Polyketides are also signal compounds that control the differentiation of Dictyostelium. The polyketide synthases (PKSs) inhibitor, cerulenin, inhibits Dictyostelium differentiation and therefore its development (Serafimidis & Kay, 2005). The diversity Pembrolizumab mouse of the biological activity of polyketides has rendered these secondary metabolites and the PKS genes that regulate their production the focus of biomedical and biopharmaceutical research. The completion of the Dictyostelium genome project revealed that the Dictyostelium genome contains more than 40 PKS genes, indicating that it has huge potential for polyketide production. In addition, the Dictyostelium genome contained two novel hybrid-type PKS
genes (Eichinger et al., 2005; Zucko et al., 2007). This novel structure was known as ‘Steely’. In Steely PKS proteins, the type III PKS domain was fused to
the C-terminus of a multidomain type I PKS (Eichinger et al., 2005; Austin et al., 2006). The two Steely-type PKSs were called SteelyA and SteelyB. SteelyB was reported to be responsible for the production of the stalk-inducing factor DIF-1 and the knockout mutant of stlB lacked DIF-1 (Austin et al., 2006). This stlB mutant aided the elucidation of the functions of DIF-1 in vivo (Saito et al., 2008). selleck compound However, two different reports associated with SteelyA expression pattern and its products have been identified. According to one report in 2006, an in vitro product was identified as pyrone and the stlA gene was expressed maximally in early development before cell aggregation. Another report in 2008 identified 4-methyl-5-pentylbenzene-1,3-diol (MPBD) as the main in vitro product and the stlA gene was found to be expressed only in late development (Austin et al., 2006; Ghosh et al., 2008). In this study, we re-examined the expression pattern of stlA using two different primer sets and observed that it was similar to that in the dictyExpress database and our previous report (Austin et al., 2006; Rot et al., 2009). Furthermore, we used an stlA mutant and showed that one of the in vivo products of SteelyA was MPBD, a differentiation-inducing factor that was
STK38 identified in the conditioned medium for a dmtA mutant (Saito et al., 2006). Finally, we observed that MPBD induced the formation of mature spore cells in the fruiting body. The Dictyostelium discoideum Ax2 strain was grown in an axenic medium at 22 °C and was harvested at a density of approximately 5 × 106 cells mL−1. A stlA null strain that we reported previously (Austin et al., 2006) was grown in an axenic medium in the presence of 10 μg mL−1 balsticidin S. The axenically grown cells were washed and were developed at 22 °C on the phosphate buffer (2.7 mM Na2HPO4/10.7 mM K2HPO4 pH 6.2) agar plates at a density of 1–2 × 106 cells cm−2. For reverse transcription (RT)-PCR analysis, developing cells were harvested every 3 h until t21 (late culmination stage) and used for RNA purification.