The lamina-associated polypeptide 2 (LAP2) isoforms β, γ and ω of zebrafish: Developmental expression and behavior during the cell cycle

Abstract

Zebrafish lamina-associated polypeptides 2 (ZLAP2) β, γ and ω have in common an N-terminal region with a LEM domain, and in the C-terminal half of the molecule a lamina binding domain and a membrane spanning sequence. The maternally synthesized ω is the largest isoform and the only LAP2 present in the rapidly dividing embryonic cells up to the gastrula stage. ZLAP2ω levels decrease during development, concomitant with the increase of the somatic isoforms ZLAP2β and γ. In somatic zebrafish cells ZLAP2γ is the predominant isoform, whereas only small amounts of ZLAP2β are present. During early embryonic development, ZLAP2ω becomes associated with mitotic chromosomes before anaphase. The surface of these chromosomes is decorated with vesicles, and each chromosome assembles its own nuclear envelope at the end of mitosis (karyomere formation). Ectopically expressed ZLAP2ω-green fluorescent protein (GFP) fusion protein targets vesicles to mitotic chromosomes in Xenopus A6 cells, suggesting that ZLAP2ω is involved in karyomere formation during early zebrafish development. When ZLAP2β and γ were expressed as GFP fusion proteins in Xenopus A6 cells, the β- but not the γ-isoform was found in association with mitotic chromosomes, and ZLAP2β-containing chromosomes were decorated with vesicles. Further analysis of ZLAP2-GFP fusion proteins containing only distinct domains of the ZLAP2 isoforms revealed that the common N-terminal region in conjunction with β- or ω-specific sequences mediate binding to mitotic chromosomes in vivo.