Calcium stimulates molecular and cellular events during the yeast-to-mycelium transition in Sporothrix schenckii

Calcium ions (Ca2+) have been identified as mediators of proliferative and morphogenetic processes in many eukaryotic cells. The effects of these ions on the cellular and macromolecular processes that accompany the dimorphic transition from the yeast-to-mycelial form of Sporothrix schenckii have been studied. Ca2+ were found to stimulate germ tube formation and growth in these cells at an optimal concentration of 1.0 mM. Studies concerning the effects of this cation on the molecular processes that precede germ tube formation revealed that the earliest molecular event which was stimulated by 1.0 mM Ca2+ was RNA synthesis. An increased incorporation of radioactivity into RNA in the presence of 1.0 mM Ca2+ was first observed at 0-3 h, and subsequently at all other times tested, following inoculation. A stimulation in rRNA and tRNA synthesis was detected in the presence of 1.0 mM Ca2+. The incorporation of radioactivity into proteins was stimulated 3-5 h following induction in the presence of Ca2+ suggesting a specific effect of Ca2+ on protein synthesis. This increased incorporation takes place prior to the start of DNA synthesis. Incorporation of radioactivity into DNA was also stimulated in the presence of Ca2+, 6 and 9 h after inoculation. This stimulation resulted in nuclear division taking place with a shorter lag period and proceeding with increased kinetics. The results reported here are evidence that Ca2+ plays a role in the control of the early molecular and cellular processes that accompany the yeast-to-mycelium transition in S. schenckii and offer an explanation of how Ca2+ can control the expression of the dimorphic potential of this fungus.