Centrosomes (arrowheads) stray from the nucleus if emerin is missing (bottom).

Cells lacking emerin, one of the proteins whose loss causes a form of muscular dystrophy, cannot hook their centrosome to the nucleus, show Salpingidou et al. The lost linkage might weaken contractile cells, including those diseased muscles.

Besides harboring the genome, the nucleus is becoming increasingly recognized as a load-bearing structure. By hooking to the cytoskeleton, the nuclear envelope probably helps to absorb mechanical forces. The links that hook the nuclear envelope to the actin and intermediate filament networks are known. Now, the microtubule link is identified as emerin.

In cells lacking emerin, the microtubule-organizing center—the centrosome—drifted away from its usual nucleus-adjacent spot. In normal cells, emerin bound to β-tubulin, a component of both microtubules and centrosomes. Since the centrosome normally lies within 1.5 μm of the nucleus, emerin probably hooks directly to centrosomes rather than to long microtubule filaments.

Emerin was previously found only on the inner nuclear envelope, but closer inspection identified a portion on the outer envelope, where it can reach centrosomes. Other proteins must hold it in place there and link it to the nuclear lamina. The authors would like to identify these proteins and more centrosomal proteins that are part of the linkage. As ∼50% of patients with Emery Dreifuss muscular dystrophy do not have mutations in the known causal genes (emerin and lamins A and C), such a list should provide more candidates.

Reference:

Salpingidou, G., et al.
2007
.
J. Cell Biol.
178
:
897
–904.