Abstract-The Pitx2 gene regulates left-right (L/R) asymmetrical cardiac morphogenesis. Constitutive Pitx2 knock out (ko) mice die before birth and display, among other defects, right atrial isomerism, atrial and ventricular septal defects, and double outlet right ventricle. The myocardial role of the gene has not been dissected. In particular, how Pitx2 regulates the differential L/R cardiac identity program is not clear. Additionally, the relation between Pitx2 ko ventricular defects and the gene expression pattern is not understood. In this article we analyze Pitx2 myocardial function during mouse heart development. By in situ hybridization analysis we show that myocardial Pitx2 expression delineates the remodeling of the left atrioventricular canal, the inner curvature, the ventral part of the interventricular ring, and the ventral portion of the right and left ventricle. By genetic analysis using an allelic series of Pitx2 mutants, among which a myocardial specific ko (ko myo ) we show it has a crucial role in this process. Pitx2 ko myo mutants survive to adulthood, when they present strong cardiac morphological and functional defects.

ThemechanismofcGMPproductioninolfactorysensoryneurons(OSNs)ispoorlyunderstood,althoughthismessengertakespartinseveralkey processes such as adaptation, neuronal development, and long-term cellular responses to odorant stimulation. Many aspects of the regulation of cGMP in OSNs are still unknown or highly controversial, such as its subcellular heterogeneity, mechanism of coupling to odorant receptors and downstream targets. Here, we have investigated the dynamics and the intracellular distribution of cGMP in living rat OSNs in culture transfected with a genetically encoded sensor for cGMP. We demonstrate that OSNs treated with pharmacological stimuli able to activate membrane or soluble guanylyl cyclase (sGC) presented an increase in cGMP in the entire neuron, from cilia-dendrite to the axon terminus-growth cone. Upon odorant stimulation, a rise in cGMP was again found in the entire neuron, including the axon terminus, where it is locally synthesized. The odorant-dependent rise in cGMP is due to sGC activation by nitric oxide (NO) and requires an increase of cAMP. The link between cAMP and NO synthase appears to be the rise in cytosolic Ca 2ϩ concentration elicited by either plasma membrane Ca 2ϩ channel activation or Ca 2ϩ mobilization from stores via the guanine nucleotide exchange factor Epac. Finally, we show that a cGMP rise can elicit both in vitro and in vivo the phosphorylation of nuclear CREB, suggesting that this signaling pathway may be relevant for both local events (pathfinding, neurotransmitter release) and more distal processes involving gene expression regulation.