It has been a long-standing mystery how complex biological structures emerge from such seemingly uncoordinated building blocks as cells and tissues, in the presence of only minimal environmental... Show moreIt has been a long-standing mystery how complex biological structures emerge from such seemingly uncoordinated building blocks as cells and tissues, in the presence of only minimal environmental guidance. In particular, unifying descriptions independent of microscopic details of a specific organism are rare. In recent years, hydrodynamics has successfully been applied to describe certain types living systems. The thesis is concerned with understanding different aspects of structure formation in active liquids and biological systems. In the first chapter we investigate the coarsening dynamics in the Toner-Tu theory and compare it with an experimental colloidal system. Afterwards, we investigate the effect of chirality in active nematics, with applications to biological tissues. In the last part we derive and study a model to explain geometric deformations due to the presence of activity. The resulting dynamics might be able to explain morphogenetic processes. Show less
We developed the bitterling as a unique, well-studied model organism in the area of the evolutionary ecology of brood parasitism. The bitterling-mussel relationship, interspecific mussel host... Show moreWe developed the bitterling as a unique, well-studied model organism in the area of the evolutionary ecology of brood parasitism. The bitterling-mussel relationship, interspecific mussel host preference, and mussel gill structure are studied in detail, to help understand the developmental adaptation of bitterling embryos in response to their mussel hosts. Our complete stage series of the bitterling species R. ocellatus in Chapter 2 is a new, character-based systems that are compatible with the widely-used zebrafish staging system. With time-lapse video, we demonstrated the dynamic processes of hatching moment of the rosy bitterling in real time, which indicates the hatching process is mechanical rather than enzymatic. In Chapter 3, we described the neuroanatomy of bitterling for the first time, filling the gaps in the previous embryonic research in various bitterling taxa. Combined with the molecular analysis of brain early development in Chapter 4, brain development in the rosy bitterling is compared with that in the zebrafish. In Chapter 5, we studied the morphogenetic process of blastokinesis in the bitterling embryo, and its possible relation to brood parasitism. Show less
Bacteria have the ability to alter their morphology in order to adapt to changing environments. We have investigated the role of the cell envelope in the development and stress-adaptation... Show moreBacteria have the ability to alter their morphology in order to adapt to changing environments. We have investigated the role of the cell envelope in the development and stress-adaptation strategies of Actinobacteria. Here, we demonstrate how cryo-electron microscopy techniques can be used as efficient tools to study cell envelope of various bacteria. An in-depth study on the Streptomyces cell wall with cryo-electron tomography reveals the structural complexity of the Gram-positive cell wall in apically growing bacteria. Additionally, we report the formation of intracellular membrane accumulations in Streptomyces as a result of exposure to a stress-inducing agent. Furthermore, we studied the ability of the filamentous actinomycete Kitasatospora viridifaciens to extrude wall-deficient cells or S-cells upon exposure to hyperosmotic stress. We characterized the structural alterations associated with S-cell formation using cryo-electron microscopy and reveal that S-cell formation requires cytoskeletal protein FilP in K. viridifaciens. To summarize, this thesis provides new insights in the structural complexity and stress-induced alterations of the bacterial cell envelope. Show less
The filamentous soil bacteria of the genus Streptomyces are commercially exploited for the production of a wide range of natural products such as antibiotics, anticancer agents and... Show moreThe filamentous soil bacteria of the genus Streptomyces are commercially exploited for the production of a wide range of natural products such as antibiotics, anticancer agents and immunosuppressants. Additionally, there is a strong interest in the use of these bacteria for the production of industrial proteins. Optimal production of these secondary metabolites and enzymes is tightly coupled to morphology. However, relatively little is known about the genetic determinants influencing the morphology of streptomycetes in liquid-grown cultures. The work presented in this thesis focuses on the formation of extracellular macromolecules and their influence on morphogenesis, with a special emphasis on the role of the cellulose synthase-like protein CslA and the radical copper oxidase GlxA in the production of a tip-localized glycan. This research is of fundamental importance for understanding the determinants of growth and development of this multicellular model organism, and at the same time may help us to further optimize their exploitation for the industrial production of secondary metabolites and enzymes. Show less
The research described in this thesis aims to get more fundamental insights in the molecular mechanisms used by Aspergillus niger in relation to control morphology and protein secretion. Knowledge... Show moreThe research described in this thesis aims to get more fundamental insights in the molecular mechanisms used by Aspergillus niger in relation to control morphology and protein secretion. Knowledge on these two aspects is highly relevant to further optimization of A.niger as a cell factory Show less
Supraventricular tachycardias (SVTs) are amongst the most commonly encountered cardiac arrhythmias in clinical practice in both children and adults. The causative mechanisms underlying the... Show moreSupraventricular tachycardias (SVTs) are amongst the most commonly encountered cardiac arrhythmias in clinical practice in both children and adults. The causative mechanisms underlying the appearance of most of these SVTs have however still remained as intriguing as they are unexplained. In this thesis, cardiac development is analyzed in relation to the etiology of clinical supraventricular arrhythmias with a special focus on structure-function relations. Firstly, in PART I of this thesis, both the (patho) physiological development of the annulus fibrosus cordis and the etiological origin of clinical accessory AV pathway (AP) mediated AVRT in children and adults is analyzed in experimental animal models and human sections. Secondly, in PART II of this thesis a review of the different ontogenic theories on the embryonic development of the AV Node (AVN) in literature is followed by an experimental study postulating a new concept on the developmental origin of the AVN in relation to the etiology of AV Nodal Reentrant Tachycardia (AVNRT). As a general introduction to both these basic research (I & II) and the clinical (III) parts of this thesis, structural cardiac development in avians (with references to equivalent mouse and human developmental timelines) (Figure 1) will first be described since the development of the cardiac conduction system (CCS) and structural cardiogenesis are intimately related. Next, the developmental transitions in impulse propagation and the construction of the individual components of the specialized CCS and the AVN in particular will be shortly outlined. Following a description of the changes in electrocardiograms (ECGs) during cardiogenesis, current concepts on the transitions in ventricular activation sequences during embryogenesis will be discussed. Thereafter, contemporary knowledge on the development of the isolating annulus fibrosis, the key structure involved in AP persistence, in relation to general CCS development will be reviewed. Subsequently, relevant genera l characteristics of the different animal models and the immunohistochemical markers used in this thesis are briefly discussed. Following the description of the structural basics of cardiogenesis, attention will be focused on current knowledge of clinical SVTs in neonates and children and the treatment of these arrhythmias. These therapeutic clinical issues will be further outlined in PART III of this thesis. Show less
