Neurospora crassa heat shock factor 1 Is an essential gene; a second heat shock factor-like gene, hsf2, is required for asexual spore formation.

Appropriate responses of organisms to heat stress are essential for their survival. In eukaryotes, adaptation to high temperatures is mediated by heat shock transcription factors (HSFs). HSFs regulate the expression of heat shock proteins, which function as molecular chaperones assisting in protein folding and stability. In many model organisms a great deal is known about the products of hsf genes. An important exception is the filamentous fungus and model eukaryote Neurospora crassa. Here we show that two Neurospora crassa genes whose protein products share similarity to known HSFs play different biological roles. We report that heat shock factor 1 (hsf1) is an essential gene and that hsf2 is required for asexual development. Conidiation may be blocked in the hsf2 knockout (hsf2(KO)) strain because HSF2 is an integral element of the conidiation pathway or because it affects the availability of protein chaperones. We report that genes expressed during conidiation, for example fluffy, conidiation-10, and repressor of conidiation-1 show wild-type levels of expression in a hsf2(KO) strain. However, consistent with the lack of macroconidium development, levels of eas are much reduced. Cultures of the hsf2(KO) strain along with two other aconidial strains, the fluffy and aconidial-2 strains, took longer than the wild type to recover from heat shock. Altered expression profiles of hsp90 and a putative hsp90-associated protein in the hsf2(KO) strain after exposure to heat shock may in part account for its reduced ability to cope with heat stress.

Epithelial Bmpr1a regulates differentiation and proliferation in postnatal hair follicles and is essential for tooth development.

Bone morphogenetic protein (BMP) signaling is thought to perform multiple functions in the regulation of skin appendage morphogenesis and the postnatal growth of hair follicles. However, definitive genetic evidence for these roles has been lacking. Here, we show that Cre-mediated mutation of the gene encoding BMP receptor 1A in the surface epithelium and its derivatives causes arrest of tooth morphogenesis and lack of external hair. The hair shaft and hair follicle inner root sheath (IRS) fail to differentiate, and expression of the known transcriptional regulators of follicular differentiation Msx1, Msx2, Foxn1 and Gata3 is markedly downregulated or absent in mutant follicles. Lef1 expression is maintained, but nuclear beta-catenin is absent from the epithelium of severely affected mutant follicles, indicating that activation of the WNT pathway lies downstream of BMPR1A signaling in postnatal follicles. Mutant hair follicles fail to undergo programmed regression, and instead continue to proliferate, producing follicular cysts and matricomas. These results provide definitive genetic evidence that epithelial Bmpr1a is required for completion of tooth morphogenesis, and regulates terminal differentiation and proliferation in postnatal hair follicles.