Project description:The marine opisthobranch mollusk, Aplysia californica, is a powerful experimental system in cellular, molecular, and behavioral neuroscience as well as cell and evolutionary biology because of the distinctive organization of its nervous system, which makes it advantageous for cellular and comparative analysis of a variety of behaviors and learning and memory. Aplysia's large neurons allow examination of neuronal architecture of instinctive and learned behaviors at the level of single characterized cells and defined cellular compartments (e.g., synapses). As a result, many fundamental problems in neurobiology can be analyzed more effectively in Aplysias than in Drosophila, C. elegans, and vertebrates. In a larger sense work on Aplysia is synergistic with these other experimental systems. Here, we are sequencing the genome of Aplysia both to gain access to genomic mechanisms of basic neuronal and other functions and to study these mechanisms in real physiological time with single-neuron resolution. The distinction of Aplysia as a neurobiological and cellular model system is due to the following: (1) Its nervous system has a relatively small number of nerve cells. (2) Many of these cells are large (sometimes gigantic, up to 1 mm in diameter). (3) As a result of their size, pigmentation, and position in the nervous system, many cells can easily be uniquely identified at the single cell level and can be reliably linked to the animal's behavior. (4) The cells provide enough messenger RNA to generate cDNA libraries from single cells. (5) These neurons can be isolated and cultured in vitro and they form circuits which can be explored in detail at molecular and cellular levels. (6) The animal generates a variety of behaviors, many of which can be specified in terms of their underlying circuitry. (7) Some of these behaviors can be modified by different forms of learning. Aplysia are easy to rear in the laboratory from fertilized ova to mature adults and it is possible to obtain an inbred stock of reproducing animals. In 1995, the NIH established a National Resource Center for Aplysia at the University of Miami to meet the growing needs of the biomedical community. This Center supplies over 20,000 cultured Aplysia at all developmental stages annually to the research community throughout the world. This community consists of more than 100 laboratories and over a thousand investigators with overall research budgets of tens of millions of dollars annually. In addition to its value to the neurobiological community, Aplysia is also of interest from a comparative biological perspective. Aplysia is a free-living representative of Mollusca, the second largest animal phylum (after Arthropoda). Members of this phylum have received relatively little genetic study, even though they are of considerable significance for evolutionary and developmental biology and for basic and applied biomedical studies. Aplysia has a stable diploid genome consisting of 17 haploid chromosomes with highly polyploid central neurons. The genome size of about 850 million base pairs is typical for many molluscan species. Expressed sequence tags (ESTs) have already been sequenced, including more than 50,000 unique sequences representing several thousand genes, from the central nervous system of Aplysia – see Moroz et al (2006) . These ESTs have revealed many signaling molecules and pathways, including their key receptors, kinases and substrate proteins, but many rare yet key genes (e.g., ionic channels) have escaped detection so far. To achieve a complete understanding of the biologically important genes and their regulatory elements, a careful annotation and analysis of the sequenced genome is analysis is required. The Aplysia genome project will serve two major functions. First, it will be important for neuroscience by providing a critical resource for facilitating: (a) identification of all genes and regulatory regions of this valuable organism, (b) assembling microarrays and cDNA libraries for global expression studies, including those based on single neurons and their processes, and (c) gene function analysis by RNA interference screens. Second, the Aplysia genome will be important for comparative, developmental and evolutionary biology. Aplysia will serve as a complementary invertebrate/molluscan genomic model from the most diverse and second largest clade of bilaterally symmetrical animals. The Aplysia genome will promote studies of metazoan evolution, developmental biology, neuroscience, and human health, including identifying and validating therapeutic targets for human disorders that are related to aging, cancer, the central nervous system, as well as learning and memory mechanisms.

Project description:The monitoring of global transcription patterns during development is a useful first step to understand mechanisms underlying growth, differentiation and patterning in a given species. However such large scale developmental studies are so far only available from a few selected model organisms such as mouse, Drosophila and the nematode C. elegans. Genomic scale information from the lophotrochozoa is now emerging. The recently characterized neuronal transcriptome of the sea hare Aplysia californica (~200’000 ESTs and ~40,000 unique non-redundant sequences representing about 55-70% of all neuronal transcripts including splice forms and non-coding RNAs) provides new insights and opportunities into problems of molluscan development and specifically neurogenesis. Regulatory genes used in development are recruited for the functions of adult nervous systems such as synaptogenesis, specific wiring in networks and structural changes underlying synaptic plasticity. While this similarity reflects a basic concept in biology, namely the recruitment of the same genes for different functions, it has never been tested on a large scale genomic level. We used representative oligo-arrays constructed from transcripts obtained from the Aplysia nervous system to explore the following two questions: 1) What neuronal genes are differentially expressed during embryonic development of the sea hare Aplysia. 2) What gene expression changes can be observed in correlation with gastrulation, metamorphosis, and larval neurogenesis. For this purpose we hybridized RNA from 3 embryonic (64 cells, gastrula, trochophore) and 4 larval stages (pre-hatching, post-hatching, pre-metamorphosis, postmetamorphosis) against a reference sample consisting of equal contributions from all stages. Our analysis revealed that all embryonic and larval stages can be distinguished based on their transcription profiles. A comparison of the Aplysia atlas with similar studies in Drosophila and mouse reveals interesting differences. We identified several new transcription factors which are differentially expressed during early embryonic development. Various other transcripts involved in metabolism and differentiation were characterized. These genes can be candidate targets for understanding neuronal growth, synaptogenesis and memory mechanisms. We conclude that the microarray technology provides us with a powerful tool for efficient survey and functional annotation of the neuronal transcriptome in Aplysia.

Project description:The monitoring of global transcription patterns during development is a useful first step to understand mechanisms underlying growth, differentiation and patterning in a given species. However such large scale developmental studies are so far only available from a few selected model organisms such as mouse, Drosophila and the nematode C. elegans. Genomic scale information from the lophotrochozoa is now emerging. The recently characterized neuronal transcriptome of the sea hare Aplysia californica (~200’000 ESTs and ~40,000 unique non-redundant sequences representing about 55-70% of all neuronal transcripts including splice forms and non-coding RNAs) provides new insights and opportunities into problems of molluscan development and specifically neurogenesis. Regulatory genes used in development are recruited for the functions of adult nervous systems such as synaptogenesis, specific wiring in networks and structural changes underlying synaptic plasticity. While this similarity reflects a basic concept in biology, namely the recruitment of the same genes for different functions, it has never been tested on a large scale genomic level. We used representative oligo-arrays constructed from transcripts obtained from the Aplysia nervous system to explore the following two questions: 1) What neuronal genes are differentially expressed during embryonic development of the sea hare Aplysia. 2) What gene expression changes can be observed in correlation with gastrulation, metamorphosis, and larval neurogenesis. For this purpose we hybridized RNA from 3 embryonic (64 cells, gastrula, trochophore) and 4 larval stages (pre-hatching, post-hatching, pre-metamorphosis, postmetamorphosis) against a reference sample consisting of equal contributions from all stages. Our analysis revealed that all embryonic and larval stages can be distinguished based on their transcription profiles. A comparison of the Aplysia atlas with similar studies in Drosophila and mouse reveals interesting differences. We identified several new transcription factors which are differentially expressed during early embryonic development. Various other transcripts involved in metabolism and differentiation were characterized. These genes can be candidate targets for understanding neuronal growth, synaptogenesis and memory mechanisms. We conclude that the microarray technology provides us with a powerful tool for efficient survey and functional annotation of the neuronal transcriptome in Aplysia. We used a reference design for this study where we hybridized each of the 8 developmental stages of Aplysia (cleavage, gastrula, trochophore, first veliger, hatching veliger, pre-metamorphosis (stage 6), post-metamorphosis (stage 7), post-metamorphosis 60 hours (pm60)

Dataset Information

Mechanisms of action of escapin, a bactericidal agent in the ink secretion of the sea hare Aplysia californica: rapid and long-lasting DNA condensation and involvement of the OxyR-regulated oxidative stress pathway.

Publications

Mechanisms of action of escapin, a bactericidal agent in the ink secretion of the sea hare Aplysia californica: rapid and long-lasting DNA condensation and involvement of the OxyR-regulated oxidative stress pathway.

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