Date Thesis Awarded

5-2015

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Biology

Advisor

Margaret S. Saha

Committee Member

Shanta D. Hinton

Committee Member

Lisa M. Landino

Committee Member

Oliver Kerscher

Abstract

Plasticity, the ability to redifferentiate and change cellular identity, is an integral part of development as cells must develop and specify while being able to respond to any changes in the environment. Many instances of cell identity changes have been identified during development, but the mechanisms that allow certain cells to do this while others remain in a fixed fate are unclear. The patterning of the neural axis in the central nervous system involves the specification and determination of neural cell identity along the anterior-posterior axis. While the mechanisms that determine the anterior-posterior neural axis early in development are well characterized, the plasticity that underlies this process remains poorly understood. While expression of genes such as Suv4-20h, Prc2, and ezH2 are known to bring about loss of potency-related factors, neither the temporal or spatial parameters of this developmental neural plasticity nor the molecular mechanisms governing the process are understood. This investigation was designed to examine the spatial-temporal limits of plasticity in the development of the vertebrate central nervous system. A rotation transplant system with a labeled donor embryo and unlabeled host embryo was used to transplant neural ectoderm covering the median half of the dorsal ectoderm from the donor embryo and rotate the anterior-posterior axis 180º onto the host embryo. This allowed for the testing of physically perturbing the axis and assaying its ability to re-differentiate. Results suggest that there is a period between mid gastrula (11.5) and late gastrula (12.5) during which the axis has been determined based on expression of regional marker genes along the axis (XCG-1, Otx2, En2, and Krox20) but remains competent to re-differentiation. In addition, the results indicate that the tissue itself loses competency as late gastrula embryos are still able to re-differentiate mid gastrula neural tissue to the correct pattern, but neural transplants from late gastrula embryos are unable to re-differentiate even in the presence of the mid gastrula inducing environment. Hence, the neural tissue remains plastic for a limited time period after acquisition of an anterior-posterior fate during development.

Available for download on Monday, May 14, 2018

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