Access Type

Open Access Dissertation

Date of Award

January 2017

Degree Type


Degree Name



Biological Sciences

First Advisor

Lori A. Pile


SIN3 is a master transcriptional regulator, conserved from yeast to mammals, that acts as a scaffold protein for a histone modifying complex. In Drosophila, a single Sin3A gene is alternatively spliced to produce distinct SIN3 isoforms; SIN3 220, SIN3 190 and SIN3 187, that differ only at their C-terminus. These isoforms are differentially expressed during development. We have shown that there is an interplay between the predominant isoforms of SIN3, SIN3 220 and SIN3 187, that possibly regulates the overall level of SIN3 in the cell. Exogenous expression of SIN3 187 reduces the level of transcript and accelerates the proteasomal degradation of endogenous SIN3 220. This feedback can possibly ensure that the appropriate isoform is present during the correct developmental stage during embryogenesis. Differential expression of the SIN3 isoforms during embryo development suggests that they perform unique and specialized functions. The SIN3 proteins form distinct isoform specific complexes. SIN3 187 interacts with a single catalytic enzyme, the HDAC RPD3, while SIN3 220 interacts with two enzymes, RPD3 and the HDM dKDM5/LID. This differential interaction of SIN3 isoforms with distinct histone modifying activities may play a role in the non-redundant functions performed by SIN3. Using previously published transcriptome data, we have identified common and unique gene targets of SIN3 and LID. In Drosophila S2 cells, knockdown of LID results in an increase in the level of H3K9ac, H3K14ac and H3K27ac at genes commonly regulated by SIN3 and LID. Since LID preferentially interacts with the SIN3 220 complex, we have investigated the histone modification patterns established by the SIN3 isoform specific complexes. We have established Drosophila cultured cells which express either the SIN3 187 or the SIN3 220 complex. The SIN3 187 and SIN3 220 complexes establish distinct histone modification patterns at target genes and differentially regulate the expression of these genes. It is possible, that the differential histone modification patterns and the consequent alteration of expression of target genes contributes to the functional differences between the SIN3 isoforms. This work enhances our understanding of SIN3 isoform function and provides further insight into the molecular mechanisms of epigenetic control of gene expression by histone modifying complexes.

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