COL11A1 accumulation in the zona pellucida is associated with morphological severity of agar-like zona pellucida in human oocytes.

Agar-like zona pellucida (AZP) is a rare abnormality of the zona pellucida (ZP) characterized by a compact, homogeneous matrix and a markedly narrowed or absent perivitelline space. In this study, we integrated clinical phenotyping, ultrastructural analysis, single-oocyte RNA sequencing, immunofluorescence, and collagenase treatment to investigate molecular features associated with AZP severity. Immunofluorescence showed no obvious loss or redistribution of the canonical ZP glycoproteins ZP1-ZP4, whereas ultrastructural analysis revealed marked matrix compaction and disorganization. Single-oocyte RNA sequencing identified COL11A1 as a prominently upregulated candidate gene in AZP oocytes. At the protein level, COL11A1 accumulated within the ZP, and stronger COL11A1 signals were observed with increasing morphological severity from mild to typical AZP. In a limited number of AZP oocytes, collagenase treatment produced partial re-expansion of the perivitelline space and reduced ZP compactness, indicating a partial morphological response. Collectively, these findings identify COL11A1 upregulation and ZP-associated COL11A1 accumulation as prominent molecular features of AZP and suggest that COL11A1 accumulation is associated with morphological severity. Further studies are required to determine whether COL11A1 contributes causally to ZP remodeling and whether it can serve as a reliable severity-associated biomarker.