Biomedical subjects

Frédéric M Rosa

Publications and source records attributed to Frédéric M Rosa.

9 recordsLinked to original sources

PubMed2006

Duplicate sfrp1 genes in zebrafish: sfrp1a is dynamically expressed in the developing central nervous system, gut and lateral line.

The secreted frizzled-related proteins (Sfrp) are a family of soluble proteins with diverse biological functions having the capacity to bind Wnt ligands, to modulate Wnt signalling, and to signal directly via the Wnt receptor, Frizzled. In an enhancer trap screen for embryonic expression in zebrafish we identified an sfrp1 gene. Previous studies suggest an important role for sfrp1 in eye development, however, no data have been reported using the zebrafish model. In this paper, we describe duplicate sfrp1 genes in zebrafish and present a detailed analysis of the expression profile of both genes. Whole mount in situ hybridisation analyses of sfrp1a during embryonic and larval development revealed a dynamic expression profile, including: the central nervous system, where sfrp1a was regionally expressed throughout the brain and developing eye; the posterior gut, from the time of endodermal cell condensation; the lateral line, where sfrp1a was expressed in the migrating primordia and interneuromast cells that give rise to the sensory organs. Other sites included the blastoderm, segmenting mesoderm, olfactory placode, developing ear, pronephros and fin-bud. We have also analysed sfrp1b expression during embryonic development. Surprisingly this gene exhibited a divergent expression profile being limited to the yolk syncytium under the elongating tail-bud, which later covered the distal yolk extension, and transiently in the tail-bud mesenchyme. Overall, our studies provide a basis for future analyses of these developmentally important factors using the zebrafish model.

Amino Acid Sequence↗

PubMed2004

Nodal and Fgf pathways interact through a positive regulatory loop and synergize to maintain mesodermal cell populations.

Interactions between Nodal/Activin and Fibroblast growth factor (Fgf) signalling pathways have long been thought to play an important role in mesoderm formation. However, the molecular and cellular processes underlying these interactions have remained elusive. Here, we address the epistatic relationships between Nodal and Fgf pathways during early embryogenesis in zebrafish. First, we find that Fgf signalling is required downstream of Nodal signals for inducing the Nodal co-factor One-eyed-pinhead (Oep). Thus, Fgf is likely to be involved in the amplification and propagation of Nodal signalling during early embryonic stages. This could account for the previously described ability of Fgf to render cells competent to respond to Nodal/Activin signals. In addition, overexpression data shows that Fgf8 and Fgf3 can take part in this process. Second, combining zygotic mutations in ace/fgf8 and oep disrupts mesoderm formation, a phenotype that is not produced by either mutation alone and is consistent with our model of an interdependence of Fgf8 and Nodal pathways through the genetic regulation of the Nodal co-factor Oep and the cell propagation of Nodal signalling. Moreover, mesodermal cell populations are affected differentially by double loss-of-function of Zoep;ace. Most of the dorsal mesoderm undergoes massive cell death by the end of gastrulation, in contrast to either single-mutant phenotype. However, some mesoderm cells are still able to undergo myogenic differentiation in the anterior trunk of Zoep;ace embryos, revealing a morphological transition at the level of somites 6-8. Further decreasing Oep levels by removing maternal oep products aggravates the mesodermal defects in double mutants by disrupting the fate of the entire mesoderm. Together, these results demonstrate synergy between oep and fgf8 that operates with regional differences and is involved in the induction, maintenance, movement and survival of mesodermal cell populations.

Animals↗

PubMed2004

[Mechanotransduction of hemodynamic forces regulates organogenesis].

Endothelial cells (EC) of the vertebrate cardiovascular system (CVS) are bona fide, yet enigmatic mechanoreceptors. When cultured in vitro and exposed to fluid forces, EC modify their physiological behaviour at the structural, metabolical and gene expression levels in response to the mechanical stimulus. However, as a direct consequence of the hypoxic bias (and often the lethality) that results from blocking blood flow in most animal systems, the in vivo role of EC mechanosensation (ECMS) remains poorly understood. The zebrafish has recently emerged as an alternative genetic model for the study of vertebrate development. Its striking ability to survive until larval stages in the absence of blood circulation circumveys the usual caveats that are inherent to CVS research, and offers the exciting opportunity to dissect the function of ECMS in vivo. Two groups have already uncovered an essential role for ECMS in zebrafish organogenesis, particularly in heart morphogenesis. In embryos in which intracardiac blood flow is genetically or physically compromised, several features of the normally developing heart, including valve formation, are specifically disrupted. In addition, impressive imaging studies of zebrafish hemodynamics demonstrate that the shear stress exerted upon the cardiac endothelium is largely in the range of the stimulus that in vitro activates cytoskelettal remodeling and gene expression changes in EC. Hence the cardiac phenotypes observed in vivo may indeed directly result from a lack of ECMS-dependent EC activity. These data shed first light on the role of ECMS in vivo. Notably, they also suggest that a number of human congenital cardiomyopathies may arise through abnormal fetal hemodynamics and/or EC sensory activity. Finally, these discoveries reinforce the too often neglected role of epigenetic factors (in this case, fluid forces) in the regulation of animal development.

Animals↗

PubMed2003

Maternal induction of ventral fate by zebrafish radar.

In vertebrate embryos, maternal determinants are thought to preestablish the dorsoventral axis by locally activating zygotic ventral- and dorsal-specifying genes, e.g., genes encoding bone morphogenetic proteins (BMPs) and BMP inhibitors, respectively. Whereas the canonical Wntbeta-catenin pathway fulfills this role dorsally, the existence of a reciprocal maternal ventralizing signal remains hypothetical. Maternal noncanonical WntCa(2+) signaling may promote ventral fates by suppressing Wntbeta-catenin dorsalizing signals; however, whether any maternal determinant is directly required for the activation of zygotic ventral-specifying genes is unknown. Here, we show that such a function is achieved, in part, in the zebrafish embryo by the maternally encoded transforming growth factor beta (TGF-beta) signaling molecule, Radar. Loss-of-function experiments, together with epistasis analyses, identify maternal Radar as an upstream activator of bmps expression. Maternal induction of bmps by Radar is essential for zebrafish development as its removal results in larval-lethal dorsalized phenotypes. Double-morphant analyses further suggest that Radar functions through the TGF-beta receptor Alk8 to initiate the expression of bmp genes. Our results support the existence of a previously uncharacterized maternal ventralizing pathway. They might further indicate that maternal TGF-betaRdr and WntCa(2+) pathways complementarily specify ventral cell fates, with the former triggering bmps expression and the latter indirectly repressing genes encoding BMP antagonists.

Animals↗

PubMed2002

Molecular basis of cell migration in the fish lateral line: role of the chemokine receptor CXCR4 and of its ligand, SDF1.

Cell migration plays an essential role in many morphogenetic processes, and its deregulation has many dramatic consequences. Yet how migration is controlled during normal development is still a largely unresolved question. We examined this process in the case of the posterior lateral line (PLL), a mechanosensory system present in fish and amphibians. In zebrafish, the embryonic PLL comprises seven to eight sense organs (neuromasts) aligned from head to tail along the flank of the animal and is formed by a primordium that originates from a cephalic placode. This primordium migrates along a stereotyped pathway toward the tip of the tail and deposits in its wake discrete groups of cells, each of which will become a neuromast. We show that a trail of SDF1-like chemokine is present along the pathway of the primordium and that a CXCR4-like chemokine receptor is expressed by the migrating cells. The inactivation of either the ligand or its receptor blocks migration, whereas in mutants in which the normal SDF1 trail is absent, the primordium path is redirected to the next, more ventral sdf1 expression domain. In all cases, the sensory axons remain associated to the primordium, indicating that the extension of the neurites to form the PLL nerve depends on the movement of the primordium. We conclude that both the formation and the innervation of this system depend on the SDF1-CXCR4 system, which has also been implicated in several migration events in humans, including metastasis formation and lymphocyte homing.

Animals↗

PubMed2002

Cripto, a multifunctional partner in signaling: molecular forms and activities.

Within a multicellular organism, communication between cells is essential during development to ensure proper execution of cell migration, cell fate decisions, and differentiation events. It is also essential in the adult for the coordination of many physiological functions. Cell-to-cell communications often rely on the interaction of cell surface receptors with soluble or membrane-bound ligands. Receptors or ligands may interact with additional partners to trigger specific signaling cascades inside the cell. In most cases, partners act in a specific configuration, either as a diffusible "co-ligand" or a membrane-bound co-receptor. Here, we examine the case of Cripto, a signaling molecule that has prominent functions during vertebrate development. Conflicting results have suggested that Cripto has the unusual capacity to act both as a secreted ligand and as a cell surface component to control a single signaling pathway. Here, we review the recent experiments that attempt to reconcile those results. Furthermore, three reports have described the fact that Cripto is modified by the addition of sugar residues, including a rare case of fucosylation. These modifications are essential for Cripto function, suggesting that, as is the case for other key developmental or physiological regulators such as Notch or selectins, the activity of Cripto may be controlled by the extent of its glycosylation or fucosylation (or both).

Animals↗

PubMed2002

Regulation of nodal signalling and mesendoderm formation by TARAM-A, a TGFbeta-related type I receptor.

Nodal signalling is essential for many developmental events during vertebrate development, including the establishment of left-right asymmetry, of dorsoventral axis of the central nervous system, and endoderm and mesoderm formation. The zebrafish TGFbeta-related type I receptor, TARAM-A (Tar), is expressed in the prospective mesendodermal territory and, when activated, can transfate early blastomeres into endoderm, suggesting that Nodal and Tar may represent similar signalling pathways. We have analysed the functional relationships between those two pathways in zebrafish. We first demonstrate that tar and the zebrafish nodal genes cyc and sqt functionally interact. We also show that a dominant-negative isoform of Tar, TarMR, interferes specifically with the function of Cyc and Sqt in vitro, but does not interfere with the function of BMP2, another TGFbeta-related molecule. TarMR interferes also with Nodal signalling in vivo since it enhances the phenotype of embryos with weakened Nodal signalling. Overexpression of tarMR in wild-type embryos interfered with the formation of endoderm-derived structures. Conversely, overexpression of tar enlarged the presumptive mesendodermal region at the onset of gastrulation. Together, our results point to Tar as an essential factor for endoderm formation and an important modulator of Nodal signalling, potentially representing one of the Nodal receptors. (c)2001 Elsevier Science.

Activins↗

PubMed2002

Requirement for endoderm and FGF3 in ventral head skeleton formation.

The vertebrate head skeleton is derived in part from neural crest cells, which physically interact with head ectoderm, mesoderm and endoderm to shape the pharyngeal arches. The cellular and molecular nature of these interactions is poorly understood, and we explore here the function of endoderm in this process. By genetic ablation and reintroduction of endoderm in zebrafish, we show that it is required for the development of chondrogenic neural crest cells, including their identity, survival and differentiation into arch cartilages. Using a genetic interference approach, we further identify Fgf3 as a critical component of endodermal function that allows the development of posterior arch cartilages. Together, our results reveal for the first time that the endoderm provides differential cues along the anteroposterior axis to control ventral head skeleton development and demonstrate that this function is mediated in part by Fgf3.

Animals↗

PubMed2002

Molecular integration of casanova in the Nodal signalling pathway controlling endoderm formation.

Endoderm originates from a large endomesodermal field requiring Nodal signalling. The mechanisms that ensure segregation of endoderm from mesoderm are not fully understood. We first show that the timing and dose of Nodal activation are crucial for endoderm formation and the endoderm versus mesoderm fate choice, because sustained Nodal signalling is required to ensure endoderm formation but transient signalling is sufficient for mesoderm formation. In zebrafish, downstream of Nodal signals, three genes encoding transcription factors (faust, bonnie and clyde and the recently identified gene casanova) are required for endoderm formation and differentiation. However their positions within the pathway are not completely established. In the present work, we show that casanova is the earliest specification marker for endodermal cells and that its expression requires bonnie and clyde. Furthermore, we have analysed the molecular activities of casanova on endoderm formation and found that it can induce endodermal markers and repress mesodermal markers during gastrulation, as well as change the fate of marginal blastomeres to endoderm. Overexpression of casanova also restores endoderm markers in the absence of Nodal signalling. In addition, casanova efficiently restores later endodermal differentiation in these mutants, but this process requires, in addition, a partial activation of Nodal signalling.

Animals↗