Exploring the interaction between Histone H1.4 and HP1α: a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Genetics at Massey University, Palmerston North, New Zealand

Abstract

In eukaryotic organisms, the genome is organised into chromatin. Inside the nucleus, this chromatin is compartmentalised into regions of transcriptionally active euchromatin and transcriptionally inactive heterochromatin. The homeostasis of these two chromatin domains is essential for genomic stability and structural stability of the nucleus. Both histone H1.4 and the heterochromatin protein HP1α are enriched in heterochromatin and contribute to heterochromatin homeostasis. These two proteins have been demonstrated to interact through the C-terminal domain (CTD) of H1.4 and the hinge region (HR) of HP1α. This study investigated the H1.4-HP1α interaction in vitro and in vivo to determine how truncations or alterations to the H1.4 CTD impact its interaction with HP1α. The rare genetic disorder, Rahman Syndrome, is caused by a frameshift mutation occurring in the CTD of H1.4. Disruptions to heterochromatin homeostasis have been observed in Rahman syndrome patient fibroblast cells highlighting the importance of histone H1.4 in heterochromatin. It was demonstrated that the H1.4 CTD is important for the in vivo co-localisation of H1.4 to HP1α. H1.4 with a CTD altered due to a truncation or frameshift mutation showed a reduction in its co localisation with HP1α. Expression of Rahman syndrome H1.4 was associated with alterations to HP1α mediated heterochromatin changes to nuclear morphology, indicating that it may be impacting chromatin condensation and the mechanical properties of the nucleus. Overall, these findings demonstrate the importance of the H1.4 CTD in HP1α mediated heterochromatin homeostasis.