No description available.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, for the Degree of Doctor of Philosophy. / The comparative structure of the diencephalon was investigated in the elephant shrew, the tree-shrew and several of the prosimian and anthropoid primates, including man. The brains were perfused with and fixed in formol saline. Most of those brains were sectioned transversely; others horizontally and sagitaliy. Sections of the diencophalon were stained with the cresyl-echt violet method for cytology and the study of cytoarchitectonics, and with the Kluver and Barrera, and Simmons techniques for myeloarchitectonics. / WHSLYP2017

The development of the diencephalon can be summarised as a process in which cells that initially appear similar give rise to a complex structure that contains a variety of cell groups called nuclei. It involves two stages: the early patterning of the diencephalic prosomeres and the later formation of the individual nuclei. It has been shown that transcription factors and morphogens regulate the first stage but their further effects on the second stage remain unclear. The ventral lateral geniculate nucleus (vLGN) is involved in the visual system and is shown to have complex origins from the thalamus, the zona limitans intrathalamica (ZLI) and the prethalamus. The transcription factor Pax6 is involved in the development of brain structures including the cortex, the diencephalon and the major axonal tracts in the forebrain by playing a multifaceted role in patterning, proliferation, differentiation, migration and axon guidance. It is known that Pax6 is essential in setting up the prosomeric boundaries in the developing diencephalon but its role in the formation of individual nuclei has not yet been explored. By using a conditional Pax6 knock-out mouse driven by Zic4Cre with a green fluorescent protein (GFP) reporter showing the Cre activity, the formation of the thalamic nuclei vLGN, dorsal lateral geniculate nucleus (dLGN) and VP (ventral posterior nuclei) was examined in postnatal day 0 (P0) Pax6+/+, Pax6fl/+ and Pax6fl/fl pups. Using this mouse model, I found an increase in nuclear volume at the rostral level and a global decrease in cell density in the P0 Pax6fl/fl vLGN, whereas in the dLGN an increase of GFP+ve cell proportion was observed. In Pax6fl/+, I found an increase in GFP+ve cell proportion in the caudal part of the vLGN and across the dLGN. No significant change was observed in the VP in either the Pax6fl/+ or the Pax6fl/fl. The defects in the vLGN and dLGN could be caused by: 1. disruption of the expression of patterning factors such as Shh and Nkx2.2; 2. cell proliferation defcts and abnormal apoptosis; 3. ocular developmental defects; 4. failure in cell sorting/migration; 5. cell fate change. During my PhD, I tested the first three theories and explored the fourth but was not able to pursue the last due to the time limit of the project. To test the hypothesized mechanisms underlying those defects seen in the vLGN and dLGN, I performed BrdU labelling to study the time origin of cells that contribute to these two nuclei and discovered that E11.5 and E12.5 are the main ages when these cells and the GFP+ve subpopulation are born. Then I carried out experiments to examine the cell proliferation and cell apoptosis in the thalamus (pTH-R, rostral part of the progenitor zone of the thalamus, and pTH-C, caudal part of the progenitor zone of the thalamus) and the prethalamus (Pth) from E11.5 to E13.5 and found: 1. the proliferation rate decreased in the pTH-R in Pax6fl/+ at E11.5; 2. the growth fraction decreased in both pTH-C and pTH-R in E12.5 Pax6fl/fl; 3. there is no change in cell proliferation in the GFP+ve subpopulation; 4. no abnormal apoptosis is observed in either the whole cell population or the GFP+ve subpopulation. Judging by the amplitude of the change in proliferation in the pTH-R and pTH-C at E11.5 and E12.5, it is unlikely that these changes alone are responsible for the phenotypes seen in P0 vLGN and dLGN. Then I examined the expression patterns of Shh and Nkx2.2 and the expansion of both was observed in Pax6fl/fl at both E12.5 and E13.5, which could explain the volume change of the vLGN but not the change in the proportion of GFP+ve subpopulation in both the vLGN and dLGN. Then I continued to examine if the ocular input from the retinal ganglionic cells are severely affected by the deletion of Pax6 and found no gross change in the conditional mutants, which rejected the ocular developmental defects theory. At the end of my PhD, I performed a BrdU short-term survival experiment and a brain slice culture combined with live imaging experiment to explore the possibility of abnormal cell migration causing the vLGN and dLGN phenotypes and found that the cells moving along the border of the thalamus and prethalamus move faster in the Pax6fl/fl than in the Pax6fl/+, but rather than moving directly toward the lateral surface of the diencephalon, they take a detour. These findings indicate that the deletion of Pax6 causes minor changes in the proliferation of E11.5 to E13.5 diencephalon and expansion of regional marker expression such as Shh and Nkx2.2, which could potenially affect the volume and change the proportion of GFP+ve cells in P0 vLGN and dLGN. Migration defects caused by Pax6 could also contribute to the phenotype observed in those two nuclei. Potential cell fate change caused by Pax6 deletion could be another factor that contributes to the defects in the conditional mutants. More work needs to be done to test the migration defect and cell fate change hypotheses in future.

No description available.

No description available.

Diencephalic development requires the transcription factors Pax6 and Barhl2 in order to proceed correctly. Both genes are necessary for the normal development of the organizer region known as the zona limitans intrathalamica (ZLI). The ZLI goes on to pattern the diencephalon via its secretion of the morphogen Shh, which inhibits the expression of Pax6. These findings suggest that interactions between Pax6, Barhl2 and Shh may be involved in the control of diencephalic development. This project aims to characterise these interactions and investigate their roles. The expression domains of Pax6 and Barhl2 were mapped during the early development of the mouse diencephalon. Qualitative approaches were employed to confirm the high complementarity of their expression domains and obtain evidence of a mutually repressive relationship existing between the two genes. The findings from a quantitative analysis suggested that this inhibition is incomplete within the thalamus. Investigations using the Pax6-null mutant mouse confirmed that in the absence of Pax6 the thalamic Barhl2 expression domain expands beyond the ventricular zone, the site of thalamic neurogenesis. The influence of Shh signalling on the expression of Pax6 and Barhl2 was investigated via a gain-of-function approach utilising in utero electroporation to activate the Shh pathway. This led to a downregulation of both Pax6 and Barhl2 within the thalamus. In Shh loss-of-function experiments drug treatment with the Shh antagonist vismodegib led to an upregulation of Barhl2 and the loss of the GABAergic pTh-R in the Pax6-null mutant thalamus, but not in the wild type thalamus, suggesting that Pax6 and Shh may be required to inhibit Barhl2 in order for GABAergic neurogenesis to proceed. Barhl2 expression was detected in the Shh-null mutant mouse confirming that, in contrast with their homologues in Drosophila, Shh may be expressed downstream of Barhl2. Together these findings have been used to develop a novel model of thalamic development in which Barhl2 induces ZLI development, inhibition of Barhl2 by Pax6 restricts its expansion, and secretion of Shh by the ZLI then goes on to inhibit Pax6 and Barhl2 in the pTh-R while mutual repression between Pax6 and Barhl2 modulates neurogenesis in the more caudal regions of the thalamic neuroepithelium.

Honors Project--Smith College, Northampton, Mass., 2010. / Includes bibliographical references (p. 91-96).

Thesis (M.A.)--State University of New York at Binghamton, Department of Psychology, 2005. / Includes bibliographical references.

<p>Chicken and Japanese quail are commonly used models in developmental and sex specific neuroendocrine research. There is relatively little known about the mechanisms behind their sex specific brain development, especially regarding the impact of the sex chromosomes (male: ZZ, female ZW) in relation to gonadal hormones. This thesis explores several aspects of these processes. Gene expression analysis with cDNA and Affymetrix arrays on brain tissue from both pre-gonadal embryos and embryos with differentiated gonads indicate a strong sex chromosomal presence in sexual dimorphic somatic tissue development in both chicken and Japanese quail. This sex chromosome pattern seems to remain in adult brain tissue. The data demonstrates that chicken males exhibit a significant level of Z-gene dosage compared to females in both somatic and germ line derived embryonic tissues. Several avian sex determination gene candidates (MHM non-coding RNA, DMRT1, HINTW, and HINTZ) were analyzed by real-time PCR. DMRT1 is dosage compensated in male brain tissue, in contrast to its reported gene dosage in male gonads. Early embryonic ethinylestradiol (EE2) exposure did not affect male or female neural gene expression patterns during later development. A peptidomics analysis on quail embryonic day 12 (ed12) and ed17 diencephalon by LC-MS identified over 60 endogenous peptides and analyzed the expression patterns for 38 of them with regard to age, sex and early EE2 exposure. There was a general upregulation between ed12 and ed17, but no clear sex effects were detected. Multivariate analysis indicates that EE2 exposed individuals differ from control individuals in a gender independent manner, and that Gonadotropin-inhibiting hormone related peptide 2 (GnIH-RP2) is a candidate for EE2 induced peptidomic alterations in male embryonic brain.</p>

Chicken and Japanese quail are commonly used models in developmental and sex specific neuroendocrine research. There is relatively little known about the mechanisms behind their sex specific brain development, especially regarding the impact of the sex chromosomes (male: ZZ, female ZW) in relation to gonadal hormones. This thesis explores several aspects of these processes. Gene expression analysis with cDNA and Affymetrix arrays on brain tissue from both pre-gonadal embryos and embryos with differentiated gonads indicate a strong sex chromosomal presence in sexual dimorphic somatic tissue development in both chicken and Japanese quail. This sex chromosome pattern seems to remain in adult brain tissue. The data demonstrates that chicken males exhibit a significant level of Z-gene dosage compared to females in both somatic and germ line derived embryonic tissues. Several avian sex determination gene candidates (MHM non-coding RNA, DMRT1, HINTW, and HINTZ) were analyzed by real-time PCR. DMRT1 is dosage compensated in male brain tissue, in contrast to its reported gene dosage in male gonads. Early embryonic ethinylestradiol (EE2) exposure did not affect male or female neural gene expression patterns during later development. A peptidomics analysis on quail embryonic day 12 (ed12) and ed17 diencephalon by LC-MS identified over 60 endogenous peptides and analyzed the expression patterns for 38 of them with regard to age, sex and early EE2 exposure. There was a general upregulation between ed12 and ed17, but no clear sex effects were detected. Multivariate analysis indicates that EE2 exposed individuals differ from control individuals in a gender independent manner, and that Gonadotropin-inhibiting hormone related peptide 2 (GnIH-RP2) is a candidate for EE2 induced peptidomic alterations in male embryonic brain.