Allelic Exchange of Pheromones and Their Receptors Reprograms Sexual Identity in Cryptococcus neoformans

Cell type specification is a fundamental process that all cells must carry out to ensure appropriate behaviors in response to environmental stimuli. In fungi, cell identity is critical for defining “sexes” known as mating types and is controlled by components of mating type (MAT) loci. MAT–encoded genes function to define sexes via two distinct paradigms: 1) by controlling transcription of components common to both sexes, or 2) by expressing specially encoded factors (pheromones and their receptors) that differ between mating types. The human fungal pathogen Cryptococcus neoformans has two mating types (a and α) that are specified by an extremely unusual MAT locus. The complex architecture of this locus makes it impossible to predict which paradigm governs mating type. To identify the mechanism by which the C. neoformans sexes are determined, we created strains in which the pheromone and pheromone receptor from one mating type (a) replaced the pheromone and pheromone receptor of the other (α). We discovered that these “αa” cells effectively adopt a new mating type (that of a cells); they sense and respond to α factor, they elicit a mating response from α cells, and they fuse with α cells. In addition, αa cells lose the α cell type-specific response to pheromone and do not form germ tubes, instead remaining spherical like a cells. Finally, we discovered that exogenous expression of the diploid/dikaryon-specific transcription factor Sxi2a could then promote complete sexual development in crosses between α and αa strains. These data reveal that cell identity in C. neoformans is controlled fully by three kinds of MAT–encoded proteins: pheromones, pheromone receptors, and homeodomain proteins. Our findings establish the mechanisms for maintenance of distinct cell types and subsequent developmental behaviors in this unusual human fungal pathogen

Assessing Lipid Composition of Cell Membranes in Escherichia coli under Aerobic and Anaerobic Conditions

Although Escherichia coli is a well-studied bacteria in the world of microbiology, there are still unknowns about its metabolism. For example, global changes during the transition from aerobic to anaerobic respiration with respect to pathways outside central carbon metabolism are poorly documented. In this research, I investigated the change in cell membrane lipid composition when aerobic cultures of Escherichia coli were put under anaerobic conditions. To set a baseline, my co-author and I incubated Escherichia coli in batches of 18, dividing the groups into 3 and taking UV-Vis measurements of colony growth at timepoints 3hrs, 4.5hrs, and 5hrs+. Half of the flasks were exposed to environmental oxygen while the other half were sealed with rubber stoppers. We planned to observe the transition of aerobic to anaerobic respiration, so we did not flush the sealed flasks with nitrogen gas. The growth curves indicated a slowdown of cell growth when oxygen was suspected to be depleted from the sealed flasks, but a resurgence of growth after a period of time. We collected 72 total samples over the course of 4 days. Cells were harvested at 3 hours, 4.5 hours, and 5 hours and then stored as frozen pellets. Half of these pellets were then sonicated and the lipid membrane was extracted via Folch lipid extraction. Samples of intact cells were analyzed directly with MALDI-MS. We determined there was a greater degree of unsaturation in the lipids from the anaerobic samples as compared to the aerobic samples, indicating a change from a more saturated phospholipid to a less saturated one. This project has laid the groundwork for future study of Escherichia coli lipid membrane transition. Escherichia coli is pathogenic in its anaerobic form in the human gut. Therefore, further research could explore therapies that could disrupt the Escherichia coli cell membrane transition as a treatment for Escherichia coli-caused food poisoning or other maladies

Sexually Dimorphic Alterations in the Transcriptome and Behavior with Loss of Histone Demethylase <i>KDM5C</i>

Chromatin dysregulation has emerged as a major hallmark of neurodevelopmental disorders such as intellectual disability (ID) and autism spectrum disorders (ASD). The prevalence of ID and ASD is higher in males compared to females, with unknown mechanisms. Intellectual developmental disorder, X-linked syndromic, Claes-Jensen type (MRXSCJ), is caused by loss-of-function mutations of lysine demethylase 5C (KDM5C), a histone H3K4 demethylase gene. KDM5C escapes X-inactivation, thereby presenting at a higher level in females. Initially, MRXSCJ was exclusively reported in males, while it is increasingly evident that females with heterozygous KDM5C mutations can show cognitive deficits. The mouse model of MRXSCJ, male Kdm5c-hemizygous knockout animals, recapitulates key features of human male patients. However, the behavioral and molecular traits of Kdm5c-heterozygous female mice remain incompletely characterized. Here, we report that gene expression and behavioral abnormalities are readily detectable in Kdm5c-heterozygous female mice, demonstrating the requirement for a higher KDM5C dose in females. Furthermore, we found both shared and sex-specific consequences of a reduced KDM5C dose in social behavior, gene expression, and genetic interaction with the counteracting enzyme KMT2A. These observations provide an essential insight into the sex-biased manifestation of neurodevelopmental disorders and sex chromosome evolution

Data from: Local adaptation of fish consumers alters primary production through changes in algal community composition and diversity

Ecological research has focused on understanding how changes in consumer abundance affect community structure and ecosystem processes. However, there is increasing evidence that evolutionary changes in consumers can also alter community structure and ecosystem processes. Typically, the effects of consumer phenotype on communities and ecosystem processes are measured as net effects that integrate numerous ecological pathways. Here, we analyze new data from experimental manipulations of Trinidadian guppy Poecilia reticulata presence, density and phenotype to examine how effects on the algal community cause changes in gross-primary production (GPP). We combine analytical tools borrowed from path analysis with experimental exclosures in mesocosms to separate the ecological and evolutionary effects of guppies into direct and indirect components. We show that the evolutionary effects of guppy phenotype act through different ecological pathways than the effects of guppy presence and density on GPP. As reported in previous studies that used a different measure of algal biomass, adding guppies and doubling their densities decreased algal biovolume through direct effects. In contrast to these previously reported results, exchanging guppy phenotypes that live without predators for phenotypes that live with predators did not affect algal biovolume. Instead, guppies from populations that live with predators increased the diversity of algal species and increased GPP compared to guppies that live without predators. These changes in the algal community were driven primarily by guppy phenotypes that live with predators—algal communities in mesocosms without fish were similar to those with guppies from predator-free locations, but both were different from mesocosms with guppies from populations that live with predators. Changes in the algal community were driven directly by differences in foraging behavior between the two consumer phenotypes. We reconcile these results with our previous findings, thereby enhancing our understanding of the relationship between ecological and evolutionary processes