[The potential of G-quadruplexes as a therapeutic target for neurological diseases]

Disruption of a DNA G-quadruplex causes a gain-of-function SCL45A1 variant relevant to developmental disorders

SLC45A1 encodes a glucose transporter protein highly expressed in the brain. Mutations in SLC45A1 may lead to neurological diseases and developmental disorders, but its exact role is poorly understood. DNA G-quadruplexes (DNA G4s) are stable structures formed by four guanine bases and play a role in gene regulation and genomic stability. Changes in DNA G4s may affect brain development and function. The mechanism linking alterations in DNA G-quadruplex structures to SLC45A1 pathogenicity remains unknown. In this study, we identify a functional DNA G-quadruplex and its key binding site on SLC45A1 (NM_001080397.3: exon 2: c.449 G>A: p.R150K). This variant results in the upregulation of mRNA and protein expression, which may lead to intellectual developmental disorder with neuropsychiatric features. Mechanistically, the mutation is found to disrupt DNA G-quadruplex structures on SLC45A1, leading to transcriptional enhancement and a gain-of-function mutation, which further causes increased expression and function of the SLC45A1 protein. The identification of the functional DNA G-quadruplex and its effects on DNA G4s may provide new insights into the genetic basis of SLC45A1 pathogenicity and highlight the importance of DNA G4s of SLC45A1 in regulating gene expression and brain development.

G-quadruplex occurrence and conservation: more than just a question of guanine–cytosine content

G-quadruplexes are motifs found in DNA and RNA that can fold into tertiary structures. Until now, they have been studied experimentally mainly in humans and a few other species. Recently, predictions have been made with bacterial and archaeal genomes. Nevertheless, a global comparison of predicted G4s (pG4s) across and within the three living kingdoms has not been addressed. In this study, we aimed to predict G4s in genes and transcripts of all kingdoms of living organisms and investigated the differences in their distributions. The relation of the predictions with GC content was studied. It appears that GC content is not the only parameter impacting G4 predictions and abundance. The distribution of pG4 densities varies depending on the class of transcripts and the group of species. Indeed, we have observed that, in coding transcripts, there are more predicted G4s than expected for eukaryotes but not for archaea and bacteria, while in noncoding transcripts, there are as many or fewer predicted G4s in all species groups. We even noticed that some species with the same GC content presented different pG4 profiles. For instance, Leishmania major and Chlamydomonas reinhardtii both have 60% of GC content, but the former has a pG4 density of 0.07 and the latter 1.16.