Investigation of Fourth Chromosome Reporter Expression

Cells must be able to silence and activate lineage specific genes. In Drosophila melanogaster, this process is controlled in part by Polycomb (Pc) and trithorax (trx) group proteins. Among other targets, Pc group proteins act upon homeotic genes to maintain a silenced genetic state, while trx group proteins act upon these same genes in different cell lineages and at different developmental times to activate them. When investigating the chromatin environment of reporter insertions on Drosophila’s fourth chromosome using data produced by the modENCODE consortium, we discovered a correlation between the insertion site of P-element reporter lines showing a red eye (as opposed to the majority, which exhibit a variegating phenotype) and domains enriched for Polycomb protein. We hypothesized that Pc or trx group proteins might control gene regulation in the domains occupied by red-eyed fourth chromosome reporters. I introduced mutations in Pc and trx group genes into several reporter strains to determine how reporter expression would be affected. Only heterozygous mutations in ash1, encoding a trx group protein with histone-methyltransferase activity, consistently decreased expression from red-eyed reporters on chromosome four, measured by assaying eye pigment levels. I then tested if the observed trend represented a global effect on gene expression or was unique to fourth chromosome insertions. I discovered that the effect of the ash1B1 mutation is dependent on the insertion site of the transgene reporter, ruling out a global effect on gene expression. My current work includes chromatin immunoprecipitation experiments and additional genetic analyses using double-mutants. My results indicate that ash1 mutations are capable of influencing the transcriptional state of red-eyed and variegating reporters on several chromosomes