On the History and Applications of Congenic Strains in Cryptococcus Research

Abstract

Congenic strains have been utilized in numerous model organisms to determine the genetic underpinning of various phenotypic traits. Congenic strains are usually derived after 10 backcrosses to a recipient parent, at which point they are 99.95% genetically identical to the parental strain. In recent decades, congenic pairs have provided an invaluable tool for genetics and molecular biology research in the Cryptococcus neoformans species complex. Here, we summarize the history of Cryptococcus congenic pairs and their application in Cryptococcus research on topics including the impact of the mating type locus on unisexual reproduction, virulence, tissue tropism, uniparental mitochondrial inheritance, and the genetic underpinning of other various traits. We also discuss the limitations of these approaches and other biological questions, which could be explored by employing congenic pairs.

The RAM signaling pathway links morphology, thermotolerance, and CO2 tolerance in the global fungal pathogen Cryptococcus neoformans

“…In this intranasal infection model, the WT H99 strain establishes lung infection first and typically disseminates to other organs including the brain at about 7-10 days post-infection (DPI). Mice infected by H99 normally reach clinical endpoint around 3-4 weeks post-infection and these mice have a high fungal burden in the lungs, brain, and kidney (Chadwick & Lin, 2020; Jianfeng Lin et al, 2022). As expected, all mice infected by H99 were moribund by DPI 26 (Figure 5A) while the cbk1 Δ mutant failed to cause any mortality when we terminated the experiment at DPI 60.…”

Identification and Characterization of an Intergenic “Safe Haven” Region in Human Fungal Pathogen Cryptococcus gattii

“…Furthermore, its genome has been sequenced and annotated [39] and transcriptome data are available [26,40]. Lastly, congenic pair strains (AIR265a and AIR265α), which are genetically similar and differ primarily in the mating type locus, are only available in an R265 background [41,42]. Therefore, characterization of safe haven regions in this C. gattii reference strain would likely generate most impact in this field.…”

Methods for Manipulating Cryptococcus Spores

“…x JEC21 [15,16]: spores from crosses between the congenic laboratory type strains JEC20 and JEC21 are relatively easy to purify because they produce large quantities of spores, and the yeast from these crosses do not co-sediment with spores during centrifugation, making yeast impurities generally low (<1%). The following purification protocol has been optimized for this strain pair.…”