The nuclear envelope (NE) plays critical roles in gene expression through controlling access to the nucleus, anchoring of chromosomes at the nuclear periphery and serving as platform for chromatin-interacting proteins, such as histone modifiers and transcription factors. Several human diseases are attributed to alterations in NE structure, including the laminopathies, whose name refers to underlying mutations in components of the nuclear lamina and lamina-associated proteins. One example is Emery-Dreifuss muscular dystrophy, which is caused by mutations in the inner nuclear membrane protein emerin or in lamin.
We recently found that emerin/EMR-1 is required for correct neuromuscular junction activity in C. elegans. Firstly, EMR-1 associates with genes involved in muscle and neuronal function and deletion of emr-1 causes local changes in nuclear architecture. Secondly, transcriptome analyses revealed that EMR-1 is associated with gene repression, particularly of genes implicated in muscle and nervous system function. Thirdly we demonstrated that emr-1 mutants are sensitive to the cholinesterase inhibitor aldicarb, indicating altered activity at neuromuscular junctions.
Although many NE proteins are ubiquitously expressed, laminopathies often affect a single tissue. This has led to the hypothesis that tissue-specific alterations in nuclear organization are responsible for particular clinical manifestations of laminopathies. Specifically, changes in interactions between NE proteins and chromatin are thought to be relevant, but has not been explored in intact organisms due to technical limitations. This triggered us to develop novel tools to dissect the function of EMR-1 in tissue-specific nuclear organization. Using an optimized FLP recombinase, we show specific and efficient activation of dual color reporters is selected tissues. Importantly, our system is based on single-copy FLP and Frt transgenes integrated into the genome by MosSCI to ensure reproducible expression and to facilitate crosses. Until now, the repertoire of cell types amenable to analysis includes striated and nonstriated muscles, intestine, M cell lineage, seam cell lineage, hypodermis, and neurons (pan-neuronal and specific neuronal subtypes). We have implemented our FLP/Frt system to perform tissue-specific DamID, which has provided EMR-1/chromatin interaction profiles for different cell types, but the tool kit can easily be adapted for spatiotemporal control of other transgenes, including fluorescent reporters, dominant alleles or suicide genes.