Cloning and expression pattern of the lysozyme C gene in zebrafish

Here, we report isolation and developmental expression pattern of the zebrafish lysozyme C gene. Amino acid sequence analysis showed that the zebrafish lysozyme C protein shared approximately 37-80% identities with the mouse, human, chicken, and carp counterparts. Whole-mount in situ hybridization showed that the lysozyme C gene was expressed in macrophages, as its expression was co-localized with the known myeloid lineage markers L-plastin and PU.1. At 20 hours postfertilization (hpf), most of the lysozyme C positive cells were localized in the yolksac and head mesenchyme but not in the intermediate cell mass, supporting the notion that the primitive macrophage originated from the yolksac (Development 126 (1999) 3735). At 36hpf, the lysozyme C positive cells scattered within the head and yolksac, and began to appear in the caudal part of axial vein. By 6 days postfertilization (dpf), the lysozyme C positive cells accumulated in the kidney where hematopoiesis had been indicated to take place after 4dpf (Dev. Dyn. 214 (1999) 323). Taken together, our results demonstrate that the lysozyme C gene is specifically expressed in myeloid lineage, suggesting that it could serve as an excellent marker for genetic screening of both primitive and definitive myeloid lineage development in zebrafish.     

Roles of fetal G gamma-globin promoter elements and the adult beta-globin 3'' enhancer in the stage-specific expression of globin genes.

The human fetal G gamma-globin and adult beta-globin genes are expressed in a tissue- and developmental stage-specific pattern in transgenic mice: the G gamma gene in embryonic cells and the beta gene in fetal and adult erythroid cells. Several of the cis-acting DNA sequences thought to be responsible for these patterns of expression are located 5' to the G gamma-globin gene and 3' to the beta-globin gene. To further define the locations and functional roles of these elements, we examined the effects of 5' truncations on the expression of the G gamma-globin gene, as well as the ability of G gamma-globin upstream sequences to alter the developmental regulation of a beta-globin gene, as well as the ability of G gamma-globin upstream sequences to alter the developmental regulation of a beta-globin gene. We found that sequences between -201 and -136 are essential for expression of the G gamma-globin gene, whereas those upstream of -201 have little effect on the level or tissue or stage specificity of G gamma-globin expression. The G gamma-globin upstream sequences from -201 to -136 were, furthermore, capable of activating a linked beta-globin gene in embryonic blood cells; however, a G gamma-globin fragment from -383 to -206 was similarly active in this assay, and the complete fragment from -383 to -136 was considerably more active than either of the smaller fragments, suggesting the presence of multiple cis-acting elements for embryonic blood cells. Our data also suggested the possibility of a negative regulatory element between -201 and -136. These results are discussed in relation to several DNA elements in the G gamma-globin upstream region, which have been shown to bind nuclear factors in erythroid cells. Finally, we observed that removal of the beta-globin 3'-flanking sequences, including the 3' enhancer, from the G gamma-globin upstream-beta-globin hybrid gene resulted in a 25-fold reduction in expression in embryonic blood cells. This suggests that the beta-globin 3' enhancer is potentially active at the embryonic stage and thus cannot be solely responsible for the fetal or adult specificity of the beta-globin gene.