Components of an ESCRT-independent nuclear envelope assembly pathway

In many cells, the nuclear envelope (NE) must be reassembled after mitosis, and holes in the nuclear membrane must be sealed. During NE assembly, the NE-specific adaptor, Cmp7, recruits/activates endosomal sorting complex required for transport (ESCRT)-III proteins to mediate NE sealing. However, recent evidence suggests the presence of additional mechanisms. In a screen using the fission yeast, Schizosaccharomycesjaponicus, we recently implicated the ESCRT adaptor, Alx1, and a conserved but little-studied protein, Vid27, in Cmp7-independent NE assembly. Here, we provide direct evidence that Alx1 functions in a Cmp7- and ESCRT-independent NE assembly pathway via positive regulation of Vid27. Consistent with a role in membrane remodeling, Vid27 localizes to sites of postmitotic NE sealing and is essential in S. japonicus. Alx1 and Vid27 interact, and mutations disrupting the predicted interaction interface abolish Alx1's enhancement of Vid27 function at the NE. These findings define components of a new Cmp7- and ESCRT-independent NE assembly pathway, advancing our understanding of mechanisms that maintain the integrity of the nucleus.