STUDY QUESTION: Can single-cell, mass spectrometry-based proteomics identify proteins associated with reduced developmental competence of Patl2-/- Metaphase II (MII) mouse oocytes and reveal therapeutic targets for Patl2-related infertility? SUMMARY ANSWER: Abnormal protein content is detected in Patl2-/- MII oocytes, which can be rescued by spindle transfer (ST). WHAT IS KNOWN ALREADY: PATL2 is an RNA-binding protein that represses maternal mRNA translation during oocyte maturation. PATL2 mutations in humans often cause germinal vesicle (GV) arrest, although some affected patients produce MII oocytes with reduced fertilization and embryo developmental potential. Consequently, oocyte donation is required. The Patl2-/- knockout mouse model offers a unique opportunity to study Patl2-related infertility and evaluate potential treatments. STUDY DESIGN, SIZE, DURATION: Patl2 -/- mice (C57BL/6NTac-Patl2tm1a), with deletion of exon 7, were bred from April 2021 to October 2023, yielding 36 homozygous females from 271 pups. To investigate the role of Patl2 at the MII stage, in vivo MII oocytes from Patl2-/- and Patl2+/+ females were collected for analysis of key quality markers and single-cell proteomics. Based on these results, maternal ST was tested to rescue abnormal embryo development. At least three replicates were conducted per experiment. PARTICIPANTS/MATERIALS, SETTINGS, METHODS: Four- to 12-week-old mice underwent superovulation and oocyte collection to assess in vitro and in vivo maturation. In vivo-matured MII oocytes were used to evaluate activation (AR) and blastocyst rates (BR) after PIEZO-ICSI, spindle configuration, and calcium oscillatory patterns following SrCl2 exposure. Vitrified-warmed oocytes were used for single-cell proteomics using a timsTOF ultra mass spectrometer operated in diaPASEF mode. ST involved transferring the Patl2-/- spindle to Patl2+/+ enucleated cytoplasm, followed by parthenogenetic activation (PA) via SrCl2 exposure. MAIN RESULTS AND THE ROLE OF CHANCE: Patl2 -/- females exhibit lower in vivo MII rates (79.63%) than Patl2+/+ females (89.39%, P = 0.0123) but similar in vitro maturation rates (GV-MII = 48.74%) compared to Patl2+/+ females (52.85%, P = 0.5230). After PIEZO-ICSI with wild-type sperm, reduced AR (Patl2-/- = 31.71%, Patl2+/+ = 76.74%, P < 0.0001) and BR (Patl2-/- = 7.69%, Patl2+/+ = 42.42%, P = 0.0237) were observed in knockout oocytes. However, Patl2-/- oocytes exhibited normal spindle rates (78.57%) as seen in Patl2+/+ oocytes (86.00%, P = 0.3491), as well as a similar capacity to sustain long-lasting calcium oscillations (A×F = 6.15 ± 4.80) compared to Patl2+/+ oocytes (A×F = 4.59 ± 2.96, P = 0.1453). Single-cell proteomics identified 4882 proteins and confirmed the absence of Patl2 in knockout oocytes, from analyzing 25 Patl2+/+ and 27 Patl2-/- MII oocytes. After filtering, 3747 proteins were used for statistical analysis, revealing 1508 differentially expressed proteins (q-value < 0.05; 992 downregulated, 516 upregulated in Patl2-/- oocytes). The levels of multiple RNA-binding proteins, some of which are proposed Patl2 interactors (Cpeb1, Eif4e1b), were found to be significantly reduced in Patl2-/- oocytes. Additionally, the protein products of several maternal effect genes (MEGs) implicated in mRNA regulation (Zar1, Igf2bp2) and cell cycle division (Tcl1a, Cdk1, Mos) were downregulated, while MEGs participating in epigenetic modifications (Zfp57, Trim28) were upregulated in the knockout group. Consistent with these observations, ST-PA treatment significantly increased AR (100%) and BR (75%) in the Patl2-/- oocytes in comparison to PA alone (AR = 75.95%, P = 0.0078; BR = 45.00%, P = 0.0128), effectively rescuing development to wild-type levels. Lastly, ST-PA treatment did not alter embryonic development in Patl2+/+ oocytes and produced outcomes comparable to PA alone, supporting the technical safety and applicability of the technique. LARGE SCALE DATA: The mass spectrometry proteomics data have been deposited to the ProteomeXchange Consortium via the PRIDE massIVE partner repository with the dataset identifier MSV000100606. LIMITATIONS, REASONS FOR CAUTION: Patl2 -/- mice exhibit a less severe phenotype compared to patients carrying PATL2 variants. Patl2-/- female mice display a high MII rate without significant spindle abnormalities, which contrasts with a previously published report. Additionally, ST treatment was conducted using parthenogenetically activated oocytes, rather than biparental embryos. WIDER IMPLICATIONS OF THE FINDINGS: ST represents a promising treatment for PATL2-related female infertility in patients with MII oocytes, as it appears to restore cytoplasmic defects linked to abnormal RNA-binding proteins and MEGs identified by single-cell proteomics. In contrast, other proposed treatments for poor embryo development, such as assisted oocyte activation, is unlikely to be effective since Patl2-/- oocytes show a normal calcium response. STUDY FUNDING/COMPETING INTEREST(S): This study was supported by the Special Research Fund (BOF) (starting grant BOF.STG.2021.0042.01 awarded to B.H.) and the Research Foundation-Flanders (FWO) (fellowship 1177425 N awarded to E.A.). B.H. has been receiving unrestricted educational funding from Ferring Pharmaceuticals (Aalst, Belgium). A.C.B., E.A., A.C., M.F-I-A., J.G., A.R., M.B., A.B., C.A., K.C.P., D.S., K.G., and F.V.M. have nothing to disclose. B.H. reports being board member of the Belgian Ethical Committee on embryo research.
Barberán et al. (Fri,) studied this question.