Novel PLCZ1 compound heterozygous mutations indicate gene dosage effect involved in total fertilisation failure after ICSI.

In brief: PLCZ1 mutations are related to total fertilisation failure (TFF) after intracytoplasmic sperm injection (ICSI), characterised by abnormal oocyte oscillations. The novel PLCZ1 compound heterozygous mutations reported by this study were associated with TFF after ICSI, with one of the mutations indicating a gene dosage effect. Abstract: Oocyte activation failure is thought to be one of the main factors for total fertilisation failure (TFF) after intracytoplasmic sperm injection (ICSI), which could be induced by abnormal calcium oscillations. Phospholipase C zeta (PLCZ), a sperm factor, is associated with Ca2+ oscillations in mammalian oocytes. To date, some mutations in PLCZ1 (the gene that encodes PLCZ) have been linked to TFF, as demonstrated by the observed reduction in protein levels or activity to induce Ca2+ oscillations. In this study, normozoospermic males whose sperms exhibited TFF after ICSI and their families were recruited. First, mutations in the PLCZ1 sequence were identified by whole exome sequencing and validated using Sanger sequencing. Then, the locations of PLCZ1/PLCZ and the transcript and protein levels in the sperm of the patients were studied. Subsequently, in vitro function analysis and in silico analysis were performed to investigate the function-structure correlation of mutations identified in PLCZ1 using western blotting, immunofluorescence, RT-qPCR, and molecular simulation. Ca2+ oscillations were detected after cRNA microinjection into MII mouse oocytes to investigate calcium oscillations induced by abnormal PLCZ. Five variants with compound heterozygosity were identified, consisting of five new mutations and three previously reported mutations distributed across the main domains of PLCZ, except the EF hands domain. The transcript and protein levels decreased to varying degrees among all detected mutations in PLCZ1 when transfected in HEK293T cells. Among these, mutations in M138V and R391* of PLCZ were unable to trigger typical Ca2+ oscillations. In case 5, aberrant localisation of PLCZ in the sperm head and an increased expression of PLCZ in the sperm were observed. In conclusion, this study enhances the potential for genetic diagnosis of TFF in clinics and elucidates the possible relationship between the function and structure of PLCZ in novel mutations.

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.