Box C/D-type small nucleolar RNAs (snoRNAs) are functional RNAs responsible for mediating 2′-O-ribose methylation of ribosomal RNAs (rRNAs) within the nucleolus. In the past years, evidence for the involvement of human U50 snoRNA in tumorigenesis has been accumulating. We previously identified U50HG, a non-protein-coding gene that hosted a box C/D-type U50 snoRNA, in a chromosomal breakpoint in a human B-cell lymphoma. Mouse genome analysis revealed four mouse U50 (mU50) host-genes: three mU50HG-a gene variants that were clustered in the genome and an mU50HG-b gene that we supposed to be the U50HG ortholog. In this study, to investigate the physiological importance of mU50 snoRNA and its involvement in tumorigenesis, we eliminated mU50 snoRNA sequences from the mU50HG-b gene. The established mouse line (ΔmU50(HG-b)) showed a significant reduction of mU50 snoRNA expression without alteration of the host-gene length and exon-intron structure, and the corresponding target rRNA methylation in various organs was reduced. Lifelong phenotypic monitoring showed that the ΔmU50(HG-b) mice looked almost normal without accelerated tumorigenicity; however, a notable difference was the propensity for anomalies in the lymphoid organs. Transcriptome analysis showed that dozens of genes, including heat shock proteins, were differentially expressed in ΔmU50(HG-b) mouse lymphocytes. This unique model of a single snoRNA knockdown with intact host-gene expression revealed further new insights into the discrete transcriptional regulation of multiple mU50 host-genes and the complicated dynamics involved in organ-specific processing and maintenance of snoRNAs.

Fusion of the branchial arch derivatives is a crucial event in the development of the craniofacial architecture. Here, we surveyed the gene expression profile, focusing on the fusion process of the mouse mandibular arch at embryonic day 10.5. In order to identify the genes that are relevant to the midline fusion process, we subdivided the mandibular arch medially and laterally, and determined gene expression using microarray and real-time quantitative PCR. By comparing the transcriptomes of the medial and lateral regions, 362 genes were identified as medial regionspecific genes, while 346 genes were designated lateral region-specific. Taken with Gene Ontology analysis, KEGG pathways and Ingenuity Pathway Analysis (IPA), a survey of the medial regionspecific gene dataset revealed significant expression of the insulin-like growth factor (Igf) family as well as other growth factor families (Hh, Wnt, Tgf-Bmp, Mapk-Fgf and Notch). To determine the discrete expression pattern of Igf family genes in the medial region, we microdissected the medial part of the mandibular arch into epithelial and mesenchymal components, and found that Igf1 was highly expressed in the mesenchyme, Igf2 and Igf1r were expressed in both the midline epithelium and surrounding mesenchyme, and Igfbp5 was highly expressed in the epithelium. Immunohistochemical findings validated the regional Igf gene expression profiles. Our observations suggest that in the "merging" fusion of the mandibular arch, the Igf cascade may contribute to generation of proliferation pressure from the mesenchyme and preservation of epithelial phenotypes and architecture during mesenchymal confluence.

Mouse tongue development is initiated with the formation of lateral lingual swellings just before fusion between the mediodorsal surfaces of the mandibular arches at around embryonic day 11.0. Here, we investigated the role of Sonic hedgehog (Shh) signaling in embryonic mouse tongue morphogenesis. For this, we used an organ culture model of the mandibular arches from mouse embryos at embryonic day 10.5. When the Shh signaling inhibitor jervine was added to the culture medium for 24-96 h, the formation of lateral lingual swellings and subsequent epithelial invagination into the mesenchyme were impaired markedly, leading to a hypoplastic tongue with an incomplete oral sulcus. Notably, jervine treatment reduced the proliferation of non-myogenic mesenchymal cells at the onset of forming the lateral lingual swellings, whereas it did not affect the proliferation and differentiation of a myogenic cell lineage, which created a cell community at the central circumferential region of the lateral lingual swellings as seen in vivo and in control cultures lacking the inhibitor. Thus, epithelium-derived Shh signaling stimulates the proliferation of non-myogenic mesenchymal cells essential for forming lateral lingual swellings and contributes to epithelial invagination into the mesenchyme during early tongue development.

Cleft palate following cleft lip may include a developmental disorder during palatogenesis. CL/Fr mice fetuses, which develop cleft lip and palate spontaneously, have less capability for in vivo cell proliferation in palatal mesenchyme compared with CL/Fr normal fetuses. In order to know the changes of signaling molecules contributing to cleft palate morphogenesis following cleft lip, the mRNA expression profiles were compared in palatal shelves oriented vertically (before elevation) in CL/Fr fetuses with or without cleft lip. The changes in mRNA profile of cleft palate morphogenesis were presented in a microarray analysis, and genes were restricted to lists contributing to cleft palate development in CL/Fr fetuses with cleft lip. Four candidate genes (Ywhab, Nek2, Tacc1 and Frk) were linked in a gene network that associates with cell proliferation (cell cycle, MAPK, Wnt and Tgf beta pathways). Quantitative real-time RT-PCR highlighted the candidate genes that significantly changed in CL/Fr fetuses with cleft lip (Ywhab, Nek2 and Tacc1). The results of these molecular contributions will provide useful information for a better understanding of palatogenesis in cleft palate following cleft lip. Our data indicated the genetic contribution to cleft palate morphogenesis following cleft lip.

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