Search for appropriate reference genes for quantitative reverse transcription PCR studies in somite, prosencephalon and heart of early mouse embryo.

qRT-PCR requires reliable internal control genes stably expressed in different samples and experimental conditions. The stability of reference genes is rarely tested experimentally, especially in developing tissues given the singularity of these samples. Here we evaluated the suitability of a set of reference genes (Actb, Gapdh, Tbp, Pgk1 and Sdha) using samples from early mouse embryo tissues that are widely used in research (somites, prosencephalon and heart) at different developmental stages. The comparative ΔCq method and five software packages (NormFinder, geNorm, BestKeeper, DataAssist and RefFinder) were used to rank the most stable genes while GenEx and GeNorm programs determined the optimal total number of reference genes for a reliable normalization. The ranking of most reliable reference genes was different for each tissue evaluated: (1) in somite from embryos with 16-18 somite pairs stage, the combination of Pgk1 and Actb provided the best normalization and Actb also presented high stability levels at an earlier developmental stage; (2) Gapdh is the most stable gene in prosencephalon in the two developmental stages tested; and (3) in heart samples, Sdha, Gapdh and Actb were the best combination for qPCR normalization. The analysis of these three tissues simultaneously indicated the combination of Gapdh, Actb and Tbp as the most reliable internal control. This study highlights the importance of appropriate reference genes according to the cell type and/or tissue of interest. The data here described can be applied in future research using mouse embryos as a model for mammalian development.

BMP signaling modulates hepcidin expression in zebrafish embryos independent of hemojuvelin.

Hemojuvelin (Hjv), a member of the repulsive-guidance molecule (RGM) family, upregulates transcription of the iron regulatory hormone hepcidin by activating the bone morphogenetic protein (BMP) signaling pathway in mammalian cells. Mammalian models have identified furin, neogenin, and matriptase-2 as modifiers of Hjv's function. Using the zebrafish model, we evaluated the effects of hjv and its interacting proteins on hepcidin expression during embryonic development. We found that hjv is strongly expressed in the notochord and somites of the zebrafish embryo and that morpholino knockdown of hjv impaired the development of these structures. Knockdown of hjv or other hjv-related genes, including zebrafish orthologs of furin or neogenin, however, failed to decrease hepcidin expression relative to liver size. In contrast, overexpression of bmp2b or knockdown of matriptase-2 enhanced the intensity and extent of hepcidin expression in zebrafish embryos, but this occurred in an hjv-independent manner. Furthermore, we demonstrated that zebrafish hjv can activate the human hepcidin promoter and enhance BMP responsive gene expression in vitro, but is expressed at low levels in the zebrafish embryonic liver. Taken together, these data support an alternative mechanism for hepcidin regulation during zebrafish embryonic development, which is independent of hjv.

VPA-related axial skeletal defects and apoptosis: a proposed event cascade.

VPA axial malformations are related to embryonic somitic histone hyperacetylation. In cancer, histone hyperacetylation activates apoptosis. To verify if apoptosis is involved in somitic abnormalities, VPA-exposed embryos were evaluated for DNA fragmentation and for pro- (p53, acetylated p53, caspase 3) and anti-apoptotic (Sirt 1) protein expression. Pregnant mice were i.p. dosed on day 8 with VPA 400mg/kg or TSA (16 mg/kg). Embryos, collected 3, 5, 9 or 24h after treatment, were examined and processed for apoptosis or protein analysis. An event cascade has been observed at the level of somites and proposed as related to VPA-induced axial skeletal defects: increased p53 (3h), DNA fragmentation (9h), abnormalities (24h). TSA, used as alternative HDAC inhibitor, induced apoptosis and somitic abnormalities, strengthening our hypothesized link between HDAC inhibition and axial defects.

Cooperation of Mtmr8 with PI3K regulates actin filament modeling and muscle development in zebrafish.

BACKGROUND: It has been shown that mutations in at least four myotubularin family genes (MTM1, MTMR1, 2 and 13) are causative for human neuromuscular disorders. However, the pathway and regulative mechanism remain unknown. METHODOLOGY/PRINCIPAL FINDINGS: Here, we reported a new role for Mtmr8 in neuromuscular development of zebrafish. Firstly, we cloned and characterized zebrafish Mtmr8, and revealed the expression pattern predominantly in the eye field and somites during early somitogenesis. Using morpholino knockdown, then, we observed that loss-of-function of Mtmr8 led to defects in somitogenesis. Subsequently, the possible underlying mechanism and signal pathway were examined. We first checked the Akt phosphorylation, and observed an increase of Akt phosphorylation in the morphant embryos. Furthermore, we studied the PH/G domain function within Mtmr8. Although the PH/G domain deletion by itself did not result in embryonic defect, addition of PI3K inhibitor LY294002 did give a defective phenotype in the PH/G deletion morphants, indicating that the PH/G domain was essential for Mtmr8's function. Moreover, we investigated the cooperation of Mtmr8 with PI3K in actin filament modeling and muscle development, and found that both Mtmr8-MO1 and Mtmr8-MO2+LY294002 led to the disorganization of the actin cytoskeleton. In addition, we revealed a possible participation of Mtmr8 in the Hedgehog pathway, and cell transplantation experiments showed that Mtmr8 worked in a non-cell autonomous manner in actin modeling. CONCLUSION/SIGNIFICANCE: The above data indicate that a conserved functional cooperation of Mtmr8 with PI3K regulates actin filament modeling and muscle development in zebrafish, and reveal a possible participation of Mtmr8 in the Hedgehog pathway. Therefore, this work provides a new clue to study the physiological function of MTM family members.

Snail genes at the crossroads of symmetric and asymmetric processes in the developing mesoderm.

Retinoic acid (RA) signalling ensures that vertebrate mesoderm segmentation is bilaterally synchronized, and corrects transient interferences from asymmetric left-right (L-R) signals involved in organ lateralization. Snail genes participate in both these processes and, although they are expressed symmetrically in the presomitic mesoderm (PSM), Snail1 transcripts are asymmetrically distributed in the L-R lateral mesoderm. We show that the alteration of the symmetric Snail expression in the PSM induces asynchronous somite formation. Furthermore, in the absence of RA signalling, normal asymmetric Snail1 expression in the lateral mesoderm is extended to the PSM, desynchronizing somitogenesis. Thus, Snail1 is the first cue corrected by RA in the PSM to ensure synchronized bilateral segmentation.

Differential tissue expression of a calpastatin isoform in Xenopus embryos.

This study is aimed at demonstrating the role played by a calpastatin isoform (Xcalp3) in Xenopus embryos. A specific monoclonal antibody (mAb) was raised against a glutathione S-transferase (GST)-Xcalp3 fusion protein and characterized by immunoblotting and confocal fluorescence microscopy on stage 20-36 embryos. Under these conditions, calpastatin reactivity is associated with a major 110kDa protein fraction and preferentially expressed by notochord and somitic cells. In notochord cells, anti-calpastatin reactive sites were initially restricted to the luminal space of the vacuoles and later became diffused throughout the cytoplasm. In contrast, anti-calpastatin reactive sites in somitic cells were initially diffused throughout the cytoplasm and became restricted to a few intracellular granules in the later developmental stages. At the ultrastructural level, notochord cells appeared as flattened discs containing several vacuoles and numerous electron-dense granules. During transition from stages 26 to 32, electron-dense granules were gradually reduced in number as vacuoles enlarged in size and losed their calpastatin reactivity. Electron-dense granules were also present in myoblast cells and their number gradually reduced during development. To determine whether these observations bear any causal relationship to the calpain/calpastatin system, a number of Xenopus embryos were examined both ultrastructurally and histochemically following exposure to a specific calpain inhibitor (CI3). Under these conditions, Xenopus embryos exhibited an altered right-left symmetry and an abnormal axial shortening. In CI3-treated stage 32 embryos, notochord cells had a reduced vacuolar extension and exhibited at the same time an increase in granular content. The overall morphology of the somites was also distorted and myoblasts were altered both in shape and granular content. Based on these findings, it is concluded that the calpain/calpastatin may play an important role in the control of notochord elongation and somite differentiation during Xenopus embryogenesis.

Dact1 presomitic mesoderm expression oscillates in phase with Axin2 in the somitogenesis clock of mice.

During segmentation (somitogenesis) in vertebrate embryos, somites form in a rostral-to-caudal sequence according to a species-specific rhythm called the somitogenesis clock. The expression of genes participating in somitogenesis oscillates in the presomitic mesoderm (PSM) in time with this clock. We previously reported that the Dact1 gene (aka Dpr1/Frd1/ThyEx3), which encodes a Dishevelled-binding intracellular regulator of Wnt signaling, is prominently expressed in the PSM as well as in a caudal-rostral gradient across the somites of mouse embryos. This observation led us to examine whether Dact1 expression oscillates in the PSM. We have found that Dact1 PSM expression does indeed oscillate in time with the somitogenesis clock. Consistent with its known signaling functions and with the "clock and wavefront" model of signal regulation during somitogenesis, the oscillation of Dact1 occurs in phase with the Wnt signaling component Axin2, and out of phase with the Notch signaling component Lfng.

Segmental expression of the T-box transcription factor, Tbx2, during early somitogenesis.

Tbx2 belongs to the T-box transcription factor gene family and is expressed in a variety of tissues and structures throughout development, although not all expression domains have been thoroughly described. Two areas of segmented expression along the rostral-caudal axis of E10.5-11.5 embryos were identified as inter-somitic vessels and dorsal root ganglia. In addition, Tbx2 expression is observed during somitogenesis beginning at E9.5, both in the posterior half of prospective somites and in a progressively restricted pattern in recently formed somites.

SOX13 exhibits a distinct spatial and temporal expression pattern during chondrogenesis, neurogenesis, and limb development.

SOX13 is a member of the SOX family of transcription factors. SOX proteins play essential roles in development, and some are associated with human genetic diseases. SOX13 maps to a multi-disease locus on chromosome 1q31-32, yet its function is unknown. Here we describe the temporal and spatial expression of SOX13 protein during mouse organogenesis. SOX13 is expressed in the three embryonic cell lineages, suggesting that it may direct various developmental processes. SOX13 is expressed in the developing central nervous system including the neural tube and the developing brain. Expression is also detected in the condensing mesenchyme and cartilage progenitor cells during endochondral bone formation in the limb as well as the somite sclerotome and its derivatives. SOX13 is also detected in the developing kidney, pancreas, and liver as well as in the visceral mesoderm of the extra-embryonic yolk sac and spongiotrophoblast layer of the placenta.

Mohawk is a novel homeobox gene expressed in the developing mouse embryo.

Homeodomain-containing proteins comprise a superfamily of transcription factors that participate in the regulation of almost all aspects of embryonic development. Here, we describe the mouse embryonic expression pattern of Mohawk, a new member of the TALE superclass of atypical homeobox genes that is most-closely related to the Iroquois class. During mouse development, Mohawk was transcribed in cell lineages derived from the somites. As early as embryonic day 9.0, Mohawk was expressed in an anterior to posterior gradient in the dorsomedial and ventrolateral lips of the dermomyotome of the somites that normally give rise to skeletal muscle. Mohawk transcription in the dorsomedial region required the expression of the transcription factor paraxis. As somites matured, Mohawk transcription was observed in the tendon-specific syndetome and the sclerotome-derived condensing mesenchyme that prefigures the proximal ribs and vertebral bodies. In the limbs, Mohawk was expressed in a pattern consistent with the developing tendons that form along the dorsal and ventral aspect of the phalanges. Finally, Mohawk was detectable in the tips of the ureteric buds in the metanephric kidneys and the testis cords of the male gonad. Together, these observations suggest that Mohawk is an important regulator of vertebrate development.

Asymmetric localization of numb in the chick somite and the influence of myogenic signals.

Whereas Notch signaling is known to play an essential role in the formation of somites, its role during later stages of somite maturation is less well understood. Here, we examine the signals and transcription factors that control the expression of the Notch antagonist, Numb, during somite maturation in the chick embryo. Numb mRNA is present in the epithelial somite and is increased in expression in the forming myotome. Numb protein displays a very specific subcellular localization and dynamic expression during somite maturation. Numb protein is asymmetrically localized in a cortical crescent on the basal side of dividing cells in the dorsomedial lip of the dermomyotome and is subsequently uniformly distributed throughout differentiated myotomal cells. Treatment of somites with either the combination of Wnt-3a and Shh, or ectodermal signals plus noggin, both of which induce somitic myogenesis, did not significantly affect Numb transcript levels but did lead to a dramatic increase in the levels of Numb protein, which was uniformly distributed throughout the cytoplasm of the resultant myotubes. Forced expression of MyoD in somites similarly induced high levels of Numb protein throughout the cytoplasm, without affecting Numb mRNA levels. We also found that signals that promote somitic myogenesis or forced MyoD expression induced expression of the Notch ligand, Serrate-2. Our findings suggest that Notch signals are specifically repressed in the myotome and that asymmetric expression of Numb in dividing cells of the dorsomedial lip of the dermomyotome may modulate whether these cells continue to divide or differentiate into myotomal cells.

Expression of a novel somite-formation-related gene, AmphiSom, during amphioxus development.

A novel gene, AmphiSom, was identified in amphioxus Branchiostoma belcheri tsingtauense. Its sequence and developmental expression pattern were determined. AmphiSom transcripts were first detected in the presomitic mesoderm at the late gastrula stage and reached the highest level in the forming and nascent somites in neurulae. However, the expression of AmphiSom was rapidly down-regulated after somites were formed. It was maintained in the most anterior somite and most posterior somite at neurula stages. By 48 h, AmphiSom transcripts were detected only in the developing tail bud but were no longer detected in 72-h larva. Our data demonstrated that the AmphiSom gene is expressed during the development of somites in amphioxus and could play a role in somite formation.

Retinoic acid activates myogenesis in vivo through Fgf8 signalling.

Retinoic acid (RA) has been shown to regulate muscle differentiation in vitro. Here, we have investigated the role of RA signalling during embryonic myogenesis in zebrafish. We have altered RA signalling from gastrulation stages onwards by either inhibiting endogenous RA synthesis using an inhibitor of retinaldehyde dehydrogenases (DEAB) or by addition of exogenous RA. DEAB reduces expression of the myogenic markers myoD and myogenin in somites, whereas RA induces increased expression of these genes and strongly induces premature myoD expression in the presomitic mesoderm (psm). The expression dynamics of myf5 in presomitic and somitic mesoderm suggest that RA promotes muscle differentiation, a role supported by the fact that RA activates expression of fast myosin, while DEAB represses it. We identify Fgf8 as a major relay factor in RA-mediated activation of myogenesis. We show that fgf8 expression in somites and anterior psm is regulated by RA, and find that in the absence of Fgf8 signalling in the acerebellar mutant RA fails to promote myoD expression. We propose that, in the developing embryo, localised synthesis of RA by Raldh2 in the anterior psm and in somites activates fgf8 expression which in turn induces the expression of myogenic genes and fast muscle differentiation.

Core binding factor in the early avian embryo: cloning of Cbfbeta and combinatorial expression patterns with Runx1.

We have isolated the avian ortholog for CBFbeta, the common non-DNA binding subunit of the core binding factor (CBF) that has important regulatory roles in major developmental pathways. CBFbeta forms heterodimers with the DNA-binding Runx proteins and increases their affinity for DNA and their protein stability. Here, we describe the Cbfbeta expression pattern during the first 4 days of chick embryo development, with a special interest in the developing hematopoietic system. We have compared its expression pattern to that of Runx1, which is crucial for the generation of definitive hematopoietic cells, and to other hematopoietic- or endothelial-specific markers (c-Myb, Pu.1, CD45, c-Ets-1 and VE-Cadherin). Initially, Cbfbeta is widely expressed in the early mesoderm in both the yolk sac and the embryo proper, but later its expression becomes restricted to specific organs or cell types. We have found that Cbfbeta expression overlaps with Runx1 in the hematopoietic system and neural tube. The somitic and mesonephric structures, however, express Cbfbeta in the absence of detectable Runx1. Finally, Cbfbeta and Runx1 display multiple combinatorial patterns in the endoderm and in specific nerves or ganglia. Taken together, we show that Cbfbeta exhibits a dynamic expression pattern that varies according to the organ, cell type or developmental stage. By revealing multiple combinatorial patterns between Cbfbeta and Runx1, these data provide new insights into the role of CBF during early development.

Changes in gravitational force affect gene expression in developing organ systems at different developmental times.

BACKGROUND: Little is known about the affect of microgravity on gene expression, particularly in vivo during embryonic development. Using transgenic zebrafish that express the gfp gene under the influence of a beta-actin promoter, we examined the affect of simulated-microgravity on GFP expression in the heart, notochord, eye, somites, and rohon beard neurons. We exposed transgenic zebrafish to simulated-microgravity for different durations at a variety of developmental times in an attempt to determine periods of susceptibility for the different developing organ systems. RESULTS: The developing heart had a period of maximum susceptibility between 32 and 56 hours after fertilization when there was an approximately 30% increase in gene expression. The notochord, eye, somites, and rohon beard neurons all showed periods of susceptibility occurring between 24 and 72 hours after fertilization. In addition, the notochord showed a second period of susceptibility between 8 and 32 hours after fertilization. Interestingly, all organs appeared to be recovering by 80 hours after fertilization despite continued exposure to simulated-microgravity. CONCLUSION: These results support the idea that exposure to microgravity can cause changes in gene expression in a variety of developing organ systems in live embryos and that there are periods of maximum susceptibility to the effects.

Cloning and functional characterization of a novel connexin expressed in somites of Xenopus laevis.

Connexin-containing gap junctions play an essential role in vertebrate development. More than 20 connexin isoforms have been identified in mammals. However, the number identified in Xenopus trails with only six isoforms described. Here, identification of a new connexin isoform from Xenopus laevis is described. Connexin40.4 was found by screening expressed sequence tag databases and carrying out polymerase chain reaction on genomic DNA. This new connexin has limited amino acid identity with mammalian (<50%) connexins, but conservation is higher (approximately 62%) with fish. During Xenopus laevis development, connexin40.4 was first expressed after the mid-blastula transition. There was prominent expression in the presomitic paraxial mesoderm and later in the developing somites. In adult frogs, expression was detected in kidney and stomach as well as in brain, heart, and skeletal muscle. Ectopic expression of connexin40.4 in HEK293 cells, resulted in formation of gap junction like structures at the cell interfaces. Similar ectopic expression in neural N2A cells resulted in functional electrical coupling, displaying mild, asymmetric voltage dependence. We thus cloned a novel connexin from Xenopus laevis, strongly expressed in developing somites, with no apparent orthologue in mammals.

Skeletal defects in ringelschwanz mutant mice reveal that Lrp6 is required for proper somitogenesis and osteogenesis.

Here, we present evidence that Lrp6, a coreceptor for Wnt ligands, is required for the normal formation of somites and bones. By positional cloning, we demonstrate that a novel spontaneous mutation ringelschwanz (rs) in the mouse is caused by a point mutation in Lrp6, leading to an amino acid substitution of tryptophan for the evolutionarily conserved residue arginine at codon 886 (R886W). We show that rs is a hypomorphic Lrp6 allele by a genetic complementation test with Lrp6-null mice, and that the mutated protein cannot efficiently transduce signals through the Wnt/beta-catenin pathway. Homozygous rs mice, many of which are remarkably viable, exhibit a combination of multiple Wnt-deficient phenotypes, including dysmorphologies of the axial skeleton, digits and the neural tube. The establishment of the anteroposterior somite compartments, the epithelialization of nascent somites, and the formation of segment borders are disturbed in rs mutants, leading to a characteristic form of vertebral malformations, similar to dysmorphologies in individuals suffering from spondylocostal dysostosis. Marker expression study suggests that Lrp6 is required for the crosstalk between the Wnt and notch-delta signaling pathways during somitogenesis. Furthermore, the Lrp6 dysfunction in rs leads to delayed ossification at birth and to a low bone mass phenotype in adults. Together, we propose that Lrp6 is one of the key genetic components for the pathogenesis of vertebral segmentation defects and of osteoporosis in humans.

Mouse MafA, homologue of zebrafish somite Maf 1, contributes to the specific transcriptional activity through the insulin promoter.

Large Maf transcription factors, which are members of the basic leucine zipper (b-Zip) superfamily, have been reported to be involved in embryonic development and cell differentiation. Previously, we isolated a novel zebrafish large Maf cDNA, somite Maf1 (SMaf1), which possesses transactivational activity within its N-terminus domain. To elucidate SMaf1 function in mammals, we tried to isolate the mouse homologue of zebrafish SMaf1. We isolated the mouse homologue of zebrafish SMaf1, which is the same molecule as the recently reported MafA. MafA mRNA was detected in formed somites, head neural tube, and liver cells in the embryos. In the adult mouse, MafA transcript was amplified in the brain, lung, spleen, and kidney by RT-PCR. MafA mRNA was also detectable in beta-cell line. Next, we analyzed the transcriptional activity of MafA using rat insulin promoters I and II (RIPI and II), since a part of RIP sequence was similar to the Maf recognition element (MARE) and MafA was expressed in pancreatic beta cells. MafA was able to activate transcription from RIPII, but not RIPI, in a dose dependent manner and the activity was dependent on RIPE3b/C1 sequences. In addition, the amount of MafA protein was regulated by glucose concentration. These results indicate that MafA is the homologue of zebrafish SMaf1 and acts as a transcriptional activator of the insulin gene promoter through the RIPE3b element.

The identity and distribution of neural cells expressing the mesodermal determinant spadetail.

BACKGROUND: The spadetail (spt) gene of zebrafish is expressed in presomitic mesoderm and in neural cells previously suggested to be Rohon-Beard neurons. The mechanism(s) generating the apparently irregular rostrocaudal distribution of spt-expressing cells in the developing CNS is unknown. RESULTS: spt-expressing neural cells co-express huC, a marker of neurons. These cells also co-express the genes islet-1, -2 and -3 but not valentino. The islet-1 gene expression, irregular distribution and dorsolateral position of spt-expressing cells in the developing CNS are characteristic of dorsal longitudinal ascending (DoLA) interneurons. Shortly after their birth, these neurons extend processes rostrally into which spt mRNA is transported. At 24 hours post fertilisation(hpf), spt-expressing neurons occur most frequently at rostral levels caudal of the 5th-formed somite pair. There is no apparent bias in the number of spt-expressing cells on the left or right sides of embryos. Extended staining for spt-transcription reveals expression in the dorsocaudal cells of somites at the same dorsoventral level as the spt-expressing neurons. There is frequent juxtaposition of spt-expression in newly formed somites and in neurons. This suggests that both types of spt-expressing cell respond to a common positional cue or that neurons expressing spt are patterned irregularly by flanking somitic mesoderm. CONCLUSIONS: spt-expressing cells in the developing CNS appear to be DoLA interneurons. The irregular distribution of these cells along the rostrocaudal axis of the spinal cord may be due to "inefficient" patterning of neural spt expression by a signal(s) from flanking, regularly distributed somites also expressing spt.

The spatial and temporal expression of HNK-1 by myogenic and skeletogenic cells in the embryonic rat.

The existence of phenotypic differences within a population of cells provides evidence for discrete stages in cellular differentiation and/or identifies subsets of cells with unique functional properties. The monoclonal antibody HNK-1 has been widely shown to identify subpopulations of cells in the developing nervous system. In this paper we focus on the developmental expression of HNK-1 immunoreactivity by derivatives of somitic (paraxial) mesoderm. We show that between embryonic day 12 and 14 (E12-E14) the HNK-1 epitope is transiently expressed by postmitotic myotomal cells. In E14-E17 developing vertebral columns (which are derived from somitic sclerotomal cells), HNK-1 immunolabeling was expressed by subpopulations of skeletogenic cells, including perinotochordal cells associated with the forming annulus fibrosus and cells within or adjacent to the perichondrium. Chondrocytes within forming centra and vertebral arches did not exhibit HNK-1 immunoreactivity. These results, taken together, show that the expression of the HNK-1 epitope can be used to identify subsets of myogenic and skeletogenic cells both spatially and temporally in the developing rat.