Differentially expressed genes that encode potential markers of goldfish macrophage development in vitro

Primary kidney macrophage (PKM) cultures derived from goldfish hematopoietic tissues develop from early progenitors to mature macrophages in response to endogenous growth factor(s). When grown in vitro, PKM shift from a proliferative phase, where most of the proliferation and differentiation events take place, to a senescence phase, where there is cessation of proliferation and differentiation events and ultimately cell death through a process of apoptosis. The phenotypic changes of PKM from the proliferative to senescence phase are a reflection of specific changes in gene expression; therefore, comparison of gene expression patterns between the two phases should lead to the identification of macrophage genes directly involved in the positive and negative regulation of hematopoietic events, as well as genes that are modulated downstream from these regulatory points. Differential cross-screening of the proliferative phase PKM cDNA library using proliferative and senescence phase (32)P-labeled cDNA probes identified several differentially expressed genes. Specifically, initial screen of 9200 clones yielded 734 differential primary clones that were isolated and analyzed using a PCR-based secondary screen. The majority of these clone isolates encoded a single transcript as determined by PCR amplification of the primary clones. The secondary screen confirmed the differential expression of 306 clones (3.32% of the total number of screened clones). Two hundred and forty four clones were sequenced; 158 and 86 were preferentially expressed during proliferative and senescence phases, respectively. Several potential candidates of fish macrophage hematopoiesis were identified. These include, for example, zinc finger protein 147, nucleophosmin, 14-3-3 protein, adenine nucleotide translocator 2 (ANT2), granulin, survivin-1, and apoptosis inhibitor-5. In addition, several potential markers of macrophage differentiation and/or function were identified and their expression patterns characterized across three distinct stages of macrophage development in vitro. These include legumain, CD63, interferon-inducible protein, macrosialin (CD68), transcription factor MafB, and the molecular chaperone BiP/GRP78. These analyses will facilitate future characterization of macrophage developmental events by providing a more global perspective of various facets of macrophage hematopoiesis.