Biallelic variants in DLGAP5 cause spindle assembly defects and human early embryonic arrest.

Study question: What effects do DLGAP5 defects have on human early embryo development?

Summary answer: DLGAP5 deficiency disrupts normal spindle assembly through its interaction with TACC3, leading to female infertility characterized by recurrent early embryonic arrest (REEA).

What is known already: REEA is a significant contributor to failures in assisted reproductive technology. While genetic factors play a crucial role, known gene variants account for only a small proportion of affected individuals, leaving many underlying genetic factors yet to be elucidated. The relationship between spindle assembly and early embryonic development has emerged as a key research focus, however, our understanding of bipolar spindles in human oocytes and early embryos remains limited, highlighting the need for further investigation into the essential molecular players involved.

Study design, size, duration: A total of 488 female patients experiencing infertility characterized as REEA were recruited from a university-affiliated center from November 2021 to December 2023.

Participants/materials, setting, methods: Whole-exome sequencing was performed on the REEA cohort to identify candidate variants. HeLa cells were transiently transfected with wild-type and mutant plasmids to evaluate protein abundance and localization. Mutant mRNAs were expressed at the zygote stage to monitor subsequent embryonic development. Immunoprecipitation-mass spectrometry was employed to identify altered interacting molecules associated with the candidate variants. Additionally, a site-directed mutant mouse model was developed to investigate the pathogenic mechanisms in vivo, validated with patient oocytes and arrested embryos.

Main results and the role of chance: The study identified two nonsense variants, one frameshift variant, and one missense pathogenic variant in the DLGAP5 gene of three independent families from the cohort of 488 REEA patients through whole-exome sequencing. All affected individuals displayed a Mendelian recessive inheritance pattern. These variants significantly altered protein length, abundance, or localization, resulting in spindle abnormalities in HeLa cells and mouse zygotes. Furthermore, the microinjection of exogenous mutant DLGAP5 mRNA into mouse zygote and the construction of Dlgap5 site-directed mutant mice successfully replicated the patient phenotypes. Functional studies, both in vivo and in vitro, revealed that DLGAP5 deficiency disrupts normal spindle assembly through its interaction with TACC3.

Limitations, reasons for caution: This study was unable to observe the dynamic changes in spindle assembly in oocytes from patients with DLGAP5 variants due to ethical restrictions. Additionally, a larger patient cohort is needed, particularly multi-center and multi-ethnic studies, to further establish the relationship between DLGAP5 variants and female infertility.

Wider implications of the findings: These findings suggest that DLGAP5 is essential for spindle assembly in oocytes through its interaction with TACC3. This could position DLGAP5 as a novel molecular diagnostic marker and a potential target for interventions in female infertility related to REEA.

Study funding/competing interest(s): This work was supported by the National Natural Science Foundation of China (82371672 and 82371667), the National Key Research and Development Program of China (2023YFC2705504 and 2022YFC2702300), the Natural Science Foundation of Hunan Province (2024JJ2083), the Science and Technology Innovation Program of Hunan Province (2023RC3233) and the Scientific Research Foundation of Reproductive and Genetic Hospital of CITIC-XIANGYA (YNXM-202202 and YNXM-202402), and Hunan Provincial Grant for Innovative Province Construction (2019SK4012). The authors declare they have no conflict of interest.

Trial registration number: N/A.