Impaired mechanical response of an EDMD mutation leads to motility phenotypes that are repaired by loss of prenylation.

There are roughly 14 distinct heritable autosomal dominant diseases associated with mutations in lamins A/C, including Emery-Dreifuss muscular dystrophy (EDMD). The mechanical model proposes that the lamin mutations change the mechanical properties of muscle nuclei, leading to cell death and tissue deterioration. Here, we developed an experimental protocol that analyzes the effect of disease-linked lamin mutations on the response of nuclei to mechanical strain in living Caenorhabditis elegans We found that the EDMD mutation L535P disrupts the nuclear mechanical response specifically in muscle nuclei. Inhibiting lamin prenylation rescued the mechanical response of the EDMD nuclei, reversed the muscle phenotypes and led to normal motility. The LINC complex and emerin were also required to regulate the mechanical response of C. elegans nuclei. This study provides evidence to support the mechanical model and offers a potential future therapeutic approach towards curing EDMD.

Measuring the effects of high CO2 levels in Caenorhabditis elegans.

Carbon dioxide (CO2) is an important molecule in cell metabolism. It is also a byproduct of many physiological processes. In humans, impaired lung function and lung diseases disrupt the body's ability to dispose of CO2 and elevate its levels in the body (hypercapnia). Animal models allow further understanding of how CO2 is sensed in the body and what are the physiological responses to high CO2 levels. This information can provide new strategies in the battle against the detrimental effects of CO2 accumulation in lung diseases. The nematode Caenorhabditis elegans provides us with such a model animal due to its natural ability to sense and navigate through varying concentrations of CO2, as well as the fact that it can be genetically manipulated with ease. Here we describe the different methods used to measure the effects elevated levels of CO2 have on the molecular sensing mechanism and physiology of C. elegans.

Lamins in development, tissue maintenance and stress.

Lamins are nuclear intermediate filament proteins. They provide mechanical stability, organize chromatin and regulate transcription, replication, nuclear assembly and nuclear positioning. Recent studies provide new insights into the role of lamins in development, differentiation and tissue response to mechanical, reactive oxygen species and thermal stresses. These studies also propose the existence of separate filament networks for A- and B-type lamins and identify new roles for the different networks. Furthermore, they show changes in lamin composition in different cell types, propose explanations for the more than 14 distinct human diseases caused by lamin A and lamin C mutations and propose a role for lamin B1 in these diseases.

Global transcriptional changes caused by an EDMD mutation correlate to tissue specific disease phenotypes in C. elegans.

There are numerous heritable diseases associated with mutations in the LMNA gene. Most of these laminopathic diseases, including several muscular dystrophies, are autosomal dominant and have tissue-specific phenotypes. Our previous studies have shown that the globally expressed Emery-Dreifuss muscular dystrophy (EDMD)-linked lamin mutation, L535P, disrupts nuclear mechanical response specifically in muscle nuclei of C. elegans leading to atrophy of the body muscle cells and to reduced motility. Here we used RNA sequencing to analyze the global changes in gene expression caused by the L535P EDMD lamin mutation in order to gain better understanding of disease mechanisms and the correlation between transcription and phenotype. Our results show changes in key genes and biological pathways that can help explain the muscle specific phenotypes. In addition, the differential gene expression between wild-type and L535P mutant animals suggests that the pharynx function in the L535P mutant animals is affected by this lamin mutation. Moreover, these transcriptional changes were then correlated with reduced pharynx activity and abnormal pharynx muscle structure. Understanding disease mechanisms will potentially lead to new therapeutic approaches toward curing EDMD.

Intermediate Filaments in Caenorhabditis elegans.

More than 70 different genes in humans and 12 different genes in Caenorhabditis elegans encode the superfamily of intermediate filament (IF) proteins. In C. elegans, similar to humans, these proteins are expressed in a cell- and tissue-specific manner, can assemble into heteropolymers and into 5-10nm wide filaments that account for the principal structural elements at the nuclear periphery, nucleoplasm, and cytoplasm. At least 5 of the 11 cytoplasmic IFs, as well as the nuclear IF, lamin, are essential. In this chapter, we will include a short review of our current knowledge of both cytoplasmic and nuclear IFs in C. elegans and will describe techniques used for their analyses.

Matefin/SUN-1 Phosphorylation on Serine 43 Is Mediated by CDK-1 and Required for Its Localization to Centrosomes and Normal Mitosis in C. elegans Embryos.

Matefin/SUN-1 is an evolutionary conserved C. elegans inner nuclear membrane SUN-domain protein. By creating a bridge with the KASH-domain protein ZYG-12, it connects the nucleus to cytoplasmic filaments and organelles. Matefin/SUN-1 is expressed in the germline where it undergoes specific phosphorylation at its N-terminal domain, which is required for germline development and homologous chromosome pairing. The maternally deposited matefin/SUN-1 is then essential for embryonic development. Here, we show that in embryos, serine 43 of matefin/SUN-1 (S43) is phosphorylated in a CDK-1 dependent manner and is localized throughout the cell cycle mostly to centrosomes. By generating animals expressing phosphodead S43A and phosphomimetic S43E mutations, we show that phosphorylation of S43 is required to maintain centrosome integrity and function, as well as for the localization of ZYG-12 and lamin. Expression of S43E in early embryos also leads to an increase in chromatin structural changes, decreased progeny and to almost complete embryonic lethality. Down regulation of emerin further increases the occurrence of chromatin organization abnormalities, indicating possible collaborative roles for these proteins that is regulated by S43 phosphorylation. Taken together, these results support a role for phosphorylation of serine 43 in matefin/SUN-1 in mitosis.