| Summary: | <p>Abstract</p> <p>Background</p> <p><it>Paracoccidioides brasiliensis </it>is a human pathogen with a broad distribution in Latin America. The fungus is thermally dimorphic with two distinct forms corresponding to completely different lifestyles. Upon elevation of the temperature to that of the mammalian body, the fungus adopts a yeast-like form that is exclusively associated with its pathogenic lifestyle. We describe expressed sequence tags (ESTs) analysis to assess the expression profile of the mycelium to yeast transition. To identify <it>P. brasiliensis </it>differentially expressed sequences during conversion we performed a large-scale comparative analysis between <it>P. brasiliensis </it>ESTs identified in the transition transcriptome and databases.</p> <p>Results</p> <p>Our analysis was based on 1107 ESTs from a transition cDNA library of <it>P. brasiliensis</it>. A total of 639 consensus sequences were assembled. Genes of primary metabolism, energy, protein synthesis and fate, cellular transport, biogenesis of cellular components were represented in the transition cDNA library. A considerable number of genes (7.51%) had not been previously reported for <it>P. brasiliensis </it>in public databases. Gene expression analysis using in silico EST subtraction revealed that numerous genes were more expressed during the transition phase when compared to the mycelial ESTs <abbrgrp><abbr bid="B1">1</abbr></abbrgrp>. Classes of differentially expressed sequences were selected for further analysis including: genes related to the synthesis/remodeling of the cell wall/membrane. Thirty four genes from this family were induced. Ten genes related to signal transduction were increased. Twelve genes encoding putative virulence factors manifested increased expression. The in silico approach was validated by northern blot and semi-quantitative RT-PCR.</p> <p>Conclusion</p> <p>The developmental program of <it>P. brasiliensis </it>is characterized by significant differential positive modulation of the cell wall/membrane related transcripts, and signal transduction proteins, suggesting the related processes important contributors to dimorphism. Also, putative virulence factors are more expressed in the transition process suggesting adaptation to the host of the yeast incoming parasitic phase. Those genes provide ideal candidates for further studies directed at understanding fungal morphogenesis and its regulation.</p>
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