca-interstitial cells at 4 and 8 hr after hCG, then transitioned to granulosa cells at 12 hr, and decreased in newly forming corpora lutea at 24 hr. Ifrd1 mRNA, on the other hand, was primarily induced in granulosa cells, and expression remained elevated in newly forming corpora lutea. Interestingly, Errfi1 and Ifrd1 were also expressed in the COC, suggesting a potential role in cumulus cell expansion or oocyte maturation. Inhibition of progesterone or prostaglandin synthesis reduced Errfi1 and Ifrd1 transcription, whereas inhibition of epidermal growth factor signaling inhibited only Errfi1 mRNA abundance. Down-regulation of both genes led to further suppression of progesterone. Our findings thus suggest that the stimulation of Errfi1 and Ifrd1 may be important for theca and granulosa cell differentiation and COC expansion. Mol. Reprod. Dev. 83: 714-723, 2016 © 2016 Wiley Periodicals, Inc.

With the spread of hexavalent chromium (Cr(VI)) contamination, Cr(VI)-induced hepatotoxicity has attracted increasing attention in recent years. To date, however, the exact mechanism of Cr(VI) toxicity remains unclear. In this study, we investigated the role of apoptosis signal-regulating kinase 1 (ASK1)/c-Jun aminoterminal kinase (JNK) in Cr(VI)-induced hepatic toxicity and the possible related mechanisms. AML-12 hepatocyte cell-lines were treated with 0, 1, 4, and 16 μmol/Lof Cr(VI) with or without GS-444271 (an ASK1 inhibitor). Adult male mice were administered with 0, 2, 8, and 32 mg/kg body mass (BM)/day of Cr(VI) for 5 days. The level of hepatocyte apoptosis/proliferation, generation of reactive oxygen species (ROS), and expression levels of mRNAs and proteins related to ASK1/JNK and nuclear factor-E2-related factor 2 (Nrf2) signaling were assessed. Results showed that high Cr(VI) exposure induced hepatocyte apoptosis and liver injury by generation of ROS and down-regulation of Nrf2 signaling. In addition, ASK1/JNK signaling activity was upregulated in the Cr(VI)-treated group. Furthermore, GS-444217 treatment significantly rescued Cr(VI)-induced hepatocyte apoptosis and liver dysfunction in vitro and in vivo by down-regulation of ASK1/JNK signaling. Thus, ASK1/JNK signaling appears to play an important role in Cr(VI)-induced hepatocyte apoptosis and liver injury. This study should help improve our understanding of the mechanism of Cr(VI)-induced liver injury and provide support for future investigations on liver disease therapy.

Migration of myoblasts derive from the occipital somites is critical for tongue morphogenesis. However, the molecular mechanisms of myoblast migration remain elusive. In this study, we report that deletion of Isl1 in the mandibular epithelium leads to aglossia due to myoblast migration defects. Isl1 regulates the expression pattern of chemokine ligand 12 (Cxcl12) in the first branchial arch through the Shh/Wnt5a cascade. Cxcl12+ mesenchymal cells in Isl1ShhCre embryos were unable to migrate to the distal region, but instead clustered in a relatively small proximal domain of the mandible. CXCL12 serves as a bidirectional cue for myoblasts expressing its receptor CXCR4 in a concentration-dependent manner, attracting Cxcr4+ myoblast invasion at low concentrations but repelling at high concentrations. The accumulation of Cxcl12+ mesenchymal cells resulted in high local concentrations of CXCL12, which prevented Cxcr4+ myoblast invasion. Furthermore, transgenic activation of Ihh alleviated defects in tongue development and rescued myoblast migration, confirming the functional involvement of Hedgehog signaling in tongue development. In summary, this study provides the first line of genetic evidence that the ISL1/SHH/CXCL12 axis regulates myoblast migration during tongue development.