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- Dynamics and interactions of nuclear proteins revealed by quantitative photobleaching microscopyPublication . Rino, José; Fonseca, M. Carmo, 1959-; Soares, Eduardo Ducla, 1944-The nucleus is a complex cellular organelle, exhibiting a high degree of organization and also a highly dynamic nature. Live cell imaging using fluorescent proteins (FPs) as molecular tags and photobleaching techniques have been essential in revealing the dynamic nature of the cell nucleus. In this thesis, these tools were used to study molecular dynamics and interactions inside this cellular compartment. Fluorescence Recovery After Photobleaching (FRAP) and Fluorescence Loss In Photobleaching (FLIP) were used to analyze the kinetic behavior of spliceosome components SmE, U2AF65, U2AF35, SF1 and SC35 in the nucleus of living cells. The recruitment mechanism of splicing factors (SFs) to the sites of transcription is still poorly understood. Our results rule out the hypothesis that a transcription specific signal recruits SFs from the speckles. They also suggest the formation of multi-protein complexes distinct from the spliceosome. The existence of these complexes was confirmed by Fluorescence Resonance Energy Transfer (FRET) techniques, which revealed that SFs could interact with each other even in the absence of active splicing. A novel U2AF65 self-interaction was also detected, suggesting altogether that levels of SFs in speckles are consistent with self-organization mechanisms. The intranuclear mobility of mRNPs was studied using two GFP-tagged mRNA-binding proteins, PABPN1 and TAP, as mRNA markers. A novel FLIP method was devised to quantify the mobility of the RNA-bound and unbound pools of molecules and used to test whether myosin motors were implicated in mRNP movement. We show that this is not the case and that myosin inhibition appears to affect transcription instead. A novel FLIP after Photoactivation method was developed to study the nucleocytoplasmic exchange dynamics of nuclear proteins, yielding the permanence times of molecules inside the nucleus. The method was used to study the role of the structural domains of TAP in its shuttling activity.
- Frontiers in fluorescence microscopyPublication . Rino, José; Braga, José; Henriques, Ricardo; Carmo-Fonseca, MariaHow we see organisms and cells depends on the tools at our disposal. For over 150 years, biologists were forced to rely on fixed, dehydrated and stained specimens in order to guess how the living cells could function. It all changed abruptly during the last two decades when the rapid development of novel imaging techniques revolutionized the way scientists look at the structures of life alive.