Biomedical subjects

Marcelo Bento Soares

Publications and source records attributed to Marcelo Bento Soares.

5 recordsLinked to original sources

PubMed2007

The commonality of plasticity underlying multipotent tumor cells and embryonic stem cells.

Aggressive cancer cells and pluripotent stem cells converge in their capacity for self-renewal, proliferation and plasticity. Recent studies have capitalized on these similarities by demonstrating that tumors arise from specific cancer stem cell populations that, in a manner reminiscent of normal stem cells, are able to both self-renew and give rise to a heterogeneous tumor population. This stem cell like function of aggressive cancer cells is likely attributable to the ectopic expression of embryonic factors such as Nodal and Cancer Testis Specific Antigens (CTAs), which maintain a functional plasticity by promoting pluripotency and immortality. During development, the expression of these embryonic factors is tightly regulated by a dynamic array of mediators, including the spatial and temporal expression of inhibitors such as Lefty, and the epigenetic modulation of the genome. In aggressive cancer cells, particularly melanoma, this balance of regulatory mediators is disrupted, leading to the aberrant expression of pluripotency-associated genes. By exposing aggressive cancer cells to embryonic microenvironments, this balance of regulatory mediators is restored, thereby reprogramming tumor cells to a more benign phenotype. These stem cell-derived mediators, as well as the genes they regulate, provide therapeutic targets designed to specifically differentiate and eradicate aggressive cancers.

Cell Lineage↗

PubMed2006

A biphasic pattern of gene expression during mouse retina development.

BACKGROUND: Between embryonic day 12 and postnatal day 21, six major neuronal and one glia cell type are generated from multipotential progenitors in a characteristic sequence during mouse retina development. We investigated expression patterns of retina transcripts during the major embryonic and postnatal developmental stages to provide a systematic view of normal mouse retina development, RESULTS: A tissue-specific cDNA microarray was generated using a set of sequence non-redundant EST clones collected from mouse retina. Eleven stages of mouse retina, from embryonic day 12.5 (El2.5) to postnatal day 21 (PN21), were collected for RNA isolation. Non-amplified RNAs were labeled for microarray experiments and three sets of data were analyzed for significance, hierarchical relationships, and functional clustering. Six individual gene expression clusters were identified based on expression patterns of transcripts through retina development. Two developmental phases were clearly divided with postnatal day 5 (PN5) as a separate cluster. Among 4,180 transcripts that changed significantly during development, approximately 2/3 of the genes were expressed at high levels up until PN5 and then declined whereas the other 1/3 of the genes increased expression from PN5 and remained at the higher levels until at least PN21. Less than 1% of the genes observed showed a peak of expression between the two phases. Among the later increased population, only about 40% genes are correlated with rod photoreceptors, indicating that multiple cell types contributed to gene expression in this phase. Within the same functional classes, however, different gene populations were expressed in distinct developmental phases. A correlation coefficient analysis of gene expression during retina development between previous SAGE studies and this study was also carried out. CONCLUSION: This study provides a complementary genome-wide view of common gene dynamics and a broad molecular classification of mouse retina development. Different genes in the same functional clusters are expressed in the different developmental stages, suggesting that cells might change gene expression profiles from differentiation to maturation stages. We propose that large-scale changes in gene regulation during development are necessary for the final maturation and function of the retina.

Animals↗

PubMed2006

Robust semiparametric microarray normalization and significance analysis.

Microarray technology allows the monitoring of expression levels of thousands of genes simultaneously. A semiparametric location and scale model is proposed to model gene expression levels for normalization and significance analysis purposes. Robust estimation based on weighted least absolute deviation regression and significance analysis based on the weighted bootstrap are investigated. The proposed approach naturally combines normalization and significance analysis, and incorporates the variations due to normalization into the significance analysis properly. A small simulation study is used to compare finite sample performance of the proposed approach with alternatives. We also demonstrate the proposed method with a real dataset.

Biometry↗

PubMed2005

Pax9 and Jagged1 act downstream of Gli3 in vertebrate limb development.

From early in limb development the transcription factor Gli3 acts to define boundaries of gene expression along the anterior-posterior (AP) axis, establishing asymmetric patterns required to provide positional information. As limb development proceeds, posterior mesenchyme expression of Sonic hedgehog (Shh) regulates Gli3 transcription and post-translational processing to specify digit number and identity. The molecular cascades dependent on Gli3 at later stages of limb development, which link early patterning events with final digit morphogenesis, remain poorly characterised. By analysing the transcriptional consequences of loss of Gli3 in the anterior margin of the E11.5 and E12.5 limb bud in the polydactylous mouse mutant extra-toes (Gli3(Xt/Xt)), we have identified a number of known and novel transcripts dependent on Gli3 in the limb. In particular, we demonstrated that the genes encoding the paired box transcription factor Pax9, the Notch ligand Jagged1 and the cell surface receptor Cdo are dependent on Gli3 for correct expression in the anterior limb mesenchyme. Analysis of expression in compound Shh;Gli3 mutant mouse embryos and in both in vitro and in vivo Shh signaling assays, further defined the importance of Shh regulated processing of Gli3 in controlling gene expression. In particular Pax9 regulation by Shh and Gli3 was shown to be context dependent, with major differences between the limb and somite revealed by Shh bead implantation experiments in the chick. Jagged1 was shown to be induced by Shh in the chick limb and in a C3H10T1/2 cell based signaling assay, with Shh;Gli3 mutant analysis indicating that expression is dependent on Gli3 derepression. Our data have also revealed that perturbation of early patterning events within the Gli3(Xt/Xt) limb culminates in a specific delay of anterior chondrogenesis which is subsequently realised as extra digits.

Animals↗

PubMed2005

A robust two-way semi-linear model for normalization of cDNA microarray data.

BACKGROUND: Normalization is a basic step in microarray data analysis. A proper normalization procedure ensures that the intensity ratios provide meaningful measures of relative expression values. METHODS: We propose a robust semiparametric method in a two-way semi-linear model (TW-SLM) for normalization of cDNA microarray data. This method does not make the usual assumptions underlying some of the existing methods. For example, it does not assume that: (i) the percentage of differentially expressed genes is small; or (ii) the numbers of up- and down-regulated genes are about the same, as required in the LOWESS normalization method. We conduct simulation studies to evaluate the proposed method and use a real data set from a specially designed microarray experiment to compare the performance of the proposed method with that of the LOWESS normalization approach. RESULTS: The simulation results show that the proposed method performs better than the LOWESS normalization method in terms of mean square errors for estimated gene effects. The results of analysis of the real data set also show that the proposed method yields more consistent results between the direct and the indirect comparisons and also can detect more differentially expressed genes than the LOWESS method. CONCLUSIONS: Our simulation studies and the real data example indicate that the proposed robust TW-SLM method works at least as well as the LOWESS method and works better when the underlying assumptions for the LOWESS method are not satisfied. Therefore, it is a powerful alternative to the existing normalization methods.

Algorithms↗