Biomedical subjects

Annamaria Locascio

Publications and source records attributed to Annamaria Locascio.

8 recordsLinked to original sources

PubMed2006

The ascidian homolog of the vertebrate homeobox gene Rx is essential for ocellus development and function.

The tadpole larvae prosencephalon of the ascidian Ciona intestinalis contains a single large ventricle, along the inner walls of which lie two sensory organs: the otolith (a gravity-sensing organ) and the ocellus (a photo-sensing organ composed of a single cup-shaped pigment cell, about 20 photoreceptor cells, and three lens cells). Comparison has been drawn between the morphology and physiology of photoreceptor cells in the ascidian ocellus and the vertebrate eye. The development of vertebrate and invertebrate eyes requires the activity of several conserved genes and it is regulated by precise expression patterns and cell fate decisions common to several species. We have isolated a Ciona homeobox gene (Ci-Rx) that belongs to the paired-like class of homeobox genes. Rx genes have been identified from a variety of organisms and have been demonstrated to have a role in vertebrate eye formation. Ci-Rx is expressed in the anterior neural plate in the middle tailbud stage and subsequently in the larval stage in the sensory vesicle around the ocellus. Loss of Ci-Rx function leads to an ocellus-less phenotype that shows a loss of photosensitive swimming behavior, suggesting the important role played by Ci-Rx in basal chordate photoreceptor cell differentiation and ocellus formation. Furthermore, studies on Ci-Rx regulatory elements electroporated into Ciona embryos using LacZ or GFP as reporter genes indicate the presence of Ci-Rx in pigment cells, photoreceptors, and neurons surrounding the sensory vesicle. In Ci-Rx knocked-down larvae, neither basal swimming activity nor shadow responses develop. Thus, Rx has a role not only in pigment cells and photoreceptor formation but also in the correct development of the neuronal circuit that controls larval photosensitivity and swimming behavior. The results suggest that a Ci-Rx "retinal" territory exists, which consists of pigment cells, photoreceptors, and neurons involved in transducing the photoreceptor signals.

Amino Acid Sequence↗

PubMed2004

Ci-POU-IV expression identifies PNS neurons in embryos and larvae of the ascidian Ciona intestinalis.

Several lines of evidence suggest that members of the POU domain gene family may regulate invertebrate and vertebrate neurogenesis. In particular, POU IV genes appear to be neural genes involved in differentiation of sensory neurons, as demonstrated in mollusc, Drosophila, Caenorhabditis elegans and vertebrates. In the present work, we describe the developmental expression of a homologue of POU IV genes, Ci-POU-IV, in the ascidian Ciona intestinalis. Ci-POU-IV is expressed in the precursor cells of the neural system during development and in the neural system of the larva. In particular, transcripts are prevalent in the peripheral nervous system (PNS), with expression in the central nervous system (CNS) restricted to the posterior sensory vesicle. Therefore, the evolution of a complex sensory system seems to be under the control of a common genetic mechanism.

Amino Acid Sequence↗

PubMed2004

Regulatory elements controlling Ci-msxb tissue-specific expression during Ciona intestinalis embryonic development.

The msh/Msx family is a subclass of homeobox-containing genes suggested to perform a conserved function in the patterning of the early embryo. We had already isolated a member of this gene family (Ci-msxb) in Ciona intestinalis, which has a very complex expression pattern during embryogenesis. To identify the regulatory elements controlling its tissue-specific expression, we have characterized the gene structure and the regulatory upstream region. By electroporation experiments, we demonstrated that a 3.8-kb region located upstream of the gene contains all the regulatory elements able to reproduce its spatial expression pattern. Analyzing progressively truncated fragments of this region, three discrete and separate regions driving LacZ reporter gene expression in the ventral epidermis, primordial pharynx and neural territories have been identified. We further investigated the element(s) necessary for Ci-msxb activation in the nervous system during embryonic development by in vivo and in vitro experiments. Both electroporation and gel-shift assays of overlapping wild type and mutated oligonucleotides demonstrated that a unique sequence of 30 bp is involved in Ci-msxb neural activation from neurula to larva stage. This sequence contains consensus binding sites for various ubiquitous transcription factors such as TCF11 whose possible implication in formation of the regulatory complexes is discussed.

Animals↗

PubMed2003

Structural organization of the sea urchin DNA (cytosine-5)-methyltransferase gene and characterization of five alternative spliced transcripts.

Sea urchin DNA (cytosine-5)-methyltransferase (Dnmt1) that is responsible for maintenance of DNA methylation patterns clearly shares similarity with various Dnmt1s identified in vertebrates. In this study, we determined the structure of the sea urchin Dnmt1 gene by screening a genomic library of the sea urchin Paracentrotus lividus with the complementary DNA (cDNA) as probe. Analysis of the positive clones demonstrated that the Dnmt1 gene consists of 34 exons and 33 introns spanning a distance of 35 kb. All exon-intron junction sequences agree with the GT/AG consensus with the exception of the 3' acceptor site of intron 8 where CT replaces AG consensus. The differences in the total number of exons between sea urchin and mouse genes reside mainly in the N-terminal region of the protein (exons 5-7 of the sea urchin, exons 5-12 of the mouse) where there is very low similarity in the amino acid sequence. By reverse transcription-polymerase chain reaction using oligonucleotides spanning different regions of the cDNA we carried out a comprehensive analysis of alternative splicing of the Dnmt1 messenger RNA (mRNA) in sea urchin embryos at different stages of development. We demonstrated the presence of at least five alternative spliced mRNAs that are regulated during development and are translated in truncated or deleted proteins.

Alternative Splicing↗

PubMed2002

Modularity and reshuffling of Snail and Slug expression during vertebrate evolution.

Gene duplication has been a major mechanism for increasing genomic complexity and variation during evolution. The evolutionary history of duplicated genes has been poorly studied along the vertebrate lineage. Here, we attempt to study that history by analyzing the expression of two members of the Snail family, Snail and Slug, in representatives of the major vertebrate groups. We find a surprising degree of variability in a subset of the expression sites for both genes in different species. Although some of the changes can be explained by neofunctionalization or subfunctionalization, others imply reciprocal changes in the expression of the two genes and the reappearance of expression in sites lost earlier in evolution. Because these changes do not fit easily into current models, we need to invoke additional mechanisms acting on enhancer elements to distribute expression domains and functions of duplicated genes unequally during evolution.

Animals↗

PubMed2002

Biological potential of a functional human SNAIL retrogene.

Snail genes encode zinc finger transcription factors required for the development of vertebrate and invertebrate embryos. They trigger epithelial to mesenchymal transitions (EMTs), thereby allowing epithelial cells to emigrate from their place of origin and form tissues such as the mesoderm and the neural crest. Snail genes are also involved in the EMTs responsible for the acquisition of invasiveness during tumor progression. This aspect of their activity is associated with their ability to directly repress E-cadherin transcription. Here we describe the existence of an active human Snail retrogene, inserted within an intron of a novel evolutionarily conserved gene and expressed in different human tissues and cell lines. Functional analyses in cell culture show that this retrogene maintains the potential to induce EMTs, conferring migratory and invasive properties to epithelial cells. In light of this data, we have renamed it SNAIL-like, a new player that must be considered in both physiological and pathological studies of SNAIL function in humans.

Amino Acid Sequence↗

PubMed2002

Correlation of Snail expression with histological grade and lymph node status in breast carcinomas.

Snail is a zinc finger transcription factor that triggers the epithelial-mesenchymal transition (EMT) by directly repressing E-cadherin expression. Snail is required for mesoderm and neural crest formation during embryonic development and has recently been implicated in the EMT associated with tumour progression. In a series of human breast carcinomas, we have analysed the expression of Snail and that of molecules of the E-cadherin/catenin complexes. We have also correlated these data with the pathological features of the tumours. We show that Snail expression inversely correlates with the grade of differentiation of the tumours and that it is expressed in all the infiltrating ductal carcinomas (IDC) presenting lymph node metastases that were analysed. In addition, Snail is expressed in some dedifferentiated tumours with a negative nodal status. Considering that Snail is involved in the induction of the invasive and migratory phenotype in epithelial cells, these results indicate that it is also involved in the progression of breast ductal tumours, where it could additionally serve as a marker of the metastatic potential.

Breast Neoplasms↗

PubMed2002

The epithelial mesenchymal transition confers resistance to the apoptotic effects of transforming growth factor Beta in fetal rat hepatocytes.

Fetal rat hepatocytes treated with transforming growth factor beta (TGF-beta) die by apoptosis. However, a subpopulation of them survives and undergoes an epithelial mesenchymal transition (EMT). This transition also occurs upon incubation with fetal bovine serum. We have isolated the subpopulations that undergo EMT (TGF-beta-treated-fetal hepatocytes: TbetaT-FH; serum-treated-fetal hepatocytes: ST-FH) and show that they present high levels of vimentin and Snail expression and lack cytokeratin 18 and E-cadherin. Both TbetaT-FH and ST-FH cells require mitogens to grow and maintain the response to TGF-beta in terms of growth inhibition. However, they lack differentiation markers such as the liver-enriched transcription factors hepatocyte nuclear factor 4 (HNF-4) or HNF-1alpha and express the progenitor marker OV-6. Interestingly, the EMT process confers them resistance to the apoptotic effect of TGF-beta, with cells showing higher levels of active AKT and Bcl-x(L) than fetal hepatocytes. In summary, these cells are refractory to the apoptotic effects of TGF-beta, showing characteristics of liver progenitors and of some hepatocellular carcinoma cells.

Animals↗