The major source of calcium for the developing chick embryo is the eggshell. However, the actual mechanism of calcium solubilization from the shell is unknown. The temporal correlation of carbonic anhydrase activity to calcium movement implies that an acidic environment is essentail. To clarify the role of carbonic anhydrase in calcium solubilization and uptake by the chorioallantoic membrane of the chick embryo treatment effects on embryo development, carbonic anhydrase activity and calcium and pH levels were investigated. The treatments consisted of solutions of acid, base, calcium and strontium chlorides, and the enzyme inhibitor-acetazolamide.Experimental sampling was conducted from eleven to sixteen days of incubation. The treatments were administered daily by dipping the eggs into a treatment solution with subsguent sampling on the following day. The acid treatment solution produced a significant (P≤0.05) increase in calcium solubilization and a decrease in carbonic anhydrase activity from the control levels. The base treatment solution produced a significant decrease in calcium solubilization and an increase in carbonic anhydrase activity from the control levels. The calcium chloride treatment solution (providing a partial source of a calcium non-carbonate compound) and the strontium chloride treatment solution (providing a partial source of a non-calcium non-carbonate compound) showed no overall effect on embryonic calcium concentrations. However, there was a decrease in carbonic anhydrase activity from that of the control. This decrease did not appear to be due to a calcium mediated process but was more sensitive to changes in bicarbonate or carbonate levels. Treatments with acetazolamide demonstrated that there was a decrease in carbonic anhydrase activity and also a decrease in calcium transported. However, when an acid treatment was combined with the acetazolamide treatment, calcium was transported even though carbonic anhydrase activity was greatly suppressed. These results confirm that carbonic anhydrase activity appears to be fimctioriing in calcium solubilization and maintenance of the embryonic acid-base balance. It does not appear that the enzyme functions primarily in the transport of calcium across the chorioallantoic membrane. / Land and Food Systems, Faculty of / Graduate

No description available.

Surgical removal of presumptive bursal tissue at 72 hr in ovo results in high mortality before hatching and low survival in the first week thereafter. The viable chicks are underweight and usually remain so. Both the spleen and thymus of the bursectomized (Bx) chicks are reduced in size and lymphoid population. The effect on the thymus may be related to stress and subsequent adrenal cortical activity or may reflect some endocrine function of the bursa necessary for the maturation of thymic lymphoid tissue. The effect on the spleen seems to be more direct. In the absence of the primary level organ which induces maturation of the stem cells, the number of germinal centres in the secondary level organ is reduced. Some of the remaining germinal centres may be of T-cell origin, although these cells are more commonly found in diffuse lymphoid areas. The bulk of the germinal centres found in the Bx spleen must be of B-cell origin. Repeated stimulation of the humoral immune system with antigens and mitogens elicits a response in some Bx birds. The response is generally not found in the primary stimulation and is rarely of the magnitude of a normal response even after several stimulations. Antibody production may be limited to IgM type immunoglobulin; further studies are necessary to verify this. Autopsy and histological examination of the tissues of the responsive birds failed to show any evidence of residual bursal tissue. Whether these findings constitute proof of the role of the bursa in the humoral immune response or whether they reflect the broader consequences of bursectomy in the development of the bird requires further study. The inductive capacities of the bursa and the source and autonomous capacity of the stem cells thought to be induced in the bursa should also be investigated. The effects of early hormonal and late surgical bursectomy are similar to those found in this study, where an early embryonic surgical technique was used to avoid the possible complications of these other methods. / Land and Food Systems, Faculty of / Graduate

Kwan Suet-ming. / Bibliography: leaves 75-94 / Thesis (M.Ph.)--Chinese University of Hong Kong, 1984

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Call number: LD2668 .T4 1984 S88 / Master of Science

A Dissertation submitted to the Faculty of Science, University of Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. 2015. / Prdm1/Blimp1 is a transcription factor whose mechanism of action is mainly repression; however it has been identified as an activator in some cases. As a transcriptional repressor, it plays multiple roles during embryonic development, including neural crest specification. Prdm1 acts by repressing large sets of genes via sequence specific recruitment of co-repressors, many of which are epigenetic modifiers. Neural crest is a transient, migrating cell population that gives rise to a number of diverse cell lineages that form important structures in the vertebrate embryo. Examples of these include peripheral nervous system, melanocytes and cranial cartilage. Prdm1 is expressed during neural crest specification in Xenopus, zebrafish and lamprey. The expression of Prdm1 had not yet been investigated in the neural crest during chick embryonic development. The mechanism of Prdm1 action or the nature of possible binding partners that mediate its effects in the neural crest had not yet been addressed. Prdm1 binding partners are known to play important roles during embryonic development, yet in many cases no spatiotemporal expression analysis during early vertebrate development has been performed. Single and double in situ hybridization for Prdm1 and all the binding partners was performed to determine localization of mRNA during early stages of chick embryonic development. We report the expression patterns of Prdm1 and seven of its known or putative binding partners (Hdac1, Hdac2, Tle1, Tle3, G9a, Prmt5 and Lsd1) during early stages (HH4-HH10) of chicken embryogenesis. Prdm1 expression was observed in the neural plate border and pre-migratory neural crest during chick development. Six Prdm1 binding partners (except Tle1) are co- expressed with Prdm1 in the prospective neural plate border at HH4-HH6, and all seven show strong and specific expression in the neural plate border at HH7-HH8, suggesting all of them co-operate with Prdm1 during neural crest development in chick embryos. Future work will focus on protein interaction studies in order to directly demonstrate the association between Prdm1 and the binding partners it co-localizes with.

The concept of genetic penetrance, "the frequency of manifestation of a genetic factor," was introduced by Timofeef-Ressovsky (Naturwissenschaften 19:493,1931). Incomplete penetrance has been used to explain the absence of phenotypic expression when otherwise anticipated. Studies of Embryonic Chick Edema, ECE (Poultry Sci. 77(suppl. 1):69, 1998) have been conducted in order to determine the origins for incomplete penetrance of this disorder. ECE was originally reported as the expression of two autosomal recessive loci with incomplete penetrance. Pedigreed inter se mating of ECE individuals have resulted in familial incidences ranging for 0 to 100% with a mean of 48.2% in the most recent generation selected. With consideration of a third contributing locus, current data and 2 sets of previous data were evaluated. Heterogeneity and pooled chi square tests when applied to the data sets support the hypothesis that ECE was the result of two completely dominant loci and one homozygous recessive locus. / Graduation date: 2004

Graduation date: 1990

No description available.