Mestrado em Ciências Forenses / Master Degree Course in Forensic Sciences / A possibilidade de analisar amostras com quantidades exíguas de material genético (amostras Low Copy Number ou LCN), em que estão presentes apenas algumas células, tem alterado a forma de encarar a cena do crime. Alguns vestígios que até agora não eram considerados como susceptíveis de proporcionarem resultados, podem actualmente ser analisados com sucesso. As impressões digitais são um bom exemplo. Estes vestígios apresentam um baixo número de células, permitindo apenas recuperar quantidades de DNA inferiores a 100 pg. Assim, para a análise do DNA nuclear, é necessário implementar sistemas muito sensíveis que consistem, habitualmente, no aumento do número de ciclos da PCR. Contudo, alguns artefactos são produzidos, tornando difícil a interpretação dos electroforectogramas. Neste trabalho pretendeu-se comparar a aplicação do estudo de STR autossómicos, Y-STR e miniSTR na análise genética de impressões digitais, partindo do conceito do aumento do número de ciclos como estratégia para se obter maior sensibilidade. Procedeu-se também à amplificação total do genoma e nested-PCR, como métodos alternativos ao aumento do número de ciclos. Adicionalemente, neste estudo tentou-se perceber a influência dos principais métodos reveladores de impressões digitais (cianoacrilato, pó magnético e pó branco) na análise do DNA. Os resultados mostram que o aumento do número de ciclos é a melhor opção como método para aumentar a sensibilidade. Constata-se também que o DNA extraído de impressões digitais encontra-se parcialmente degradado, obtendo-se diferenças significativas entre loci com fragmentos de amplificação menores e maiores do que 200 pb. Dos diferentes marcadores caracterizados verifica-se que, em termos de percentagem de alelos detectados, os miniSTR proporcionam os melhores resultados. Por outro lado, os Y-STR parecem altamente sensíveis à degradação ou presença de inibidores, pelo que são menos robustos para este tipo de análises. Verifica-se também que os perfis LCN são drasticamente afectados por artefactos, principalmente os derivados de variação estocástica, como o allele dropout e o desequilíbrio heterozigótico. A determinação de perfis de consenso permite reduzir alguns destes artefactos. Dos métodos de revelação estudados, o cianoacrilato é o que apresenta menor influência na análise e, pelo contrário, o pó branco provoca os resultados mais negativos. / The possibility to perform low copy number DNA typing, when just a few cells are available, as changed the way how crime scene investigations is faced. Nowadays it is possible to successfully type some evidence that couldn t be considered until now. Fingerprints are a good example of those. Since that just a few cells are present in this evidence (enabling recovery of low quantities of DNA, fewer than 100pg) just very sensitive systems can detect nuclear DNA. The most used method is definitely increasing the number of PCR cycles. However, increased occurrence of stutters and artifacts that reduced the quality of the DNA profile is normally observed. The present work aimed to compare the application of autosomic STR, Y-STR and miniSTR markers, based on the concept of increased number of PCR cycles as a strategy to achieve more sensitivity. Some other methods, such as whole genome amplification and nested-PCR, were also evaluated as an alternative way to reach the desired sensitivity. Another goal was to determine the influence of several reagents for developing latent fingerprints (cyanoacrylate fuming, magnetic powder and white powder) in DNA typing. The results shows that increasing the number of PCR cycles still is the best way to attain the required sensitivity. Moreover we could realize that DNA was partially degraded, once there were observed significant differences between loci larger and smaller than 200bp. Among all markers miniSTR showed to perform the best results in terms of detected alleles percentage. On the other hand, Y-STR seemed to be highly affected in the presence of degraded DNA and PCR inhibitors, which makes them less robust for these analyses. LCN profiles are significantly affected by artifacts, like allele dropout and heterozygous imbalance, derived from stochastic fluctuation. Reporting consensus profiles reduces artifact inherent errors. Finally, cyanoacrylate proved to have a minimum negative effect on DNA profiling, while white powder was the worst reagent.

When offenders commit crime there is the potential that they may leave behind trace amounts of their DNA, even when there has been no apparent body fluid spill. During the examination of crime scenes, scene investigators try to identify areas that may be sampled to locate these traces. Specialist techniques are then required within the laboratory to enable such small amounts to be analysed to obtain a profile. These techniques are referred to as Low Template DNA analysis (LTDNA), of which Low Copy Number DNA (LCN DNA) is one instance. In 2008, following the Omagh Bombing trial, and comments made by Judge Weir, the UK Forensic Regulator commissioned a review of the science of LTDNA analysis. The subsequent report made specific mention of the fact that there was no available information on the success rate of the use of such DNA techniques and that there seemed to be confusion over what constituted a success. The report went on to state that there was no information on where such trace amounts of DNA were likely to be found, or what factors could influence the likelihood of obtaining a trace DNA profile (Caddy, 2008). This research considered the outcomes of LCN DNA analysis from 3,552 samples to try to establish where trace amounts of DNA could be found, whether some areas sampled were more successful in generating profiles than others, and the likelihood of the profiles obtained being of use to a criminal investigation. Analysis of results identified areas that were more successful in generating profiles of use to an investigation and highlighted significant differences in results across a variety of items from which samples were taken. DNA samples taken from items associated with communication such as mobile phones were much more likely to produce a profile useful to a criminal investigation than those taken from fixed surfaces within premises. The results obtained showed that obtaining a DNA profile did not necessarily correlate with the profile being of use to a criminal investigation. This was due to the fact that a large number of these profiles were anticipated eliminations from legitimate sources. Items that produced high numbers of profiles but were anticipated eliminations, and therefore of no value to an investigation, came from items associated with skin samples and clothing. The research went further to identify key factors that affected the profiling rates. Factors that had a positive influence on the ability to obtain a profile included: any area that had been in close proximity to saliva (direct contact was not required); samples that had been recovered from the inside of premises or vehicles and therefore protected from the elements; those that were dry; items that were of a porous nature; and those that had a rough texture. No differences were found between the actual surface materials (plastic, glass, wood, metal), as all showed a propensity to generate profiles. Other factors that were considered but proved to have no effect on the profiling rates included seasonal differences and whether the area targeted for sampling was clearly defined. Items that had had high contact with a victim, were recovered from outside or had been wet, all proved to be less useful to an nvestigation. A further finding of the research was that swabs that had been recovered and stored frozen appeared to deteriorate in their ability to profile. This was particularly notable if they were submitted later than 5 months after recovery. Items stored in dry conditions did not deteriorate in this way. Overall the research can be used to provide investigators with the knowledge of what areas of crime scenes are most likely to yield trace DNA material, the key factors that can affect the likelihood of obtaining a profile, and those areas that are more likely to produce profiles useful to criminal investigations.

Stochastic fluctuations in mRNA and protein copy number between cells are inevitable during the process gene expression, even when cells carry identical chromosomes. Such fluctuations are able to impact the phenotypic fate of the cell, and are known to have greater impact when the copy number of the molecule involved is low. Additionally, up to 50% of proteins in Escherichia coli are present in the cell at a level of 10 molecules per cell or fewer (Taniguchi et al. 2010). As such, quantification of low copy number gene expression products and their distribution in cellular populations is key in understanding the process of gene expression. Currently, there are few techniques that allow investigation with the single cell and single molecule resolution required to study low copy number gene expression products. This work presents a novel method for protein quantification at the single molecule level, Quantitative HaloTag-TMR labelling, and uses the technique to quantify the absolute numbers of the low copy number RecB, RecC and RecD subunits of the bacterial DNA repair enzyme RecBCD, finding each subunit is present at between two and eight molecules per cell with mean numbers per cell of 4.9, 4.7 and 4.5 respectively. Additionally single molecule mRNA FISH was used to quantify the mRNA levels of recB and recD within cells, with means of 0.21 and 0.31 mRNA per cell being observed respectively. Finally this work presents a new method for use detecting both mRNA and protein simultaneously in individual cells by combining the HaloTag and FISH protocols to give HaloFISH. This work introduces two novel techniques that allow for single cell examination of gene expression, and investigates RecBCD expression at the single molecule level.

No description available.

Frequently evidentiary items contain an insufficient quantity of DNA to obtain complete or even partial DNA profiles using standard forensic gentotyping techniques. Here, various methods of post PCR purification were evaluated for their effects on the sensitivity of fluophore-based allelic detection. A method of post PCR purification is described which increases the sensitivity of standard 28 cycle PCR such that low copy number DNA templates (<100 pg DNA) can be analyzed. Full profiles were consistently obtained with as little as 20 pg template DNA without increased cycle number. In mock case type samples with dermal ridge fingerprints, genetic profiles were obtained by amplification with 28 cycles followed by post-PCR purification whereas no profiles were obtained without purification of the PCR product. Allele drop-out, increased stutter, and contamination (allele drop-in) typical of LCN analysis were observed. A single incident of contamination was observed in a reagent blank (not duplicated upon re-amplification) however, no contamination was observed in negative amplification controls.

P1 prophage is stably maintained in E. coli as a low-copy-number plasmid. Stable maintenance of P1 is dependent on the function of the plasmid encoded partition system, parABS. ParA is the partition ATPase, ParB is the partition-site binding protein, and parS is the partition site. The concerted action of these proteins results in dynamic movement of the plasmid over the bacterial nucleoid, which results in its stable maintenance. Plasmid movement has been proposed to be caused by interactions between parS bound ParB and nucleoid bound ParA. In this thesis, I have identified a complex of ParA, ParB, and DNA that is capable of promoting plasmid stability. ParA, ParB, DNA interactions required the ATP bound conformation of ParA. The ParA-ParB-DNA complex was dynamically regulated by nucleotide hydrolysis, which promoted complex disassembly. Complex formation resulted from the cooperative binding of ParA and ParB to DNA. ParA-ParB and ParB-DNA interactions were both necessary for complex formation. ParA-ParB-DNA complex size was regulated by ParB stimulation of ParA-ATP hydrolysis. Microscopy demonstrated that complexes resulted in the association of multiple DNA molecules due to protein binding. The properties of complex assembly, dynamics, and DNA grouping lead me to propose a model where associations between ParA bound to the bacterial nucleoid and the partition complex mediated plasmid movement and localization.

P1 prophage is stably maintained in E. coli as a low-copy-number plasmid. Stable maintenance of P1 is dependent on the function of the plasmid encoded partition system, parABS. ParA is the partition ATPase, ParB is the partition-site binding protein, and parS is the partition site. The concerted action of these proteins results in dynamic movement of the plasmid over the bacterial nucleoid, which results in its stable maintenance. Plasmid movement has been proposed to be caused by interactions between parS bound ParB and nucleoid bound ParA. In this thesis, I have identified a complex of ParA, ParB, and DNA that is capable of promoting plasmid stability. ParA, ParB, DNA interactions required the ATP bound conformation of ParA. The ParA-ParB-DNA complex was dynamically regulated by nucleotide hydrolysis, which promoted complex disassembly. Complex formation resulted from the cooperative binding of ParA and ParB to DNA. ParA-ParB and ParB-DNA interactions were both necessary for complex formation. ParA-ParB-DNA complex size was regulated by ParB stimulation of ParA-ATP hydrolysis. Microscopy demonstrated that complexes resulted in the association of multiple DNA molecules due to protein binding. The properties of complex assembly, dynamics, and DNA grouping lead me to propose a model where associations between ParA bound to the bacterial nucleoid and the partition complex mediated plasmid movement and localization.

The availability of DNA samples that are of adequate quality and quantity is essential for any genetic analysis. The fields of forensic biology and clinical diagnostic pathology testing often suffer from limited samples that yield insufficient DNA material to allow extensive analysis. This study examined the utility of a recently introduced whole genome amplification method termed Multiple Displacement Amplification (MDA) for amplifying a variety of limited sample types that are commonly encountered in the fields of forensic biology and clinical diagnostics. The MDA reaction, which employs the highly processive bacteriophage φ29 DNA polymerase, was found to generate high molecular weight template DNA suitable for a variety of downstream applications from low copy number DNA samples down to the single genome level. MDA of single cells yielded sufficient DNA for up to 20,000,000 PCR assays, allowing further confirmatory testing on samples of limited quantities or the archiving of precious DNA material for future work. The amplification of degraded DNA material using MDA identified a requirement for samples of sufficient quality to allow successful synthesis of product DNA templates. Furthermore, the utility of MDA products in comparative genomic hybridisation (CGH) assays identified the presence of amplification bias. However, this bias was overcome by introducing a novel modification to the MDA protocol. Future directions for this work include investigations into the utility of MDA products in short tandem repeat (STR) assays for human identifications and application of the modified MDA protocol for testing of single cell samples for genetic abnormalities.