Roles of LAP2 Proteins in Nuclear Assembly and DNA Replication: Truncated LAP2β Proteins Alter Lamina Assembly, Envelope Formation, Nuclear Size, and DNA Replication Efficiency in Xenopus laevis Extracts

• Published in: The Journal of cell biology 1999-03, Vol.144 (6), p.1083-1096
• Main Authors: Gant, Tracey Michele, Harris, Crafford A., Wilson, Katherine L.
• Format: Article
• Language: English
• Subjects: Cell cycle; Chromatin; DNA; DNA replication; Exons; Lamins; Nuclear lamina; Nuclear membrane; Ova; Protein isoforms; Regular; Xenopus laevis
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.144.6.1083

Humans express three major splicing isoforms of LAP2, a lamin- and chromatin-binding nuclear protein. LAP2β and γ are integral membrane proteins, whereas α is intranuclear. When truncated recombinant human LAP2β proteins were added to cell-free Xenopus laevis nuclear assembly reactions at high concentrations, a domain common to all LAP2 isoforms (residues 1-187) inhibited membrane binding to chromatin, whereas the chromatin- and lamin-binding region (residues 1-408) inhibited chromatin expansion. At lower concentrations of the common domain, membranes attached to chromatin with a unique scalloped morphology, but these nuclei neither accumulated lamins nor replicated. At lower concentrations of the chromatin- and lamin-binding region, nuclear envelopes and lamins assembled, but nuclei failed to enlarge and replicated on average 2.5-fold better than controls. This enhancement was not due to rereplication, as shown by density substitution experiments, suggesting the hypothesis that LAP2β is a downstream effector of lamina assembly in promoting replication competence. Overall, our findings suggest that LAP2 proteins mediate membrane-chromatin attachment and lamina assembly, and may promote replication by influencing chromatin structure.