Cloning and expression analysis of a mouse gene related to Drosophila odd-skipped

Comprehensive bioinformatics analysis reveals biomarkers of DNA methylation-related genes in varicose veins

Background: Patients with Varicose veins (VV) show no obvious symptoms in the early stages, and it is a common and frequent clinical condition. DNA methylation plays a key role in VV by regulating gene expression. However, the molecular mechanism underlying methylation regulation in VV remains unclear. Methods: The mRNA and methylation data of VV and normal samples were obtained from the Gene Expression Omnibus (GEO) database. Methylation-Regulated Genes (MRGs) between VV and normal samples were crossed with VV-associated genes (VVGs) obtained by weighted gene co-expression network analysis (WGCNA) to obtain VV-associated MRGs (VV-MRGs). Their ability to predict disease was assessed using receiver operating characteristic (ROC) curves. Biomarkers were then screened using a random forest model (RF), support vector machine model (SVM), and generalized linear model (GLM). Next, gene set enrichment analysis (GSEA) was performed to explore the functions of biomarkers. Furthermore, we also predicted their drug targets, and constructed a competing endogenous RNAs (ceRNA) network and a drug target network. Finally, we verified their mRNA expression using quantitative real-time polymerase chain reaction (qRT-PCR). Results: Total three VV-MRGs, namely Wnt1-inducible signaling pathway protein 2 (WISP2), Cysteine-rich intestinal protein 1 (CRIP1), and Odd-skipped related 1 (OSR1) were identified by VVGs and MRGs overlapping. The area under the curves (AUCs) of the ROC curves for these three VV-MRGs were greater than 0.8. RF was confirmed as the optimal diagnostic model, and WISP2, CRIP1, and OSR1 were regarded as biomarkers. GSEA showed that WISP2, CRIP1, and OSR1 were associated with oxidative phosphorylation, extracellular matrix (ECM), and respiratory system functions. Furthermore, we found that lncRNA MIR17HG can regulate OSR1 by binding to hsa-miR-21-5p and that PAX2 might treat VV by targeting OSR1. Finally, qRT-PCR results showed that the mRNA expression of the three genes was consistent with the results of the datasets. Conclusion: This study identified WISP2, CRIP1, and OSR1 as biomarkers of VV through comprehensive bioinformatics analysis, and preliminary explored the DNA methylation-related molecular mechanism in VV, which might be important for VV diagnosis and exploration of potential molecular mechanisms.

Transgenic Mouse Models to Study the Development and Maintenance of the Adrenal Cortex

The cortex of the adrenal gland is organized into concentric zones that produce distinct steroid hormones essential for body homeostasis in mammals. Mechanisms leading to the development, zonation and maintenance of the adrenal cortex are complex and have been studied since the 1800s. However, the advent of genetic manipulation and transgenic mouse models over the past 30 years has revolutionized our understanding of these mechanisms. This review lists and details the distinct Cre recombinase mouse strains available to study the adrenal cortex, and the remarkable progress total and conditional knockout mouse models have enabled us to make in our understanding of the molecular mechanisms regulating the development and maintenance of the adrenal cortex.

Single-cell transcriptome reveals insights into the development and function of the zebrafish ovary

Zebrafish are an established research organism that has made many contributions to our understanding of vertebrate tissue and organ development, yet there are still significant gaps in our understanding of the genes that regulate gonad development, sex, and reproduction. Unlike the development of many organs, such as the brain and heart that form during the first few days of development, zebrafish gonads do not begin to form until the larval stage (≥5 days post-fertilization). Thus, forward genetic screens have identified very few genes required for gonad development. In addition, bulk RNA-sequencing studies that identify genes expressed in the gonads do not have the resolution necessary to define minor cell populations that may play significant roles in the development and function of these organs. To overcome these limitations, we have used single-cell RNA sequencing to determine the transcriptomes of cells isolated from juvenile zebrafish ovaries. This resulted in the profiles of 10,658 germ cells and 14,431 somatic cells. Our germ cell data represents all developmental stages from germline stem cells to early meiotic oocytes. Our somatic cell data represents all known somatic cell types, including follicle cells, theca cells, and ovarian stromal cells. Further analysis revealed an unexpected number of cell subpopulations within these broadly defined cell types. To further define their functional significance, we determined the location of these cell subpopulations within the ovary. Finally, we used gene knockout experiments to determine the roles of foxl2l and wnt9b for oocyte development and sex determination and/or differentiation, respectively. Our results reveal novel insights into zebrafish ovarian development and function, and the transcriptome profiles will provide a valuable resource for future studies.

The nephric mesenchyme lineage of intermediate mesoderm is derived from Tbx6-expressing derivatives of neuro-mesodermal progenitors via BMP-dependent Osr1 function

In vertebrate embryos, the kidney primordium metanephros is formed from two distinct cell lineages, Wolffian duct and metanephric mesenchyme, which were classically grouped as intermediate mesoderm. Whereas the reciprocal interactions between these two cell populations in kidney development have been studied extensively, the mechanisms generating them remain elusive. Here, we show that the mouse cell lineage that forms nephric mesenchyme develops as a subpopulation of Tbx6-expressing mesodermal precursor derivatives of neuro-mesodermal progenitors (NMPs) under the condition of bone morphogenetic protein (BMP)-signal-dependent Osr1 expression. The Osr1-expressing nephric mesenchyme precursors were confirmed as descendants of NMPs because they were labeled by Sox2 N1 enhancer-EGFP. In Tbx6 mutant embryos, nephric mesenchyme changed its fate into neural tissues, which reflected its NMP origin. In Osr1 mutant embryos, the specific region of the Tbx6-expressing mesoderm precursor, which normally expresses Osr1 and develops into the nephric mesenchyme, instead expressed the somite marker FoxC2. BMP signaling activated Osr1 expression in a region of TBX6-expressing mesoderm and elicited nephric mesenchyme development. This study suggested a new model of cell lineage segregation during gastrulation.

How to Make a Rodent Giant: Genomic Basis and Tradeoffs of Gigantism in the Capybara, the World's Largest Rodent

Gigantism results when one lineage within a clade evolves extremely large body size relative to its small-bodied ancestors, a common phenomenon in animals. Theory predicts that the evolution of giants should be constrained by two tradeoffs. First, because body size is negatively correlated with population size, purifying selection is expected to be less efficient in species of large body size, leading to increased mutational load. Second, gigantism is achieved through generating a higher number of cells along with higher rates of cell proliferation, thus increasing the likelihood of cancer. To explore the genetic basis of gigantism in rodents and uncover genomic signatures of gigantism-related tradeoffs, we assembled a draft genome of the capybara (Hydrochoerus hydrochaeris), the world's largest living rodent. We found that the genome-wide ratio of nonsynonymous to synonymous mutations (ω) is elevated in the capybara relative to other rodents, likely caused by a generation-time effect and consistent with a nearly neutral model of molecular evolution. A genome-wide scan for adaptive protein evolution in the capybara highlighted several genes controlling postnatal bone growth regulation and musculoskeletal development, which are relevant to anatomical and developmental modifications for an increase in overall body size. Capybara-specific gene-family expansions included a putative novel anticancer adaptation that involves T-cell-mediated tumor suppression, offering a potential resolution to the increased cancer risk in this lineage. Our comparative genomic results uncovered the signature of an intragenomic conflict where the evolution of gigantism in the capybara involved selection on genes and pathways that are directly linked to cancer.

Facial shape and allometry quantitative trait locus intervals in the Diversity Outbred mouse are enriched for known skeletal and facial development genes

The biology of how faces are built and come to differ from one another is complex. Discovering normal variants that contribute to differences in facial morphology is one key to untangling this complexity, with important implications for medicine and evolutionary biology. This study maps quantitative trait loci (QTL) for skeletal facial shape using Diversity Outbred (DO) mice. The DO is a randomly outcrossed population with high heterozygosity that captures the allelic diversity of eight inbred mouse lines from three subspecies. The study uses a sample of 1147 DO animals (the largest sample yet employed for a shape QTL study in mouse), each characterized by 22 three-dimensional landmarks, 56,885 autosomal and X-chromosome markers, and sex and age classifiers. We identified 37 facial shape QTL across 20 shape principal components (PCs) using a mixed effects regression that accounts for kinship among observations. The QTL include some previously identified intervals as well as new regions that expand the list of potential targets for future experimental study. Three QTL characterized shape associations with size (allometry). Median support interval size was 3.5 Mb. Narrowing additional analysis to QTL for the five largest magnitude shape PCs, we found significant overrepresentation of genes with known roles in growth, skeletal and facial development, and sensory organ development. For most intervals, one or more of these genes lies within 0.25 Mb of the QTL's peak. QTL effect sizes were small, with none explaining more than 0.5% of facial shape variation. Thus, our results are consistent with a model of facial diversity that is influenced by key genes in skeletal and facial development and, simultaneously, is highly polygenic.

Zinc-finger transcription factor Odd-skipped related 1 regulates cranial bone formation

Knowledge of the molecular mechanisms of bone formation has been advanced by novel findings related to genetic control. Odd-skipped related 1 (Osr1) is known to play important roles in embryonic, heart, and urogenital development. To elucidate the in vivo function of Osr1 in bone formation, we generated transgenic mice overexpressing full-length Osr1 under control of its 2.8-kb promoter, which were smaller than their wild-type littermates. Notably, abnormalities in the skull of Osr1 transgenic mice were revealed by analysis of X-ray, skeletal preparation, and morphological findings, including round skull and cranial dysraphism. Furthermore, primary calvarial cells obtained from these mice showed increased proliferation and expression of chondrocyte markers, while expression of osteoblast markers was decreased. BMP2 reduced Osr1 expression and Osr1 knockdown by siRNA-induced alkaline phosphatase and osteocalcin expression in mesenchymal and osteoblastic cells. Together, our results suggest that Osr1 plays a coordinating role in appropriate skull closure and cranial bone formation by negative regulation.

Generation of branching ureteric bud tissues from human pluripotent stem cells

Recent progress in kidney regeneration research is noteworthy. However, the selective and robust differentiation of the ureteric bud (UB), an embryonic renal progenitor, from human pluripotent stem cells (hPSCs) remains to be established. The present study aimed to establish a robust induction method for branching UB tissue from hPSCs towards the creation of renal disease models. Here, we found that anterior intermediate mesoderm (IM) differentiates from anterior primitive streak, which allowed us to successfully develop an efficient two-dimensional differentiation method of hPSCs into Wolffian duct (WD) cells. We also established a simplified procedure to generate three-dimensional WD epithelial structures that can form branching UB tissues. This system may contribute to hPSC-based regenerative therapies and disease models for intractable disorders arising in the kidney and lower urinary tract.

Non-myogenic Contribution to Muscle Development and Homeostasis: The Role of Connective Tissues

Skeletal muscles belong to the musculoskeletal system, which is composed of bone, tendon, ligament and irregular connective tissue, and closely associated with motor nerves and blood vessels. The intrinsic molecular signals regulating myogenesis have been extensively investigated. However, muscle development, homeostasis and regeneration require interactions with surrounding tissues and the cellular and molecular aspects of this dialogue have not been completely elucidated. During development and adult life, myogenic cells are closely associated with the different types of connective tissue. Connective tissues are defined as specialized (bone and cartilage), dense regular (tendon and ligament) and dense irregular connective tissue. The role of connective tissue in muscle morphogenesis has been investigated, thanks to the identification of transcription factors that characterize the different types of connective tissues. Here, we review the development of the various connective tissues in the context of the musculoskeletal system and highlight their important role in delivering information necessary for correct muscle morphogenesis, from the early step of myoblast differentiation to the late stage of muscle maturation. Interactions between muscle and connective tissue are also critical in the adult during muscle regeneration, as impairment of the regenerative potential after injury or in neuromuscular diseases results in the progressive replacement of the muscle mass by fibrotic tissue. We conclude that bi-directional communication between muscle and connective tissue is critical for a correct assembly of the musculoskeletal system during development as well as to maintain its homeostasis in the adult.

A strategy for generating kidney organoids: Recapitulating the development in human pluripotent stem cells

Directed differentiation of human pluripotent stem cells (hPSCs) can provide us any required tissue/cell types by recapitulating the development in vitro. The kidney is one of the most challenging organs to generate from hPSCs as the kidney progenitors are composed of at least 4 different cell types, including nephron, collecting duct, endothelial and interstitium progenitors, that are developmentally distinguished populations. Although the actual developmental process of the kidney during human embryogenesis has not been clarified yet, studies using model animals accumulated knowledge about the origins of kidney progenitors. The implications of these findings for the directed differentiation of hPSCs into the kidney include the mechanism of the intermediate mesoderm specification and its patterning along with anteroposterior axis. Using this knowledge, we previously reported successful generation of hPSCs-derived kidney organoids that contained all renal components and modelled human kidney development in vitro. In this review, we explain the developmental basis of the strategy behind this differentiation protocol and compare strategies of studies that also recently reported the induction of kidney cells from hPSCs. We also discuss the characterization of such kidney organoids and limitations and future applications of this technology.

Osr1 Interacts Synergistically with Wt1 to Regulate Kidney Organogenesis

Renal hypoplasia is a common cause of pediatric renal failure and several adult-onset diseases. Recent studies have associated a variant of the OSR1 gene with reduction of newborn kidney size and function in heterozygotes and neonatal lethality with kidney defects in homozygotes. How OSR1 regulates kidney development and nephron endowment is not well understood, however. In this study, by using the recently developed CRISPR genome editing technology, we genetically labeled the endogenous Osr1 protein and show that Osr1 interacts with Wt1 in the developing kidney. Whereas mice heterozygous for either an Osr1 or Wt1 null allele have normal kidneys at birth, most mice heterozygous for both Osr1 and Wt1 exhibit defects in metanephric kidney development, including unilateral or bilateral kidney agenesis or hypoplasia. The developmental defects in the Osr1+/-Wt1+/- mouse embryos were detected as early as E10.5, during specification of the metanephric mesenchyme, with the Osr1+/-Wt1+/- mouse embryos exhibiting significantly reduced Pax2-positive and Six2-positive nephron progenitor cells. Moreover, expression of Gdnf, the major nephrogenic signal for inducing ureteric bud outgrowth, was significantly reduced in the metanephric mesenchyme in Osr1+/-Wt1+/- embryos in comparison with the Osr1+/- or Wt1+/- littermates. By E11.5, as the ureteric buds invade the metanephric mesenchyme and initiate branching morphogenesis, kidney morphogenesis was significantly impaired in the Osr1+/-Wt1+/- embryos in comparison with the Osr1+/- or Wt1+/- embryos. These results indicate that Osr1 and Wt1 act synergistically to regulate nephron endowment by controlling metanephric mesenchyme specification during early nephrogenesis.

Bat Accelerated Regions Identify a Bat Forelimb Specific Enhancer in the HoxD Locus

The molecular events leading to the development of the bat wing remain largely unknown, and are thought to be caused, in part, by changes in gene expression during limb development. These expression changes could be instigated by variations in gene regulatory enhancers. Here, we used a comparative genomics approach to identify regions that evolved rapidly in the bat ancestor, but are highly conserved in other vertebrates. We discovered 166 bat accelerated regions (BARs) that overlap H3K27ac and p300 ChIP-seq peaks in developing mouse limbs. Using a mouse enhancer assay, we show that five Myotis lucifugus BARs drive gene expression in the developing mouse limb, with the majority showing differential enhancer activity compared to the mouse orthologous BAR sequences. These include BAR116, which is located telomeric to the HoxD cluster and had robust forelimb expression for the M. lucifugus sequence and no activity for the mouse sequence at embryonic day 12.5. Developing limb expression analysis of Hoxd10-Hoxd13 in Miniopterus natalensis bats showed a high-forelimb weak-hindlimb expression for Hoxd10-Hoxd11, similar to the expression trend observed for M. lucifugus BAR116 in mice, suggesting that it could be involved in the regulation of the bat HoxD complex. Combined, our results highlight novel regulatory regions that could be instrumental for the morphological differences leading to the development of the bat wing.

Concise Review: Understanding the Renal Progenitor Cell Niche In Vivo to Recapitulate Nephrogenesis In Vitro

Chronic kidney disease (CKD), defined as progressive kidney damage and a reduction of the glomerular filtration rate, can progress to end-stage renal failure (CKD5), in which kidney function is completely lost. CKD5 requires dialysis or kidney transplantation, which is limited by the shortage of donor organs. The incidence of CKD5 is increasing annually in the Western world, stimulating an urgent need for new therapies to repair injured kidneys. Many efforts are directed toward regenerative medicine, in particular using stem cells to replace nephrons lost during progression to CKD5. In the present review, we provide an overview of the native nephrogenic niche, describing the complex signals that allow survival and maintenance of undifferentiated renal stem/progenitor cells and the stimuli that promote differentiation. Recapitulating in vitro what normally happens in vivo will be beneficial to guide amplification and direct differentiation of stem cells toward functional renal cells for nephron regeneration.

SIGNIFICANCE

Kidneys perform a plethora of functions essential for life. When their main effector, the nephron, is irreversibly compromised, the only therapeutic choices available are artificial replacement (dialysis) or renal transplantation. Research focusing on alternative treatments includes the use of stem cells. These are immature cells with the potential to mature into renal cells, which could be used to regenerate the kidney. To achieve this aim, many problems must be overcome, such as where to take these cells from, how to obtain enough cells to deliver to patients, and, finally, how to mature stem cells into the cell types normally present in the kidney. In the present report, these questions are discussed. By knowing the factors directing the proliferation and differentiation of renal stem cells normally present in developing kidney, this knowledge can applied to other types of stem cells in the laboratory and use them in the clinic as therapy for the kidney.

Directed Differentiation of Pluripotent Stem Cells into Kidney

Pluripotent stem cells (PSCs), including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), represent an ideal substrate for regenerating kidney cells and tissue lost through injury and disease. Recent studies have demonstrated the ability to differentiate PSCs into populations of nephron progenitor cells that can organize into kidney epithelial structures in three-dimensional contexts. While these findings are highly encouraging, further studies need to be performed to improve the efficiency and specificity of kidney differentiation. The identification of specific markers of the differentiation process is critical to the development of protocols that effectively recapitulate nephrogenesis in vitro. In this review, we summarize the current studies describing the differentiation of ESCs and iPSCs into cells of the kidney lineage. We also present an analysis of the markers relevant to the stages of kidney development and differentiation and propose a new roadmap for the directed differentiation of PSCs into nephron progenitor cells of the metanephric mesenchyme.

osr1 is required for podocyte development downstream of wt1a

Odd-skipped related 1 (Osr1) encodes a zinc finger transcription factor required for kidney development. Osr1 deficiency in mice results in metanephric kidney agenesis, whereas knockdown or mutation studies in zebrafish revealed that pronephric nephrons require osr1 for proximal tubule and podocyte development. osr1-deficient pronephric podocyte progenitors express the Wilms' tumor suppressor wt1a but do not undergo glomerular morphogenesis or express the foot process junctional markers nephrin and podocin. The function of osr1 in podocyte differentiation remains unclear, however. Here, we found by double fluorescence in situ hybridization that podocyte progenitors coexpress osr1 and wt1a. Knockdown of wt1a disrupted podocyte differentiation and prevented expression of osr1. Blocking retinoic acid signaling, which regulates wt1a, also prevented osr1 expression in podocyte progenitors. Furthermore, unlike the osr1-deficient proximal tubule phenotype, which can be rescued by manipulation of endoderm development, podocyte differentiation was not affected by altered endoderm development, as assessed by nephrin and podocin expression in double osr1/sox32-deficient embryos. These results suggest a different, possibly cell- autonomous requirement for osr1 in podocyte differentiation downstream of wt1a. Indeed, osr1-deficient embryos did not exhibit podocyte progenitor expression of the transcription factor lhx1a, and forced expression of activated forms of the lhx1a gene product rescued nephrin expression in osr1-deficient podocytes. Our results place osr1 in a framework of transcriptional regulators that control the expression of podocin and nephrin and thereby mediate podocyte differentiation.

Recreating kidney progenitors from pluripotent cells

Access to human pluripotent cells theoretically provides a renewable source of cells that can give rise to any required cell type for use in cellular therapy or bioengineering. However, successfully directing this differentiation remains challenging for most desired endpoints cell type, including renal cells. This challenge is compounded by the difficulty in identifying the required cell type in vitro and the multitude of renal cell types required to build a kidney. Here we review our understanding of how the embryo goes about specifying the cells of the kidney and the progress to date in adapting this knowledge for the recreation of nephron progenitors and their mature derivatives from pluripotent cells.

Bone morphogenetic protein signaling in nephron progenitor cells

Bone morphogenetic protein (BMP) signaling plays an essential role in many aspects of kidney development, and is a major determinant of outcome in kidney injury. BMP treatment is also an essential component of protocols for differentiation of nephron progenitors from pluripotent stem cells. This review discusses the role of BMP signaling to nephron progenitor cells in each of these contexts.

Osr1 acts downstream of and interacts synergistically with Six2 to maintain nephron progenitor cells during kidney organogenesis

Mammalian kidney organogenesis involves reciprocal epithelial-mesenchymal interactions that drive iterative cycles of nephron formation. Recent studies have demonstrated that the Six2 transcription factor acts cell autonomously to maintain nephron progenitor cells, whereas canonical Wnt signaling induces nephron differentiation. How Six2 maintains the nephron progenitor cells against Wnt-directed commitment is not well understood, however. We report here that Six2 is required to maintain expression of Osr1, a homolog of the Drosophila odd-skipped zinc-finger transcription factor, in the undifferentiated cap mesenchyme. Tissue-specific inactivation of Osr1 in the cap mesenchyme caused premature depletion of nephron progenitor cells and severe renal hypoplasia. We show that Osr1 and Six2 act synergistically to prevent premature differentiation of the cap mesenchyme. Furthermore, although both Six2 and Osr1 could form protein interaction complexes with TCF proteins, Osr1, but not Six2, enhances TCF interaction with the Groucho family transcriptional co-repressors. Moreover, we demonstrate that loss of Osr1 results in β-catenin/TCF-mediated ectopic activation of Wnt4 enhancer-driven reporter gene expression in the undifferentiated nephron progenitor cells in vivo. Together, these data indicate that Osr1 plays crucial roles in Six2-dependent maintenance of nephron progenitors during mammalian nephrogenesis by stabilizing TCF-Groucho transcriptional repressor complexes to antagonize Wnt-directed nephrogenic differentiation.

odd-skipped related 2 is required for fin chondrogenesis in zebrafish

BACKGROUND

odd-skipped related 2 (osr2) encodes a vertebrate ortholog of the Drosophila odd-skipped zinc-finger transcription factor. Osr2 in mouse is required for proper palate, eyelid, and bone development. Zebrafish knock-down experiments have also suggested a role for osr2, along with its paralog osr1, in early pectoral fin specification and pronephric development.

RESULTS

We show here that osr2 has a specific function later in development, independent of osr1, in the regulation of sox9a expression and promoting fin chondrogenesis. mRNA in situ hybridization demonstrated osr2 expression in the developing floorplate and later during organogenesis in the pronephros and gut epithelium. In the pectoral fin buds, osr2 was specifically expressed in fin mesenchyme. osr2 knock down in zebrafish embryos disrupted both three and five zinc finger alternatively spliced osr2 isoforms and eliminated wild-type osr2 mRNA. osr2 morphants exhibited normal pectoral fin bud specification but exhibited defective fin chondrogenesis, with loss of differentiated chondrocytes. Defects in chondrogenesis were paralleled by loss of sox9a as well as subsequent col2a1 expression, linking osr2 function to essential regulators of chondrogenesis.

CONCLUSIONS

The zebrafish odd-skipped related 2 gene regulates sox9a and col2a1 expression in chondrocyte development and is specifically required for zebrafish fin morphogenesis.

Gata4 is required for formation of the genital ridge in mice

In mammals, both testis and ovary arise from a sexually undifferentiated precursor, the genital ridge, which first appears during mid-gestation as a thickening of the coelomic epithelium on the ventromedial surface of the mesonephros. At least four genes (Lhx9, Sf1, Wt1, and Emx2) have been demonstrated to be required for subsequent growth and maintenance of the genital ridge. However, no gene has been shown to be required for the initial thickening of the coelomic epithelium during genital ridge formation. We report that the transcription factor GATA4 is expressed in the coelomic epithelium of the genital ridge, progressing in an anterior-to-posterior (A-P) direction, immediately preceding an A-P wave of epithelial thickening. Mouse embryos conditionally deficient in Gata4 show no signs of gonadal initiation, as their coelomic epithelium remains a morphologically undifferentiated monolayer. The failure of genital ridge formation in Gata4-deficient embryos is corroborated by the absence of the early gonadal markers LHX9 and SF1. Our data indicate that GATA4 is required to initiate formation of the genital ridge in both XX and XY fetuses, prior to its previously reported role in testicular differentiation of the XY gonad.

During mammalian fetal development, the precursor of the testis or ovary first appears as a simple thickening, in a specific region, of the epithelial cell layer that lines the body cavity. The resulting structure is called the genital ridge, which then differentiates into either testis or ovary, depending on whether the sex chromosome constitution is XY or XX. A handful of genes, including Lhx9, Sf1, Wt1, and Emx2, are required to sustain the growth of the genital ridge. However, mice with mutations in any of these genes still undergo the initial step of epithelial thickening, suggesting that an additional step (or factor) is required to initiate genital ridge formation. We found that the evolutionarily conserved transcription factor GATA4 is expressed in the epithelium of the genital ridge before initial thickening. We produced a mouse with a Gata4 mutation in this tissue and demonstrated that the initial thickening does not take place; the mutant embryos fail to initiate gonad development. In support of this observation, the Gata4 mutant does not express the early gonadal markers LHX9 and SF1. These findings indicate that a genetically discrete, Gata4-dependent initiation step precedes the previously known processes that result in formation of testes and ovaries.

The odd-skipped related genes Osr1 and Osr2 are induced by 1,25-dihydroxyvitamin D3

The odd-skipped related genes Osr1 and Osr2 encode closely related zinc finger containing transcription factors that are expressed in developing limb. However, their role in osteoblast proliferation and differentiation remains controversial and little is known about their regulation. In this study we showed that both Osr1 and Osr2 were expressed in several murine and human osteoblast cell lines as well as in primary osteoblast cultures. Moreover, their transcript levels were regulated by a number of osteogenic stimuli in murine pre-osteoblast MC3T3-E1 cells. The most robust regulation of Osr1 and Osr2 mRNA levels was observed after stimulation with 1,25-dihydroxyvitamin D3. 1,25-Dihydroxyvitamin D3 induced transcript levels of Osr1 and Osr2 and this up-regulation was confirmed in other osteoblast cultures, both from murine and human origin. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Tbx18 expression demarcates multipotent precursor populations in the developing urogenital system but is exclusively required within the ureteric mesenchymal lineage to suppress a renal stromal fate

The mammalian urogenital system derives from multipotent progenitor cells of different germinal tissues. The contribution of individual sub-populations to specific components of the mature system, and the spatiotemporal restriction of the respective lineages have remained poorly characterized. Here, we use comparative expression analysis to delineate sub-regions within the developing urogenital system that express the T-box transcription factor gene Tbx18. We show that Tbx18 is transiently expressed in the epithelial lining and the subjacent mesenchyme of the urogenital ridge. At the onset of metanephric development Tbx18 expression occurs in a band of mesenchyme in between the metanephros and the Wolffian duct but is subsequently restricted to the mesenchyme surrounding the distal ureter stalk. Genetic lineage tracing reveals that former Tbx18(+) cells of the urogenital ridge and the metanephric field contribute substantially to the adrenal glands and gonads, to the kidney stroma, the ureteric and the bladder mesenchyme. Loss of Tbx18 does not affect differentiation of the adrenal gland, the gonad, the bladder and the kidney. However, ureter differentiation is severely disturbed as the mesenchymal lineage adopts a stromal rather than a ureteric smooth muscle fate. DiI labeling and tissue recombination experiments show that the restriction of Tbx18 expression to the prospective ureteric mesenchyme does not reflect an active condensation process but is due to a specific loss of Tbx18 expression in the mesenchyme out of range of signals from the ureteric epithelium. These cells either contribute to the renal stroma or undergo apoptosis aiding in severing the ureter from its surrounding tissues. We show that Tbx18-deficient cells do not respond to epithelial signals suggesting that Tbx18 is required to prepattern the ureteric mesenchyme. Our study provides new insights into the molecular diversity of urogenital progenitor cells and helps to understand the specification of the ureteric mesenchymal sub-lineage.

Molecular physiology of SPAK and OSR1: two Ste20-related protein kinases regulating ion transport

SPAK (Ste20-related proline alanine rich kinase) and OSR1 (oxidative stress responsive kinase) are members of the germinal center kinase VI subfamily of the mammalian Ste20 (Sterile20)-related protein kinase family. Although there are 30 enzymes in this protein kinase family, their conservation across the fungi, plant, and animal kingdom confirms their evolutionary importance. Already, a large volume of work has accumulated on the tissue distribution, binding partners, signaling cascades, and physiological roles of mammalian SPAK and OSR1 in multiple organ systems. After reviewing this basic information, we will examine newer studies that demonstrate the pathophysiological consequences to SPAK and/or OSR1 disruption, discuss the development and analysis of genetically engineered mouse models, and address the possible role these serine/threonine kinases might have in cancer proliferation and migration.

Molecular and evolutionary basis of limb field specification and limb initiation

Specification of limb field and initiation of limb development involve multiple steps, each of which is tightly regulated both spatially and temporally. Recent developmental analyses on various vertebrates have provided insights into the molecular mechanisms that specify limb field and have revealed several genetic interactions of signals involved in limb initiation processes. Furthermore, new approaches to the study of the developmental mechanisms of the lateral plate mesoderm of amphioxus and lamprey embryos have given us clues to understand the evolutionary scenarios that led to the acquisition of paired appendages during evolution. This review highlights such recent findings and discusses the mechanisms of limb field specification and limb bud initiation during development and evolution.

Cleft palate defect of Dlx1/2-/- mutant mice is caused by lack of vertical outgrowth in the posterior palate

BACKGROUND

Mice lacking the activities of Dlx1 and Dlx2 (Dlx1/2-/-) exhibit cleft palate, one of the most common human congenital defects, but the etiology behind this phenotype has been unknown. Therefore, we analyzed the morphological, cellular, and molecular changes caused by inactivation of Dlx1 and Dlx2 as related to palate development.

RESULTS

Dlx1/2-/- mutants exhibited lack of vertical growth in the posterior palate during the earliest stage of palatogenesis. We attributed this growth deficiency to reduced cell proliferation. Expression of a cell cycle regulator Ccnd1 was specifically down-regulated in the same region. Previous studies established that the epithelial-mesenchymal signaling loop involving Shh, Bmp4, and Fgf10 is important for cell proliferation and tissue growth during palate development. This signaling loop was disrupted in Dlx1/2-/- palate. Interestingly, however, the decreases in Ccnd1 expression and mitosis in Dlx1/2-/- mutants were independent of this signaling loop. Finally, Dlx1/2 activity was required for normal expression of several transcription factor genes whose mutation results in palate defects.

CONCLUSIONS

The functions of Dlx1 and Dlx2 are crucial for the initial formation of the posterior palatal shelves, and that the Dlx genes lie upstream of multiple signaling molecules and transcription factors important for later stages of palatogenesis.

Suppression of Bmp4 signaling by the zinc-finger repressors Osr1 and Osr2 is required for Wnt/β-catenin-mediated lung specification in Xenopus

Embryonic development of the respiratory system is regulated by a series of mesenchymal-epithelial interactions that are only partially understood. Mesenchymal FGF and Wnt2/Wnt2b signaling are implicated in specification of mammalian pulmonary progenitors from the ventral foregut endoderm, but their epistatic relationship and downstream targets are largely unknown. In addition, how wnt2 and wnt2b are regulated in the developing foregut mesenchyme is unknown. We show that the Odd-skipped-related (Osr) zinc-finger transcriptional repressors Osr1 and Osr2 are redundantly required for Xenopus lung specification in a molecular pathway linking foregut pattering by FGFs to Wnt-mediated lung specification and RA-regulated lung bud growth. FGF and RA signals are required for robust osr1 and osr2 expression in the foregut endoderm and surrounding lateral plate mesoderm (lpm) prior to respiratory specification. Depletion of both Osr1 and Osr2 (Osr1/Osr2) results in agenesis of the lungs, trachea and esophagus. The foregut lpm of Osr1/Osr2-depleted embryos fails to express wnt2, wnt2b and raldh2, and consequently Nkx2.1(+) progenitors are not specified. Our data suggest that Osr1/Osr2 normally repress bmp4 expression in the lpm, and that BMP signaling negatively regulates the wnt2b domain. These results significantly advance our understanding of early lung development and may impact strategies to differentiate respiratory tissue from stem cells.

The Osr1 and Osr2 genes act in the pronephric anlage downstream of retinoic acid signaling and upstream of Wnt2b to maintain pectoral fin development

Vertebrate odd-skipped related genes (Osr) have an essential function during the formation of the intermediate mesoderm (IM) and the kidney structures derived from it. Here, we show that these genes are also crucial for limb bud formation in the adjacent lateral plate mesoderm (LPM). Reduction of zebrafish Osr function impairs fin development by the failure of tbx5a maintenance in the developing pectoral fin bud. Osr morphant embryos show reduced wnt2b expression, and increasing Wnt signaling in Osr morphant embryos partially rescues tbx5a expression. Thus, Osr genes control limb bud development in a non-cell-autonomous manner, probably through the activation of Wnt2b. Finally, we demonstrate that Osr genes are downstream targets of retinoic acid (RA) signaling. Therefore, Osr genes act as a relay within the genetic cascade of fin bud formation: by controlling the expression of the signaling molecule Wnt2ba in the IM they play an essential function transmitting the RA signaling originated in the somites to the LPM.

Odd-skipped related genes regulate differentiation of embryonic limb mesenchyme and bone marrow mesenchymal stromal cells

The regulation of progenitor cell differentiation to a specific tissue type is one of the fundamental questions of biology. Here, we identify Osr1 and Osr2, 2 closely related genes encoding zinc finger transcription factors, as being strongly expressed in irregular connective tissue (ICT) fibroblasts in the chicken embryo, suitable as a developmental marker. We provide evidence that both Osr1 and Osr2 regulate mesenchymal cell-type differentiation. Both Osr1 and Osr2 can promote the formation of ICT, a cell type of so far unknown molecular specification, while suppressing differentiation of other tissues such as cartilage and tendon from uncommitted progenitors. Conversely, knockdown of either Osr gene alone or in combination reverses this effect, thereby leading to decreased differentiation of ICT fibroblasts and increased chondrogenesis in vitro. This indicates that Osr genes play a pivotal role in ICT fibroblast differentiation. Undifferentiated mesenchymal cells reside in the adult body in the form of mesenchymal stem cells in the bone marrow cavity. Using bone marrow stromal cells (BMSCs) isolated from chicken fetal long bones, we show that Osr1 and Osr2 have an intrinsic role in BMSC differentiation similar to their role in early embryonic development, that is, the enforcement of CT fibroblast differentiation and the repression of other cell types as exemplified here by osteoblast differentiation.

Generation of Osr1 conditional mutant mice

The Odd-skipped related 1 (Osr1) gene encodes a zinc finger protein homologous to the Drosophila Odd-skipped transcription factor. During mouse embryogenesis, Osr1 is expressed in multiple tissues, including the developing heart, kidney, limb, lung, and craniofacial structures. Although characterization of targeted mutant mice has revealed essential roles for Osr1 in heart and kidney development, the embryonic lethality of the Osr1 null mice has hindered investigation of its role in many other developmental processes. We report here the generation of conditional mutant mice containing two loxP sites flanking exon 2 of the Osr1 gene. Mice homozygous for this targeted Osr1( fneo) allele are normal and fertile. Crossing the Osr1(fneo/fneo) mice with the EIIa-Cre transgenic mice resulted in Cre-mediated deletion of the loxP-flanked Exon2 in the germ line and mice homozygous for this deletion recapitulated the Osr1 null mutant phenotypes. The Osr1( fneo) conditional mice will be valuable for tissue-specific analysis of the roles of Osr1 in embryonic and postnatal developmental processes. genesis 49:419-422, 2011.

The zinc finger transcription factors Osr1 and Osr2 control synovial joint formation

Synovial joints enable smooth articulations between different skeletal elements and are essential for the motility of vertebrates. Despite decades of extensive studies of the molecular and cellular mechanisms of limb and skeletal development, the molecular mechanisms governing synovial joint formation are still poorly understood. In particular, whereas several signaling pathways have been shown to play critical roles in joint maintenance, the mechanism controlling joint initiation is unknown. Here we report that Osr1 and Osr2, the mammalian homologs of the odd-skipped family of zinc finger transcription factors that are required for leg joint formation in Drosophila, are both strongly expressed in the developing synovial joint cells in mice. Whereas Osr1(-/-) mutant mice died at midgestation and Osr2(-/-) mutant mice had only subtle defects in synovial joint development, tissue-specific inactivation of Osr1 in the developing limb mesenchyme in Osr2(-/-) mutant mice caused fusion of multiple joints. We found that Osr1 and Osr2 function is required for maintenance of expression of signaling molecules critical for joint formation, including Gdf5, Wnt4 and Wnt9b. In addition, joint cells in the double mutants failed to upregulate expression of the articular cartilage marker gene Prg4. These data indicate that Osr1 and Osr2 function redundantly to control synovial joint formation.

Functional equivalence of the zinc finger transcription factors Osr1 and Osr2 in mouse development

Osr1 and Osr2 are the only mammalian homologs of the Drosophila odd-skipped family developmental regulators. The Osr1 protein contains three zinc-finger motifs whereas Osr2 exists in two isoforms, containing three and five zinc-finger motifs respectively, due to alternative splicing of the transcripts. Targeted null mutations in these genes in mice resulted in distinct phenotypes, with heart and urogenital developmental defects in Osr1(-/-) mice and with cleft palate and open eyelids at birth in Osr2(-/-) mice. To investigate whether these contrasting mutant phenotypes are due to differences in their protein structure or to differential expression patterns, we generated mice in which the endogenous Osr2 coding region was replaced by either Osr1 cDNA or Osr2A cDNA encoding the five-finger isoform. The knockin alleles recapitulated endogenous Osr2 mRNA expression patterns in most tissues and completely rescued cleft palate and cranial skeletal developmental defects of Osr2(-/-) mice. Mice hemizygous or homozygous for either knockin allele exhibited open-eyelids at birth, which correlated with differences in expression patterns between the knockin allele and the endogenous Osr2 gene during eyelid development. Molecular marker analyses in Osr2(-/-) and Osr2(Osr1ki/Osr1ki) mice revealed that Osr2 controls eyelid development through regulation of the Fgf10-Fgfr2 signaling pathway and that Osr1 rescued Osr2 function in maintaining Fgf10 expression during eyelid development in Osr2(Osr1ki/Osr1ki) mice. These results indicate that the distinct functions of Osr1 and Osr2 during mouse development result from evolutionary divergence of their cis regulatory sequences rather than distinct biochemical activities of their protein products.

odd skipped related1 reveals a novel role for endoderm in regulating kidney versus vascular cell fate

The kidney and vasculature are intimately linked both functionally and during development, when nephric and blood/vascular progenitor cells occupy adjacent bands of mesoderm in zebrafish and frog embryos. Developmental mechanisms that underlie the differentiation of kidney versus blood/vascular lineages remain unknown. The odd skipped related1 (osr1) gene encodes a zinc-finger transcription factor that is expressed in the germ ring mesendoderm and subsequently in the endoderm and intermediate mesoderm, prior to the expression of definitive kidney or blood/vascular markers. Knockdown of osr1 in zebrafish embryos resulted in a complete, segment-specific loss of anterior kidney progenitors and a compensatory increase in the number of angioblast cells in the same trunk region. Histology revealed a subsequent absence of kidney tubules, an enlarged cardinal vein and expansion of the posterior venous plexus. Altered kidney versus vascular development correlated with expanded endoderm development in osr1 knockdowns. Combined osr1 loss of function and blockade of endoderm development by knockdown of sox32/casanova rescued anterior kidney development. The results indicate that osr1 activity is required to limit endoderm differentiation from mesendoderm; in the absence of osr1, excess endoderm alters mesoderm differentiation, shifting the balance from kidney towards vascular development.

Odd-skipped related 1 gene expression is regulated by Runx2 and Ikzf1 transcription factors

Odd-skipped related 1 (Osr1) gene encodes a zinc-finger transcription factor that plays important roles in embryonic, heart, and urogenital development, however, it is unknown how its expression is regulated. In this study, we analyzed the promoter region of Osr1 to elucidate its regulation mechanism. The mouse Osr1 promoter region was cloned and characterized, and found to have two repressor elements in the -4504/-2766 and -1616/-109 regions, and two enhancer elements in the -2766/-1616 and -109/+199 regions. Several Runx2 and Ikzf1 binding sites were found in both mouse and human Osr1 promoters. Osr1 promoter activity was suppressed by cotransfection with Runx2- and Ikzf1-expressing vectors in a dose-dependent manner. Electrophoresis mobility shift assays showed that purified Runx2 bound to proximal (-611/-606) Runx2 binding motifs and that Ikzf1 bound to proximal (-1652/-1644) Ikzf1 binding motifs. Chrosmatin immunoprecipitation demonstrated that Runx2 bound to both the distal (-3047/-3042) and proximal regions, and that Ikzf1 bound to both the far-distal (-3036/-3028) and proximal elements. These findings indicate that Osr1 expression is regulated by Runx2 and Ikzf1, which are known as master-gene of osteogenesis and hematopoiesis, respectively.

A Cre transgene active in developing endodermal organs, heart, limb, and extra-ocular muscle

Cre-mediated recombination, a method widely used in mice for tissue-specific inactivation of endogenous genes or activation of transgenes, is critically dependent on the availability of mouse lines in which Cre recombinase functions in the tissue of interest or its progenitors. Here we describe a transgenic mouse line, Osr1-cre, in which Cre is active from embryonic day (E)11.5 in a few specific tissues. These include the endoderm of the posterior foregut, midgut, hindgut, and developing urogenital system, the heart left atrium, extra-ocular muscle progenitors, and mesenchyme in particular regions of the limb. Furthermore, starting at E12.5, Cre functions in limb interdigital mesenchyme. Within the urogenital system, recombination appears to be virtually complete in the epithelium of the bladder and urethra just posterior to it by E14.5. In males, some of these urethral cells form the prostate. The spatiotemporal pattern of Cre activity in Osr1-cre makes it a unique resource among the lines available for Cre-mediated recombination experiments.

Zinc-finger transcription factor odd-skipped related 2 is one of the regulators in osteoblast proliferation and bone formation

We report that Osr2 is one of the regulators of osteoblast function, because dominant-negative Osr2 transgenic mice exhibited decreased osteoblast activity and delayed mineralization in calvarial and tibial bone tissues. Our results indicate that Osr2 functions in regulation of osteoblast proliferation.

INTRODUCTION

Molecular mechanisms that control bone formation have received attention with increasing knowledge related to genetic control of osteoblast differentiation. The odd-skipped related (Osr) gene is a zinc-finger transcription factor recently suggested to be involved in bone formation, although little is known about its role.

MATERIALS AND METHODS

To elucidate the in vivo function of Osr2, we generated transgenic mice overexpressing dominant-negative Osr2.

RESULTS

In this study, N-terminal-deleted Osr2 was found to act as a dominant-negative mutant toward both Osr1 and Osr2. Dominant-negative Osr2 (Osr2DeltaN) transgenic mice showed delayed mineralization in calvarial and cortical bone tissues. Furthermore, soft X-ray analysis of transgenic mice bones revealed distinctly increased radiolucency. Examinations of newborn Osr2DeltaN transgenic mice skeletons stained with alcian blue and alizarin red showed reduced intensities in the skull and skeletal elements. Morphologically, calvariae and tibias of Osr2DeltaN transgenic mice were composed of markedly thinner parietal and cortical bones and lower numbers of osteoblastic cells on bone surfaces, indicating a reduced proliferation of osteoblasts. Furthermore, calvarial osteoblasts obtained from Osr2DeltaN transgenic mice showed highly attenuated osteoblast differentiation and proliferation, confirming that Osr2 is needed for osteogenesis. Finally, results of Runx2-deficient cell assays suggested that Osr2 induces alkaline phosphatase (ALP) expression, but to a lesser degree than Runx2-expressing cells.

CONCLUSIONS

Our genetic observations showed that the Osr2 gene plays a key role in osteoblastic cell proliferation.

Blood Cells and Blood Cell Development in the Animal Kingdom

Recent findings strongly suggest that the molecular pathways involved in the development and function of blood cells are highly conserved among vertebrates and various invertebrate phyla. This has led to a renewed interest regarding homologies between blood cell types and their developmental origin among different animals. One way to address these areas of inquiry is to shed more light on the biology of blood cells in extant invertebrate taxa that have branched off the bilaterian tree in between insects and vertebrates. This review attempts, in a broadly comparative manner, to update the existing literature that deals with early blood cell development. I begin by providing a brief survey of the different types of blood cell lineages among metazoa. There is now good reason to believe that, in vertebrates and invertebrates alike, blood cell lineages diverge from a common type of progenitor cell, the hemocytoblast. I give a synopsis of the origin and determination of the hematocytoblast, beginning with a look at the hematopoietic organs that house hemocytoblasts in adult animals, followed by a more detailed overview of the embryonic development of the hematopoietic organ. Finally, I compare the process of blood lineage diversification in vertebrates and Drosophila.

Odd-skipped genes encode repressors that control kidney development

Odd-skipped family of proteins (Odd in Drosophila and Osr in vertebrates) are evolutionarily conserved zinc finger transcription factors. Two Osr genes are present in mammalian genomes, and it was recently reported that Osr1, but not Osr2, is required for murine kidney development. Here, we show that in Xenopus and zebrafish both Osr1 and Osr2 are necessary and sufficient for the development of the pronephros. Osr genes are expressed in early prospective pronephric territories, and morphants for either of the two genes show severely impaired kidney development. Conversely, overexpression of Osr genes promotes formation of ectopic kidney tissue. Molecularly, Osr proteins function as transcriptional repressors during kidney formation. We also show that Drosophila Odd induces kidney tissue in Xenopus. This might be accomplished through recruitment of Groucho-like co-repressors. Odd genes may also be required for proper development of the Malpighian tubules, the Drosophila renal organs. Our results highlight the evolutionary conserved involvement of Odd-skipped transcription factors in the development of kidneys.

Comparative expression pattern of Odd-skipped related genes Osr1 and Osr2 in chick embryonic development

Odd-skipped genes encode zinc-finger transcription factors with widespread roles in embryonic development. In Drosophila, odd-skipped acts as a pair-rule gene, while its orthologous gene in Caenorhabditis elegans is involved in gut development. In mammals two paralogs exist, Osr1 and Osr2, with functions described in heart and urogenital, and in secondary palate development, respectively. As the chicken embryo is a widely used system for analysing gene function in vivo, we determined the expression pattern of the two chicken orthologues, cOsr1 and cOsr2, during embryonic development. We demonstrate expression of both genes in a variety of organs and structures, such as kidney, eye, branchial arches and dermis. Both genes show a highly dynamic expression pattern with partially overlapping, but mostly distinct domains of expression. Special emphasis in this study was laid on the investigation of cOsr1 and cOsr2 in limb development, where we compared their expression pattern with the expression of Osr1 and Osr2 in the mouse.

Odd-Skipped Related 2 gene transcription is regulated by CCAAT enhancer-binding protein δ in mesenchymal C3H10T1/2 cells

Odd-skipped related 2 (Osr2) gene is mouse homolog of Drosophila Odd-skipped gene involved with the pair-rule segmentation phenotype in Drosophila mutant embryos. In this study, to examine Osr2 expression regulation, the mouse Osr2 promoter region was cloned and characterized, and found to have two enhancer elements in the -1463/-1031 (distal) and -581/+3 (proximal) regions, and a repressor region (-4845/-1463, far distal). CCAAT/enhancer binding protein (C/EBP) binding sites were found in both the distal and proximal enhancer elements. Osr2 promoter activity was enhanced by C/EBPdelta, a member of the C/EBP family, in a dose-dependent manner. Electrophoresis mobility shift assays showed that purified GST-C/EBPdelta bound to distal (-1295/-1261) and proximal (-89/-55) C/EBP binding motifs. Chromatin immunoprecipitation demonstrated that acetylated histones H3, H4, and C/EBPdelta in the proximal region (-280/-43), but not the distal region (-1438/-1196), indicating that the Osr2 promoter proximal region was transcriptionally activated in C3H10T1/2 cells. Our results suggest that Osr2 expression is regulated by C/EBP regulatory elements.

Odd-skipped related 1 (Odd 1) is an essential regulator of heart and urogenital development

The Odd-skipped related 1 (Odd 1) gene encodes a zinc finger protein homologous to the Drosophila Odd-skipped class transcription factors that play critical roles in embryonic patterning and tissue morphogenesis. We have generated mice carrying a targeted null mutation in the Odd 1 gene and show that Odd 1 is essential for heart and intermediate mesoderm development. Odd 1(-/-) mutant mouse embryos fail to form atrial septum, display dilated atria with hypoplastic venous valves, and exhibit blood backflow from the heart into systemic veins. In contrast to other transcription factors implicated in atrial septum development, Odd 1 mRNA expression is restricted to the central dorsal domain of the atrial myocardium during normal heart development. Moreover, expression patterns of known key regulatory genes of atrial septum development, including Nkx2.5, Pitx2, and Tbx5, are unaltered in the developing heart in Odd 1(-/-) mutants compared to that of the wild-type littermates. Furthermore, homozygous Odd 1(-/-) mutant embryos exhibit complete agenesis of adrenal glands, metanephric kidneys, gonads, and defects in pericardium formation. Detailed molecular marker analyses show that key regulators of early intermediate mesoderm development, including Lhx1, Pax2, and Wt1, are all down-regulated and nephrogenic mesenchyme undergoes massive apoptosis, resulting in disruption of nephric duct elongation and failure of metanephric induction in the Odd 1(-/-) mutant embryos. These data provide new insights into the molecular mechanisms underlying heart morphogenesis and urogenital development.

Angioblast-mesenchyme induction of early kidney development is mediated by Wt1 and Vegfa

Most studies on kidney development have considered the interaction of the metanephric mesenchyme and the ureteric bud to be the major inductive event that maintains tubular differentiation and branching morphogenesis. The mesenchyme produces Gdnf, which stimulates branching, and the ureteric bud stimulates continued growth of the mesenchyme and differentiation of nephrons from the induced mesenchyme. Null mutation of the Wt1 gene eliminates outgrowth of the ureteric bud, but Gdnf has been identified as a target of Pax2, but not of Wt1. Using a novel system for microinjecting and electroporating plasmid expression constructs into murine organ cultures, it has been demonstrated that Vegfa expression in the mesenchyme is regulated by Wt1. Previous studies had identified a population of Flk1-expressing cells in the periphery of the induced mesenchyme, and adjacent to the stalk of the ureteric bud, and that Vegfa was able to stimulate growth of kidneys in organ culture. Here it is demonstrated that signaling through Flk1 is required to maintain expression of Pax2 in the mesenchyme of the early kidney, and for Pax2 to stimulate expression of Gdnf. However, once Gdnf stimulates branching of the ureteric bud, the Flk1-dependent angioblast signal is no longer required to maintain branching morphogenesis and induction of nephrons. Thus,this work demonstrates the presence of a second set of inductive events,involving the mesenchymal and angioblast populations, whereby Wt1-stimulated expression of Vegfa elicits an as-yet-unidentified signal from the angioblasts, which is required to stimulate the expression of Pax2 and Gdnf,which in turn elicits an inductive signal from the ureteric bud.

Bmp signaling promotes intermediate mesoderm gene expression in a dose-dependent, cell-autonomous and translation-dependent manner

The intermediate mesoderm lies between the somites and the lateral plate and is the source of all kidney tissue in the developing vertebrate embryo. While bone morphogenetic protein (Bmp) signaling is known to regulate mesodermal cell type determination along the medio-lateral axis, its role in intermediate mesoderm formation has not been well characterized. The current study finds that low and high levels of Bmp ligand are both necessary and sufficient to activate intermediate and lateral mesodermal gene expression, respectively, both in vivo and in vitro. Dose-dependent activation of intermediate and lateral mesodermal genes by Bmp signaling is cell-autonomous, as demonstrated by electroporation of the avian embryo with constitutively active Bmp receptors driven by promoters of varying strengths. In explant cultures, Bmp activation of Odd-skipped related 1 (Odd-1), the earliest known gene expressed in the intermediate mesoderm, is blocked by cyclohexamide, indicating that the activation of Odd-1 by Bmp signaling is translation-dependent. The data from this study are integrated with that of other studies to generate a model for the role of Bmp signaling in trunk mesodermal patterning in which low levels of Bmp activate intermediate mesoderm gene expression by inhibition of repressors present in medial mesoderm, whereas high levels of Bmp repress both medial and intermediate mesoderm gene expression and activate lateral plate genes.

Odd-skipped related 2 splicing variants show opposite transcriptional activity

Odd-skipped related 2 (Osr2) is expressed in the domain of epithelial-mesenchymal interactions during tooth and kidney development. In this study, we report that alternative splicing of exon 4 resulted in two transcripts, Osr2A and Osr2B. These variants utilized a different splice acceptor, and Osr2B exhibited a frameshift followed by an early stop codon. Osr2A mRNA produced a protein that was 36 amino acids longer than Osr2B at the C-terminus and had five zinc-finger domains, whereas Osr2B had three zinc-finger motives. The 2 Osr2 variants were found in kidney, skeletal muscle, and testis, and Osr2B was predominantly transcribed in each. Flag-tagged variants showed the same localization in cell nuclei, however, Gal4 fusion proteins showed opposite transcriptional activities. Further, Flag-tagged variants also showed opposite transcriptional activities, though they were in contrast to the findings for the Gal4-fused variants. Our results indicate that Osr2 bifurcates its function by alternative splicing.

The forkhead genes, Foxc1 and Foxc2, regulate paraxial versus intermediate mesoderm cell fate

During vertebrate embryogenesis, the newly formed mesoderm is allocated to the paraxial, intermediate, and lateral domains, each giving rise to different cell and tissue types. Here, we provide evidence that the forkhead genes, Foxc1 and Foxc2, play a role in the specification of mesoderm to paraxial versus intermediate fates. Mouse embryos lacking both Foxc1 and Foxc2 show expansion of intermediate mesoderm markers into the paraxial domain, lateralization of somite patterning, and ectopic and disorganized mesonephric tubules. In gain of function studies in the chick embryo, Foxc1 and Foxc2 negatively regulate intermediate mesoderm formation. By contrast, their misexpression in the prospective intermediate mesoderm appears to drive cells to acquire paraxial fate, as revealed by expression of the somite markers Pax7 and Paraxis. Taken together, the data indicate that Foxc1 and Foxc2 regulate the establishment of paraxial versus intermediate mesoderm cell fates in the vertebrate embryo.

The Drm-Bowl-Lin relief-of-repression hierarchy controls fore- and hindgut patterning and morphogenesis

The elucidation of pathways linking patterning to morphogenesis is a problem of great interest. We show here that, in addition to their roles in patterning and morphogenesis of the hindgut, the Drosophila genes drumstick (drm) and bowl are required in the foregut for spatially localized gene expression and the morphogenetic processes that form the proventriculus. drm and bowl belong to a family of genes encoding C(2)H(2) zinc finger proteins; the other two members of this family are odd-skipped (odd) and sob. In both the fore- and hindgut, drm acts upstream of lines (lin), which encodes a putative transcriptional regulator, and relieves its repressive function. In spite of its phenotypic similarities with drm, bowl was found in both foregut and hindgut to act downstream, rather than upstream, of lin. These results support a hierarchy in which Drm relieves the repressive effect of Lin on Bowl, and Bowl then acts to promote spatially localized expression of genes (particularly the JAK/STAT pathway ligand encoded by upd) that control fore- and hindgut morphogenesis. Since the odd-family and lin are conserved in mosquito, mouse, and humans, we propose that the odd-family genes and lin may also interact to control patterning and morphogenesis in other insects and in vertebrates.

Odd-skipped related 2 (Osr2) encodes a key intrinsic regulator of secondary palate growth and morphogenesis

Development of the mammalian secondary palate involves multiple steps of highly regulated morphogenetic processes that are frequently disturbed during human development, resulting in the common birth defect of cleft palate. Neither the molecular processes governing normal palatogenesis nor the causes of cleft palate is well understood. In an expression screen to identify new transcription factors regulating palate development, we previously isolated the odd-skipped related 2 (Osr2) gene, encoding a zinc-finger protein homologous to the Drosophila odd-skipped gene product, and showed that Osr2 mRNA expression is specifically activated in the nascent palatal mesenchyme at the onset of palatal outgrowth. We report that a targeted null mutation in Osr2 impairs palatal shelf growth and causes delay in palatal shelf elevation, resulting in cleft palate. Whereas palatal outgrowth initiates normally in the Osr2 mutant embryos, a significant reduction in palatal mesenchyme proliferation occurs specifically in the medial halves of the downward growing palatal shelves at E13.5, which results in retarded, mediolaterally symmetric palatal shelves before palatal shelf elevation. The developmental timing of palatal growth retardation correlates exactly with the spatiotemporal pattern of Osr1 gene expression during palate development. Furthermore, we show that the Osr2 mutants exhibit altered gene expression patterns, including those of Osr1, Pax9 and Tgfb3, during palate development. These data identify Osr2 as a key intrinsic regulator of palatal growth and patterning.

Identification of novel genes of the bone-specific transcription factor Runx2

INTRODUCTION

The transcription factor Runx2 is a key regulator of osteoblast development and plays a role in chondrocyte maturation. The identification of transcriptional target genes of Runx2 may yield insight into how osteoblastic differentiation is achieved on a molecular level.

MATERIALS AND METHODS

Using a differential hybridization technique (selective amplification through biotin and restriction-mediated enrichment [SABRE]) and cDNA microarray analysis, 15 differentially expressed genes were identified using mRNA from C3H 10Tl/2 cells with constitutive and inducible overexpression of Runx2.

RESULTS AND CONCLUSIONS

Among the 15 genes identified, 4 encode the extracellular matrix proteins Ecml, Mgp, Fbn5, and Osf-2, three represent the transcription factors Esxl, Osrl, and Sox9, whereas others were Ptn, Npdc-1, Higl, and Tem l. The gene for Pttg1ip was upregulated in Runx2-expressing cells. Pttg1ip is widely expressed during development, but at highest levels in limbs and gonads. The Pttg1ip promoter binds Runx2 in a sequence specific manner, and Runx2 is able to transactivate the Pttg lip promoter in MC3T3-El cells. Therefore, Pttg1ip is likely tobe a novel direct transcriptional target gene of Runx2. In conclusion, the genes identified in this study are important candidates for mediating Runx2 induced cellular differentiation.