Damage to DNA from a variety of sources can lead to damaged proteins, genomic instability, aneuploidy, and cancer. It is therefore essential to repair DNA damage, and to do so a variety of DNA repair mechanisms have evolved. One of the repair mechanisms, known as homologous recombination (HR) repair, uses an undamaged sister chromatid as a template to make error free repairs to double-strand (ds) DNA breaks. While many proteins are involved in HR, this work focuses on testing the interactions of a subset of these proteins known as the Rad51 paralogs. The goal of this study is to determine if the putative Rad51 paralogs in Drosophila melanogaster are sufficiently conserved as to function in the same manner as their human counterparts. This research is part of a larger project to determine if Drosophila melanogaster is a good model organism for studying HR in humans (Hs). The D. melanogaster Rad51 gene, and its four paralogs Spn D, Spn B, Rad51D, XRCC2 (the last 2 identified by sequence homology), and human hsRad51D and hsXRCC2, were cloned into Invitrogen's TOPO protein expression vector. When induced with IPTG, the resulting fusion proteins contains either aN-terminal Xpress TM epitope or a C-terminal V5 epitope. The fusion proteins were used in immunoprecipitation assays with antibodies against the epitope tags to test for proteinprotein interactions. While many of the assays were inconclusive and are still being optimized, the interaction of the C-terminally tagged dmXRCC2 with theN-terminally tagged hsRad51D gave a positive result. This single interspecies result suggests that homologous recombination is highly conserved between D. melanogaster and humans.

京都大学 / 新制・課程博士 / 博士(農学) / 甲第23521号 / 農博第2468号 / 新制||農||1087(附属図書館) / 学位論文||R3||N5352(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 本田 与一, 教授 田中 千尋, 准教授 坂本 正弘 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

<p>Understanding how genes affect behavior is critical to develop precise therapies for human behavioral disorders. The ability to investigate the relationship between genes and behavior has been greatly advanced over the last few decades due to progress in gene-targeting technology. Recently, the Tet gene family was discovered and implicated in epigenetic modification of DNA methylation by converting 5-methylcytosine to 5-hydroxymethylcytosine (5hmC). 5hmC and its catalysts, the TET proteins, are highly abundant in the postnatal brain but with unclear functions. To investigate their neural functions, we generated new lines of Tet1 and Tet3 mutant mice using a gene targeting approach. We designed both mutations to cause a frameshift by deleting the largest coding exon of Tet1 (Tet1Δe4) and the catalytic domain of Tet3 (Tet3Δe7-9). As Tet1 is also highly expressed in embryonic stem cells (ESCs), we generated Tet1 homozygous deleted ESCs through sequential targeting to compare the function of Tet1 in the brain to its role in ESCs. To test our hypothesis that TET proteins epigenetically regulate transcription of key neural genes important for normal brain function, we examined transcriptional and epigenetic differences in the Tet1Δe4 mouse brain. The oxytocin receptor (OXTR), a neural gene implicated in social behaviors, is suggested to be epigenetically regulated by an unknown mechanism. Interestingly, several human studies have found associations between OXTR DNA hypermethylation and a wide spectrum of behavioral traits and neuropsychiatric disorders including autism spectrum disorders. Here we report the first evidence for an epigenetic mechanism of Oxtr transcription as expression of Oxtr is reduced in the brains of Tet1Δe4-/- mice. Likewise, the CpG island overlapping the promoter of Oxtr is hypermethylated during early embryonic development and persists into adulthood. We also discovered altered histone modifications at the hypermethylated regions, indicating the loss of TET1 has broad effects on the chromatin structure at Oxtr. Unexpectedly, we discovered an array of novel mRNA isoforms of Oxtr that are selectively reduced in Tet1Δe4-/- mice. Additionally, Tet1Δe4-/- mice display increased agonistic behaviors and impaired maternal care and short-term memory. Our findings support a novel role for TET1 in regulating Oxtr expression by preventing DNA hypermethylation and implicate TET1 in social behaviors, offering novel insight into Oxtr epigenetic regulation and its role in neuropsychiatric disorders.</p> / Dissertation

The bald eagle, Haliaeetus leucocephalus, population declined dramatically in the early 20th century reducing the population from tens of thousands of birds within the lower 48 states, to <450 pairs of birds, effectively inducing a population bottleneck. The overall population has recovered and was removed from the endangered species list in 2007. This study investigates whether such overall population statistics are appropriate descriptors for this widespread species. I investigated the genetic differentiation between three populations of bald eagles from Alaska, North Florida and Florida Bay using both mitochondrial and nuclear DNA loci to determine whether discrete subpopulations comprise the broad range. Significant FST values, for both mtDNA and microsatellites, were found between both Florida populations and Alaska, but not within Florida populations. Results indicate that there is strong population structure, rejecting the null hypothesis of a panmictic population. Future conservation efforts should focus on subpopulations rather than the overall population. / by Ericka Elizabeth Helmick. / Thesis (M.S.)--Florida Atlantic University, 2011. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2011. Mode of access: World Wide Web.

Lee Yiu Fai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves 178-183). / Abstracts in English and Chinese. / Acknowledgements --- p.ii / Abstract --- p.iii / Abstract (Chinese version) --- p.vi / Table of contents --- p.viii / List of Abbreviations --- p.xvi / List of Figures --- p.xviii / List of Tables --- p.xxiv / Chapter Chapter 1 --- INTRODUCTON / Chapter 1.1 --- Cytochrome P450 (P450) --- p.1 / Chapter 1.1.1 --- Cytochrome P450 family --- p.1 / Chapter 1.1.2 --- Role in metabolism --- p.4 / Chapter 1.1.3 --- P450 catalytic cycle --- p.6 / Chapter 1.2 --- NADPH-cytochrome P450 reductase (RED) --- p.6 / Chapter 1.2.1 --- Characterization and distribution --- p.6 / Chapter 1.2.2 --- Structural and functional domains --- p.8 / Chapter 1.2.3 --- Role in P450 catalytic cycle --- p.10 / Chapter 1.3 --- Drug metabolism --- p.10 / Chapter 1.3.1 --- Understanding of drug metabolism is important for drug development --- p.10 / Chapter 1.3.2 --- Role of P450 in drug metabolism --- p.12 / Chapter 1.4 --- Production of RED knockout in vivo mouse model for screening of P450-dependent new drugs --- p.13 / Chapter 1.4.1 --- Background --- p.13 / Chapter 1.4.2 --- Gene targeting --- p.13 / Chapter 1.4.3 --- Gene targeting vector --- p.15 / Chapter 1.4.3.1 --- Classical knockout --- p.15 / Chapter 1.4.3.2 --- Conditional knockout --- p.19 / Chapter 1.4.4 --- Gene knockout mice and its use --- p.21 / Chapter Chapter 2 --- OBJECTIVES --- p.22 / Chapter Chapter 3 --- MATERIALS AND METHODS --- p.24 / Chapter 3.1 --- Preparation of RED cDNA by RT-PCR --- p.24 / Chapter 3.1.1 --- Total RNA isolation --- p.24 / Chapter 3.1.1.1 --- Materials --- p.24 / Chapter 3.1.1.2 --- Methods --- p.24 / Chapter 3.1.2 --- Reverse transcription- polymerase chain reaction (RT-PCR) --- p.25 / Chapter 3.1.2.1 --- Materials --- p.25 / Chapter 3.1.2.2 --- Methods --- p.25 / Chapter 3.1.3 --- T/A cloning of RED cDNA --- p.28 / Chapter 3.1.3.1 --- Materials --- p.28 / Chapter 3.1.3.2 --- Methods --- p.28 / Chapter 3.1.4 --- Midi-preparation of RED cDNA clone --- p.32 / Chapter 3.1.4.1 --- Materials --- p.33 / Chapter 3.1.4.2 --- Methods --- p.33 / Chapter 3.1.5 --- Confirmation of RED cDNA clone --- p.34 / Chapter 3.1.5.1 --- Restriction enzyme mapping --- p.34 / Chapter 3.1.5.1.1 --- Materials --- p.34 / Chapter 3.1.5.1.2 --- Methods --- p.34 / Chapter 3.1.5.2 --- DNA sequencing of RED cDNA sequence --- p.35 / Chapter 3.1.5.2.1 --- Materials --- p.35 / Chapter 3.1.5.2.2 --- Methods --- p.35 / Chapter 3.1.6 --- Preparation and purification of RED cDNA for probe labeling --- p.38 / Chapter 3.1.6.1 --- Materials --- p.38 / Chapter 3.1.6.2 --- Methods --- p.38 / Chapter 3.1.7 --- Non-radioactive random-primed labeling of RED cDNA --- p.39 / Chapter 3.1.7.1 --- Materials --- p.39 / Chapter 3.1.7.2 --- Methods --- p.39 / Chapter 3.2 --- Isolation of RED gene by genomic library screening --- p.40 / Chapter 3.2.1 --- Titering of genomic library --- p.41 / Chapter 3.2.1.1 --- Materials --- p.41 / Chapter 3.2.1.2 --- Methods --- p.41 / Chapter 3.2.2 --- Primary screening of genomic library by RED cDNA probe --- p.42 / Chapter 3.2.2.1 --- Plaque lift --- p.42 / Chapter 3.2.2.1.1 --- Materials --- p.42 / Chapter 3.2.2.1.2 --- Methods --- p.42 / Chapter 3.2.2.2 --- Proteinase K treatment --- p.43 / Chapter 3.2.2.2.1 --- Materials --- p.43 / Chapter 3.2.2.2.2 --- Methods --- p.43 / Chapter 3.2.2.3 --- "Pre-hybridization, hybridization and detection" --- p.44 / Chapter 3.2.2.3.1 --- Materials --- p.44 / Chapter 3.2.2.3.2 --- Methods --- p.44 / Chapter 3.3 --- Isolation of RED by hybridization screening by Genome System Inc. --- p.45 / Chapter 3.4 --- Characterization of BAC clones containing RED genomic DNA fragments commercially obtained from Genome System Inc. --- p.45 / Chapter 3.4.1 --- Large scale preparation of BAC DNA --- p.45 / Chapter 3.4.1.1 --- Materials --- p.47 / Chapter 3.4.1.2 --- Methods --- p.47 / Chapter 3.4.2 --- Restriction enzyme mappings and Southern blotting analysis of BAC DNA fragments --- p.47 / Chapter 3.4.2.1 --- Materials --- p.48 / Chapter 3.4.2.2 --- Methods --- p.48 / Chapter 3.4.3 --- Shot-gun sub-cloning of RED genomic DNA fragments from BAC clone in pGEM®-3Z vector --- p.49 / Chapter 3.4.3.1 --- Preparation of cloning vector and DNA insert for ligation --- p.50 / Chapter 3.4.3.1.1 --- Materials --- p.50 / Chapter 3.4.3.1.2 --- Methods --- p.50 / Chapter 3.4.3.1.2.1 --- Cloning vectors --- p.50 / Chapter 3.4.3.1.2.2 --- DNA inserts --- p.52 / Chapter 3.4.3.2 --- Preparation of competent cells and transformation --- p.52 / Chapter 3.4.3.2.1 --- Materials --- p.52 / Chapter 3.4.3.2.2 --- Methods --- p.53 / Chapter 3.4.3.3 --- Screening for positive recombinant clones --- p.54 / Chapter 3.4.3.3.1 --- Picking of colonies randomly from the agar plates (method 1) --- p.54 / Chapter 3.4.3.3.1.1 --- Materials --- p.54 / Chapter 3.4.3.3.1.2 --- Methods --- p.54 / Chapter 3.4.3.3.2 --- Colony lifts and hybridization with RED cDNA probes (method 2) --- p.55 / Chapter 3.4.3.3.2.1 --- Materials --- p.55 / Chapter 3.4.3.3.2.2 --- Methods --- p.55 / Chapter 3.5 --- Restriction enzyme mappings and Southern blotting analysis of RED gene subcloned in pGEM®-3Z vector --- p.56 / Chapter 3.5.1 --- Materials --- p.56 / Chapter 3.5.2 --- Methods --- p.56 / Chapter 3.6 --- Exon mappings of the RED genomic DNA fragments by PCR --- p.57 / Chapter 3.6.1 --- Materials --- p.57 / Chapter 3.6.2 --- Methods --- p.57 / Chapter 3.7 --- Construction of gene targeting vector --- p.57 / Chapter 3.7.1 --- Gene targeting vectors la and lb derived from clone H (strategy 1) --- p.60 / Chapter 3.7.1.1 --- Sub-cloning 3.65 kb Hind Ill/Hind III RED gene fragment to pGEM®-3Z vector --- p.60 / Chapter 3.7.1.1.1 --- Materials --- p.62 / Chapter 3.7.1.1.2 --- Methods --- p.62 / Chapter 3.7.1.2 --- Deletion of exonic sequence of RED gene and modification of the digested restriction end to Xho I site --- p.62 / Chapter 3.7.1.2.1 --- Materials --- p.63 / Chapter 3.7.1.2.2 --- Methods --- p.63 / Chapter 3.7.1.3 --- Preparation of neo cassette --- p.63 / Chapter 3.7.1.3.1 --- Materials --- p.64 / Chapter 3.7.1.3.2 --- Methods --- p.64 / Chapter 3.7.1.4 --- Cloning of neo cassette --- p.66 / Chapter 3.7.1.4.1 --- Methods --- p.66 / Chapter 3.7.1.5 --- Sub-cloning the neo cassette containing RED genomic fragment to pMCI-Thymidine kinase (TK) Poly A vector --- p.67 / Chapter 3.7.1.5.1 --- Materials --- p.67 / Chapter 3.7.1.5.2 --- Methods --- p.67 / Chapter 3.7.2 --- "Gene targeting vectors 2a/2b, 3a/3b and 4a derived from clone X8 (strategy 2,3 and 4 respectively)" --- p.67 / Chapter 3.8 --- Preparation and testing the genomic probes for screening recombinant embryonic stem (ES) cells --- p.73 / Chapter 3.8.1 --- Cloning of genomic probes --- p.73 / Chapter 3.8.1.1 --- Materials --- p.73 / Chapter 3.8.1.2 --- Methods --- p.73 / Chapter 3.8.2 --- Purification of DNA for labeling --- p.78 / Chapter 3.8.2.1 --- Materials --- p.78 / Chapter 3.8.2.2 --- Methods --- p.78 / Chapter 3.8.3 --- ECF random prime labeling of genomic probes --- p.79 / Chapter 3.8.3.1 --- Materials --- p.79 / Chapter 3.8.3.2 --- Methods --- p.79 / Chapter 3.8.4 --- Restriction enzyme digestion of genomic DNA and Southern blotting --- p.80 / Chapter 3.8.4.1 --- Materials --- p.80 / Chapter 3.8.4.2 --- Methods --- p.80 / Chapter 3.8.5 --- Testing the specificity of genomic probes --- p.80 / Chapter 3.8.5.1 --- Materials --- p.80 / Chapter 3.8.5.2 --- Methods --- p.80 / Chapter Chapter 4 --- RESULTS --- p.86 / Chapter 4.1 --- Total RNA isolation and RT-PCR of RED cDNAs --- p.86 / Chapter 4.2 --- Confirmation of the RT-PCR RED cDNA clone --- p.86 / Chapter 4.2.1 --- Restriction enzyme mapping --- p.86 / Chapter 4.2.2 --- DNA sequencing --- p.86 / Chapter 4.3 --- Genomic library screening of RED gene --- p.90 / Chapter 4 4 --- Restriction enzyme mappings and Southern blotting analysis of RED Gene containing BAC clone from Genome System Inc. --- p.90 / Chapter 4.5 --- Shot-gun sub-cloning of RED gene containing genomic DNA fragments to pGEM®-3Z vectors --- p.93 / Chapter 4.5.1 --- Cloning of Hind III cut RED gene fragment --- p.93 / Chapter 4.5.2 --- Cloning of Xba I cut RED gene fragment --- p.93 / Chapter 4.5.3 --- Cloning of EcoR I cut RED gene fragment --- p.95 / Chapter 4.6 --- Identification of RED exons in the shot-gun sub-cloning clones by PCR --- p.95 / Chapter 4.7 --- Construction of restriction enzyme maps of the RED gene containing clones --- p.100 / Chapter 4.7.1 --- Clone H --- p.100 / Chapter 4.7.1.1 --- Single restriction enzyme digestions and Southern blotting --- p.100 / Chapter 4.7.1.2 --- Double restriction enzyme digestions and Southern blotting --- p.100 / Chapter 4.7.1.3 --- Restriction enzyme map --- p.101 / Chapter 4.7.2 --- Clone X8 --- p.101 / Chapter 4.7.2.1 --- Single restriction enzyme digestions and Southern blotting --- p.101 / Chapter 4.7.2.2 --- Double restriction enzyme digestion and Southern blotting --- p.104 / Chapter 4.7.2.3 --- Restriction enzyme map --- p.104 / Chapter 4.7.3 --- Clone El4 --- p.105 / Chapter 4.7.3.1 --- Single restriction enzyme digestions and Southern blotting --- p.105 / Chapter 4.7.3.2 --- Double restriction enzyme digestion and Southern blotting --- p.108 / Chapter 4.7.3.3 --- Restriction enzyme map --- p.108 / Chapter 4.8 --- Construction of gene targeting vector --- p.108 / Chapter 4.8.1 --- Gene targeting vector based on the clone H (strategy 1) with deletion of RED exon 16 --- p.113 / Chapter 4.8.1.1 --- Cloning a smaller RED genomic DNA into pGEM®-3Z vectors --- p.113 / Chapter 4.8.1.2 --- Replacement of exon of RED gene by neo cassette --- p.113 / Chapter 4.8.1.3 --- Cloning to TK vector --- p.113 / Chapter 4.8.2 --- Targeting vector based on the clone X8 --- p.124 / Chapter 4.8.2.1 --- Strategy 2 (deletion of RED exon 4) --- p.124 / Chapter 4.8.2.1.1 --- Cloning 3.9 kb Kpn I/Hinc II RED genomic DNA into pGEM®-3Z vectors --- p.124 / Chapter 4.8.2.1.2 --- Replacement of exon of RED gene by neo cassette --- p.124 / Chapter 4.8.2.1.3 --- Cloning to TK vector --- p.124 / Chapter 4.8.2.2 --- Strategy 3 (deletion of RED exon 5-8) --- p.136 / Chapter 4.8.2.2.1 --- Cloning the genomic DNA into pGEM®-3Z vectors --- p.136 / Chapter 4.8.2.2.2 --- Replacement of exon of RED gene by neo cassette --- p.136 / Chapter 4.8.2.2.3 --- Cloning to TK vector --- p.136 / Chapter 4.8.2.3 --- Strategy 4 (deletion of RED exon 7-10) --- p.136 / Chapter 4.8.2.3.1 --- Cloning the genomic DNA into pGEM®-3Z vectors --- p.136 / Chapter 4.8.2.3.2 --- Replacement of exon of RED gene by neo cassette --- p.152 / Chapter 4.8.2.3.3 --- Cloning to TK vector --- p.152 / Chapter 4.9 --- Testing for the specificity of genomic DNA probes --- p.152 / Chapter 4.9.1 --- Preparation of restriction enzyme digested genomic DNA --- p.152 / Chapter 4.9.2 --- Hybridization of the probes to genomic DNA --- p.163 / Chapter Chapter 5 --- DISCUSSION --- p.167 / Chapter 5.1 --- Proposed significant of RED knockout mice for new drug screening --- p.167 / Chapter 5.2 --- Experimental problems --- p.168 / Chapter 5.2.1 --- Genomic library screening --- p.168 / Chapter 5.2.2 --- Cloning --- p.168 / Chapter 5.3 --- RED gene targeting vector construction / Chapter 5.3.1 --- Isolation of RED gene for gene targeting vectors construction --- p.169 / Chapter 5.3.2 --- Deletion of different exons in different RED gene targeting vectors --- p.169 / Chapter 5.3.3 --- Components in the targeting vectors --- p.170 / Chapter 5.3.4 --- Enhancements of homologous recombination --- p.171 / Chapter Chapter 6 --- CONCLUSIONS --- p.173 / Chapter Chapter 7 --- FUTURE STUDIES --- p.175 / Chapter 7.1 --- Identification of the sizes of RED gene introns --- p.175 / Chapter 7.2 --- Production of RED knockout mice --- p.175 / Chapter 7.3 --- Characterization of RED knockout mice --- p.175 / Chapter 7.4 --- Conditional gene knockout for RED gene --- p.177 / REFERENCES --- p.178 / APPENDIX --- p.184

Human pluripotent stem cells (hPSCs) such as, human embryonic stem cells (hES) and human induced pluripotent stem cells (hiPS) are a valuable resource to generate bespoke cell types for a number of therapeutic applications involving cell therapy, drug screening and disease modelling. The overarching goal of this project was to generate a set of transgenic tools by gene targeting and genetic modification of hESCs for applications in stem cell biology such as the in vitro isolation, analyses and derivation of lineage specific cell types. The transgenic tools generated in this study were designed and tested in particular for the human 3rd pharyngeal pouch epithelium (3PPE) like cells and its derivatives, namely the thymus and parathyroid, which are key organs involved in T-cell development and calcium homeostasis respectively. The forkhead transcription factor FOXN1 is considered a master regulator of the development of the thymic epithelium (TEC), the major functional component of the thymic stroma, which is intimately involved in T-cell differentiation. So, to facilitate the prospective isolation of FOXN1 expressing TECs, gene targeting was employed to place a fluorescent reporter and a lineage selection antibiotic resistance gene under the direct control of the endogenous FOXN1 promoter. To date, I have not been able to detect either the fluorescent reporter, or FOXN1 expression using published directed differentiation protocols, but only what can be deemed as precursors expressing the cytokeratin K5 and other markers associated with the development of the thymus and parthyroid from 3PPE. The lack of endogenous FOXN1 activation was observed in both the unmodified parent and the targeted FOXN1 knock-in human ES lines. Further, over-expression of FOXN1 cDNA during the differentiation protocol did not result in the activation of endogenous FOXN1. So, the results evinced in this study could be due to a number of reasons such as, technical issues associated with transference of the published protocols to the cell lines used in this study, differences in hESC lines, and effects of different hESC culture methods and practices. The homeobox gene HOXA3 is expressed in the 3PPE during development. So, a HOXA3 transgenic reporter hESC line could be an invaluable tool for prospective isolation of in vitro derived 3PPE like cells. The reporter was generated by Piggy Bac transposase mediated transposition of a HOXA3 containing Bacterial Artificial Chromsome (BAC) in the FOXN1 knock-in human ES line. To date, this is biggest reported cargo that has been successfully transposed in human ESCs. Moreover, this is the first lineage specific double reporter transgenic hESC line that has been reported for this lineage. This HOXA3 reporter line was then used to isolate and enrich for HOXA3 expressing 3PPE like cells with very high efficiencies during the directed differentiation of hESCs, thus demonstrating the key objective of this transgenic hESC line for this study. In a novel parallel approach, I have conceived, designed and generated transgenic hESCs lines capable of inducible and constitutive over-expression of key transcription factors involved in the development of 3PPE and its derivatives, the thymus and parathyroid. The objective of the said over-expression hESC lines was to interrogate if such a system could elicit morphological and gene expression changes in hESCs following over-expression. By testing the chosen panel of transcription factors in hESCs, I was able to detect cells expressing FOXN1 and GCMB, which are key markers of TECs and PTECs. Further, I have isolated an expandable population of cells expressing markers analogous to their in vivo counterpart found in the 3PPE of a developing mouse embryo around E9.0. The in vivo potency of these in vitro derived 3PPE like cells is yet to be ascertained. Nevertheless, transgenic constructs generated in this experiment could also be tested during future attempts at the differentiation of hESCs to TECs and PTECs, and also used as a basis for future studies involving the direct conversion of patient specific fibroblasts to 3PPE like cells and its derivatives. In summary, several transgenic tools developed in this project, namely the FOXN1 knock-in transgenic hESC line, FOXN1-HOXA3 double transgenic hESC line, over-expression 3PPE transgenes and hESC transgenic lines, and results from the deployment of these tools provide a foundation, from which protocols to generate functional TECs and PTECs can be refined and optimised. These transgenic hESC lines also provide a tractable model, which could be used to interrogate the development of human TECs and PTECs from human 3PPE, and identify hitherto unknown early events in their development in an in vitro reductionist setting.

<p>Members of the transforming growth factor-β (TGF-β) superfamily of growth and differentiation factors regulate a vast array of biological functions in the adult, and are of great importance in governing cell fate determination and patterning in the developing embryo. The TGF-β signal is propagated intracellularly by Smad proteins resulting in transcriptional responses. Smad6 and Smad7 are inhibitory Smads known to downregulate the TGF-β signal and thereby possibly modulating the biological response. This thesis describes a functional analysis of the inhibitory Smad7 from an <i>in vitro </i>and <i>in vivo </i>perspective<i>.</i></p><p>The prostate gland is dependent on androgens for its growth and differentiation. Androgen withdrawal can cause regression and apoptosis in normal and malignant prostate. Previous studies suggest a role for TGF-β in the apoptotic mechanism. We investigated the expression levels of Smad proteins in the rat ventral prostate as well as in an androgen sensitive prostate tumor model (Dunning R3327 PAP) by immunohistochemistry. We observed an increased immunoreactivity for Smad3, Smad4 and phosphorylated Smad2 in the rat ventral prostate epithelial cells after castration, as well as in the prostate tumor cells. Expression of inhibitory Smad6 and Smad7 were also increased in both normal and malignant prostate in response to castration. </p><p>Several studies have shown that Smad7 is upregulated in response to TGF-β stimuli, suggesting a role in a negative feedback loop attenuating the TGF-β response. We investigated the molecular mechanism behind that response by studying the transcriptional regulation of the Smad7 gene. We identified a palindromic Smad binding element (SBE) in the promoter. Point mutations introduced into the SBE abolished transcriptional activation via TGF-β. We also observed that mutating or deleting binding motifs for Sp1 and AP-1, led to an attenuation of the TGF-β mediated transcriptional induction as well as the basal promoter activity.</p><p>Gene ablation of Smad proteins has revealed specific physiological and developmental roles. We analysed mice targeted on the Smad7 locus. The mice appeared viable and fertile with a slight reduction in litter size, suggesting a perinatal loss. Biochemical analysis of mouse embryonic fibroblasts (MEFs) showed no major difference between wild type and mutant MEFs. </p>

Members of the transforming growth factor-β (TGF-β) superfamily of growth and differentiation factors regulate a vast array of biological functions in the adult, and are of great importance in governing cell fate determination and patterning in the developing embryo. The TGF-β signal is propagated intracellularly by Smad proteins resulting in transcriptional responses. Smad6 and Smad7 are inhibitory Smads known to downregulate the TGF-β signal and thereby possibly modulating the biological response. This thesis describes a functional analysis of the inhibitory Smad7 from an in vitro and in vivo perspective. The prostate gland is dependent on androgens for its growth and differentiation. Androgen withdrawal can cause regression and apoptosis in normal and malignant prostate. Previous studies suggest a role for TGF-β in the apoptotic mechanism. We investigated the expression levels of Smad proteins in the rat ventral prostate as well as in an androgen sensitive prostate tumor model (Dunning R3327 PAP) by immunohistochemistry. We observed an increased immunoreactivity for Smad3, Smad4 and phosphorylated Smad2 in the rat ventral prostate epithelial cells after castration, as well as in the prostate tumor cells. Expression of inhibitory Smad6 and Smad7 were also increased in both normal and malignant prostate in response to castration. Several studies have shown that Smad7 is upregulated in response to TGF-β stimuli, suggesting a role in a negative feedback loop attenuating the TGF-β response. We investigated the molecular mechanism behind that response by studying the transcriptional regulation of the Smad7 gene. We identified a palindromic Smad binding element (SBE) in the promoter. Point mutations introduced into the SBE abolished transcriptional activation via TGF-β. We also observed that mutating or deleting binding motifs for Sp1 and AP-1, led to an attenuation of the TGF-β mediated transcriptional induction as well as the basal promoter activity. Gene ablation of Smad proteins has revealed specific physiological and developmental roles. We analysed mice targeted on the Smad7 locus. The mice appeared viable and fertile with a slight reduction in litter size, suggesting a perinatal loss. Biochemical analysis of mouse embryonic fibroblasts (MEFs) showed no major difference between wild type and mutant MEFs.

Because of shared physiological, anatomical and metabolical features with humans, mice have served for a long time as mammalian disease models. In particular, these last ten years have been the golden age for this favoured model animal. Human and mouse genome projects show that there is 95% genome homology. Spurred by this fact, research attention has shifted from reading these sequences to deciphering the functions of these genes. The 1980s saw the remarkable achievement of homologous recombination in mammalian cell culture systems. Later in the 1990s, innovative gene trapping strategies were developed to enabled random mutagenesis. Today, the goal is to generate more versatile tools to avoid limitations posed by these earlier mutagenesis strategies. Many public and private research centers have united with the aim of mutating all mouse genes. In order to achieve this mutagenesis, the first requirement is a set of practical and efficient viral or plasmid based vectors that can be used globally in the genome. This will be aided by advances in understanding of biological events such as gene transcription, recombination, and embryonic stem cell cycle. In addition, technical improvements such as vector development, precise cell culture assay, and recombinant DNA delivery will also be important. The vector design work in this PhD thesis encompasses 0.00001 % ofthese efforts but may to out to be highly relevant...

DNA damage occurs through endogenous and exogenous sources, and can lead to stalled replication forks, genetic disorders, cancer, and cell death. Homologous recombination (HR) is a relatively fast and error-free repair pathway for damaged DNA, which can occur through a gene conversion event or through a crossing-over event with the exchange of genetic material. Homologous recombination occurs most frequently in the G2 phase of the cell cycle and utilizes the sister chromatid as the repair template. When the sister chromatid is unavailable, the homologous chromosome or a homologous sequence in an ectopic location can be used to repair the lesion; the latter of which is referred to as ectopic homologous recombination (EHR). Rad51 is a key protein involved in HR, and to test its role in EHR, variant Rad51 proteins were expressed in murine hybridoma cells. These Rad51 variants were assayed for their effects on EHR. Excess wild-type Rad51 as well as a deficiency of wild-type Rad51 decreased EHR from the background level found in these cell lines. Thus, Rad51 is necessary for EHR, but there may be an optimal amount of Rad51 required for efficient EHR. Expression of the Rad51 catalytic mutants Rad51K133A and Rad51K133R was found to have an inhibitory effect on EHR, as expected based on the loss of ATP binding and ATP hydrolysis, respectively, in these variants. Excess wild-type Rad51 was verified in this study to increase HR via a gene targeting assay. MMC treatment, but not ionizing radiation, leads to an increase in EHR in the presence of excess wild-type Rad51. Thus, endogenous levels of Rad51 are sufficient to maintain EHR, but in the presence of excess wild-type Rad51, the level of EHR can increase in response to certain DNA damaging agents and in response to gene targeting.