Identification of tissue-specific regulatory region in the zebrafish lamin A promoter

Abstract

Lamins are major structural proteins present in the nuclei of metazoan cells and contribute significantly to nuclear organization and function. The expression of different types of lamins is developmentally regulated and lamin A is detectable in most differentiated tissues. Although the proximal promoter of the mammalian lamin A gene has been characterized, the tissue-specific regulatory elements of the gene have not been identified. In this study, we have cloned and functionally characterized a 2.99kb segment upstream of exon 1 in the zebrafish lamin A gene. This fragment was able to drive GFP expression in several tissues of the developing embryo at 14–72h post fertilization in stable transgenic lines. Deletion fragments of the 2.99kb promoter were analyzed by microinjection into zebrafish embryos in transient assays as well as by luciferase reporter assays in cultured cells. A minimal promoter segment of 1.24kb conferred tissue-specific expression of GFP in the zebrafish embryo as well as in a myoblast cell line. An 86bp fragment of this 1.24kb segment was able to activate a heterologous promoter in myoblasts. Mutational analysis revealed the importance of muscle-specific regulatory motifs in the promoter. Our results have important implications for understanding the tissue-specific regulation and functions of the lamin A gene.