Date of Award
Fall 1998
Document Type
Dissertation - Restricted
Degree Name
Doctor of Philosophy (PhD)
Department
Biological Sciences
First Advisor
Munroe, Stephen
Second Advisor
Karrer, Kathleen
Third Advisor
McNally, Mark
Abstract
The erbAa gene codes for two functionally antagonistic nuclear hormone receptors. Alternative processing at the 3' end of the erbAa pre-mRNA produces either a1 mRNA, which codes for the thyroid hormone receptor, or a2 mRNA, which codes for an orphan nuclear receptor which blocks thyroid hormone activity. Thus, regulation of erbAa alternative processing is a way for the cell to modulate its response to thyroid hormone, a process with important consequences in development and growth. Despite the importance for control of a1 and a2 mRNA production, little is known about the regulation of erbAa alternative pre-mRNA processing. An unusual feature of the erbAa gene is the presence of another gene, RevErb, encoded on the opposite DNA strand. Because of the alternative processing of erbAa pre-mRNA, RevErb overlaps with a2-specific sequence but not with a1. It is interesting to note that RevErb also codes for a physiologically relevant nuclear hormone receptor. Because of the overlap between the two genes, the 3' ends of a2 and RevErb RNA are complementary and have the ability to basepair to form an RNA duplex which may inhibit expression of the mRNAs. Specifically, RevErb may affect the balance of erbAa alternative mRNA expression by negatively influencing a2 levels. Such an antisense mechanism for regulation of gene expression is rare in eukaryotes and not well characterized. The organization of the erbAa gene, including the unusual processing choices at its 3' end and the presence of the antisense RevErb gene, make it an intriguing and valuable model for investigation of cellular mechanisms involved in the regulation of gene expression. This study addresses both the control of basal erbAa. alternative pre-mRNA processing as well as regulation of a.1/a.2 mRNA by RevErb expression. Basal erbAa. pre-mRNA processing was addressed by identification of cis-acting elements important for achieving the balance between a1 and a2 processing. The effect that expression of the antisense transcript RevErb has on the production of the complementary a2 mRNA was addressed in two ways. First, the effect of RevErb on a2 was examined indirectly by assaying expression of the transcripts in a developmental system. Second, the effect of RevErb was tested directly using a model system for expression of erbAa and RevErb minigenes in cell culture.