Histoplasma capsulatum causes pulmonary infection after inhaling microconidia, which convert to yeast form in lung macrophages. The temperature-dependent dimorphism switch from mold to yeast is mediated by:

• A cAMP-PKA signaling pathway activated by CO2 in lung alveoli
• B MAPK Hog1 signaling pathway sensing osmotic changes in macrophage phagosome
• C Calcineurin pathway activated by calcium released from phagolysosome
• D Transcription factor Ryp1 activating yeast-phase specific genes in response to 37°C heat shock ✓

Explanation

In Histoplasma capsulatum, the regulatory yeast-phase program (Ryp) transcription factors (Ryp1/WOR1, Ryp2, Ryp3) are master regulators of the mold-to-yeast transition; Ryp1 is a WOR1 homolog that, when activated at 37°C, induces yeast-phase gene expression including the surface protein Yps3 and virulence determinants. The cAMP-PKA pathway regulates morphogenesis in Candida albicans (hyphal switch). Hog1 MAPK responds to osmotic and oxidative stress. Calcineurin is important for azole tolerance in Aspergillus and Candida.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.