Muscular Dystrophy Mutations Impair the Nuclear Envelope Emerin Self-assembly Properties

Area of Science:

• Cell Biology
• Biochemistry
• Genetics

Background:

• X-linked Emery-Dreifuss muscular dystrophy (X-EDMD) is linked to over 100 mutations in the emerin gene.
• Most mutations result in absent emerin protein, but mechanisms for loss-of-function in other variants are unclear due to emerin's disordered regions.

Purpose of the Study:

• To investigate the self-assembly properties of the emerin nucleoplasmic (EmN) region.
• To determine how specific emerin variants affect its self-assembly and cellular localization.
• To elucidate the molecular mechanisms underlying X-EDMD pathogenesis.

Main Methods:

• Nuclear magnetic resonance (NMR) spectroscopy to characterize EmN monomeric state.
• In vitro assembly assays monitored by electron microscopy, Thioflavin-T binding, and Fourier-transform Infrared spectrometry (FTIR).
• Analysis of five EmN variants (del95-99, Q133H, P183H, P183T) in vitro and in cellular models.

Main Results:

• The EmN region, though intrinsically disordered, self-assembles in vitro into 10 nm filaments, favored by increased concentration and temperature.
• Filament formation involves beta-structure development.
• Variants del95-99 and Q133H showed impaired filament assembly, leading to reduced emerin-emerin and emerin-lamin interactions in cells.
• Variant P183H promoted in vitro aggregation, while P183T caused cytoplasmic mislocalization of emerin in cells.

Conclusions:

• Emerin self-assembly is essential for its nuclear envelope function and preventing X-EDMD.
• Disruption of emerin assembly, either by protein absence or altered self-assembly properties, leads to disease.
• Specific mutations can cause X-EDMD by affecting emerin's oligomerization and localization.