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Vesa Kaartinen

Publications and source records attributed to Vesa Kaartinen.

At least 19 recordsLinked to original sources
PubMed2007

BMP type I receptor ALK2 is essential for proper patterning at late gastrulation during mouse embryogenesis.

Bone morphogenetic proteins (BMPs) have multiple functions during vertebrate development. Previously, it was shown that BMP type I receptor ALK2 (also known as ACVRI, ActRI, or ActRIA) was important for normal mouse gastrulation by deleting exon 4 or exon 5 of Alk2. Recently, flanking exon 7 by loxP sites generated a conditional allele for Alk2. To assess whether the deletion of exon 7 causes functional null of ALK2, and does not produce a dominant negative form or a partially functional form of ALK2, we performed a comparative analysis between Alk2 homozygous mutant embryos with an exon 5 deletion (Alk2(Delta5/Delta5)) and embryos with an exon 7 deletion (Alk2(Delta7/Delta7)). Both Alk2(Delta5/Delta5) and Alk2(Delta7/Delta7) mutants showed identical morphological gastrulation defects. Histological examinations and molecular marker analyses revealed identical abnormal gastrulation phenotypes in Alk2(Delta5/Delta5) and Alk2(Delta7/Delta7) mutants. Although Fgf8 was expressed in the primitive streak of Alk2(Delta5/Delta5) and Alk2(Delta7/Delta7) mutants, Brachyury, Wnt3a, and Tbx6 were dramatically downregulated in Alk2(Delta5/Delta5) and Alk2(Delta7/Delta7) mutants. These results indicate that deletion of exon 7 for Alk2 leads to a functionally null mutation in vivo, and Alk2 is crucial for sustaining the proper gastrulation events in early mouse embryogenesis.

Activin Receptors, Type I↗
PubMed2006

Abr and Bcr, two homologous Rac GTPase-activating proteins, control multiple cellular functions of murine macrophages.

Small GTPases of the Rho family are key regulators of phagocytic leukocyte function. Abr and Bcr are homologous, multidomain proteins. Their C-terminal domain has GTPase-activating protein (GAP) activity that, in vitro, is specific for Rac and Cdc42. To address the in vivo relevance of these entire proteins, of which little is known, the current study examined the effect of the genetic ablation of Abr and Bcr in murine macrophages. The concomitant loss of Abr and Bcr induced multiple alterations of macrophage cellular behavior known to be under the control of Rac. Macrophages lacking both Abr and Bcr exhibited an atypical, elongated morphology that was reproduced by the ectopic expression of GAP domain mutant Abr and Bcr in a macrophage cell line and of constitutively active Rac in primary macrophages. A robust increase in colony-stimulating factor 1 (CSF-1)-directed motility was observed in macrophages deficient for both proteins and, in response to CSF-1 stimulation, Abr and Bcr transiently translocated to the plasma membrane. Phagocytosis of opsonized particles was also increased in macrophages lacking both proteins and correlated with sustained Rac activation. Bcr and Abr GAP mutant proteins localized around phagosomes and induced distinct phagocytic cup formation. These results identify Abr and Bcr as the only GAPs to date that specifically negatively regulate Rac function in vivo in primary macrophages.

Animals↗
PubMed2006

Defective ALK5 signaling in the neural crest leads to increased postmigratory neural crest cell apoptosis and severe outflow tract defects.

BACKGROUND: Congenital cardiovascular diseases are the most common form of birth defects in humans. A substantial portion of these defects has been associated with inappropriate induction, migration, differentiation and patterning of pluripotent cardiac neural crest stem cells. While TGF-beta-superfamily signaling has been strongly implicated in neural crest cell development, the detailed molecular signaling mechanisms in vivo are still poorly understood. RESULTS: We deleted the TGF-beta type I receptor Alk5 specifically in the mouse neural crest cell lineage. Failure in signaling via ALK5 leads to severe cardiovascular and pharyngeal defects, including inappropriate remodeling of pharyngeal arch arteries, abnormal aortic sac development, failure in pharyngeal organ migration and persistent truncus arteriosus. While ALK5 is not required for neural crest cell migration, our results demonstrate that it plays an important role in the survival of post-migratory cardiac neural crest cells. CONCLUSION: Our results demonstrate that ALK5-mediated signaling in neural crest cells plays an essential cell-autonomous role in the pharyngeal and cardiac outflow tract development.

Activin Receptors, Type I↗
PubMed2006

Palatal fusion - where do the midline cells go? A review on cleft palate, a major human birth defect.

Formation of the palate, the organ that separates the oral cavity from the nasal cavity, is a developmental process characteristic to embryos of higher vertebrates. Failure in this process results in palatal cleft. During the final steps of palatogenesis, two palatal shelves outgrowing from the sides of the embryonic oronasal cavity elevate above the tongue, meet in the midline, and rapidly fuse together. Over the decades, multiple mechanisms have been proposed to explain how the superficial mucous membranes disappear from the contact line, thus allowing for normal midline mesenchymal confluence. A substantial body of experimental evidence exists for cell death, cell migration, epithelial-to-mesenchymal transdifferentiation (EMT), replacement through new tissue intercalation, and other mechanisms. However, the most recent use of gene recombination techniques in cell fate tracking disfavors the EMT concept, and suggests that apoptosis is the major fate of the midline cells during physiological palatal fusion. This article summarizes the benefits and drawbacks of histochemical and molecular tools used to determine the fates of cells within the palatal midline. Mechanisms of normal disintegration of the midline epithelial seam are reviewed together with pathologic processes that prevent this disintegration, thus causing cleft palate.

Animals↗
PubMed2006

Epithelial and ectomesenchymal role of the type I TGF-beta receptor ALK5 during facial morphogenesis and palatal fusion.

Transforming growth factor beta (TGF-beta) proteins play important roles in morphogenesis of many craniofacial tissues; however, detailed biological mechanisms of TGF-beta action, particularly in vivo, are still poorly understood. Here, we deleted the TGF-beta type I receptor gene Alk5 specifically in the embryonic ectodermal and neural crest cell lineages. Failure in signaling via this receptor, either in the epithelium or in the mesenchyme, caused severe craniofacial defects including cleft palate. Moreover, the facial phenotypes of neural crest-specific Alk5 mutants included devastating facial cleft and appeared significantly more severe than the defects seen in corresponding mutants lacking the TGF-beta type II receptor (TGFbetaRII), a prototypical binding partner of ALK5. Our data indicate that ALK5 plays unique, non-redundant cell-autonomous roles during facial development. Remarkable divergence between Tgfbr2 and Alk5 phenotypes, together with our biochemical in vitro data, imply that (1) ALK5 mediates signaling of a diverse set of ligands not limited to the three isoforms of TGF-beta, and (2) ALK5 acts also in conjunction with type II receptors other than TGFbetaRII.

Activin Receptors, Type I↗
PubMed2006

Genetically modified bone morphogenetic protein signalling alters traumatic brain injury-induced gene expression responses in the adult mouse.

Three genetic mouse models were examined to define effects of bone morphogenetic protein (BMP) signalling on gene expression in normal and injured adult brain. CaMKII-Cre eliminated the BMP receptor Acvr1 (Alk2) and the common TGFbeta superfamily signal mediator Smad4 or activated a constitutively active Acvr1 in postnatal forebrain neurons. All mutants followed mendelian ratios, with no overt phenotypic changes. In situ hybridization demonstrated normal patterns of the dendritic marker MAP2 (Mtap2) throughout cortex despite neuron-specific losses of Acvr1 or Smad4. However, strong up-regulation of Mtap2 transcript in these mice was found by quantitative RT-PCR (qRT-PCR), indicating that Mtap2 is normally suppressed by BMP. Traumatic brain injury (TBI) resulted in increases of histone-associated DNA fragments in both control and Smad4-deficient cortex. Several cell-type-specific transcripts known to be involved in injury-related responses were measured by qRT-PCR. Gfap mRNA was strongly up-regulated in controls as well as in the loss-of-BMP-signalling mutants. Notably, activated Acvr1 signalling gave significantly lower TBI-induced up-regulations of Gfap and Phox2a mRNA levels, indicating reductions in astroglial and neuronal reactions to injury. Strong impairment in injury-induced Timp1 transcript up-regulation was also seen in these mice. In contrast, osteopontin (Spp1) transcript levels in activated microglia were not reduced by Acvr1 signalling. Altogether, the data suggest that BMP signalling is dispensable in adult cortical neurons but that augmented BMP signalling affects molecular changes associated with neuronal lesions.

Activin Receptors, Type I↗
PubMed2005

Atrioventricular cushion transformation is mediated by ALK2 in the developing mouse heart.

Developmental abnormalities in endocardial cushions frequently contribute to congenital heart malformations including septal and valvular defects. While compelling evidence has been presented to demonstrate that members of the TGF-beta superfamily are capable of inducing endothelial-to-mesenchymal transdifferentiation in the atrioventricular canal, and thus play a key role in formation of endocardial cushions, the detailed signaling mechanisms of this important developmental process, especially in vivo, are still poorly known. Several type I receptors (ALKs) for members of the TGF-beta superfamily are expressed in the myocardium and endocardium of the developing heart, including the atrioventricular canal. However, analysis of their functional role during mammalian development has been significantly complicated by the fact that deletion of the type I receptors in mouse embryos often leads to early embryonal lethality. Here, we used the Cre/loxP system for endothelial-specific deletion of the type I receptor Alk2 in mouse embryos. The endothelial-specific Alk2 mutant mice display defects in atrioventricular septa and valves, which result from a failure of endocardial cells to appropriately transdifferentiate into the mesenchyme in the AV canal. Endocardial cells deficient in Alk2 demonstrate decreased expression of Msx1 and Snail, and reduced phosphorylation of BMP and TGF-beta Smads. Moreover, we show that endocardial cells lacking Alk2 fail to delaminate from AV canal explants. Collectively, these results indicate that the BMP type I receptor ALK2 in endothelial cells plays a critical non-redundant role in early phases of endocardial cushion formation during cardiac morphogenesis.

Activin Receptors, Type I↗
PubMed2005

Generation of rac3 null mutant mice: role of Rac3 in Bcr/Abl-caused lymphoblastic leukemia.

Numerous studies indirectly implicate Rac GTPases in cancer. To investigate if Rac3 contributes to normal or malignant cell function, we generated rac3 null mutants through gene targeting. These mice were viable, fertile, and lacked an obvious external phenotype. This shows Rac3 function is dispensable for embryonic development. Bcr/Abl is a deregulated tyrosine kinase that causes chronic myelogenous leukemia and Ph-positive acute lymphoblastic leukemia in humans. Vav1, a hematopoiesis-specific exchange factor for Rac, was constitutively tyrosine phosphorylated in primary lymphomas from Bcr/Abl P190 transgenic mice, suggesting inappropriate Rac activation. rac3 is expressed in these malignant hematopoietic cells. Using lysates from BCR/ABL transgenic mice that express or lack rac3, we detected the presence of activated Rac3 but not Rac1 or Rac2 in the malignant precursor B-lineage lymphoblasts. In addition, in female P190 BCR/ABL transgenic mice, lack of rac3 was associated with a longer average survival. These data are the first to directly show a stimulatory role for Rac in leukemia in vivo. Moreover, our data suggest that interference with Rac3 activity, for example, by using geranyl-geranyltransferase inhibitors, may provide a positive clinical benefit for patients with Ph-positive acute lymphoblastic leukemia.

Alleles↗
PubMed2004

Tgf-beta3-induced palatal fusion is mediated by Alk-5/Smad pathway.

Cleft palate is among the most common birth defects in humans, caused by a failure in the complex multistep developmental process of palatogenesis. It has been recently shown that transforming growth factor beta3 (Tgf-beta3) is an absolute requirement for successful palatal fusion, both in mice and humans. However, very little is known about the mechanisms of Tgf-beta3 signaling during this process. Here we show that putative Tgf-beta type I receptors, Alk-1, Alk-2, and Alk-5, are all endogenously expressed in the palatal epithelium. Activation of Alk-5 in the Tgf-beta3 (-/-) palatal epithelium is able to rescue palatal fusion, whereas inactivation of Alk-5 in the wild-type palatal epithelium prevents palatal fusion. The effect of Alk-2 is similar, but less pronounced. The induction of fusion by activation of Alk-5 or Alk-2 is stronger in the posterior parts of the palates at the embryonic day 14 (E14), while their activation at E13.5 also restores anterior fusion, reflecting the natural anterior-posterior direction of palate maturation in vivo. We also show that Smad2 is endogenously activated in the palatal midline epithelial seam (MES) during the fusion process. By using a mutant Alk-5 receptor that is an active kinase but is unable to activate Smads, we show that activation of Smad-independent Tgf-beta responses is not sufficient to induce fusion of shelves deficient in Tgf-beta3. Based on these observations, we conclude that the Smad2-dependent Alk-5 signaling pathway is dominant in palatal fusion driven by Tgf-beta3.

Activin Receptors, Type I↗
PubMed2004

Craniofacial defects in mice lacking BMP type I receptor Alk2 in neural crest cells.

Neural crest cells (NCCs) are pluripotent migratory cells that contribute to the development of various craniofacial structures. Many signaling molecules have been implicated in the formation, migration and differentiation of NCCs including bone morphogenetic proteins (BMPs). BMPs signal through a receptor complex composed of type I and type II receptors. Type I receptors (Alk2, Alk3 and Alk6) are the primary determinants of signaling specificity and therefore understanding their function is important in revealing the developmental roles of molecular pathways regulated by BMPs. Here we used a Cre/loxP system for neural crest specific deletion of Alk2. Our results show that mice lacking Alk2 in the neural crest display multiple craniofacial defects including cleft palate and a hypotrophic mandible. Based on the present results we conclude that signaling via Alk2 receptors is non-redundant and regulates normal development of a restricted set of structures derived from the cranial neural crest.

Activin Receptors, Type I↗
PubMed2004

Cardiac outflow tract defects in mice lacking ALK2 in neural crest cells.

Cardiac neural crest cells are multipotent migratory cells that contribute to the formation of the cardiac outflow tract and pharyngeal arch arteries. Neural crest-related developmental defects account for a large proportion of congenital heart disorders. Recently, the genetic bases for some of these disorders have been elucidated, and signaling pathways required for induction, migration and differentiation of cardiac neural crest have emerged. Bone morphogenetic proteins comprise a family of secreted ligands implicated in numerous aspects of organogenesis, including heart and neural crest development. However, it has remained generally unclear whether BMP ligands act directly on neural crest or cardiac myocytes during cardiac morphogenesis, or function indirectly by activating other cell types. Studies on BMP receptor signaling during organogenesis have been hampered by the fact that receptor knockouts often lead to early embryonic lethality. We have used a Cre/loxP system for neural crest-specific deletion of the type I receptor, ALK2, in mouse embryos. Mutant mice display cardiovascular defects, including persistent truncus arteriosus, and abnormal maturation of the aortic arch reminiscent of common forms of human congenital heart disease. Migration of mutant neural crest cells to the outflow tract is impaired, and differentiation to smooth muscle around aortic arch arteries is deficient. Moreover, in Alk2 mutants, the distal outflow tract fails to express Msx1, one of the major effectors of BMP signaling. Thus, the type I BMP receptor ALK2 plays an essential cell-autonomous role in the development of the cardiac outflow tract and aortic arch derivatives.

Activin Receptors, Type I↗
PubMed2003

Growth factor signaling in lung morphogenetic centers: automaticity, stereotypy and symmetry.

Lung morphogenesis is stereotypic, both for lobation and for the first several generations of airways, implying mechanistic control by a well conserved, genetically hardwired developmental program. This program is not only directed by transcriptional factors and peptide growth factor signaling, but also co-opts and is modulated by physical forces. Peptide growth factors signal within repeating epithelial-mesenchymal temporospatial patterns that constitute morphogenetic centers, automatically directing millions of repetitive events during both stereotypic branching and nonstereotypic branching as well as alveolar surface expansion phases of lung development. Transduction of peptide growth factor signaling within these centers is finely regulated at multiple levels. These may include ligand expression, proteolytic activation of latent ligand, ligand bioavailability, ligand binding proteins and receptor affinity and presentation, receptor complex assembly and kinase activation, phosphorylation and activation of adapter and messenger protein complexes as well as downstream events and cross-talk both inside and outside the nucleus. Herein we review the critical Sonic Hedgehog, Fibroblast Growth Factor, Bone Morphogenetic Protein, Vascular Endothelial Growth Factor and Transforming Growth Factorbeta signaling pathways and propose how they may be functionally coordinated within compound, highly regulated morphogenetic gradients that drive first stereotypic and then non-stereotypic, automatically repetitive, symmetrical as well as asymmetrical branching events in the lung.

Aging↗
PubMed2003

Targeted expression of activated Rac3 in mammary epithelium leads to defective postlactational involution and benign mammary gland lesions.

Rac3, a novel member of the Rho subfamily of the small GTPases, is frequently activated in cultured breast cancer cells and has been shown to mediate its effect via the p21-activated kinase (Pak) pathway. In order to evaluate these findings in vivo, we generated transgenic mice that express human constitutively active V12Rac under the control of the mouse mammary tumor virus (MMTV) promoter, which targets the transgene expression to the mammary epithelium. V12Rac3 expression could be detected during the first pregnancy, and the transgenic mammary gland tissues displayed an elevated Pak1 phosphorylation. Although milk proteins, beta-casein and whey acidic protein were expressed and milk fat globules accumulated normally during pregnancy, 60% of transgenic mothers failed to nurse their pups. Surprisingly, although full lactational differentiation was never achieved in transgenic mice, gland involution was incomplete. For 5 days after weaning, involution was normal, but thereafter, epithelial islands characteristic of this early stage of involution persisted for months. The apoptotic index decreased after 5 days, and these glands were associated with increased p38 MAPK phosphorylation. Nine months postpartum, the transgenic mammary glands still demonstrated a large amount of persistent epithelial islands and abnormally large ducts with lymphocyte infiltration, whereas the tissues of non-transgenic controls had returned to their normal 'virgin-like' phenotype. These data show that sustained activation of Rac3 in the mammary epithelium leads to impaired mammary gland physiology and results in the formation of mammary gland lesions.

Animals↗
PubMed2002

BCR/ABL P190 transgenic mice develop leukemia in the absence of Crkl.

The Bcr/Abl fusion protein directly causes chronic myelogenous leukemia and Philadelphia-chromosome positive acute lymphoblastic leukemia. Multiple independent studies have implicated Crkl, a small adapter protein, in transduction of oncogenic signals of Bcr/Abl and Crkl tyrosine-phosphorylation is used as a diagnostic tool for Philadelphia-positive leukemia. To evaluate the contribution of Crkl to this type of leukemia, we generated mutant mice that lack Crkl expression. We found that the overall survival of P190 BCR/ABL crkl-/- mice was comparable to that of genetically matched P190 BCR/ABL crkl +/+ mice. Both genotypes developed lymphoid lineage leukemia/lymphoma. Western blot analysis of -/- and +/+ lymphomas showed that the related Crk protein was tyrosine phosphorylated and could be found complexed with Bcr-Abl P190. These data indicate that possible therapeutic approaches that target Crkl may be complicated by the presence of pathways that compensate for lack of Crkl function.

Animals↗
PubMed2002

Vestibular dysgenesis in mice lacking Abr and Bcr Cdc42/RacGAPs.

The inner ear develops from a simple epithelium (otic placode) into the complex structures specialized for balance (vestibule) and sound (cochlea) detection. Abnormal vestibular and cochlear development is associated with many birth defects. During recent years, considerable progress has been made in understanding the molecular bases of these conditions. To determine the biological function of two closely related GTPase activating proteins for the Cdc42/Rac GTPases, Abr and Bcr, we generated a mouse strain deficient in both of these proteins. Double null mutant mice exhibit hyperactivity, persistent circling, and are unable to swim. These phenotypes are typically found in mice with vestibular defects. Indeed, adult double null mutants display abnormal dysmorphic structures of both the saccule and utricle. Moreover, a total loss of otoconia can be seen in the utricle, whereas in the saccule, otoconia are either missing or their number is drastically decreased and they are abnormally large. Interestingly, both the cochlea and semicircular canals are normal and the double null mutant mice are not deaf. These data demonstrate that Abr and Bcr play important complementary roles during vestibular morphogenesis and that a function of Cdc42/RacGAPs and, therefore, that of the small Rho-related GTPases is critically important for balance and motor coordination.

Animals↗
PubMed2002

TGFbeta3-induced activation of RhoA/Rho-kinase pathway is necessary but not sufficient for epithelio-mesenchymal transdifferentiation: implications for palatogenesis.

TGFbeta-induced epithelio-mesenchymal transdifferentiation (EMT) has been shown to play a pivotal role in developmental processes such as palatogenesis and heart organogenesis. Interestingly, EMT has also been shown to contribute to the promotion of invasiveness during the later stages of tumorigenesis. Here we show that cells induced to undergo EMT by TGFbeta3 demonstrate increased motility on fibronectin and display a rapid activation of RhoA followed by a gradual downregulation of Cdc42 and Rac3 activity. The induced expression of a fast-cycling RhoA mutant (RhoA F30) stimulates the formation of stress fibers and spreading, and therefore the generation of mesenchymal phenotype. Inactivation of the Rho effector Rho-kinase, interferes with TGFbeta3-induced EMT by inhibiting stress fiber formation, whereas disruption of adherens and tight junctions was not significantly affected. Moreover, we show that TGFbeta3-induced RhoA/Rho-kinase activation is biologically significant, since palatal shelves from pre-fusion mouse embryos cultured in the presence of Rho-kinase inhibitors failed to fuse and midline epithelial cells did not undergo EMT. To conclude, our results indicate that TGFbeta3 induces rapid activation of the RhoA/Rho-kinase pathway and subsequently reorganization of the actin cytoskeleton. These changes are likely to be necessary in biological processes in which EMT has been shown to play a critical role, such as palatal fusion.

Animals↗