Department of Biology, Texas A&M University, College Station, Texas, United States of America.
PLoS Genet. 2010 May 13;6(5):e1000953. doi: 10.1371/journal.pgen.1000953.
Cryptococcus neoformans is a human fungal pathogen that undergoes a dimorphic transition from a unicellular yeast to multicellular hyphae during opposite sex (mating) and unisexual reproduction (same-sex mating). Opposite- and same-sex mating are induced by similar environmental conditions and involve many shared components, including the conserved pheromone sensing Cpk1 MAPK signal transduction cascade that governs the dimorphic switch in C. neoformans. However, the homeodomain cell identity proteins Sxi1alpha/Sxi2a encoded by the mating type locus that are essential for completion of sexual reproduction following cell-cell fusion during opposite-sex mating are dispensable for same-sex mating. Therefore, identification of downstream targets of the Cpk1 MAPK pathway holds the key to understanding molecular mechanisms governing the two distinct developmental fates. Thus far, homology-based approaches failed to identify downstream transcription factors which may therefore be species-specific. Here, we applied insertional mutagenesis via Agrobacterium-mediated transformation and transcription analysis using whole genome microarrays to identify factors involved in C. neoformans differentiation. Two transcription factors, Mat2 and Znf2, were identified as key regulators of hyphal growth during same- and opposite-sex mating. Mat2 is an HMG domain factor, and Znf2 is a zinc finger protein; neither is encoded by the mating type locus. Genetic, phenotypic, and transcriptional analyses of Mat2 and Znf2 provide evidence that Mat2 is a downstream transcription factor of the Cpk1 MAPK pathway whereas Znf2 functions as a more terminal hyphal morphogenesis determinant. Although the components of the MAPK pathway including Mat2 are not required for virulence in animal models, Znf2, as a hyphal morphology determinant, is a negative regulator of virulence. Further characterization of these elements and their target circuits will reveal genes controlling biological processes central to fungal development and virulence.
新生隐球菌是一种人类真菌病原体，在异性（交配）和单性（同型交配）生殖过程中经历从单细胞酵母到多细胞菌丝的二态转变。异性和同型交配都是由相似的环境条件诱导的，涉及许多共同的成分，包括保守的交配型信号转导途径中的交配型 pheromone 感知 Cpk1 MAPK 信号转导级联，该途径控制新生隐球菌的二态转换。然而，在异性交配中细胞融合后完成有性生殖所必需的交配型位点编码的同源域细胞身份蛋白 Sxi1alpha/Sxi2a 对于同型交配是可有可无的。因此，鉴定 Cpk1 MAPK 途径的下游靶标是理解控制两种不同发育命运的分子机制的关键。到目前为止，基于同源性的方法未能鉴定可能是种特异性的下游转录因子。在这里，我们通过农杆菌介导的转化和全基因组微阵列的转录分析应用插入诱变来鉴定参与新生隐球菌分化的因素。鉴定了两个转录因子 Mat2 和 Znf2，它们是同型和异型交配过程中菌丝生长的关键调节剂。Mat2 是一个 HMG 结构域因子，Znf2 是一个锌指蛋白；两者都不是由交配型位点编码的。Mat2 和 Znf2 的遗传、表型和转录分析提供了证据，证明 Mat2 是 Cpk1 MAPK 途径的下游转录因子，而 Znf2 作为菌丝形态发生的决定因素，作用更为终端。尽管包括 Mat2 在内的 MAPK 途径的成分在动物模型中不影响毒力，但作为菌丝形态决定因素的 Znf2 是毒力的负调节剂。进一步对这些元件及其靶电路的特征分析将揭示控制真菌发育和毒力的中心生物学过程的基因。
