Differential expression of chitin synthase genes during temperature-induced dimorphic transitions in Paracoccidioides brasiliensis

Fragments of five genes encoding chitin synthase enzymes were identified in the dimorphic fungus Paracoccidioides brasiliensis by polymerase chain rea ction (PCR) amplification of conserved CHS gene domains. These represent se veral classes of enzyme: PbrCHS1, class I; PbrCHS2, class II; PbrCHS3, clas s IV; and PbrCHS4 and PbrCHS5, class V. Expression of these genes during th e temperature regulated dimorphic transition from yeast to mycelium and fro m mycelium to yeast was determined by Northern analysis. One gene (PbrCHS3) was not expressed at detectable levels. The others were regulated by morph ology and/or by the growth phase of the organism. Despite the fact that yea st cells contain more chitin than hyphal cells, the levels of mRNA for PbrC HS1, PbrCHS2, PbrCHS4 and PbrCHS5 were higher in hyphal cells than in yeast cells. This supports observations in other fungi that transcript levels of ten do not correlate with chitin content and that post-transcriptional regu lation of CHS gene expression is important for morphogenesis.