Quaking is essential for blood vessel development

For nearly 40 years functional studies of the mouse quaking gene (qkI) have focused on its role in the postnatal central nervous system during myelination. However, the homozygous lethality of a number of ENU-induced alleles reveals that quaking has a critical role in embryonic development prior to the start of myelination. In this article, we show that quaking has a previously unsuspected and essential role in blood vessel development. Interestingly, we found that quaking, a nonsecreted protein, is expressed in the yolk sac endoderm, adjacent to the mesodermal site of developing blood islands, where the differentiation of blood and endothelial cells first occurs. Antibodies against PE-CAM-1, TIE-2 and SM-alpha-actin reveal that embryos homozygous for the qk(k2) allele have defective yolk sac vascular remodeling and abnormal vessels in the embryo proper at midgestation, coinciding with the timing of embryonic death. However, these mutants exhibit normal expression of Nkx2.5 and alpha-sarcomeric actin, indicating that cardiac muscle differentiation was normal. Further, they had normal embryonic heart rates in culture, suggesting that cardiac function was not compromised at this stage of embryonic development. Together, these results suggest that quaking plays an essential role in vascular development and that the blood vessel defects are the cause of embryonic death.     

Detection of Microsporidia,cryptosporidia and Giardia in swimming pools: a one-year prospective study

In order to estimate the rate of microsporidia, cryptosporidia and giardia contamination of swimming pools, sequential samples of water were collected during a one-year period in six different swimming pools in Paris, France. Fourty-eight samples were submitted to filtrations. Eluates were examined for microsporidia using polymerase chain reaction (PCR) and for cryptosporidia and giardia using immunofluorescence staining. One of 48 specimens was positive for microsporidia. Using DNA sequence analysis, unknown microsporidia species were identified, which were close to an insect microsporidia Endoreticulatus schubergi. One sample was positive for cryptosporidia and none were positive for giardia. This study shows a low level of swimming pool water contamination by microsporidia, cryptosporidia or giardia, demonstrating the efficacy of cleaning filtration and disinfection procedures used in French swimming pools.     

Atrioventricular valve development during late embryonic and postnatal stages involves condensation and extracellular matrix remodeling

Although the signaling molecules regulating the early stages of valvular development have been well described, little is known on the late steps leading to mature fibrous leaflets. We hypothesized that atrioventricular (AV) valve development continues after birth to adjust to the postnatal maturation of the heart. By doing a systematic analysis of the AV valves of mice from embryonic day (E) 15.5 to 8 weeks old, we identified key developmental steps that map the maturation process of embryonic cushion-like leaflets into adult stress-resistant valves. Condensation of the mesenchymal cells occurred between E15.5 and E18.5 and was accompanied by increased cellular proliferation and adhesion. Cellular proliferation also contributed transiently to the concomitant elongation of the leaflets. Patterning of the extracellular matrix (ECM) proteins along the AV axis was achieved 1 week after birth, with the differentiation of two reciprocal structural regions, glycosaminoglycans and versican at the atrial side, and densely packed collagen fibers at the ventricular side. Formation and remodeling of the nodular thickenings at the closure points of the leaflets occurred between N4.5 and N11.5. In conclusion, AV valve development during late embryonic and postnatal stages includes condensation, elongation, formation of nodular thickenings, and remodeling of tension-resistant ECM proteins.     

Tempting fate: BMP signals for cardiac morphogenesis

Heart muscle cell specification (cardiac myogenesis) and creating the four-chambered heart (cardiac morphogenesis) are subject to regulation, in certain model organisms, by bone morphogenetic proteins and their receptors. Extrapolation to mammals from organisms that develop outside the mother (flies, fish, frogs, and avians) has been confounded by very early lethality-at gastrulation-of many null alleles needed to prove cause-effect relations in this pathway. Here, we describe the use of lineage- or compartment-restricted null alleles as well as hypomorphic alleles, which circumvent these limitations and pinpoint novel essential functions for the bone morphogenetic protein cascade in mammalian cardiac development.     

Culturing Mouse Cardiac Valves in the Miniature Tissue Culture System

Heart valve disease is a major burden in the Western world and no effective treatment is available. This is mainly due to a lack of knowledge of the molecular, cellular and mechanical mechanisms underlying the maintenance and/or loss of the valvular structure. Current models used to study valvular biology include in vitro cultures of valvular endothelial and interstitial cells. Although, in vitro culturing models provide both cellular and molecular mechanisms, the mechanisms involved in the 3D-organization of the valve remain unclear. While in vivo models have provided insight into the molecular mechanisms underlying valvular development, insight into adult valvular biology is still elusive. In order to be able to study the regulation of the valvular 3D-organization on tissue, cellular and molecular levels, we have developed the Miniature Tissue Culture System. In this ex vivo flow model the mitral or the aortic valve is cultured in its natural position in the heart. The natural configuration and composition of the leaflet are maintained allowing the most natural response of the valvular cells to stimuli. The valves remain viable and are responsive to changing environmental conditions. This MTCS may provide advantages on studying questions including but not limited to, how does the 3D organization affect valvular biology, what factors affect 3D organization of the valve, and which network of signaling pathways regulates the 3D organization of the valve.