Ioan Ovidiu Sirbu

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Retinoic acid (RA) is thought to be a key signaling molecule involved in limb bud patterning along the proximodistal or anteroposterior axes functioning through induction of Meis2 and Shh, respectively. Here, we utilize Raldh2-/- and Raldh3-/- mouse embryos lacking RA synthesis to demonstrate that RA signaling is not required for limb expression of Shh and(More)
Somitogenesis requires bilateral rhythmic segmentation of paraxial mesoderm along the antero-posterior axis. The location of somite segmentation depends on opposing signalling gradients of retinoic acid (generated by retinaldehyde dehydrogenase-2; Raldh2) anteriorly and fibroblast growth factor (FGF; generated by Fgf8) posteriorly. Retinoic-acid-deficient(More)
Studies in amphibian embryos have suggested that retinoic acid (RA) may function as a signal that stimulates posterior differentiation of the nervous system as postulated by the activation-transformation model for anteroposterior patterning of the nervous system. We have tested this hypothesis in retinaldehyde dehydrogenase-2 (Raldh2) null mutant mice(More)
Distinct progenitor cell populations exist in cardiac mesoderm important for patterning of the heart. During heart tube formation in mouse, Tbx5 is expressed in progenitors located more laterally, whereas Isl1 and Fgf8 are expressed in progenitors located more medially. Signals that drive mesodermal progenitors into various cardiac lineages include Fgf8,(More)
We present evidence for the existence of two phases of retinoic acid (RA) signaling required for vertebrate limb development. Limb RA synthesis is under the control of retinaldehyde dehydrogenase-2 (Raldh2) expressed in the lateral plate mesoderm, which generates a proximodistal RA signal during limb outgrowth. We report that Raldh2(-/-) embryos lack trunk(More)
Retinoic acid (RA) generated by Raldh2 in paraxial mesoderm is required for specification of the posterior hindbrain, including restriction of Hoxb1 expression to presumptive rhombomere 4 (r4). Hoxb1 expression requires 3' and 5' RA response elements for widespread induction up to r4 and for r3/r5 repression, but RA has previously been detected only from(More)
It is generally assumed that the characteristic deregionalized body plan of species with a snake-like morphology evolved through a corresponding homogenization of Hox gene expression domains along the primary axis. Here, we examine the expression of Hox genes in snake embryos and show that a collinear pattern of Hox expression is retained within the(More)
The miR-290 cluster is expressed in embryonic stem cells (ESCs) and is important for the maintenance of pluripotency, but little is known about the mechanisms regulating the early embryonic microRNA cluster (EEmiRC) expression. Here we report the identification of a 332-bp intragenic enhancer (IE) able to modulate the transcription of the mouse EEmiRC(More)
Wnt proteins are critical for embryonic cardiogenesis and cardiomyogenesis by regulating different intracellular signalling pathways. Whereas canonical Wnt/β-catenin signalling is required for mesoderm induction and proliferation of cardiac progenitor cells, β-catenin independent, non-canonical Wnt signalling regulates cardiac specification and terminal(More)
Despite the recent advances in molecular medicine and health care, cardiovascular diseases are still the leading cause of morbidity and mortality throughout the world. In 2006, nearly every other death in Germany resulted from disease of the circulatory system, and congenital heart diseases are thought to account for a high number of stillbirths and(More)