Genetic interactions between Pax9 and Msx1 regulate lip development and several stages of tooth morphogenesis

Developmental abnormalities of craniofacial structures and teeth often occur sporadically and the underlying genetic defects are not well understood, in part due to unknown gene-gene interactions. Pax9 and Msx1 are co-expressed during craniofacial development, and mice that are single homozygous mutant for either gene exhibit cleft palate and an early arrest of tooth formation. Whereas in vitro assays have demonstrated that protein-protein interactions between Pax9 and Msx1 can occur, it is unclear if Pax9 and Msx1 interact genetically in vivo during development. To address this question, we compounded the Pax9 and Msx1 mutations and observed that double homozygous mutants exhibit an incompletely penetrant cleft lip phenotype. Moreover, in double heterozygous mutants, the lower incisors were consistently missing and we find that transgenic BMP4 expression partly rescues this phenotype. Reduced expression of Shh and Bmp2 indicates that a smaller “incisor field” forms in Pax9^+/−;Msx1^+/− mutants, and dental epithelial growth is substantially reduced after the bud to cap stage transition. This defect is preceded by drastically reduced mesenchymal expression of Fgf3 and Fgf10, two genes that encode known stimulators of epithelial growth during odontogenesis. Consistent with this result, cell proliferation is reduced in both the dental epithelium and mesenchyme of double heterozygous mutants. Furthermore, the developing incisors lack mesenchymal Notch1 expression at the bud stage and exhibit abnormal ameloblast differentiation on both labial and lingual surfaces. Thus, Msx1 and Pax9 interact synergistically throughout lower incisor development and affect multiple signaling pathways that influence incisor size and symmetry. The data also suggest that a combined reduction of PAX9 and MSX1 gene dosage in humans may increase the risk for orofacial clefting and oligodontia.     

Msx2 alters the timing of retinal ganglion cells fate commitment and differentiation

Timing of cell fate commitment determines distinct retinal cell types, which is believed to be controlled by a tightly coordinated regulatory program of proliferation, cell cycle exit and differentiation. Although homeobox protein Msx2 could induce apoptosis of optic vesicle, it is unclear whether Msx2 regulates differentiation and cell fate commitment of retinal progenitor cells (RPCs) to retinal ganglion cells (RGCs). In this study, we show that overexpression of Msx2 transiently suppressed the expression of Cyclin D1 and blocked cell proliferation. Meanwhile, overexpression of Msx2 delayed the expression of RGC-specific differentiation markers (Math5 and Brn3b), which showed that Msx2 could affect the timing of RGCs fate commitment and differentiation by delaying the timing of cell cycle exit of retinal progenitors. These results indicate Msx2 possesses dual regulatory functions in controlling cell cycle progression of retinal RPCs and timing of RGCs differentiation.     

Cyclical expression of the Notch/Wnt regulator Nrarp requires modulation by Dll3 in somitogenesis

Delta-like 3 (Dll3) is a divergent ligand and modulator of the Notch signaling pathway only identified so far in mammals. Null mutations of Dll3 disrupt cycling expression of Notch targets Hes1, Hes5, and Lfng, but not of Hes7. Compared with Dll1 or Notch1, the effects of Dll3 mutations are less severe for gene expression in the presomitic mesoderm, yet severe segmentation phenotypes and vertebral defects result in both human and mouse. Reasoning that Dll3 specifically disrupts key regulators of somite cycling, we carried out functional analysis to identify targets accounting for the segmental phenotype. Using microdissected embryonic tissue from somitic and presomitic mesodermal tissue, we identified new genes enriched in these tissues, including Limch1, Rhpn2, and A130022J15Rik. Surprisingly, we only identified a small number of genes disrupted by the Dll3 mutation. These include Uncx, a somite gene required for rib and vertebral patterning, and Nrarp, a regulator of Notch/Wnt signaling in zebrafish and a cycling gene in mouse. To determine the effects of Dll3 mutation on Nrarp, we characterized the cycling expression of this gene from early (8.5 dpc) to late (10.5 dpc) somitogenesis. Nrarp displays a distinct pattern of cycling phases when compared to Lfng and Axin2 (a Wnt pathway gene) at 9.5 dpc but appears to be in phase with Lfng by 10.5 dpc. Nrarp cycling appears to require Dll3 but not Lfng modulation. In Dll3 null embryos, Nrarp displayed static patterns. However, in Lfng null embryos, Nrarp appeared static at 8.5 dpc but resumed cycling expression by 9.5 and dynamic expression at 10.5 dpc stages. By contrast, in Wnt3a null embryos, Nrarp expression was completely absent in the presomitic mesoderm. Towards identifying the role of Dll3 in regulating somitogenesis, Nrarp emerges as a potentially important regulator that requires Dll3 but not Lfng for normal function.     

Characterization and expression of cry4Cb1 and cry30Ga1 from Bacillus thuringiensis strain HS18-1

We characterized a novel Bacillus thuringiensis isolate native to China (HS18-1) that shows a spherical crystal harboring two major proteins of about 70 and 130 kDa, and contains three novel cry genes (cry4Cb1, cry30Ga1, cry54-type). Furthermore, the cry4Cb1 and cry30Ga1 genes were expressed in Escherichia coli BL21 (DE3): pLysS. Insecticidal activity tests showed that the cry4Cb1 protein exhibited larvicidal activity against Aedes aegypti (Diptera) and the cry30Ga1 protein was toxic to both A. aegypti and P. xylostella (Lepidoptera).     

Notch2 is required for maintaining sustentacular cell function in the adult mouse main olfactory epithelium

Notch receptors are expressed in neurons and glia in the adult nervous system, but why this expression persists is not well-understood. Here we examine the role of the Notch pathway in the postnatal mouse main olfactory system, and show evidence consistent with a model where Notch2 is required for maintaining sustentacular cell function. In the absence of Notch2, the laminar nature of these glial-like cells is disrupted. Hes1, Hey1, and Six1, which are downstream effectors of the Notch pathway, are down-regulated, and cytochrome P450 and Glutathione S-transferase (GST) expression by sustentacular cells is reduced. Functional levels of GST activity are also reduced. These disruptions are associated with increased olfactory sensory neuron degeneration. Surprisingly, expression of Notch3 is also down-regulated. This suggests the existence of a feedback loop where expression of Notch3 is initially independent of Notch2, but requires Notch2 for maintained expression. While the Notch pathway has previously been shown to be important for promoting gliogenesis during development, this is the first demonstration that the persistent expression of Notch receptors is required for maintaining glial function in adult.     

Bmpr1a is required for proper migration of the AVE through regulation of Dkk1 expression in the pre-streak mouse embryo

Here, we report a novel mechanism regulating migration of the anterior visceral endoderm (AVE) by BMP signaling through BMPRIA. In Bmpr1a-deficient (Bmpr-null) embryos, the AVE does not migrate at all. In embryos with an epiblast-specific deletion of Bmpr1a (Bmpr1a^null/flox; Sox2Cre embryos), the AVE cells migrate randomly from the distal end of embryos, resulting in an expansion of the AVE. Dkk1, which is normally expressed in the anterior proximal visceral endoderm (PxVE), is downregulated in Bmpr-null embryos, whereas it is circumferentially expressed in Bmpr1a^null/flox; Sox2Cre embryos at E5.75-6.5. These results demonstrate an association of the position of Dkk1 expressing cells with direction of the migration of AVE. In Bmpr1a^null/flox; Sox2Cre embryos, a drastic decrease of WNT signaling is observed at E6.0. Addition of WNT3A to the culture of Bmpr1a^null/flox; Sox2Cre embryos at E5.5 restores expression patterns of Dkk1 and Cer1. These data indicate that BMP signaling in the epiblast induces Wnt3 and Wnt3a expression to maintain WNT signaling in the VE, resulting in downregulation of Dkk1 to establish the anterior expression domain. Thus, our results suggest that BMP signaling regulates the expression patterns of Dkk1 for anterior migration of the AVE.     

The interplay between SUCLA2, SUCLG2, and mitochondrial DNA depletion

SUCLA2-related mitochondrial DNA (mtDNA) depletion syndrome is a result of mutations in the β subunit of the ADP-dependent isoform of the Krebs cycle succinyl-CoA synthase (SCS). The mechanism of tissue specificity and mtDNA depletion is elusive but complementation by the GDP-dependent isoform encoded by SUCLG2, and the association with mitochondrial nucleoside diphosphate kinase (NDPK), is a plausible link.We have investigated this relationship by studying SUCLA2 deficient fibroblasts derived from patients and detected normal mtDNA content and normal NDPK activity. However, knockdown of SUCLG2 by shRNA in both patient and control fibroblasts resulted in a significant decrease in mtDNA amount, decreased NDPK and cytochrome c oxidase activities, and a marked growth impairment. This suggests that, SUCLG2, to a higher degree than SUCLA2, is crucial for mtDNA maintenance and that mitochondrial NDPK is involved. Although results pertain to a cell culture system, the findings might explain the pathomechanism and tissue specificity in mtDNA depletion caused by defective SUCLA2.     

Otx2 and Otx1 protect diencephalon and mesencephalon from caudalization into metencephalon during early brain regionalization

Otx2 is expressed in each step and site of head development. To dissect each Otx2 function we have identified a series of Otx2 enhancers. The Otx2 expression in the anterior neuroectoderm is regulated by the AN enhancer and the subsequent expression in forebrain and midbrain later than E8.5 by FM1 and FM2 enhancers; the Otx1 expression takes place at E8.0. In telencephalon later than E9.5 Otx1 continues to be expressed in the entire pallium, while the Otx2 expression is confined to the most medial pallium. To determine the Otx functions in forebrain and midbrain development we have generated mouse mutants that lack both FM1 and FM2 enhancers (DKO: Otx2^{ΔFM1ΔFM2/ΔFM1ΔFM2}) and examined the TKO (Otx1^−/−Otx2^{ΔFM1ΔFM2/ΔFM1ΔFM2}) phenotype. The mutants develop normally until E8.0, but subsequently by E9.5 the diencephalon, including thalamic eminence and prethalamus, and the mesencephalon are caudalized into metencephalon consisting of isthmus and rhombomere 1; the caudalization does not extend to rhombomere 2 and more caudal rhombomeres. In rostral forebrain, neopallium, ganglionic eminences and hypothalamus in front of prethalamus develop; we propose that they become insensitive to the caudalization with the switch from the Otx2 expression under the AN enhancer to that under FM1 and FM2 enhancers. In contrast, the medial pallium requires Otx1 and Otx2 for its development later than E9.5, and the Otx2 expression in diencepalon and mesencephalon later than E9.5 is also directed by an enhancer other than FM1 and FM2 enhancers.     

br regulates the expression of the ecdysone biosynthesis gene npc1

The growth and metamorphosis of insects are regulated by ecdysteroid hormones produced in the ring gland. Ecdysone biosynthesis-related genes are both highly and specifically expressed in the ring gland. However, the intrinsic regulation of ecdysone biosynthesis has received little attention. Here we used the Drosophila npc1 gene to study the mechanism of ring gland-specific gene expression. npc1 is important for sterol trafficking in the ring gland during ecdysone biosynthesis. We have identified a conserved ring gland-specific cis-regulatory element (RSE) in the npc1 promoter using promoter fusion reporter analysis. Furthermore, genetic loss-of-function analysis and in vitro electrophoretic mobility shift assays revealed that the ecdysone early response gene broad complex (br) is a vital factor in the positive regulation of npc1 ring gland expression. Moreover, br also affects the ring gland expression of many other ecdysone biosynthetic genes as well as torso and InR, two key factors in the regulation of ecdysone biosynthesis. These results imply that ecdysone could potentially act through its early response gene br to achieve positive feedback regulation of ecdysone biosynthesis during development.     

Mutation and expression analysis of the IDH1, IDH2, DNMT3A, and MYD88 genes in colorectal cancer

Colorectal cancer (CRC) is one of the leading causes of death around the world. Its genetic mechanism was intensively investigated in the past decades with findings of a number of canonical oncogenes and tumor-suppressor genes such as APC, KRAS, and TP53. Recent genome-wide association and sequencing studies have identified a series of promising oncogenes including IDH1, IDH2, DNMT3A, and MYD88 in hematologic malignancies. However, whether these genes are involved in CRC remains unknown. In this study, we screened the hotspot mutations of these four genes in 305 CRC samples from Han Chinese by direct sequencing. mRNA expression levels of these genes were quantified by quantitative real-time PCR (RT-qPCR) in paired cancerous and paracancerous tissues. Association analyses between mRNA expression levels and different cancerous stages were performed. Except for one patient harboring IDH1 mutation p.I99M, we identified no previously reported hotspot mutations in colorectal cancer tissues. mRNA expression levels of IDH1, DNMT3A, and MYD88, but not IDH2, were significantly decreased in the cancerous tissues comparing with the paired paracancerous normal tissues. Taken together, the hotspot mutations of IDH1, IDH2, DNMT3A, and MYD88 gene were absent in CRC. Aberrant mRNA expression of IDH1, DNMT3A, and MYD88 gene might be actively involved in the development of CRC.     

Rpi-blb2-mediated late blight resistance in Nicotiana benthamiana requires SGT1 and salicylic acid-mediated signaling but not RAR1 or HSP90

The Rpi-blb2 recognizes the presence of the Phytophthora infestans AVRblb2 and initiates effector-triggered immunity (ETI). We performed gain-of-function and loss-of-function studies in Nicotiana benthamiana to elucidate Rpi-blb2-mediated resistance to P. infestans. Rpi-blb2 triggered a hypersensitive response through SGT1-mediated, but not RAR-mediated or HSP90-mediated, pathways. NbSGT1 was also required for basal and ETI-mediated by Rpi-blb2 in N. benthamiana. Moreover, salicylic acid (SA) affected basal defense and Rpi-blb2-mediated resistance against P. infestans. The increased susceptibility of Rpi-blb2-transgenic plants in the NahG-background correlated with reduced levels of SA. These findings provide evidence for the roles of SGT1- and SA-signaling in Rpi-blb2-mediated resistance against P. infestans.