Stimulation or repression of gene expression by genome-wide regulatory mechanisms is an important epigenetic regulatory function which can act to efficiently regulate larger regions or specific groups of genes, for example by compensating for loss or gain of chromosome copy numbers. In Drosophila melanogaster there are two known chromosome-wide regulatory systems; the MSL complex, which mediates dosage compensation of the single male X-chromosome and POF, which stimulates expression from the heterochromatic 4th chromosome. POF also interacts with the heterochromatin inducing protein HP1a, which represses expression from the 4th chromosome but which also has been assigned stimulatory functions. In addition to these two, there is another more elusive and less well-characterized genome-wide mechanism called buffering, which can act to balance transcriptional output of aneuploidy regions of the genome (i.e. copy number variation). In my thesis, I describe the presence of a novel physical link between dosage compensation and heterochromatin; mediate by two female-specific POF binding sites, proximal to roX1 and roX2 on the X chromosome (the two non-coding RNAs in the MSL complex). These sites can also provide clues to the mechanisms behind targeting of chromosome-specific proteins. Furthermore, to clarify the conflicting reports about the function of HP1a, I have suggested a mechanism in which HP1a has adopted its function to different genomic locations and gene types. Different binding mechanisms to the promoter vs. the exon of genes allows HP1a to adopt opposite functions; at the promoter, HP1a binding opens up the chromatin structure and stimulates gene expression, whereas the binding to exons condense the chromatin and thus, represses expression. This also causes long genes to be more bound and repressed by HP1a. Moreover, I show that buffering of monosomic regions is a weak but significant response to loss of chromosomal copy numbers, and that this is mediated via a general mechanism which mainly acts on differentially expressed genes, where the effect becomes stronger for long genes. I also show that POF is the factor which compensates for copy number loss of chromosome 4.

<p>In Drosophila melanogaster, where males are XY and females are XX, dosage compensation is acheived by approximately two-fold upregulation of transcription of the single male X chromosome. This upregulation is mediated by the dosage compensation complex (DCC), which is assembled in a sequential manner on the male X chromosome and is composed of the two noncoding roX (RNA on the X) RNAs and at least five proteins, including the RNA helicase Maleless (MLE). MLE contains two highly conserved double stranded RNA binding domains (DRBDs) at the N terminus. We investigated the roles of the roX RNAs and MLE helicase through experiments using classical genetic methods to generate and analyze the effects of mutants and mutant transgenes, immunolocalization experiments to study MSL protein and roX RNA to chromosomes. For the first time in vivo, we demonstrate that MLE associates with double stranded RNA in a sequence non-specific manner that is independent of other DCC components. Importantly, we find that the DSRBDs of MLE are essential for dosage compensation but are not required for MLE localization to the male X chromosome. We propose that although the DSRBDs are not essential for ds RNA binding, they may act synergistically with other domains of MLE or other MSLs to associate with RNA in vivo. We propose that a MLE/ roX RNA association involving secondary structure formed by the roX RNAs may be involved in the assembly, stabilization, or function of the DCC.</p> / Dissertation

The thesis deals with the issue of indoor air quality of schools and kindergartens. It focuses particularly on the inadequate ventilation and the application of forced ventila-tion in these types of buildings. The proposed solution is applied to a kindergarten in Kuřim. Measurements of the C02 concentration levels were performed in the presence and absence of air conditioning. To elaborate the proposed solution a simulation was made using a software called ANSYS Fluent. Input values for the simulation were obtained from an experimental measurement of a ventilation diffuser made by a company called Climecon ROX using the PIV method. This diffuser was then installed in the kindergarten. The measure-ments were carried out in the framework of the project the experimental validation of numerical models of the air flow in buildings marked with FAST-S-6-3387.