transforming-growth-factor-beta and Situs-Inversus

The study of left-right axis malformations in man and mouse has greatly advanced understanding of the mechanisms regulating vertebrate left-right axis formation. Recently, the roles of the TGF-beta family, Sonic hedgehog and fibroblast growth factor signaling, homeobox genes, and cilia in left-right axis determination have been more clearly defined. The identification of genes and environmental factors affecting left-right axis formation has important implications for understanding human laterality defects.

Topics: Animals; Embryonic Induction; Fibroblast Growth Factors; Genes, Homeobox; Hedgehog Proteins; Humans; Mice; Proteins; Situs Inversus; Trans-Activators; Transforming Growth Factor beta

The generation of left-right organ asymmetry during development involves a cascade of signaling events, while the initiating event is not proven, the mechanism of such organ asymmetry involves a number of genetically defined signaling molecules and, potentially specific transcription factors. Development of asymmetry appears to involve regulation of cell migration and proliferation events, and may be mechanistically distinct for different organs, such as pulmonary asymmetry versus cardiac situs. While the precise mechanisms by which genetically linked factors exert their effects still remains incompletely defined, an outline of those events can be deduced.

Topics: Activin Receptors; Animals; Body Patterning; Dyneins; Functional Laterality; Gene Expression Regulation, Developmental; Humans; Kartagener Syndrome; Left-Right Determination Factors; Microtubules; Models, Biological; Nodal Protein; Receptors, Growth Factor; Signal Transduction; Situs Inversus; Transcription Factors; Transforming Growth Factor beta

Topics: Animals; Calcium Signaling; Chick Embryo; Cilia; Ciliary Motility Disorders; Embryo, Mammalian; Gene Expression Regulation, Developmental; Humans; Kinesins; Left-Right Determination Factors; Mechanoreceptors; Membrane Potentials; Membrane Proteins; Mice; Models, Biological; Morphogenesis; Nodal Protein; Organizers, Embryonic; Proteins; Rheology; Situs Inversus; Transcription Factors; Transforming Growth Factor beta; TRPP Cation Channels

Left-sided expression of Nodal in the lateral plate mesoderm is a conserved feature necessary for the establishment of normal left-right asymmetry during vertebrate embryogenesis. By using gain- and loss-of-function experiments in zebrafish and mouse, we show that the activity of the Notch pathway is necessary and sufficient for Nodal expression around the node, and for proper left-right determination. We identify Notch-responsive elements in the Nodal promoter, and unveil a direct relationship between Notch activity and Nodal expression around the node. Our findings provide evidence for a mechanism involving Notch activity that translates an initial symmetry-breaking event into asymmetric gene expression.

Topics: Animals; Body Patterning; Enhancer Elements, Genetic; Gene Expression Regulation; Hedgehog Proteins; Membrane Proteins; Mice; Nodal Protein; Organizers, Embryonic; Promoter Regions, Genetic; Receptors, Notch; Signal Transduction; Situs Inversus; Trans-Activators; Transforming Growth Factor beta; Zebrafish

We have shown previously that mice deficient in the activin type IIB receptor (ActRIIB) exhibit right isomerism, which is characterized by mirror-image symmetrical right lungs, complex cardiac malformations, and hypoplasia of the spleen. These observations led us to hypothesize that the signaling of a TGF-beta family member by means of ActRIIB is necessary for the determination of the left-sidedness of the visceral organs. To test this hypothesis, we examined laterality defects in mice carrying mutations in both ActRIIB and inversus viscerum (iv) genes, because iv(-/-) mice display a spectrum of laterality defects, including situs inversus, right isomerism, and left isomerism. We found that all mice homozygous for both iv and ActRIIB mutations displayed the right isomerism. The phenotype of right isomerism in the double mutants was also more severe than that in ActRIIB(-/-) mice as shown by persistent left inferior vena cava, right atrial isomerism, and hypoplasia of spleen. Interestingly, the incidence of right isomerism also increased significantly in iv(-/-);ActRIIB(+/-) and iv(+/-);ActRIIB(-/-) mice compared with homozygous mice carrying either of single gene mutations. A mechanism of the genetic modulation between ActRIIB and iv genes may be that iv modulates the asymmetric expression of a TGF-beta family member that signals through activin type II receptors, ActRIIA and ActRIIB, to specify the "left-sidedness." Nodal is the most likely candidate. We show here that the penetrance and severity of the right isomerism is significantly elevated in nodal(+/-); ActRIIB(-/-) mice, compared with ActRIIB(-/-) mice. Furthermore, the chimeric mice derived from nodal(-/-) ES cells displayed right isomerism, indistinguishable from that in (iv(-/-);ActRIIB(-/-)) mice. We propose that iv functions to establish asymmetric expression of nodal in a gene-dosage-sensitive manner and that nodal signals through the activin type II receptors to specify the left-sidedness by means of a threshold mechanism.

Topics: Activin Receptors, Type II; Animals; Animals, Newborn; Functional Laterality; Gene Dosage; Gene Expression Regulation, Developmental; Homozygote; Isomerism; Mice; Mice, Knockout; Models, Genetic; Mutation; Nodal Protein; Phenotype; Signal Transduction; Situs Inversus; Time Factors; Transforming Growth Factor beta

Heparan sulfate proteoglycans expressed on the Xenopus animal cap ectoderm have been implicated in transmitting left-right information to heart and gut primordia. We report here that syndecan-2 functions in the ectoderm to mediate cardiac and visceral situs, upstream of known asymmetrically expressed genes but independently of its ability to mediate fibronectin fibrillogenesis. Left-right development is dependent on a distinct subset of glycosaminoglycan attachment sites on syndecan-2. A novel in vivo approach with enterokinase demonstrates that syndecan-2 functions in left-right patterning during early gastrulation. We describe a cell-nonautonomous role for ectodermal syndecan-2 in transmitting left-right information to migrating mesoderm. The results further suggest that this function may be related to the transduction of Vg1-related signals.

Topics: Activin Receptors, Type I; Amino Acid Sequence; Animals; Cell Movement; Digestive System; Ectoderm; Gastrula; Gene Expression Regulation, Developmental; Glycoproteins; Heart; Heparitin Sulfate; Membrane Glycoproteins; Mesoderm; Molecular Sequence Data; Proteins; Proteoglycans; Signal Transduction; Situs Inversus; Syndecan-2; Transforming Growth Factor beta; Xenopus; Xenopus Proteins; Zebrafish Proteins

Genetic background of the fetus contributes to the pathogenesis of congenital malformation after teratogen exposure. Such contribution is illustrated in left-right axis malformations observed in the F1 offspring of nonobese diabetic (NOD) mouse dams and sires from different strains. When sires of the NOD, ICR, or C57BL/6J were mated with NOD dams, incidence varied depending on the fetal genotype, with 65% in NOD x NOD, 24% in NOD x ICR, and 7% in NOD x C57BL/6J.. As a first step in elucidating the molecular basis of the interstrain differences in susceptibility to situs defects, we compared genomic sequences of six genes HNF3beta, Acvr2b, Nodal, ZIC3, Lefty1, and Smad2, which are involved in the normal development of left-right axis among NOD, ICR, and C57BL/6J strains.. The outbred strain ICR had 1) a 0.2-kb insertion in the putative promoter region of the isoform E of HNF3beta together with a G to A change that could create a potential splice acceptor in the exon 3 of HNF3beta (gene frequency P = 0.36), 2) five single base substitutions within the 5' controlling element and a proline to serine substitution (P2S) of Lefty1 (P = 0.77), and 3) a tyrosine to histidine substitution within the prodomain of Nodal (P = 0.48). The inbred strain NOD had the same G to A change as ICR and a three-base deletion in the putative promoter of isoform E of HNF3beta.. We suggest that sequence variations in HNF3beta, Lefty1, and Nodal might account, in part, for the interstrain differences in susceptibility to situs abnormalities among the offspring of diabetic dams.

Topics: Animals; Diabetes Mellitus, Type 1; Diabetes, Gestational; DNA Mutational Analysis; DNA Primers; DNA-Binding Proteins; Female; Genetic Variation; Hepatocyte Nuclear Factor 3-beta; Homeodomain Proteins; Left-Right Determination Factors; Mice; Mice, Inbred C57BL; Mice, Inbred ICR; Mice, Inbred NOD; Multigene Family; Mutation; Nodal Protein; Nuclear Proteins; Pregnancy; Reverse Transcriptase Polymerase Chain Reaction; Sequence Analysis, DNA; Situs Inversus; Smad2 Protein; Trans-Activators; Transcription Factors; Transforming Growth Factor beta

Normal development of the left/right (L/R) body axis leads to the characteristic sidedness of asymmetric body structures, e.g., the left-sided heart. Several genes are now known to be expressed with L/R asymmetry during embryogenesis, including nodal, a member of the transforming growth factor-beta (TGF-beta) family. Mutations or experimental treatments that affect L/R development, such as those that cause situs inversus (reversal of the sidedness of asymmetric body structures), have been shown to alter or abolish nodal's asymmetric expression.. In the present study, we examined the effects on nodal expression of alpha(1)-adrenergic stimulation, known to cause a 50% incidence of situs inversus in rat embryos grown in culture, using reverse transcription-polymerase chain reaction assay and whole-mount in situ hybridization assay.. In embryos cultured with phenylephrine, an alpha(1)-adrenergic agonist, nodal's normal asymmetric expression only in the left lateral plate mesoderm was altered. In some treated embryos, nodal expression was detected in either the left or right lateral plate mesoderm. However, most treated embryos lacked lateral plate mesoderm expression. In addition, the embryos that did show expression were at a later stage than when nodal expression is normally found.. Our results demonstrate that alpha(1)-adrenergic stimulation delays the onset and perturbs the normal asymmetric pattern of nodal expression. Either of these effects might contribute to situs inversus.

Topics: Adrenergic alpha-Agonists; Amino Acid Sequence; Animals; Base Sequence; Cloning, Molecular; DNA Primers; Embryo, Mammalian; Female; In Situ Hybridization; Molecular Sequence Data; Nodal Protein; Organ Culture Techniques; Phenylephrine; Polymerase Chain Reaction; Pregnancy; Rats; Rats, Sprague-Dawley; Receptors, Adrenergic, alpha-1; Reverse Transcriptase Polymerase Chain Reaction; Sequence Homology, Amino Acid; Sequence Homology, Nucleic Acid; Situs Inversus; Transforming Growth Factor beta

Topics: Activins; Animals; Congenital Abnormalities; Embryonic Induction; Heart; Heart Defects, Congenital; Hedgehog Proteins; Humans; Lung; Morphogenesis; Nodal Protein; Oligopeptides; Peptides; Proteins; Situs Inversus; Trans-Activators; Transforming Growth Factor beta; Twins, Conjoined

We examined the nodal flow of well-characterized mouse mutants, inversus viscerum (iv) and inversion of embryonic turning (inv), and found that their laterality defects are always accompanied by an abnormality in nodal flow. In a randomized laterality mutant, iv, the nodal cilia were immotile and the nodal flow was absent. In a situs inversus mutant, inv, the nodal cilia was motile but could only produce very weak leftward nodal flow. These results consistently support our hypothesis that the nodal flow produces the gradient of putative morphogen and triggers the first L-R determination event.

Topics: Animals; Body Patterning; Cilia; Dyneins; Embryonic and Fetal Development; Gene Expression Regulation, Developmental; Left-Right Determination Factors; Mice; Mice, Transgenic; Microscopy, Fluorescence; Microscopy, Video; Microspheres; Morphogenesis; Mutation; Situs Inversus; Somites; Transforming Growth Factor beta

The handedness of visceral organs is conserved among vertebrates and is regulated by asymmetric signals relayed by molecules such as Shh, Nodal and activin. The gene Pitx2 is expressed in the left lateral plate mesoderm and, subsequently, in the left heart and gut of mouse, chick and Xenopus embryos. Misexpression of Shh and Nodal induces Pitx2 expression, whereas inhibition of activin signalling blocks it. Misexpression of Pitx2 alters the relative position of organs and the direction of body rotation in chick and Xenopus embryos. Changes in Pitx2 expression are evident in mouse mutants with laterality defects. Thus, Pitx2 seems to serve as a critical downstream transcription target that mediates left-right asymmetry in vertebrates.

Topics: Activin Receptors, Type II; Animals; Body Patterning; Chick Embryo; Culture Techniques; Hedgehog Proteins; Homeobox Protein PITX2; Homeodomain Proteins; Mice; Molecular Sequence Data; Nodal Protein; Nuclear Proteins; Paired Box Transcription Factors; Proteins; Receptors, Growth Factor; Situs Inversus; Trans-Activators; Transcription Factors; Transforming Growth Factor beta; Xenopus

Pitx2, a member of the bicoid-related family of homeobox-containing genes, is asymmetrically expressed in the left lateral plate mesoderm and derived tissues during chick and mouse development. Modifications of Pitx2 pattern of expression in the iv mouse mutation correlate with the situs alterations characteristic of the mutation. Misexpression experiments demonstrate that Shh and nodal positively regulate Pitx2 expression. Our results are compatible with a Pitx2 function in the late phase of the gene cascade controlling laterality.

Topics: Animals; Body Patterning; Chick Embryo; Conserved Sequence; Gene Expression Regulation, Developmental; Homeobox Protein PITX2; Homeodomain Proteins; Mesoderm; Mice; Mice, Inbred C57BL; Mice, Mutant Strains; Mutation; Nodal Protein; Nuclear Proteins; Paired Box Transcription Factors; Proteins; Signal Transduction; Situs Inversus; Transcription Factors; Transforming Growth Factor beta

Vertebrates have characteristic and conserved left-right (L-R) visceral asymmetries, for example the left-sided heart. In humans, alterations of L-R development can have serious clinical implications, including cardiac defects. Although little is known about how the embryonic L-R axis is established, a recent study in the chick embryo revealed L-R asymmetric expression of several previously cloned genes, including Cnr-1 (for chicken nodal-related-1), and indicated how this L-R molecular asymmetry might be important for subsequent visceral morphogenesis. Here we show that nodal is asymmetrically expressed in mice at similar stages, as is Xnr-1 (for Xenopus nodal related-1) in frogs. We also examine nodal expression in two mouse mutations that perturb L-R development, namely situs inversus viscerum (iv), in which assignment of L-R asymmetry is apparently random and individuals develop either normally or are mirror-image-reversed (situs inversus), and inversion of embryonic turning (inv), in which all individuals develop with situs inversus. In both, nodal expression is strikingly affected, being reversed or converted to symmetry. These results further support a key role for nodal and nodal-related genes in interpreting and relaying L-R patterning information in vertebrates. To our knowledge, our results provide the first direct evidence that iv and inv normally function well before the appearance of morphological L-R asymmetry.

Topics: Animals; Chick Embryo; Embryo, Mammalian; Embryo, Nonmammalian; Female; Gene Expression Regulation, Developmental; Heterozygote; Homozygote; Male; Mice; Mice, Inbred BALB C; Morphogenesis; Mutation; Nodal Protein; RNA, Messenger; Situs Inversus; Transforming Growth Factor beta; Xenopus; Xenopus Proteins