The evolutionary relationships in Xenopus genus are intensively studied for its interspecific variability and high conservation in evolution. These characteristics possess an opportunity for comparative studying of polyploidization phenomenom on interchromosomal level and an occasion to identify the genome-forming mechanisms with cytogenetic methods. XME chromosomes (X. mellotropicalis, 2n=40) were identified via p-/q- arm length ratio in a comparison with morphometric analysis of X. epitropicalis (2n=40) chromosomes. Whole chromosome painting probes were prepared from X. tropicalis (2n=20) microdissected chromosomes and they were applied to XME metaphase spreads via optimalized Zoo-FISH. 10 chromosomal quartets were detected and one balanced non-reciprocal translocation between chromosomes XME 2 and XME 9 which must have occured in a diploid ancestor. Thus, we disprove the theory of Silurana subgenus origin via only one polyploidizatin event. Powered by TCPDF (www.tcpdf.org)

Thesis advisor: Laura E. Hake / Metazoan development depends on cytoplasmic polyadenylation, a key mechanism that controls the translation of maternally deposited mRNAs. In Xenopus laevis oocytes, CPEB regulates the translation of several developmentally important mRNAs, which drive meiotic progression and the production of fertilizable eggs. Most of our current knowledge of this process, also referred to as oocyte maturation, has been acquired from experiments conducted in Xenopus laevis oocytes. Despite over 30 years of research devoted to the exploration of progesterone signaling during maturation, the very early events that occur from progesterone receptor engagement to CPEB activation are not well understood. XGef, a putative Rho family guanine nucleotide exchange factor (GEF), interacts with CPEB and facilitates CPEB activation and timely meiotic progression. To further our understanding of XGef function during meiotic progression, the requirement for exchange factor activity and the activities of several Rho GTPases during maturation were examined. Despite previous reports of XGef activation of Cdc42 in mammalian cell culture, XGef does not stimulate the activation of Cdc42 in maturing Xenopus oocytes. Further, Cdc42 activity does not affect CPEB phosphorylation and overexpression of a dominant negative Cdc42 mutant does not affect maturation. Inhibition of Toxin B sensitive Rho GTPases, including Cdc42, Rac1 and Rho A-C, also fails to affect CPEB activation or meiotic progression. Lastly, the overexpression of XGef exchange deficient point mutants did not affect maturation compared to oocytes overexpressing wildtype XGef. Together, these results suggest that as a facilitator of CPEB activation and meiotic progression, XGef functions independently of exchange factor activity and Rho GTPase activation. Additionally, we found that XGef activity influences the function of RINGO/CDK1, a novel component of the progesterone signaling pathway. XGef inhibition depresses RINGO-induced GVBD, whereas XGef overexpression enhances this process. XGef interacts with RINGO in oocyte extracts and the interaction is direct in vitro. Our protein interaction data, in total, suggest that a XGef/RINGO/MAPK/CPEB complex forms in ovo to facilitate CPEB activation. Lastly, inhibition of RINGO activity directly compromises CPEB phosphorylation during early maturation, which suggests that RINGO/CDK1 directly mediates CPEB-activation. / Thesis (PhD) — Boston College, 2009. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Biology.

In 1897 Davenport measured the wet and dry weights of amphibian embryos from the stage of hatching onwards. He observed that there was a continuous increase in the wet weight but that the dry weight remained constant until the embryo began feeding. From this he concluded that "growth is due chiefly to imbibed water". Schaper (1902) noted a similar constancy of dry weight from the early tail bud stages until the time of feeding in embryos of Rana fusca. These early observations have been confirmed by Dempster (1933) who, working with Amblystoma punctatwn, extended his experiments to include the earliest developmental stages. The increase in volume, and hence the growth, of amphibian embryos is therefore due to the uptake of water from the environment. Many embryologists have attempted to correlate this water uptake with the osmotic pressure of the embryos. The early work in this field has been extensively reviewed by Needham (1931).

Mammalian odorant receptors (ORs) are Class I G-protein coupled receptors (GPCRs) located within the nasal epithelium. Odorant receptors interact with Galpha olfactory, a Galpha S type G-protein. Activated Galpha olfactory stimulates adenylate cyclase and the resulting increase in cAMP concentration opens cyclic nucleotide gated channels allowing Ca2+ to enter the cell. The increased Ca2+ then activates a Ca2+ activated Cl- channel which further depolarizes the cell. This depolarization initiates an action potential that reaches the axon of the olfactory sensory neuron located in the main olfactory bulb. Information from the main olfactory bulb is then transmitted to higher regions of the brain. Olfactory information is initially coded through the interaction of odorant molecules with hundreds of distinct ORs, but difficulty in exogenous expression of odorant receptors has delayed the identification of ligands for individual ORs. However, expression of mouse odorant receptors in Xenopus laevis oocytes allows for a systematic screening for potential ligands, as well as for efficient study of the structure-function relationship of the receptors and their ligands. My screening of odorant receptors using Xenopus oocytes included the coexpression of a signal transduction system and the use of robotic two-electrode voltage clamp electrophysiology. In this study, I investigated the structural basis for ligand recognition in mouse odorant receptors. First, I expanded the molecular receptor ranges of seven Class I odorant receptors. By use of a high throughput assay, I was able to expand upon current knowledge in the field for the mouse odorant receptors 23-1, 31-4, 32-11, 40-4, 42-1, 42-2 and 42-3. I then examined one receptor (MOR23-1) in more detail. I used the substituted cysteine accessibility method to identify residues within transmembrane domain five of this receptor that are accessible from the extracellular space. These residues may line the ligand binding site or the ligand access pathway. Conventional mutations of A205 caused little alteration in the molecular receptive range of the receptor, suggesting that this residue may not play a significant role in ligand interaction within the binding pocket. Mutagenesis of G111, a residue within transmembrane domain three caused significant shifts in the molecular receptive range of the receptor, but the location of this residue within the binding pocket could not be confirmed by the substituted cysteine method. Previous reports had suggested significant similarity between the molecular receptive ranges of the seven mouse odorant receptors that I used in my research. By expanding upon the known aliphatic ligands for each receptor identified new ligands for each receptor, I was able to show that the molecular receptive ranges of these receptors are in fact distinct. The experimental identification of residues located within the binding pocket on transmembrane five of mouse odorant receptor 23-1 provides an improved understanding of ligand recognition by this receptor class and will aid in better computer modeling of these receptors. This increased accuracy of the computer models of these basic Class I GPCRs may aid in future drug discoveries. Since GPCRs constitute a significant fraction of current drug targets, understanding the mechanism of ligand interactions with mouse odorant receptors may aid in the development of more efficacious compounds in the treatment of many common ailments.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 126-135). Also available in electronic version.

Retinal degeneration is the progressive loss of neurons lining the posterior surface of the eye. Loss of a certain group of neurons called rod photoreceptors can occur as the result of genetic mutation. In humans, and in mammalian models of retinal degeneration, the death of these cells is permanent, and often followed by cone photoreceptor death, which leads to blindness. As a step towards understanding the implications of rod cell death in the retina, we generated transgenic X. laevis that expressed a novel form of caspase-9, with binding domains specific to the compound AP20187. We treated these transgenic animals with AP20187 and caused rod cell death by apoptosis in tadpoles and post metamorphic animals. Peak rod apoptosis occurred two days after drug exposure. We adapted an electroretinography apparatus, and protocols designed for mammals to measure functional changes in X. laevis rod and cone derived responses. We observed delayed secondary cone cell dysfunction after induced rod cell apoptosis, which was subsequently restored. These animals provide a simple and clinically relevant model of diseases like Retinitis pigmentosa, in which we will be able to probe in detail the mechanisms that govern cone cell dysfunction as a consequence of rod apoptosis. The unique ability of this species to recover from this insult will provide clues towards initiating similar recovery in humans.

Prokaryotic and eukaryotic organisms respond to various stressors with the production of heat shock proteins (HSPs). HSP110 is a large molecular mass HSP that is constitutively expressed in most adult mammalian tissues. In the present study, we have examined for the first time the expression of the hsp110 gene in Xenopus laevis cultured cells and embryos. The Xenopus hsp110 cDNA encodes an 854 amino acid protein, which shares 74% identity with mice and humans. In Xenopus A6 kidney epithelial cells hsp110 mRNA was detected constitutively and was heat inducible. Enhanced hsp110 mRNA levels were detected within 1 h, and remained elevated for at least 6 h. A similar accumulation of hsp70 mRNA was observed, but only in response to stress. Treatment of A6 cells with sodium arsenite and cadmium chloride also induced hsp110 and hsp70 mRNA accumulation. However, while ethanol treatment resulted in the accumulation of hsp70 mRNA no effect was seen for hsp110. Similarly, HSP110 and HSP70 protein increased after a 2 h heat shock and 12 h sodium arsenite treatment. The elevation in HSP110 and HSP70 protein in response to heat was detectable for up to 6 h. Recent studies with mice suggest an important role for HSP110 during development. Analysis of Xenopus embryos revealed that hsp110 mRNA was present in unfertilized eggs, indicating that it is a maternal mRNA, unlike the hsp70 message which was only detectable in response to heat shock. Heat shock-induced hsp110 mRNA accumulation was developmentally regulated, similar to hsp70, since it was not detectable until after the midblastula stage of development. Enhanced hsp110 mRNA accumulation was evident with heat shock at the blastula stage, and levels continued to increase reaching a maximum at the late tailbud stage. Message for the small heat shock protein, hsp27, was not detectable until the early tailbud stage, indicating that this hsp was not present maternally and was developmentally regulated. In situ hybridization analysis revealed that hsp110 mRNA was present in control embryos in the lens placode, spinal cord and somites, but increased upon heat shock in the anterior and posterior region, the lens placode, as well as in the somites and spinal cord. A similar distribution was observed for the hsp27 message, although it was not detectable until the early tailbud stage in control or heat-shocked embryos. The intracellular localization of HSP110 protein in response to stress was also investigated. HSP110 was detected predominantly in the cytoplasm in either a diffuse pattern or in long spindle-shaped fibres. Additionally, HSP110 was present in the nucleus. In heat shocked Xenopus A6 cells, HSP110 localized in distinct patterns surrounding the nucleus and was enhanced in the nucleus after prolonged heat stress. Sodium arsenite-treated cells displayed a similar pattern in which HSP110 localized on opposite ends of the nucleus. In contrast, in response to stress HSP30 was homogeneously distributed in the cytoplasm, moving into the nucleus only upon intense stress. This study presents, for the first time, a characterization of HSP110 in Xenopus laevis, adding to the growing knowledge of HSPs in this important model organism.

Heat shock proteins (HSPs) are stress-inducible and evolutionarily conserved molecular chaperones that are involved in protein binding and translocation. As molecular chaperones, HSPs bind to denatured proteins, inhibit their aggregation, maintain their solubility, and assist in refolding. This process inhibits the formation of protein aggregates which can be lethal to the cell. In eukaryotic cells, the ubiquitin-proteasome system (UPS) is responsible for the degradation of most non-native proteins. Furthermore, proteasome inhibition has been shown to induce hsp gene expression. Celastrol, a quinone methide triterpene, was shown to have an inhibitory effect on proteasome function in mammalian cells. The present study determined that celastrol induced the accumulation of ubiquitinated proteins and reduced proteasomal chymotrypsin-like activity in Xenopus laevis A6 kidney epithelial cells. In addition, incubation of A6 cells with celastrol induced the accumulation of HSP30 and HSP70 in a dose- and time-dependent manner with maximal levels of HSP accumulation occurring after 18 h of exposure. In A6 cells recovering from celastrol, the relative levels of HSP30 and HSP70 accumulation remained elevated for 18-24 h after removal of celastrol. The activation of heat shock factor 1 (HSF1) DNA-binding may be involved in celastrol-induced hsp gene expression in A6 cells, since the HSF1 inhibitor, KNK437, repressed the accumulation of HSP30 and HSP70. Exposure of A6 cells to simultaneous celastrol and mild heat shock treatment enhanced the accumulation of HSP30 and HSP70 to a greater extent than the sum of both stressors individually. Additionally, concurrent treatment of A6 cells with low concentrations of both celastrol and MG132 produced different patterns of HSP30 and HSP70 accumulation. While combined treatment with celastrol and MG132 acted synergistically on HSP30 accumulation, relative levels of HSP70 were similar to those observed with MG132 alone. Immunocytochemical analysis of celastrol- or MG132-treated A6 cells revealed HSP30 accumulation in a punctate pattern primarily in the cytoplasm with some staining in the nucleus. Also, in some cells treated with celastrol or MG132 large HSP30 staining structures were observed in the cytoplasm. Lastly, exposure of A6 cells to celastrol induced rounder cell morphology, reduced adherence and disorganization of the actin cytoskeleton. In conclusion, this study has shown that celastrol inhibited proteasome activity in amphibian cultured cells and induced HSF1-mediated expression of hsp genes.

Prokaryotic and eukaryotic organisms respond to various stressors with the production of heat shock proteins (HSPs). HSP110 is a large molecular mass HSP that is constitutively expressed in most adult mammalian tissues. In the present study, we have examined for the first time the expression of the hsp110 gene in Xenopus laevis cultured cells and embryos. The Xenopus hsp110 cDNA encodes an 854 amino acid protein, which shares 74% identity with mice and humans. In Xenopus A6 kidney epithelial cells hsp110 mRNA was detected constitutively and was heat inducible. Enhanced hsp110 mRNA levels were detected within 1 h, and remained elevated for at least 6 h. A similar accumulation of hsp70 mRNA was observed, but only in response to stress. Treatment of A6 cells with sodium arsenite and cadmium chloride also induced hsp110 and hsp70 mRNA accumulation. However, while ethanol treatment resulted in the accumulation of hsp70 mRNA no effect was seen for hsp110. Similarly, HSP110 and HSP70 protein increased after a 2 h heat shock and 12 h sodium arsenite treatment. The elevation in HSP110 and HSP70 protein in response to heat was detectable for up to 6 h. Recent studies with mice suggest an important role for HSP110 during development. Analysis of Xenopus embryos revealed that hsp110 mRNA was present in unfertilized eggs, indicating that it is a maternal mRNA, unlike the hsp70 message which was only detectable in response to heat shock. Heat shock-induced hsp110 mRNA accumulation was developmentally regulated, similar to hsp70, since it was not detectable until after the midblastula stage of development. Enhanced hsp110 mRNA accumulation was evident with heat shock at the blastula stage, and levels continued to increase reaching a maximum at the late tailbud stage. Message for the small heat shock protein, hsp27, was not detectable until the early tailbud stage, indicating that this hsp was not present maternally and was developmentally regulated. In situ hybridization analysis revealed that hsp110 mRNA was present in control embryos in the lens placode, spinal cord and somites, but increased upon heat shock in the anterior and posterior region, the lens placode, as well as in the somites and spinal cord. A similar distribution was observed for the hsp27 message, although it was not detectable until the early tailbud stage in control or heat-shocked embryos. The intracellular localization of HSP110 protein in response to stress was also investigated. HSP110 was detected predominantly in the cytoplasm in either a diffuse pattern or in long spindle-shaped fibres. Additionally, HSP110 was present in the nucleus. In heat shocked Xenopus A6 cells, HSP110 localized in distinct patterns surrounding the nucleus and was enhanced in the nucleus after prolonged heat stress. Sodium arsenite-treated cells displayed a similar pattern in which HSP110 localized on opposite ends of the nucleus. In contrast, in response to stress HSP30 was homogeneously distributed in the cytoplasm, moving into the nucleus only upon intense stress. This study presents, for the first time, a characterization of HSP110 in Xenopus laevis, adding to the growing knowledge of HSPs in this important model organism.

Heat shock proteins (HSPs) are stress-inducible and evolutionarily conserved molecular chaperones that are involved in protein binding and translocation. As molecular chaperones, HSPs bind to denatured proteins, inhibit their aggregation, maintain their solubility, and assist in refolding. This process inhibits the formation of protein aggregates which can be lethal to the cell. In eukaryotic cells, the ubiquitin-proteasome system (UPS) is responsible for the degradation of most non-native proteins. Furthermore, proteasome inhibition has been shown to induce hsp gene expression. Celastrol, a quinone methide triterpene, was shown to have an inhibitory effect on proteasome function in mammalian cells. The present study determined that celastrol induced the accumulation of ubiquitinated proteins and reduced proteasomal chymotrypsin-like activity in Xenopus laevis A6 kidney epithelial cells. In addition, incubation of A6 cells with celastrol induced the accumulation of HSP30 and HSP70 in a dose- and time-dependent manner with maximal levels of HSP accumulation occurring after 18 h of exposure. In A6 cells recovering from celastrol, the relative levels of HSP30 and HSP70 accumulation remained elevated for 18-24 h after removal of celastrol. The activation of heat shock factor 1 (HSF1) DNA-binding may be involved in celastrol-induced hsp gene expression in A6 cells, since the HSF1 inhibitor, KNK437, repressed the accumulation of HSP30 and HSP70. Exposure of A6 cells to simultaneous celastrol and mild heat shock treatment enhanced the accumulation of HSP30 and HSP70 to a greater extent than the sum of both stressors individually. Additionally, concurrent treatment of A6 cells with low concentrations of both celastrol and MG132 produced different patterns of HSP30 and HSP70 accumulation. While combined treatment with celastrol and MG132 acted synergistically on HSP30 accumulation, relative levels of HSP70 were similar to those observed with MG132 alone. Immunocytochemical analysis of celastrol- or MG132-treated A6 cells revealed HSP30 accumulation in a punctate pattern primarily in the cytoplasm with some staining in the nucleus. Also, in some cells treated with celastrol or MG132 large HSP30 staining structures were observed in the cytoplasm. Lastly, exposure of A6 cells to celastrol induced rounder cell morphology, reduced adherence and disorganization of the actin cytoskeleton. In conclusion, this study has shown that celastrol inhibited proteasome activity in amphibian cultured cells and induced HSF1-mediated expression of hsp genes.