lysozyme C (lyz), a glycoside hydrolase expressed exclusively in myeloid cells, is involved in the host defense against bacterial infection. We isolated a 2.4 kb zebrafish lyz promoter region and established transgenic lines that drive enhanced green fluorescent protein (EGFP) to examine how lyz expression is regulated during myelopoiesis. We found that the 2.4 kb lyz promoter is sufficient to drive myeloid-specific expression of EGFP in zebrafish. We identified potential transcriptional regulatory elements including a Runx element (TGTGGT at -1.70 kb) and a C/ebp element (TTTGGCAAT at -1.46 kb) in the lyz promoter, and showed that they are required for myeloid-specific expression of EGFP. We found that the myeloid-lineage transcription factors C/ebp1, Runx1 and Pu.1 can bind to the 2.4 kb lyz promoter. Forced expression of runx1, c/ebp1 and pu.1 together induced ectopic lyz expression in the intermediated cell mass (ICM). Thus, we propose that c/ebp1 and runx1 presumably cooperated with pu.1 in the transcriptional regulation of lyz during zebrafish myelopoiesis.
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