Functional analysis of three Arabidopsis SR proteins (SCL33, SC35, SCL30A) in plant development and splicing

2012 Fall.Includes bibliographical references.To view the abstract, please see the full text of the document

Genome-Wide Characterization of the Effects of Nucleic Acid Modifying Enzymes: Cytidine Deaminases and DNA Methylation

Activation-induced cytidine deaminase (AID) is essential for two processes of immunoglobulin diversification in germinal center B cells: somatic hypermutation (SHM), in which mutations are introduced into immunoglobulin (Ig) genes, and class-switch recombination (CSR), in which genomic constant regions are recombined to encode antibodies of different isotypes. Both of these processes require AID-catalyzed C-to-U lesions at the Ig loci, which are resolved to generate point mutations or double-stranded DNA breaks in the cases of SHM and CSR, respectively. Despite over a decade of intense study, a number of open issues remain surrounding AID. The diversity of findings regarding AID’s role in DNA demethylation raises the question of the scope of its involvement in this process. Additionally, while it is clear that AID-mediated damage occurs, the effects of this damage on the average B cell have not been characterized. Finally, the issue of whether AID is able to edit RNA in vivo has never been rigorously addressed in the literature. In each of these cases, the advent of high-throughput sequencing provides methods for genome-wide characterization of AID’s effects. This thesis presents the application of a number of genome-scale, sequencing-based methods to characterize the effects of AID deficiency and overexpression on the activated B cell: mRNA-Seq and miRNA-Seq allow for measurements of RNA expression and editing, while reduced-representation bisulfite sequencing (RRBS) assays DNA methylation. These analyses confirmed AID’s known role in immunoglobulin isotype switching, while also demonstrating that it has little other effect on gene expression. Additionally, no evidence of AID-dependent mRNA or miRNA editing could be detected. Finally, RRBS data failed to support a role for AID in the regulation of DNA methylation. Thus, despite evidence of its additional activities in other systems, antibody diversification appears to be AID’s sole physiological function in activated B cells. Following the conclusion of my studies of AID’s effects in B cells, I applied similar genomics tools to two amenable topics in nucleic acid modifications. First, I used mRNA-Seq to attempt to determine the substrate of the orphan cytidine deaminase Apolipoprotein B mRNA-editing enzyme, catalytic polypeptide 2 (APOBEC2). Next, I used whole-genome bisulfite sequencing to explore the distribution of 5-methylcytosine in Trypanosoma brucei. In both of these cases, results were inconclusive but suggest future directions for investigation

Incongruencia entre señal morfológica y molecular: una nueva propuesta sistemática para el complejo Grimmiaceae-Ptychomitriaceae (Bryophyta)

Tesis doctoral inédita de la Universidad Autónoma de Madrid. Facultad de Ciencias, Departamento de Biología. Fecha de lectura : 29-06-200

OLIG2 neural progenitor cell development and fate in Down syndrome

Down syndrome (DS) is caused by triplication of human chromosome 21 (HSA21) and is the most common genetic form of intellectual disability. It is unknown precisely how triplication of HSA21 results in the intellectual disability, but it is thought that the global transcriptional dysregulation caused by trisomy 21 perturbs multiple aspects of neurodevelopment that cumulatively contribute to its etiology. While the characteristics associated with DS can arise from any of the genes triplicated on HSA21, in this work we focus on oligodendrocyte transcription factor 2 (OLIG2). The progeny of neural progenitor cells (NPCs) expressing OLIG2 are likely to be involved in many of the cellular changes underlying the intellectual disability in DS. To explore the fate of OLIG2+ neural progenitors, we took advantage of two distinct models of DS, the Ts65Dn mouse model and induced pluripotent stem cells (iPSCs) derived from individuals with DS. Our results from these two systems identified multiple perturbations in development in the cellular progeny of OLIG2+ NPCs. In Ts65Dn, we identified alterations in neurons and glia derived from the OLIG2 expressing progenitor domain in the ventral spinal cord. There were significant differences in the number of motor neurons and interneurons present in the trisomic lumbar spinal cord depending on age of the animal pointing both to a neurodevelopment and a neurodegeneration phenotype in the Ts65Dn mice. Of particular note, we identified changes in oligodendrocyte (OL) maturation in the trisomic mice that are dependent on spatial location and developmental origin. In the dorsal corticospinal tract, there were significantly fewer mature OLs in the trisomic mice, and in the lateral funiculus we observed the opposite phenotype with more mature OLs being present in the trisomic animals. We then transitioned our studies into iPSCs where we were able to pattern OLIG2+ NPCs to either a spinal cord-like or a brain-like identity and study the OL lineage that differentiated from each progenitor pool. Similar to the region-specific dysregulation found in the Ts65Dn spinal cord, we identified perturbations in trisomic OLs that were dependent on whether the NPCs had been patterned to a brain-like or spinal cord-like fate. In the spinal cord-like NPCs, there was no difference in the proportion of cells expressing either OLIG2 or NKX2.2, the two transcription factors whose co-expression is essential for OL differentiation. Conversely, in the brain-like NPCs, there was a significant increase in OLIG2+ cells in the trisomic culture and a decrease in NKX2.2 mRNA expression. We identified a sonic hedgehog (SHH) signaling based mechanism underlying these changes in OLIG2 and NKX2.2 expression in the brain-like NPCs and normalized the proportion of trisomic cells expressing the transcription factors to euploid levels by modulating the activity of the SHH pathway. Finally, we continued the differentiation of the brain-like and spinal cord-like NPCs to committed OL precursor cells (OPCs) and allowed them to mature. We identified an increase in OPC production in the spinal cord-like trisomic culture which was not present in the brain-like OPCs. Conversely, we identified a maturation deficit in the brain-like trisomic OLs that was not present in the spinal cord-like OPCs. These results underscore the importance of regional patterning in characterizing changes in cell differentiation and fate in DS. Together, the findings presented in this work contribute to the understanding of the cellular and molecular etiology of the intellectual disability in DS and in particular the contribution of cells differentiated from OLIG2+ progenitors