The bladder urothelium is a stratified epithelium that interconnects with the ureters to form the urinary outflow tract. A defining feature of the urothelium is its luminal population of uroplakin-expressing Superficial cells that function to create a protective, waterproof barrier. As such, proper differentiation of urothelial cell types during development and regeneration is essential for bladder function. Previous work has demonstrated that the urothelium is derived from a transient endodermal progenitor population, termed P-cells. However, two remaining uncertainties are the timing and regulation of P-cell fate. Here we show through lineage tracing that the specification of P-cells into luminal, uroplakin-expressing cell types is temporally related to the timing of endogenous retinoic acid (RA) signaling. Selective inhibition of RA signaling in P-cells through ShhCre-driven expression of the RaraT403 dominant-negative (RaraDN) mutant receptor redirected cells towards an abnormal K14+ basal fate that underwent Notch-mediated stratification into a keratinizing squamous epithelium that largely resembled epidermis. Transcriptome analysis of mutant P-cells identified aberrant expression of transcriptional regulators that have critical roles in squamous differentiation and epidermal commitment. Interestingly, inhibition of RA signaling in P-cells also resulted in improper connections between the ureters and the bladder through reduced Caspase 9-mediated apoptosis and remodeling of the common nephric duct. These observations demonstrate that RA signaling in bladder urothelial progenitor cells is required not only for proper epithelial differentiation, but also for regulating inter-organ signals that orchestrate morphogenesis of the urinary outflow tract.

The segregation of progenitor somatic cells from those of the primordial germ cells during early cleavage divisions occurs in certain copepods exhibiting the phenomenon of chromatin diminution during early embryogenesis. These species provide an interesting alternative to the usual reproductive strategy of other species of freshwater cyclopoid copepods. Levels of DNA for the soma and germ cells of Mesocyclops longisetus have been determined for individual nuclei by using Feulgen-DNA cytophotometry to monitor changes of DNA amounts during gametogenesis and early cleavage stages of embryogenesis. Germ cell nuclei of both female and male adults contain marked elevations of DNA, far in excess of expected 4C DNA level for their replication prior to meiosis. The elevated amounts of DNA in these germ cells are equivalent to the elevated DNA content found during the gonomeric divisions observed in embryos. Following the gonomeric divisions there is roughly a 40% loss of germ cell heterochromatin during the chromatin diminution stages of embryogenesis. The role of this excised DNA remains unclear.

Cytokinesis is the final chapter of cell division and its last page is abscission, the physical separation of two daughter cells. During cytokinesis of vertebrate cells, two future daughter cells are connected by an intercellular bridge within which the midbody (MB) is positioned. Since becoming the focus of intense investigations on cytokinesis completion, MB is now perceived as a complicated organelle where multiple pathways for abscission are targeted and coordinated. However, whether post-mitotic midbodies, the midbody derivatives (MBds), would be retained by either daughter cell post-abscission remains unexplored. In addition, how cells manage the fate of inherited MBds is also unclear or only sketchily proposed. Finally, whether the inherited MBds in cells may play non-cytokinetic roles is also unaddressed. In the first chapter, I review the historical and current understanding of MBs, with emphasis on their roles in cytokinesis whereas potential non-cytokinetic roles are also covered. In the second chapter, the aforementioned three questions are sequentially addressed. First, the newly-formed MBd appears to be inherited by the daughter cell with the older centrosome. Second, MBds are not only inherited but also accumulated in cancer and pluripotent stem cells, but not in normal somatic (differentiated) cells. In normal somatic cells, MBds are within membrane-bound compartments for lysosomemediated degradation via autophagosome engulfment. This partially explains why MBd-accumulation is rarely observed in these cells. In contrast to the previous model, colleagues and I showed that MBd-accumulation correlates well with the autophagosomal-lysosomal activity, but not with the proliferation rate. Finally, the experimental increase of MBd levels appears to enhance the anchorage-independent growth in cancer cells and the efficiency of reprogramming in fibroblasts. In the last chapter, I conclude our findings and discuss future directions in two aspects.

To understand the gene regulatory network (GRN) governing caudal hindbrain formation in embryonic zebrafish, several early expressed factors have been manipulated, and multiple genetic mutants have been characterized. Such analyses have identified morphogens such as Retinoic Acid (RA) and Fibroblast growth factors (FGFs), as well as transcription factors like hoxb1b, hoxb1a, hnf1ba, and valentino as being required for rhombomere (r) r4-r6 formation in zebrafish. Considering that the caudal hindbrain is relatively complex – for instance, unique sets of neurons are formed in each rhombomere segment – it is likely that additional essential genes remain to be identified and integrated into the caudal hindbrain GRN. Our results reveal that r4 gene expression is unaffected by the individual loss of hoxb1b, hoxb1a or RA, but is under the combinatorial regulation of RA together with hoxb1b. In contrast, r5/r6 gene expression is dependent on RA, FGF, hnf1ba and valentino – as individual loss of these factors abolishes r5/r6 gene expression. Analysis of six mutant lines (gas6, gbx1, sall4, eglf6, celf2, and greb1l) did not reveal rhombomere or neuronal defects, but transcriptome analysis of one line (gas6 mutant) identified expression changes for genes involved in several developmental processes – suggesting that these genes may have subtle roles in hindbrain development. We conclude that r4-r6 formation is relatively robust, such that very few genes are absolutely required for this process. However, there are mechanistic differences in r4 versus r5/r6, such that no single factor is required for r4 development while several genes are individually required for r5/r6 formation.

Bibliography: p. 297-320. / In this thesis we thus wish to consider the concept of self-organization as an overall paradigm within which various theoretical approaches to the study of development may be described and evaluated. In the process, an attempt is made to give a fair and reasonably comprehensive overview of leading modelling approaches in developmental biology, with particular reference to self-organization. The work proceeds from a physical or mathematical perspective, but not unduly so - the major mathematical derivations and results are relegated to appendices - and attempts to fill a perceived gap in the extant review literature, in its breadth and attempted impartiality of scope. A characteristic of the present account is its markedly interdisciplinary approach: it seeks to place self-organization models that have been proposed for biological pattern formation and morphogenesis both within the necessary experimentally-derived biological framework, and in the wider physical context of self-organization and the mathematical techniques that may be employed in its study. Hence the thesis begins with appropriate introductory chapters to provide the necessary background, before proceeding to a discussion of the models themselves. It should be noted that the work is structured so as to be read sequentially, from beginning to end; and that the chapters in the main text were designed to be understood essentially independently of the appendices, although frequent references to the latter are given. In view of the vastness of the available information and literature on developmental biology, a working knowledge of embryological principles must be assumed. Consequently, rather than attempting a comprehensive introduction to experimental embryology, chapter 2 presents just a few biological preliminaries, to 'set the scene', outlining some of the major issues that we are dealing with, and sketching an indication of the current status of knowledge and research on development. The chapter is aimed at furnishing the necessary biological, experimental background, in the light of which the rest of the thesis should be read, and which should indeed underpin and motivate any theoretical discussions. We encounter the different hierarchical levels of description in this chapter, as well as some of the model systems whose experimental study has proved most fruitful, some of the concepts of experimental embryology, and a brief reference to some questions that will not be addressed in this work. With chapter 3, we temporarily move away from developmental biology, and consider the wider physical and mathematical concepts related to the study of self-organization. Here we encounter physical and chemical examples of spontaneous structure formation, thermodynamic considerations, and different approaches to the description of complexity. Mathematical approaches to the dynamical study of self-organization are also introduced, with specific reference to reaction-diffusion equations, and we consider some possible chemical and biochemical realizations of self-organizing kinetics. The chapter may be read in conjunction with appendix A, which gives a somewhat more in-depth study of reaction-diffusion equations, their analysis and properties, as an example of the approach to the analysis of self-organizing dynamical systems and mathematically-formulated models. Appendix B contains a more detailed discussion of the Belousov-Zhabotinskii reaction, which provides a vivid chemical paradigm for the concepts of symmetry-breaking and self-organization. Chapter 3 concludes with a brief discussion of a model biological system, the cellular slime mould, which displays rudimentary development and has thus proved amenable to detailed study and modelling. The following two chapters form the core of the thesis, as they contain discussions of the detailed application of theoretical concepts and models, largely based on self-organization, to various developmental situations. We encounter a diversity of models which has arisen largely in the last quarter century, each of which attempts to account for some aspect of biological pattern formation and morphogenesis; an aim of the discussion is to assess the extent of the underlying unity of these models in terms of the self-organization paradigm. In chapter 4 chemical pre-patterns and positional information are considered, without the overt involvement of cells in the patterning. In chapter 5, on the other hand, cellular interactions and activities are explicitly taken into account; this chapter should be read together with appendix C, which contains a brief introduction to the mathematical formulation and analysis of some of the models discussed. The penultimate chapter, 6, considers two other approaches to the study of development; one of these has faded away, while the other is still apparently in the ascendant. The assumptions underlying catastrophe theory, the value of its applications to developmental biology and the reasons for its decline in popularity, are considered. Lastly, discrete approaches, including the recently fashionable cellular automata, are dealt with, and the possible roles of rule-based interactions, such as of the so-called L-systems, and of fractals and chaos are evaluated. Chapter 7 then concludes the thesis with a brief assessment of the value of the self-organization concept to the study of biological development.

Juvenile C. errans do not feed on particulate matter and yet they can survive, apparently unchanged, for several months before maturing into the adult stage which feeds on the eggs of Cancer magister. The significance of glycogen as an energy source for maintenance of the juvenile form was investigated.

Down Syndrome is a human condition caused by an extra copy of a #21 chromosome. At least one to two percent of free (not translocated) trisomy 21 cases are mosaics, i.e., they have two or more distinct cell lines. Usually, one cell line is 47 ,XX or XY ,+21 while the other cell line is normal 46,XX or 46,XY. The purpose of the study was to establish the etiologies of the separate cell lines by determining whether the zygote was trisomic or normal. Meiotic non-disjunction in the formation of a gamete could lead to a trisomic zygote; loss of a #21 chromosome during a later mitotic division could then lead to a chromosomally normal cell line. Alternatively, a mitotic error in a normal embryo can produce a trisomy 21 cell line.

No description available.

No description available.

A period of cell death during a critical period early in life is responsible for causing permanent structural changes to many brain areas, but it is not known whether cell death plays a role in brain organization outside of early postnatal life. Puberty is considered a second sensitive period because the brain is the target organ of gonadal hormones. This study looked at global and regional patterns of cell death during pre-puberty and puberty in the mouse brain. My findings show there is more cell death happening during pre-puberty than during puberty. Cell death does happen during puberty but at adult levels. Furthermore females at P20 have more dying cells than males globally and in the hippocampus, but no other sex differences were observed. Knocking out the Bax gene, which is important for neuronal death, had only a modest effect on cell death during pre-puberty and puberty compared to what has been shown in younger ages. My findings demonstrate that prepubertal animals have more cell death than pubertal animals. Also, since Bax gene deletion only had a modest effect on cell death, cell populations other than neurons may be dying during these periods.