Characterization of Gfat1 (zeppelin) and Gfat2, Essential Paralogous Genes Which Encode the Enzymes That Catalyze the Rate-Limiting Step in the Hexosamine Biosynthetic Pathway in Drosophila melanogaster

Gfa1 (glutamine fructose-6-phosphate aminotransferase) is essential for Aspergillus fumigatus growth and virulence

BACKGROUND

Aspergillus fumigatus, the primary etiological agent of invasive aspergillosis, causes over 1.8 million deaths annually. Targeting cell wall biosynthetic pathways offers a promising antifungal strategy. Gfa1, a rate-limiting enzyme in UDP-GlcNAc synthesis, plays a pivotal role in the hexosamine biosynthetic pathway (HBP).

RESULTS

Deletion of gfa1 (Δgfa1) results in auxotrophy for glucosamine (GlcN) or N-acetylglucosamine (GlcNAc). Under full recovery (FR) conditions, where minimal medium is supplemented with 5 mM GlcN as the sole carbon source, the Δgfa1 mutant shows growth comparable to the wild-type (WT). However, when supplemented with 5 mM GlcN and 55 mM glucose, growth is partially repressed, likely due to carbon catabolite repression, a condition termed partial repression (PR). Under PR conditions, Δgfa1 exhibits compromised growth, reduced conidiation, defective germination, impaired cell wall integrity, and increased sensitivity to endoplasmic reticulum (ER) stress and high temperatures. Additionally, Δgfa1 demonstrates disruptions in protein homeostasis and iron metabolism. Transcriptomic analysis of the mutant under PR conditions reveals significant alterations in carbohydrate and amino acid metabolism, unfolded protein response (UPR) processes, and iron assimilation. Importantly, Gfa1 is essential for A. fumigatus virulence, as demonstrated in Caenorhabditis elegans and Galleria mellonella infection models.

CONCLUSIONS

These findings underscore the critical role of Gfa1 in fungal pathogenicity and suggest its potential as a therapeutic target for combating A. fumigatus infections.

Cytological heterogeneity of heterochromatin among 10 sequenced Drosophila species

In Drosophila chromosomal rearrangements can be maintained and are associated with karyotypic variability among populations from different geographic localities. The abundance of variability in gene arrangements among chromosomal arms is even greater when comparing more distantly related species and the study of these chromosomal changes has provided insights into the evolutionary history of species in the genus. In addition, the sequencing of genomes of several Drosophila species has offered the opportunity to establish the global pattern of genomic evolution, at both genetic and chromosomal level. The combined approaches of comparative analysis of syntenic blocks and direct physical maps on polytene chromosomes have elucidated changes in the orientation of genomic sequences and the difference between heterochromatic and euchromatic regions. Unfortunately, the centromeric heterochromatic regions cannot be studied using the cytological maps of polytene chromosomes because they are underreplicated and therefore reside in the chromocenter. In Drosophila melanogaster, a cytological map of the heterochromatin has been elaborated using mitotic chromosomes from larval neuroblasts. In the current work, we have expanded on that mapping by producing cytological maps of the mitotic heterochromatin in an additional 10 sequenced Drosophila species. These maps highlight 2 apparently different paths, for the evolution of the pericentric heterochromatin between the subgenera Sophophora and Drosophila. One path leads toward a progressive complexity of the pericentric heterochromatin (Sophophora) and the other toward a progressive simplification (Drosophila). These maps are also useful for a better understanding how karyotypes have been altered by chromosome arm reshuffling during evolution.

A nexus of lipid and O-Glcnac metabolism in physiology and disease

Although traditionally considered a glucose metabolism-associated modification, the O-linked β-N-Acetylglucosamine (O-GlcNAc) regulatory system interacts extensively with lipids and is required to maintain lipid homeostasis. The enzymes of O-GlcNAc cycling have molecular properties consistent with those expected of broad-spectrum environmental sensors. By direct protein-protein interactions and catalytic modification, O-GlcNAc cycling enzymes may provide both acute and long-term adaptation to stress and other environmental stimuli such as nutrient availability. Depending on the cell type, hyperlipidemia potentiates or depresses O-GlcNAc levels, sometimes biphasically, through a diversity of unique mechanisms that target UDP-GlcNAc synthesis and the availability, activity and substrate selectivity of the glycosylation enzymes, O-GlcNAc Transferase (OGT) and O-GlcNAcase (OGA). At the same time, OGT activity in multiple tissues has been implicated in the homeostatic regulation of systemic lipid uptake, storage and release. Hyperlipidemic patterns of O-GlcNAcylation in these cells are consistent with both transient physiological adaptation and feedback uninhibited obesogenic and metabolic dysregulation. In this review, we summarize the numerous interconnections between lipid and O-GlcNAc metabolism. These links provide insights into how the O-GlcNAc regulatory system may contribute to lipid-associated diseases including obesity and metabolic syndrome.