Pth1r in Neural Crest Cells Regulates Nasal Cartilage Differentiation.

Neural crest cells (NCC) arise from the dorsal margin of the neural plate border and comprise a unique cell population that migrates to and creates the craniofacial region. Although factors including Shh, Fgf8, and bone morphogenetic proteins have been shown to regulate these biological events, the role of parathyroid hormone 1 receptor (Pth1r) has been less studied. We generated an NCC-specific mouse model for Pth1r and researched gene expression, function, and interaction focusing on nasal cartilage framework and midfacial development. Wnt1-Cre;Pth1rfl/fl;Tomatofl/+ mice had perinatal lethality, but we observed short snout and jaws, tongue protrusion, reduced NCC-derived cranial length, increased mineralization in nasal septum and hyoid bones, and less bone mineralization at interfrontal suture in mutants at E18.5. Importantly, the mutant nasal septum and turbinate cartilage histologically revealed gradual, premature accelerated hypertrophic differentiation. We then studied the underlying molecular mechanisms by performing RNA seq analysis and unexpectedly found that expression of Ihh and related signaling molecules was enhanced in mutant nasomaxillary tissues. To see if Pth1r and Ihh signaling are associated, we generated a Wnt1-Cre; Ihhfl/fl;Pth1rfl/fl;Tomatofl/+ (DKO) mouse and compared the phenotypes to those of each single knockout mouse: Wnt1-Cre; Ihhfl/fl;Pth1rfl/+;Tomatofl/+ (Ihh-CKO) and Wnt1-Cre;Ihhfl/+;Pth1rfl/fl;Tomatofl/+ (Pth1r-CKO). Ihh-CKO mice displayed a milder effect. Of note, the excessive hypertrophic conversion of the nasal cartilage framework observed in Pth1r-CKO was somewhat rescued DKO embryos. Further, a half cAMP responsive element and the 4 similar sequences containing 2 mismatches were identified from the promoter to the first intron in Ihh gene. Gli1-CreERT2;Pth1rfl/fl;Tomatofl/+, a Pth1r-deficient model targeted in hedgehog responsive cells, demonstrated the enlarged hypertrophic layer and significantly more Tomato-positive chondrocytes accumulated in the nasal septum and ethmoidal endochondral ossification. Collectively, the data suggest a relevant Pth1r/Ihh interaction. Our findings obtained from novel mouse models for Pth1r signaling illuminate previously unknown aspects in craniofacial biology and development.

Pth1r Signal in Gli1+ Cells Maintains Postnatal Cranial Base Synchondrosis.

Cranial base synchondroses are the endochondral ossification centers for cranial base growth and thus indispensable for proper skull, brain, and midfacial development. The synchondroses are composed of mirror-image growth plates that are continuously maintained from the embryonic to postnatal stage through chondrocyte differentiation. Several factors, including Pth1r signaling, are known to control fetal synchondrosis development. However, there are currently no reports regarding any role for Pth1r signaling in postnatal cranial base and synchondrosis development. Also, the mesenchymal cells that source Pth1r signaling for synchondroses are not known. Here, we employed an inducible mouse model, a hedgehog-responsive Gli1-CreERT2 driver, focusing on the postnatal study. We performed 2 inducible protocols using Gli1-CreERT2;Tomatofl/+ mice that uncovered distinct patterning of Gli1-positive and Gli1-negative chondrocytes in the synchondrosis cartilage. Moreover, we generated Gli1-CreERT2;Pth1rfl/fl;Tomatofl/+ mice to assess their functions in postnatal synchondrosis and found that the mutants had survived postnatally. The mutant skulls morphologically presented unambiguous phenotypes where we noticed the shortened cranial base and premature synchondrosis closure. Histologically, gradual disorganization in mutant synchondroses caused an uncommon remaining central zone between hypertrophic zones on both sides while the successive differentiation of round, flat, and hypertrophic chondrocytes was observed in control sections. These mutant synchondroses disappeared and were finally replaced by bone. Of note, the mutant fusing synchondroses lost their characteristic patterning of Gli1-positive and Gli1-negative chondrocytes, suggesting that loss of Pth1r signaling alters the distribution of hedgehog-responsive chondrocytes. Moreover, we performed laser microdissection and RNA sequencing to characterize the flat proliferative and round resting chondrocytes where we found flat chondrocytes have a characteristic feature of both chondrocyte proliferation and maturation. Taken together, these data demonstrate that Pth1r signaling in Gli1-positive cells is essential for postnatal development and maintenance in cranial base synchondroses. Our findings will elucidate previously unknown aspects of Pth1r functions in cranial biology and development.

Replication factor C3 of Schizosaccharomyces pombe, a small subunit of replication factor C complex, plays a role in both replication and damage checkpoints.

We report here the isolation and functional analysis of the rfc3(+) gene of Schizosaccharomyces pombe, which encodes the third subunit of replication factor C (RFC3). Because the rfc3(+) gene was essential for growth, we isolated temperature-sensitive mutants. One of the mutants, rfc3-1, showed aberrant mitosis with fragmented or unevenly separated chromosomes at the restrictive temperature. In this mutant protein, arginine 216 was replaced by tryptophan. Pulsed-field gel electrophoresis suggested that rfc3-1 cells had defects in DNA replication. rfc3-1 cells were sensitive to hydroxyurea, methanesulfonate (MMS), and gamma and UV irradiation even at the permissive temperature, and the viabilities after these treatments were decreased. Using cells synchronized in early G2 by centrifugal elutriation, we found that the replication checkpoint triggered by hydroxyurea and the DNA damage checkpoint caused by MMS and gamma irradiation were impaired in rfc3-1 cells. Association of Rfc3 and Rad17 in vivo and a significant reduction of the phosphorylated form of Chk1 in rfc3-1 cells after treatments with MMS and gamma or UV irradiation suggested that the checkpoint signal emitted by Rfc3 is linked to the downstream checkpoint machinery via Rad17 and Chk1. From these results, we conclude that rfc3(+) is required not only for DNA replication but also for replication and damage checkpoint controls, probably functioning as a checkpoint sensor.

Kcc4 associates with septin proteins of Saccharomyces cerevisiae.

Kcc4, a kinase of the budding yeast Saccharomyces cerevisiae, is homologous to the bud neck protein kinases Hsl1/Nik1 and Gin4. We report here that a GFP-Kcc4 fusion protein is localized at the bud neck and that the non-kinase domain is required for this localization. We also demonstrate that Kcc4 associates with septin proteins in vitro and in vivo by two-hybrid analysis, GST pull-down experiments, immunoprecipitation, and analysis of direct association with affinity-purified GST-Kcc4 and MBP-Septin proteins. From the results obtained here, we suggest that Cdc11 is the primary association partner of Kcc4.

Rad24 is essential for proliferation of diploid cells in fission yeast.

The rad24(+) gene of Schizosaccharomyces pombe encodes a ubiquitously expressed 14-3-3 protein. We report here that Deltarad24 cells displayed a defect in diploid colony formation, although they conjugated efficiently. We found that a cumulative deletion of mei2(+) gene almost completely suppressed this defect, and demonstrated using two-hybrid analysis that Rad24 protein directly associates with Mei2 protein by recognizing Ser-438 which is a phosphorylation target of Pat1 kinase. We conclude that constitutive progression to meiosis, caused by lack of Mei2 inhibition due to the absence of Rad24 protein, is the primary cause of the proliferative deficiency observed in Deltarad24 cells.

MicroRNA-mediated upregulation of integrin-linked kinase promotes Src-induced tumor progression.

The tyrosine kinase c-Src is upregulated in various human cancers; however, the molecular mechanisms underlying c-Src-mediated tumor progression remain unclear. Here we show that downregulation of microRNA (miR)-542-3p is tightly associated with tumor progression via c-Src-related oncogenic pathways. In c-Src-transformed fibroblasts and human cancer cells that overexpress c-Src, miR-542-3p is substantially downregulated, and the ectopic expression of miR-542-3p suppresses tumor growth. We identified the integrin-linked kinase (ILK) as a conserved target of miR-542-3p. ILK upregulation promotes cell adhesion and invasion by activating the integrin-focal adhesion kinase (FAK)/c-Src pathway, and can also contribute to tumor growth via the AKT and glycogen synthase kinase 3ß pathways. MiR-542-3p expression is downregulated by the activation of c-Src-related signaling molecules, including epidermal growth factor receptor, K-Ras and Ras/Raf/mitogen-activated protein kinase/extracellular signal-regulated kinase. In human colon cancer tissues, downregulation of miR-542-3p is significantly correlated with the upregulation of c-Src and ILK. Our results suggest that the novel c-Src-miR-542-3p-ILK-FAK circuit plays a crucial role in controlling tumor progression.

MicroRNA-mediated downregulation of mTOR/FGFR3 controls tumor growth induced by Src-related oncogenic pathways.

The tyrosine kinase c-Src is upregulated in various human cancers, but the molecular mechanisms underlying c-Src-mediated tumor growth remain unclear. Here we examined the involvement of microRNAs in the c-Src-mediated tumor growth. Microarray profiling revealed that c-Src activation downregulates a limited set of microRNAs, including miR-99a, which targets oncogenic mammalian target of rapamycin (mTOR) and fibroblast growth factor receptor 3 (FGFR3). Re-expression of miR-99a suppressed tumor growth of c-Src-transformed cells, and this effect was restored by the overexpression of mTOR. The downregulation of miR-99a was also observed in epidermal growth factor- and Ras-transformed cells, and it was suppressed by inhibiting the mitogen-activated protein kinase (MAPK) pathway. Furthermore, miR-99a downregulation is associated with mTOR/FGFR3 upregulation in various human lung cancer cells/tissues. The tumorigenicity of these cells was suppressed by the introduction of miR-99a. These findings suggest that the miR-99a-mTOR/FGFR3 pathway is crucial for controlling tumor growth in a wide range of human cancers that harbor upregulation of the Src-related oncogenic pathways.

Gin4 of S. cerevisiae is a bud neck protein that interacts with the Cdc28 complex.

BACKGROUND: A number of proteins make up the Cdc28 complex in Saccharomyces cerevisiae, and regulate CDK activity. The cell cycle regulator Nik1 (Hsl1) is a protein kinase that interacts with the Cdc28 complex. The growth inhibitor Gin4 is structurally similar to Nik1 and may play a redundant role in the regulation of the cell cycle. We investigated the functions of Gin4 with respect to those of Nik1. RESULTS: GIN4 was not essential for growth, and cells deficient in the GIN4 gene displayed no obvious defects in cell cycle regulation. The delta(gin)4 delta(nik)1 strain was temperature sensitive and showed an abnormal cell shape and FACS profile at permissive temperatures. GFP-fused Gin4 was localized at the bud-neck from late G1 to the M phase. Over-production of the C-terminal portion of Gin4 was toxic for cell growth, and this domain was required for the bud-neck localization of Gin4-GFP. High copy expression of Gin4-GFP disturbed the bud-neck localization of Gin4 in the abnormally elongated cells. Cytokinesis was defective in the delta(gin)4 cdc28 double mutants. The GST-Gin4 fusion protein physically associates with the Cdc28 complex. CONCLUSIONS: Gin4 is a bud-neck protein. GIN4 and NIK1 have distinct but partially overlapping functions. The major function of GIN4 is to ensure proper mitotic progression and cytokinesis.