Investigating the role of Lysine Specific Demethylase 1 (LSD1) in embryonic development using a gastruloid model system

Lysine specific demethylase 1 (LSD1) is a chromatin modifying protein which specifically demethylates the permissive histone marks H3K4me1/2 and thereby acts as a transcriptional repressor. It performs this activity as part of the CoREST (co-repressor of Repressor Element1 Silencing Transcription Factor) complex, which also encompasses histone deacetylase 1/2 (HDAC1/2) activity and is required for stability of the complex. LSD1 is essential in embryonic development, with loss of LSD1 resulting in embryonic lethality at ~E6.5, a developmental stage which correlates with the onset of gastrulation. To further investigate the role of LSD1 in embryonic development, we employed a model system, gastruloids, which closely mimic early embryogenesis and aspects of gastrulation. We generated gastruloids from both induced and control Lsd1 conditional knockout (KO) mouse embryonic stem cells (ESCs) and utilised RNAsequencing (RNA-seq) analysis to identify differentially expressed genes at timepoints representative of ESCs, early gastrulation and late gastrulation. We identified dysregulated expression of genes associated with mesodermal lineages, epithelial-tomesenchymal transition (EMT) and the bone morphogenic protein (BMP) pathway. To investigate whether gene expression changes were a result of the loss of direct LSD1 demethylase activity or of broader CoREST complex activity, we performed similar RNAseq analysis on gastruloids generated from cells with wildtype (WT) or catalytically inactive LSD1 rescue constructs. We identified genes whose expression was not rescued, suggesting dependence on LSD1 demethylase activity, and genes whose expression was fully or partially rescued, including genes associated with EMT and the BMP pathway. The work in this thesis has enabled us to gain further insight into the role of LSD1 during embryonic development.