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Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 165-179). Also available via the Internet.

Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1933. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed July 21, 2010) Includes bibliographical references (p. 26).

Ultrastructural observations on the six-day chick embryo lens reveal that fibre cell differentiation, which involves extensive cell elongation, is characterized by the presence of numerous oriented microtubules and by marked changes in intercellular relationships which are felt to be important for cell extension. Increased Golgi activity in cells initiating elongation appears to be related to the formation of intercellular junctions and the elaboration of new surface membrane. Studies concerning the differentiation in vitro of anterior lens epithelia demonstrate that their cells elongate either to a great extent or to a limited extent, depending on factors deriving from the epithelial conformation.The conformation of an explanted anterior lens epithelium can be manipulated so that its cells elongate consistently to either a limited or a great extent. These cells, whether elongated to a limited or to a great extent, are ultrastructurally similar with respect to features reflecting cytoplasmic differentiation, including those important for morphogenesis. Their fine structure closely resembles that of fibre cells differentiating in vivo. The cells of anterior lens epithelia differentiating in vitro, whether elongating to a limited or to a great extent, are the same in terms of the nature and relative proportions of their soluble proteins as indicated by polyacrylamide gel electrophoresis. There is a change in the relative proportions of the soluble proteins accumulated by the anterior lens epithelia when they differentiate in vitro that is similar to that which occurs in cells undertaking fibre cell differentiation in vivo. It is concluded that those factors deriving from the conformation of the anterior lens epithelium that affect the degree of elongation of its cells differentiating in vitro are physical in nature. Since such physical factors are important with regard to restraining or encouraging the expression of morphogenetic potential in vitro, it is suggested that similar physical forces are important in lens morphogenesis in vivo. Observations concerning anterior lens epithelia elongating to a great extent in vitro demonstrate that their cells progressively elongate for only about three days. Well differentiated explants cultured for longer periods do not show greater elongation or further cytoplasmic differentiation. Their cells, at the ultrastructural level, resemble differentiating fibre cells in vivo rather than differentiated ones. It is concluded that the anterior lens epithelium has some capacity for differentiation independent of the ocular environment, but that the latter is essential for the expression of its full developmental potential. / Science, Faculty of / Zoology, Department of / Graduate

In this study, crystalline poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAm-co-AAc) nanoparticle network in organic solvents was obtained by self assembling precursor particles in acetone/epichlorohydrin mixture at room temperature followed by inter-sphere crosslinking at ~98 °C. The crystals thus formed can endure solvent exchanges or large distortions under a temporary compressing force with the reoccurrence of crystalline structures. In acetone, the crystals were stable, independent of temperature, while in water crystals could change their colors upon heating or changing pH values. By passing a focused white light beam through the crystals, different colors were displayed at different observation angles, indicating typical Bragg diffraction. Shear moduli of the gel nanoparticle crystals were measured in the linear stress-yield ranges for the same gel crystals in both acetone and water. Syntheses of particles of different sizes and the relationship between particle size and the color of the gel nanoparticle networks at a constant solid content were also presented. Temperature- and pH- sensitive crystalline PNIPAm-co-AAc hydrogel was prepared using osmosis crosslinking method. Not only the typical Bragg diffraction phenomenon was observed for the hydrogel but also apparent temperature- and pH- sensitive properties were performed. The phase behavior of PNIPAm nanoparticles dispersed in water was also investigated using a thermodynamic perturbation theory combined with lightscattering and spectrometer measurements. It was shown how the volume transition of PNIPAM particles affected the interaction potential and determined a novel phase diagram that had not been observed in conventional colloids. Because both particle size and attractive potential depended on temperature, PNIPAM aqueous dispersion exhibited phase transitions at a fixed particle number density by either increasing or decreasing temperature. The phase transition of PNIPAm-co-AAc colloids was also studied. The results from the comparison between pure PNIPAm and charged PNIPAm colloids showed that the introducing of carboxyl (-COOH) group not only contributed to the synthesis of three-dimensional nanoparticle network but also effectively increased the crystallization temperature and concentration range. The phase transitions at both low and high temperatures were observed from the turbidity change by using UV-Vis spectrometer. Centrifugal vibration method was used to make crystalline PNIPAm-co-AAc dispersion at high concentration (8%). The turbidity test proved the formation of iridescent pattern.

The eye forms through complex tissue interactions, and it still only partly understood. The developing vertebrate lens however, is crucial for coordinating eye development and eye growth, through releasing signals to surrounding eye structures. It is thought that the lens controls the growth of the eye through the production of the vitreous- the jelly-like substance that fills the main cavity of the eye and maintains the eye in its correct shape. Many components of the vitreous are produced by a region of the peripheral retina known as the ciliary body, and so it is believed that the lens controls eye growth through controlling the development of the ciliary body and thus, indirectly, the vitreous. This project addresses this concept. I have identified a previously unknown functional link between the lens and Vitamin A metabolism. The lens is important for maintaining retinoic acid production within the developing chick eye through controlling the expression of RDH10 in the presumptive ciliary body. RDH10 is important for the first step in retinoic acid synthesis, the conversion of Vitamin A into retinal, which is then converted into retinoic acid. The loss of RDH10 within the presumptive ciliary body is associated with a reduction in expression of other genes known to be involved in ciliary body development, BMP7, WNT2B and OTX1 along with a reduction in the growth of the eye. The reduction in retinoic acid production within the eye as a result of lens removal, in turn affects the synthesis of Collagen IX from the ciliary body, a major component of the vitreous. The data suggests that the lens controls retinoic acid production within the eye, through maintaining gene expression in the developing ciliary body. Retinoic acid signalling controls the synthesis of components of the vitreous, such as Collagen IX. The proper accumulation of the vitreous within the eye is crucial for the correct growth of the chick eye.

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