Biomedical subjects

José Xavier-Neto

Publications and source records attributed to José Xavier-Neto.

5 recordsLinked to original sources

PubMed2008

The search for non-chordate retinoic acid signaling: lessons from chordates.

Signaling by retinoic acid (RA) is an important pathway in the development and homeostasis of vertebrate and invertebrate chordates, with a critical role in mesoderm patterning. Classical studies on the distribution of nuclear receptors of animals suggested that the family of RA receptors (RARs/NR1B) was restricted to chordates, while the family of RA X receptors (RXR/NR2B) was distributed from cnidarians to chordates. However, the accumulation of data from genome projects and studies in non-model species is questioning this traditional view. Here we discuss the evidence for non-chordate RA signaling systems in the light of recent advances in our understanding of carotene (pro-Vitamin A) metabolism and of the identification of potential RARs and members of the NR1 family in echinoderms and lophotrochozoan trematodes, respectively. We conclude, as have others before (Bertrand et al., 2004. Mol Biol Evol 21(10):1923-1937), that signaling by RA is more likely an ancestral feature of bilaterians than a chordate innovation.

Amino Acid Sequence↗

PubMed2006

Amphioxus and tunicates as evolutionary model systems.

One important question in evolutionary biology concerns the origin of vertebrates from invertebrates. The current consensus is that the proximate ancestor of vertebrates was an invertebrate chordate. Today, the invertebrate chordates comprise cephalochordates (amphioxus) and tunicates (each a subphylum in the phylum Chordata, which also includes the vertebrate subphylum). It was widely accepted that, within the chordates, tunicates represent the sister group of a clade of cephalochordates plus vertebrates. However, recent studies suggest that the evolutionary positions of tunicates and cephalochordates should be reversed, the implications of which are considered here. We also review the two major groups of invertebrate chordates and compare relative advantages (and disadvantages) of each as model systems for elucidating the origin of the vertebrates.

Animals↗

PubMed2005

Lack of evidence of association between MTHFR C677T polymorphism and congenital heart disease in a TDT study design.

INTRODUCTION: Hyperhomocysteinemia is frequently associated with congenital defects of the heart and neural tube. A common missense mutation in the MTHFR gene (C to T substitution at position 677 changing valine to alanine) produces a variant with reduced enzymatic action, resulting in higher plasma levels of homocysteine. The aim of this study is to investigate whether MTHFR C677T functional genetic variant is associated with an increased risk of congenital heart disease (CHD) development using a family-based case-control design and the Transmission Disequilibrium Test (TDT) approach. METHODS: We selected 91 consecutive patients with congenital heart disease for the study. From these patients we were able to obtain samples on 147 parents. The C677T polymorphism at the MTHFR gene was determined from each participant. RESULTS: A statistically significant association was disclosed in univariate analysis using a family-based case-control design (p<0.0001 assuming an additive genetic model, p<0.0001 assuming a dominant genetic model, and p=0.01 assuming a recessive genetic model). This association was explained by an increased frequency of the T allele in patients as compared to their fathers. However, by using a TDT approach a highly non-significant result was obtained and no association could be defined between this locus and congenital heart disease. CONCLUSIONS: We did not find sufficient evidence for an association between MTHFR C677T genotype and congenital heart disease in our study group. Previous reports on such association may be due to population genetic structure.

Algorithms↗

PubMed2005

The evolutionary origin of cardiac chambers.

Identification of cardiac mechanisms of retinoic acid (RA) signaling, description of homologous genetic circuits in Ciona intestinalis and consolidation of views on the secondary heart field have fundamental, but still unrecognized implications for vertebrate heart evolution. Utilizing concepts from evolution, development, zoology, and circulatory physiology, we evaluate the strengths of animal models and scenarios for the origin of vertebrate hearts. Analyzing chordates, lower and higher vertebrates, we propose a paradigm picturing vertebrate hearts as advanced circulatory pumps formed by segments, chambered or not, devoted to inflow or outflow. We suggest that chambers arose not as single units, but as components of a peristaltic pump divided by patterning events, contrasting with scenarios assuming that chambers developed one at a time. Recognizing RA signaling as a potential mechanism patterning cardiac segments, we propose to use it as a tool to scrutinize the phylogenetic origins of cardiac chambers within chordates. Finally, we integrate recent ideas on cardiac development such as the ballooning and secondary/anterior heart field paradigms, showing how inflow/outflow patterning may interact with developmental mechanisms suggested by these models.

Animals↗

PubMed2003

A caudorostral wave of RALDH2 conveys anteroposterior information to the cardiac field.

Establishment of anteroposterior (AP) polarity is one of the earliest decisions in cardiogenesis and plays an important role in the coupling between heart and blood vessels. Recent research implicated retinoic acid (RA) in the communication of AP polarity to the heart. We utilized embryo culture, in situ hybridization, morphometry, fate mapping and treatment with the RA pan-antagonist BMS493 to investigate the relationship between cardiac precursors and RA signalling. We describe two phases of AP signalling by RA, reflected in RALDH2 expression. The first phase (HH4-7) is characterized by increasing proximity between sino-atrial precursors and the lateral mesoderm expressing RALDH2. In this phase, RA signalling is consistent with diffusion of the morphogen from a large field rather than a single hot spot. The second phase (HH7-8) is characterized by progressive encircling of cardiac precursors by a field of RALDH2 originating from a dynamic and evolutionary-conserved caudorostral wave pattern in the lateral mesoderm. At this phase, cardiac AP patterning by RA is consistent with localized action of RA by regulated activation of the Raldh2 gene within an embryonic domain. Systemic treatment with BMS493 altered the cardiac fate map such that ventricular precursors were found in areas normally devoid of them. Topical application of BMS493 inhibited atrial differentiation in left anterior lateral mesoderm. Identification of the caudorostral wave of RALDH2 as the endogenous source of RA establishing cardiac AP fates provides a useful model to approach the mechanisms whereby the vertebrate embryo confers axial information on its organs.

Aldehyde Oxidoreductases↗