COOPERATIVE AND ANTAGONISTIC ROLES FOR HETEROCHROMATIN PROTEINS IN TRANSCRIPTIONAL REGULATION OF THE DROSOPHILA SEX DETERMINATION MASTERSWITCH GENE

Author

Hui Li, University of KentuckyFollow

Date Available

1-26-2013

Year of Publication

2011

Degree Name

Doctor of Philosophy (PhD)

Document Type

Dissertation

College

Arts and Sciences

Department

Biology

First Advisor

Dr. Rebecca Kellum

Abstract

HOAP was originally identified as a component of an ORC-containing multi-protein complex of Heterochromatin Protein 1 (HP1) from early Drosophila embryos. HOAP immunostaining showed prominent association of it with telomeres, and mutants for HOAP (cav¹) showed it functions along with HP1 in forming a telomere capping complex that prevents telomeric fusions.

Weaker HOAP immunostaining is also observed in regions of pericentric heterochromatin and euchromatin. To examine the role of HOAP at these non-telomeric sites, we applied Affymetric Drosophila Genome Arrays to undertake a microarray expression profiling study of genes that are mis-expressed in cav¹ mutant larvae. The data from four publicly available databases were used to assess the normal expression patterns of the affected genes. We found that the majority (67%) of genes with decreased expression levels in cav¹ mutants (log₂R< -2.0, p_value≤ 0.01) have normally testis-specific expression. These results could indicate a role of HOAP in testis-specific gene expression. Alternatively they could reflect reduced male viability due to the loss of HOAP, which resulted in the under-representation of males in the cav¹ larval sample. The latter hypothesis is supported by the observation of 2.8-fold under-representation of males in cav¹ larvae when I used a yellow⁺-marked X chromosome to differentially mark male and female cav¹ larvae. Thus, this project is focused on determining and characterizing the cause of the reduced male viability.

Here I report a role for both HOAP and HP1 in regulating the establishment promoter, Sxl_Pe, of the sex determination masterswitch, Sex lethal (Sxl). Female-specific activation of Sxl_Pe is essential to females as it provides SXL protein to initiate productive female-specific splicing of the late Sxl transcripts which are transcribed in both sexes. We find inappropriate firing of Sxl_Pe and splicing of Sxl transcripts in male cav mutants, whereas mutants for HP1 display Sxl splicing defects in both sexes. Both proteins are associated with Sxl_Pe sequences. In embryos from HP1 mothers and Sxl mutant fathers, female viability and RNA polymerase II recruitment to Sxl_Pe is severely compromised. Our genetic and biochemical assays suggest a repressing activity for HOAP and both activating and repressing roles for HP1 at Sxl_Pe.

Recommended Citation

Li, Hui, "COOPERATIVE AND ANTAGONISTIC ROLES FOR HETEROCHROMATIN PROTEINS IN TRANSCRIPTIONAL REGULATION OF THE DROSOPHILA SEX DETERMINATION MASTERSWITCH GENE" (2011). University of Kentucky Doctoral Dissertations. 127.
https://uknowledge.uky.edu/gradschool_diss/127