Expression profiles of phosphodiesterase 4D splicing variants in osteoblastic cells

Mapping of Craniofacial Traits in Outbred Mice Identifies Major Developmental Genes Involved in Shape Determination

The vertebrate cranium is a prime example of the high evolvability of complex traits. While evidence of genes and developmental pathways underlying craniofacial shape determination is accumulating, we are still far from understanding how such variation at the genetic level is translated into craniofacial shape variation. Here we used 3D geometric morphometrics to map genes involved in shape determination in a population of outbred mice (Carworth Farms White, or CFW). We defined shape traits via principal component analysis of 3D skull and mandible measurements. We mapped genetic loci associated with shape traits at ~80,000 candidate single nucleotide polymorphisms in ~700 male mice. We found that craniofacial shape and size are highly heritable, polygenic traits. Despite the polygenic nature of the traits, we identified 17 loci that explain variation in skull shape, and 8 loci associated with variation in mandible shape. Together, the associated variants account for 11.4% of skull and 4.4% of mandible shape variation, however, the total additive genetic variance associated with phenotypic variation was estimated in ~45%. Candidate genes within the associated loci have known roles in craniofacial development; this includes 6 transcription factors and several regulators of bone developmental pathways. One gene, Mn1, has an unusually large effect on shape variation in our study. A knockout of this gene was previously shown to affect negatively the development of membranous bones of the cranial skeleton, and evolutionary analysis shows that the gene has arisen at the base of the bony vertebrates (Eutelostomi), where the ossified head first appeared. Therefore, Mn1 emerges as a key gene for both skull formation and within-population shape variation. Our study shows that it is possible to identify important developmental genes through genome-wide mapping of high-dimensional shape features in an outbred population.

Formation of the face, mandible, and skull is determined in part by genetic factors, but the relationship between genetic variation and craniofacial development is not well understood. We demonstrate how recent advances in mouse genomics and statistical methods can be used to identify genes involved in craniofacial development. We use outbred mice together with a dense panel of genetic markers to identify genetic loci affecting craniofacial shape. Some of the loci we identify are also known from past studies to contribute to craniofacial development and bone formation. For example, the top candidate gene identified in this study, Mn1, is a gene that appeared at a time when animals started to form bony skulls, suggesting that it may be a key gene in this evolutionary innovation. This further suggests that Mn1 and other genes involved in head formation are also responsible for more fine-grained regulation of its shape. Our results confirm that the outbred mouse population used in this study is suitable to identify single genetic factors even under conditions where many genes cooperate to generate a complex phenotype.

Involvement of mTOR in Type 2 CRF Receptor Inhibition of Insulin Signaling in Muscle Cells

Type 2 corticotropin-releasing factor receptor (CRFR2) is expressed in skeletal muscle and stimulation of the receptor has been shown to inhibit the effect of insulin on glucose uptake in muscle cells. Currently, little is known about the mechanisms underlying this process. In this study, we first showed that both in vivo and in vitro CRFR2 expression in muscle was closely correlated with insulin sensitivity, with elevated receptor levels observed in insulin resistant muscle cells. Stimulation of CRFR2 by urocortin 2 (Ucn 2), a CRFR2-selective ligand, in C2C12 myotubes greatly attenuated insulin-induced glucose uptake. The inhibitory effect of CRFR2 signaling required cAMP production and is involved the mammalian target of rapamycine pathway, as rapamycin reversed the inhibitory effect of CRFR2 stimulation on insulin-induced glucose uptake. Moreover, stimulation of CRFR2 failed to inhibit glucose uptake in muscle cells induced by platelet-derived growth factor, which, similar to insulin, signals through Akt-mediated pathway but is independently of insulin receptor substrate (IRS) proteins to promote glucose uptake. This result argues that CRFR2 signaling modulates insulin's action likely at the levels of IRS. Consistent with this notion, Ucn 2 reduced insulin-induced tyrosine phosphorylation of IRS-1, and treatment with rapamycin reversed the inhibitory effect of Ucn 2 on IRS-1 and Akt phosphorylation. In conclusion, the inhibitory effect of CRFR2 signaling on insulin action is mediated by cAMP in a mammalian target of rapamycine-dependent manner, and IRS-1 is a key nodal point where CRFR2 signaling modulates insulin-stimulated glucose uptake in muscle cells.

Epinephrine accelerates osteoblastic differentiation by enhancing bone morphogenetic protein signaling through a cAMP/protein kinase A signaling pathway

Topical effects of a catecholamine on bone morphogenetic protein (BMP)-induced ectopic bone formation were investigated in both in vivo and in vitro experimental systems. Epinephrine enhanced bone induction by BMP-2. Thus, the mass of ossicles ectopically induced by BMP-2 (5 μg) was increased by the addition of a low dose (10, 20, 40, or 80 μg) of epinephrine into a biodegradable BMP-2 carrier, in a dose-dependent manner. To investigate the mechanism by which epinephrine enhances BMP activity, in vitro experiments were carried out using osteogenic cells. The expression level of alkaline phosphatase (ALP) in cells, a marker of osteoblastic differentiation, was consistently elevated by BMP-2 (50 ng/ml) and was further elevated by the addition of epinephrine (10(-8)M). The epinephrine-enhanced ALP elevation was specifically abolished by an antagonist to β2-adrenergic receptors (Butoxamine) and by a protein kinase A inhibitor (H89). Furthermore, BMP-induced mRNA expression of ALP and osteocalcin (marker proteins of osteoblastic differentiation) and of Osterix (a transcription factor essential for terminal differentiation to osteoblasts) in ST2 cells was significantly enhanced by the addition of epinephrine (10(-8)M). In luciferase expression assays using the promoter sequence of the Id1 gene (an immediate early response gene to BMP), luciferase activity was elevated by BMP-2 treatment (50 ng/ml) and this activity was further enhanced by the addition of epinephrine (10(-8)M). Epinephrine-enhanced luciferase activity was abolished by mutation of the cAMP-response element (CRE) sequence in the Id1 promoter, indicating that CRE-binding transcription proteins induced by epinephrine addition may act as enhancers of Smad-mediated BMP signaling.