Particle diameter, signal-to-noise ratio and beam requirements for extended Rayleigh resolution measurements in the scanning electron microscope.

The extended Rayleigh resolution measure was introduced to give a generalized resolution measure that can be readily applied to imaging and resolving particles that have finite size. Here, we make a detailed analysis of the influence of the particle size on this resolution measure. We apply this to scanning electron microscopy, under simple assumption of a Gaussian electron beam intensity distribution and a directly proportional emitted signal yield without detailed consideration of scattering internal to the sample, other than being proportional to the sample thickness. From this, we produce beam-width normalized characteristics relating the particle diameter and resolution measure, while also taking consideration of the reduced signal yield that occurs from smaller particles. From our analysis of these characteristics, which we fit to experimental image data, we see that particle diameters <0.7 times the beam 1/e full width, d, give agreement better than 10% with the true extended Rayleigh resolution. Furthermore, we consider the signal current that must be collected to reliably distinguish between the mid-gap and peak intensity regions in the particle images. This leads to a practical guide that the signal-to-noise ratio (SNR) occurring between large area, continuous regions made of the same materials as the particle and background should typically be 10-30 times greater than the SNR that is desired to be achieved between the peak and mid-gap regions of just resolved adjacent identical particles having diameters in the size range 0.4-0.7d.

Inhibition of ß-catenin/p300 interaction proximalizes mouse embryonic lung epithelium.

BACKGROUND: Wnt/ß-catenin signaling has been suggested to regulate proximal-distal determination of embryonic lung epithelium based upon genetically modified mouse models. The previously identified and characterized small molecule inhibitor IQ1 can pharmacologically decrease the interaction between ß-catenin and its transcriptional coactivator p300, thereby enhancing the ß-catenin/CBP interaction. Inhibition of the ß-catenin/p300 interaction by IQ1 blocks the differentiation of embryonic stem cells and epicardial progenitor cells; however, whether differential coactivator usage by ß-catenin plays a role in proximal-distal determination of lung epithelium is unknown. METHODS: We examined the effects of inhibiting the ß-catenin/p300 interaction with IQ1 on lung branching morphogenesis in mouse embryos in utero and mouse embryonic lung organ culture ex vivo. The phenotype of IQ1 treated lungs was analyzed by epithelial staining, histology, quantitative PCR and in situ hybridization. RESULTS: Inhibition of the ß-catenin/p300 interaction by IQ1 disrupted the distal branching of mouse lung epithelium both in utero and ex vivo. IQ1 proximalized lung epithelium with decreased expression of the genes Bmp4 and Fgf10, hallmarks of distal lung determination, and increased expression of the proximal genes Sox2 and Scgb1a1 (CC10) as shown by quantitative PCR and in situ hybridization. The disruption of branching was reversible ex vivo as branching was reinitiated after removal of IQ1 from the media. CONCLUSIONS: The results demonstrate that the ß-catenin/p300 interaction plays a critical role in proximal-distal determination of the epithelium in mouse lung branching morphogenesis and ß-catenin/p300 inhibition pharmacologically proximalizes lung epithelium.

The small molecule Wnt signaling modulator ICG-001 improves contractile function in chronically infarcted rat myocardium.

The adult mammalian heart has limited capability for self-repair after myocardial infarction. Therefore, therapeutic strategies that improve post-infarct cardiac function are critically needed. The small molecule ICG-001 modulates Wnt signaling and increased the expression of genes beneficial for cardiac regeneration in epicardial cells. Lineage tracing experiments, demonstrated the importance of ß-catenin/p300 mediated transcription for epicardial progenitor contribution to the myocardium. Female rats given ICG-001 for 10 days post-occlusion significantly improved ejection fraction by 8.4%, compared to controls (P<0.05). Taken together, Wnt modulation via ß-catenin/CBP inhibition offers a promising therapeutic strategy towards restoration of myocardial tissues and an enhancement of cardiac functions following infarction.

Lef1 haploinsufficient mice display a low turnover and low bone mass phenotype in a gender- and age-specific manner.

We investigated the role of Lef1, one of the four transcription factors that transmit Wnt signaling to the genome, in the regulation of bone mass. Microcomputed tomographic analysis of 13- and 17-week-old mice revealed significantly reduced trabecular bone mass in Lef1(+/-) females compared to littermate wild-type females. This was attributable to decreased osteoblast activity and bone formation as indicated by histomorphometric analysis of bone remodeling. In contrast to females, bone mass was unaffected by Lef1 haploinsufficiency in males. Similarly, females were substantially more responsive than males to haploinsufficiency in Gsk3beta, a negative regulator of the Wnt pathway, displaying in this case a high bone mass phenotype. Lef1 haploinsufficiency also led to low bone mass in males lacking functional androgen receptor (AR) (tfm mutants). The protective skeletal effect of AR against Wnt-related low bone mass is not necessarily a result of direct interaction between the AR and Wnt signaling pathways, because Lef1(+/-) female mice had normal bone mass at the age of 34 weeks. Thus, our results indicate an age- and gender-dependent role for Lef1 in regulating bone formation and bone mass in vivo. The resistance to Lef1 haploinsufficiency in males with active AR and in old females could be due to the reduced bone turnover in these mice.

Ror2 modulates the canonical Wnt signaling in lung epithelial cells through cooperation with Fzd2.

BACKGROUND: Wnt signaling is mediated through 1) the beta-catenin dependent canonical pathway and, 2) the beta-catenin independent pathways. Multiple receptors, including Fzds, Lrps, Ror2 and Ryk, are involved in Wnt signaling. Ror2 is a single-span transmembrane receptor-tyrosine kinase (RTK). The functions of Ror2 in mediating the non-canonical Wnt signaling have been well established. The role of Ror2 in canonical Wnt signaling is not fully understood. RESULTS: Here we report that Ror2 also positively modulates Wnt3a-activated canonical signaling in a lung carcinoma, H441 cell line. This activity of Ror2 is dependent on cooperative interactions with Fzd2 but not Fzd7. In addition, Ror2-mediated enhancement of canonical signaling requires the extracellular CRD, but not the intracellular PRD domain of Ror2. We further provide evidence that the positive effect of Ror2 on canonical Wnt signaling is inhibited by Dkk1 and Krm1 suggesting that Ror2 enhances an Lrp-dependent STF response. CONCLUSION: The current study demonstrates the function of Ror2 in modulating canonical Wnt signaling. These findings support a functional scheme whereby regulation of Wnt signaling is achieved by cooperative functions of multiple mediators.

Distribution of macrophages, osteoclasts and the B-lymphocyte lineage in osteolytic metastasis of mouse mammary carcinoma.

The purpose of this study was to examine the localization of macrophages, B-lymphocytes and osteoclasts in tumoral lesions of mammary carcinoma metastasized to bone of non-immunocompromised mice. Mouse mammary carcinoma cells (BALB/c-MC) were injected through the left cardiac ventricle into 5-week-old female wild-type Balb/c mice. The femora and tibiae of mice with metastasized cancer were extracted, and thereafter processed for histochemical analyses. The foci of metastasized tumor cells occupied the metaphyseal area, and the cell death zones could be identified within the tumor mass. Abundant tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts were found among the alkaline phosphatase (ALP)-reactive osteoblastic cell layer that covered the bone surface neighboring the metastatic lesion. In contrast, F4/80-positive macrophages/monocytes were localized adjacent to, or invading the metastatic tissue. In addition, some F4/80-positive cells were found in the aforementioned cell death zones. Unlike F4/80-positive cells, CD45R-positive B-lymphocytes did not accumulate at the surfaces of the tumor lesions, nor infiltrate into them, but were found scattered over bone marrow. Interestingly, some CD45R-positive cells were observed close to TRAP-positive osteoclasts in the stromal tissue surrounding the tumor lesion. Our findings suggest that, in the bone metastatic lesions of non-immunocompromised mice, F4/80-positive macrophages/monocytes accumulated on and/or infiltrated into the tumor nests, while CD45R-positive B-lymphocytes were associated with osteoclasts, rather than attacking metastatic tumor cells.

Cell autonomous requirement for TGF-beta signaling during odontoblast differentiation and dentin matrix formation.

TGF-beta subtypes are expressed in tissues derived from cranial neural crest cells during early mouse craniofacial development. TGF-beta signaling is critical for mediating epithelial-mesenchymal interactions, including those vital for tooth morphogenesis. However, it remains unclear how TGF-beta signaling contributes to the terminal differentiation of odontoblast and dentin formation during tooth morphogenesis. Towards this end, we generated mice with conditional inactivation of the Tgfbr2 gene in cranial neural crest derived cells. Odontoblast differentiation was substantially delayed in the Tgfbr2(fl/fl);Wnt1-Cre mutant mice at E18.5. Following kidney capsule transplantation, Tgfbr2 mutant tooth germs expressed a reduced level of Col1a1 and Dspp and exhibited defects including decreased dentin thickness and absent dentinal tubules. In addition, the expression of the intermediate filament nestin was decreased in the Tgfbr2 mutant samples. Significantly, exogenous TGF-beta2 induced nestin and Dspp expression in dental pulp cells in the developing tooth organ. Our data suggest that TGF-beta signaling controls odontoblast maturation and dentin formation during tooth morphogenesis.

The role of TGF-beta signaling in regulating chondrogenesis and osteogenesis during mandibular development.

During craniofacial development, Meckel's cartilage and the mandible bone derive from the first branchial arch, and their development depends upon the contribution of cranial neural crest (CNC) cells. We previously demonstrated that conditional inactivation of Tgfbr2 in the neural crest of mice (Tgfbr2(fl/fl);Wnt1-Cre) results in severe defects in mandibular development, although the specific cellular and molecular mechanisms by which TGF-beta signaling regulates the fate of CNC cells during mandibular development remain unknown. We show here that loss of Tgfbr2 does not affect the migration of CNC cells during mandibular development. TGF-beta signaling is specifically required for cell proliferation in Meckel's cartilage and the mandibular anlagen and for the formation of the coronoid, condyle and angular processes. TGF-beta-mediated connective tissue growth factor (CTGF) signaling is critical for CNC cell proliferation. Exogenous CTGF rescues the cell proliferation defect in Meckel's cartilage of Tgfbr2(fl/fl);Wnt1-Cre mutants, demonstrating the biological significance of this signaling cascade in chondrogenesis during mandibular development. Furthermore, TGF-beta signaling controls Msx1 expression to regulate mandibular osteogenesis as Msx1 expression is significantly reduced in Tgfbr2(fl/fl);Wnt1-Cre mutants. Collectively, our data suggest that there are differential signal cascades in response to TGF-beta to control chondrogenesis and osteogenesis during mandibular development.

TGFbeta-mediated FGF signaling is crucial for regulating cranial neural crest cell proliferation during frontal bone development.

The murine frontal bone derives entirely from the cranial neural crest (CNC) and consists of the calvarial (lateral) aspect that covers the frontal lobe of brain and the orbital aspect that forms the roof of bony orbit. TGFbeta and FGF signaling have important regulatory roles in postnatal calvarial development. Our previous study has demonstrated that conditional inactivation of Tgfbr2 in the neural crest results in severe defects in calvarial development, although the cellular and molecular mechanisms by which TGFbeta signaling regulates the fate of CNC cells during frontal bone development remain unknown. Here, we show that TGFbeta IIR is required for proliferation of osteoprogenitor cells in the CNC-derived frontal bone anlagen. FGF acts downstream of TGFbeta signaling in regulating CNC cell proliferation, and exogenous FGF2 rescues the cell proliferation defect in the frontal primordium of Tgfbr2 mutant. Furthermore, the CNC-derived frontal primordium requires TGFbeta IIR to undergo terminal differentiation. However, this requirement is restricted to the developing calvarial aspect of the frontal bone, whereas the orbital aspect forms despite the ablation of Tgfbr2 gene, implying a differential requirement for TGFbeta signaling during the development of various regions of the frontal bone. This study demonstrates the biological significance of TGFbeta-mediated FGF signaling cascade in regulating frontal bone development, suggests that TGFbeta functions as a morphogen in regulating the fate of the CNC-derived osteoblast and provides a model for investigating abnormal craniofacial development.

Cardiovascular malformations with normal smooth muscle differentiation in neural crest-specific type II TGFbeta receptor (Tgfbr2) mutant mice.

Previous studies have demonstrated that TGFbeta induces a smooth muscle fate in primary neural crest cells in culture. By crossing a conditional allele of the type II TGFbeta receptor with the neural crest-specific Wnt1cre transgene, we have addressed the in vivo requirement for TGFbeta signaling in smooth muscle specification and differentiation. We find that elimination of the TGFbeta receptor does not alter neural crest cell specification to a smooth muscle fate in the cranial or cardiac domains, and that a smooth muscle fate is not realized by trunk neural crest cells in either control or mutant embryos. Instead, mutant embryos exhibit with complete penetrance two very specific and mechanistically distinct cardiovascular malformations--persistent truncus arteriosus (PTA) and interrupted aortic arch (IAA-B). Pharyngeal organ defects such as those seen in models of DiGeorge syndrome were not observed, arguing against an early perturbation of the cardiac neural crest cell lineage. We infer that TGFbeta is an essential morphogenic signal for the neural crest cell lineage in specific aspects of cardiovascular development, although one that is not required for smooth muscle differentiation.

LEF1 is a critical epithelial survival factor during tooth morphogenesis.

LEF1 is a cell-type-specific transcription factor and mediates Wnt signaling pathway by association with its co-activator beta-catenin. Wnt signaling is known to be critical for the specification of cranial neural crest (CNC) cells and may regulate the fate diversity of the CNC during craniofacial morphogenesis. Loss of Lef1 results in arrested tooth development at the late bud stage and LEF1 is required for a relay of a Wnt signaling to a cascade of FGF signaling activities to mediate the epithelial-mesenchymal interaction during tooth morphogenesis. It remains unclear, however, what is the cellular mechanism of LEF1 signaling in regulating tooth morphogenesis. To test the hypothesis that LEF1 signaling regulates the fate of the dental epithelial and the CNC-derived mesenchymal cells during tooth morphogenesis, we investigated and compared the cellular migration, proliferation, and apoptotic activity within the tooth germ between the wild-type and Lef1 null mutant mice. Using the Wnt1-Cre/R26R transgenic system for indelibly marking the progenies of CNC cells, we show that there is no CNC migration defect in the Lef1 null mutant mice, indicating that the arrest in tooth development is not the result of shortage of the CNC contribution into the first branchial arch in the Lef1 mutant. Furthermore, there is no alteration in cell proliferation or condensation of the CNC-derived dental mesenchyme in the Lef1 null mutant, suggesting that LEF1 may not affect the cell cycle progression of the multipotential CNC cells during tooth morphogenesis. Importantly, apoptotic activity is significantly increased within the dental epithelium in the Lef1 null mutant mice. As the result of this increased cell death, the bud stage tooth germ fails to advance to the cap stage in the absence of Lef1. Inhibition of apoptotic activity by FGF4 rescues the tooth development in the Lef1 null mutant. Our studies suggest that LEF1 is a critical survival factor for the dental epithelial cells during tooth morphogenesis.

1Alpha,25-dihydroxyvitamin D3 promotes vascularization of the chondro-osseous junction by stimulating expression of vascular endothelial growth factor and matrix metalloproteinase 9.

Vitamin D deficiency results in defects in endochondral bone development characteristic of rickets, which include elongation of the cartilaginous growth plates and disorganization of the primary spongiosa. These defects are caused in part by impaired cartilage mineralization and vascularization of the chondro-osseous junction. Blood vessel invasion of mineralized cartilage is an essential step in endochondral ossification, providing access for cells that degrade cartilage as well as those that form bone. Vascular endothelial growth factor (VEGF) was shown to be a key regulator of this process when infusion of a dominant negative VEGF receptor effectively blocked vascular invasion and endochondral ossification in the growth plates of juvenile mice. Here, we show that the active metabolite of vitamin D 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] directly stimulates transcription of mRNAs encoding VEGF121 and -165 isoforms in the CFK2 chondrogenic cell line. Enhanced VEGF expression also was evident in growth plate chondrocytes and osteoblasts in the tibia of juvenile mice treated systemically with 1alpha,25(OH)2D3. This was seen in conjunction with enhanced expression of matrix metalloproteinase (MMP) 9, which activates VEGF stored in the cartilage matrix, in osteoclastic cells adjacent to the chondro-osseous junction. The alterations in VEGF and MMP-9 expression were accompanied by enhanced vascular invasion of mineralized cartilage, as assessed by CD31 immunoreactivity. These results provide evidence that 1alpha,25(OH)2D3 signaling stimulates VEGF and MMP-9 gene expression and promotes neovascularization of the epiphyseal growth plate in vivo through increased availability of active growth factor.

Involvement of cyclo-oxygenase-2 in osteoclast formation and bone destruction in bone metastasis of mammary carcinoma cell lines.

We previously reported that mouse mammary carcinoma cell lines (MMT060562 and BALB/c-MC) induced osteoclast formation through production of prostaglandin E2 (PGE2) in cocultures with mouse bone marrow cells, but the mechanism(s) of PG production remained unclear. In the present in vitro and in vivo studies, we tested the involvement of cyclo-oxygenase-2 (COX-2), an inducible rate-limiting enzyme in PG biosynthesis, in the stimulation of osteoclast formation by mouse mammary carcinoma cell lines. Addition of a selective COX-2 inhibitor, JTE-522, to cocultures of mammary carcinoma cell lines and bone marrow cells lowered PGE2 concentration in the culture media and inhibited osteoclast formation in a dose-dependent manner. Northern blotting showed a very high level of COX-2 messenger RNA (mRNA) expression in MMT060562. The mRNA expression was low in BALB/c-MC, but it increased when BALB/c-MC and bone marrow cells were cocultured. The results of immunocytochemistry for COX-2 protein in respective cultures were compatible with the results of COX-2 mRNA. In vivo, BALB/c-MC injected into the heart of Balb/c mice metastasized to bone and formed osteolytic lesions in their hindlimbs. Histological examination revealed that tumor cells had metastasized to the bone marrow cavity and destroyed the bone trabeculae. Immunohistochemistry demonstrated that bone marrow stromal cells adjacent to tumor cells expressed COX-2 protein. These findings suggest that COX-2 plays an important role in the osteolysis of bone metastasis in vivo as well as in osteoclast formation in cocultures used as an in vitro model of metastatic bone disease.

[The biological role of blood vessels during endochondral bone formation].

Endothelial cells play an important role in endochondral bone formation. In the chondro-osseous junction, endothelial cells appear to invade into cartilage by the cellular mechanism of angiogenesis evidenced by cell duplication, disappearance of basement membranes and activated migration. The endothelial cells penetrate the unmineralized transverse partition of the cartilage columns.