1. Carbonic Anhydrase and CO2 Sensing during Cryptococcus neoformans Growth, Differentiation, and Virulence 
Yong-Sun Bahn, Gary M. Cox, John R. Perfect, Joseph Heitman 
Current Biology 
Volume 15, Issue 22, Pages (November 2005)
DOI: /j.cub
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2. Figure 1
Can2 Is the Major β-Carbonic Anhydrase Essential for Normal C. neoformans Growth and Fatty Acid Biosynthesis at Ambient CO2 Concentrations
(A) Northern blot analysis was performed with total RNA isolated from the indicated strains grown at 30°C on solid YPD medium with or without 5% CO2 and probed with CAN1 or CAN2 gene probes followed by an ACT1 probe as a control: wt (H99), can1 (YSB44), can2 (YSB100), can2+CAN2 (YSB260), and can1 can2 (YSB158).
(B) The following strains were grown on solid YPD medium at 30°C with or without 5% CO2: wt, can1, can1+CAN1 (YSB294), can2, can2+CAN2, and can1 can2.
(C) Heterologous expression of C. neoformans CA genes rescues growth of the S. cerevisiae nce103Δ mutant. Strains were grown on synthetic dextrose (SD) medium lacking uracil and incubated in ambient or high CO2 conditions at 30°C: haploid wt S. cerevisiae strain (CEN.PK2-1D) containing vector only (pTH19; WT+vector), haploid S. cerevisiae nce103Δ mutant (CEN.HE28-1α) containing vector only (pTH19; nce103Δ+vector), pADH-ScNCE103 (nce103Δ+NCE103), pADH-CAN1 (nce103Δ+CAN1), or pADH-CAN2 (nce103+CAN2).
(D) C. neoformans (wt, can2, and can2+CAN2) and S. cerevisiae (wt and nce103Δ) strains grown overnight on YPD medium in high CO2 were collected, serially diluted (10-fold), and spotted onto YPD medium containing palmitic acid with 1% Tween 80 as surfactant. Amino acid or purine/pyrimidine bases were added at a concentration of 30 mg/l: Ade (adenine), Asp (L-aspartate), and Arg (L-arginine) to SD medium containing Tween 80 (1%) and 2 mM palmitic acid. Cells were incubated at 30°C in ambient air for 5 days and photographed.
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3. Figure 2
CO2 Repression of Mating Requires Can2, which Is Essential for Sporulation in the Later Stages of Mating
(A) α and a strains were cocultured on solid V8 medium (pH 5.0) for 2 weeks at room temperature in the dark with or without a GasPak that produces 4%–10% CO2 in a jar, and representative mating patch edges were photographed at 100× magnification: α wt × a wt (H99 and KN99a), α can1 × a can1 (YSB44 and YSB133), α can2 × a can2 (YSB100 and YSB104), and α can2+CAN2 × a can2 (YSB260 and YSB104).
(B) α and a wt or can2Δ strains were cocultured on solid V8 medium containing the designated amounts of NaHCO3 and incubated for 2 weeks at room temperature in ambient conditions for wt or in a CO2 GasPak jar for the can2Δ mutants.
(C) Representative edges of the mating patches in (A) were photographed at 500× magnification.
(D) Nuclear migration during the α wt × a wt, α can1 × a can1 (in ambient air), and α can2 × a can2 mating (in high CO2) was visualized by DAPI staining and by microscopy. Scale bar equals 10 μm.
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4. Figure 3
CO2 Inhibits Cell-Cell Fusion by Repressing Pheromone Production in the Early Stages of Mating
(A) Cell fusion assays were performed with α wt × a wt (YSB119 and YSB121) and α can2 × a can2 (YSB100 and YSB104). Equal numbers of NAT-marked α and NEO-marked a cells (5 × 104 cells each) were mixed and incubated on solid V8 medium for 24 hr at room temperature with or without a CO2-generating GasPak. Cells were harvested, spread, and incubated at room temperature on YPD medium containing nourseothricin and G418, in ambient conditions for wt strains or high CO2 for can2Δ mutants. Percentage of cell fusion relative to the wt mating at ambient CO2 (100%) was calculated by averaging results from three independent experiments with standard deviation, as indicated.
(B) Cell fusion assays were performed with wt strains (α wt × a wt) in ambient conditions as described in (A). These cells were collected and further incubated for 5 days at room temperature on YPD medium containing nourseothricin and G418 with or without high CO2. For can2Δ mutants, both cell fusion and diploid incubation were performed under high CO2.
(C) Northern blot analysis was performed with total RNA isolated from single or cocultures of the indicated strain(s) grown for 24 hr under mating conditions in ambient or high CO2 and probed with the MFα1 gene and subsequently with an ACT1 control: WTα (H99), WTa (KN99a), can2α (YSB100), and can2a (YSB104).
(D) Mating was induced as described in Figure 2A between the following α and a strains: α wt × a wt (H99 and KN99a), α hog1 × a hog1 (YSB64 and YSB81), and α crg1 × a crg1 (H99 crg1 and PPW196).
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5. Figure 4
Carbonic Anhydrases Are Not Required for In Vivo Growth or Virulence of C. neoformans
(A) Immunocompromised rabbits (two for wt strains and three for can2Δ mutants) were inoculated intrathecally with a mixture of NAT-marked α and NEO-marked a wt (YSB119 and YSB121, respectively) and can2Δ strains (YSB100 and YSB104, respectively). The initial inoculum for each strain was 2.33 × 107 cells for α wt (diamond), 2.85 × 107 cells for a wt (square), and 3 × 107 cells for both α (asterisk) and a can2Δ (circle) mutants. Cerebrospinal fluid (CSF) was removed on days 2, 5, and 9 after inoculation, and the number of α, a, and α/a cell fusion products or diploid cells was determined. Each data point represents the log10 value of the average number of α and a cells for each strain, and error bars represent the standard deviation. No mating type preference was observed in either wt or can2Δ mutants in terms of fungal burden, exhibiting similar CFU/ml CSF for α and a cells at each time point.
(B) Capsules produced in vivo by wt and can2Δ mutant strains recovered from rabbit CSF (day 5) were visualized with India ink. Scale bar equals 5 μm.
(C) can2Δ mutants recovered from infected animals required CO2 to grow in vitro. Cells recovered from rabbit CSF at each time point were grown at 30°C on solid YPD medium in a 5% CO2 incubator for 2 days, replica-plated onto YPD medium, and further incubated at 30°C with or without high CO2 (5%).
Current Biology  , DOI: ( /j.cub )
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