View Program - 63rd Annual Drosophila Research Conference

Heterochromatin Protein 1 (HP1) proteins are non-histone chromosomal proteins that are highly conserved in eukaryotes. HP1 proteins can form homo- and heterodimers, which bind to other chromatin elements such as histones, DNA, and a variety of protein partners. Due to their diverse nuclear functions and maintenance of chromatin states, HP1 proteins are essential for ensuring the safety and functions of the genome. The genome of Drosophila melanogaster contains three somatically expressed HP1 genes: Su(var)205 encoding HP1a, HP1b, and HP1c. Loss of each of the three proteins has important functions, with mutations leading to the misexpression of hundreds of genes and decreased viability and/or fertility. When mutations in HP1 proteins are studied, the impact on the other HP1 family members typically is not assayed, despite them occurring together in protein complexes. Here, we investigate how HP1 proteins interact by examining double-mutant fly strains lacking HP1B and HP1C. We find that the viability of these animals is strongly dependent on genetic background, with one background producing a homozygous viable, fertile, and healthy stock despite lacking two HP1 proteins, while another background allows less than 10% of animals to survive. Examination of polytene chromosomes from these HP1b/HP1c mutants suggests that their morphology is affected, while HP1a continues to localize to the centromeres and telomeres. Our data demonstrate that complete loss of HP1B and HP1C is survivable in D. melanogaster and demonstrate the importance of genetic background. Ongoing studies focus on how pairwise HP1 loss affects gene expression and high-resolution chromatin analysis through CUT&RUN. Our study highlights possible crosstalk and cooperative functions of HP1 proteins and has the potential to provide further insights into the functions of the sole remaining HP1 protein, HP1a.

Dual loss of HP1B and HP1C impacts chromatin structure