Heterozygous mutations in ZP1 and ZP3 cause formation disorder of ZP and female infertility in human

Abstract

The human zona pellucida (ZP) is a highly organized glycoprotein matrix that encircles oocytes and plays an essential role in successful reproduction. Previous studies have reported that mutations in human ZP1, ZP2 and ZP3 influence their functions and result in a lack of ZP or in an abnormal oocytes and empty follicle syndrome, which leads to female infertility. Here, we performed whole‐exome sequencing in two probands with primary infertility whose oocytes lacked a ZP, and we identified a heterozygous mutation in ZP1 (NM_207341:c.326G>A p.Arg109His), which is situated in the N‐terminus, and a heterozygous mutation in ZP3 (NM_001110354:c.400G>A p.Ala134Thr), which is situated in the ZP domain. The effects of the mutations were investigated through structure prediction and in vitro studies in HeLa cells. The results, which were in line with the phenotype, suggested that these mutations might impede the function of cross‐linking and secretion of ZP proteins. Our study showed that the two mutations in ZP1 and ZP3 influenced the formation of the ZP, causing female infertility. Meanwhile, these data highlight the importance of the ZP1 N‐terminus in addition to the conserved domains for ZP1 function and ZP formation. Additionally, the patient with the ZP1 mutation delivered a baby following intracytoplasmic sperm injection (ICSI); thus, we suggest the targeted genetic diagnosis of ZP genes to choose appropriate fertilization methods and improve the success rate of assisted reproductive technology (ART) treatments.

Novel mutations in ZP1: Expanding the mutational spectrum associated with empty follicle syndrome in infertile women

“…Prediction of ZP1 protein structure showed that the mutation p.C376Y may disable the formation of the disulfide bond and cause a potential instability of ZP1 protein, but the mutation p.R109C may not affect the stability of ZP1 structure, and might influence the interactions with the residues of other protein nearby (Figure 1(C)). It was noted that the previously reported mutation (c.326G > A, p.R109H) had the same protein mutation site as the present mutation (c.325C > T, p.R109C), and this study reported the p.R109H mutation caused ZP‐free oocytes due to reduced interaction with ZP2 and ZP3 17 . Therefore, we speculated that the mutation p.R109C might also impede the crosslink function of ZP1, resulting in ZP formation failure.…”

New Insights into the Mammalian Egg Zona Pellucida

“…A compilation of ZP1, ZP2, and ZP3 mutations in women can be found in [ 22 ]. Recent studies indicated that ZP1 mutations are related with infertility, which may be associated with empty follicle syndrome (EFS) [ 64 , 65 , 66 , 67 , 68 , 69 ] or with ZP-free oocytes [ 70 , 71 , 72 , 73 ]. It was suggested that ZP1 mutations may affect the shuttling of glycoproteins to the secretory pathway, which would prevent the formation of the ZP around the oocyte, but also the formation and development of eggs [ 70 ].…”

“…It was suggested that ZP1 mutations may affect the shuttling of glycoproteins to the secretory pathway, which would prevent the formation of the ZP around the oocyte, but also the formation and development of eggs [ 70 ]. However, it was recently suggested that this lack of ZP is due to an impairment of ZP1 secretion that leads to the absence of filament crosslinking [ 73 , 74 ]. On the other hand, ZP2 mutations produce ZP-free oocytes [ 72 ] or oocytes surrounded by a thin ZP [ 68 , 72 , 75 ], as observed in KO mice for Zp2 [ 45 ].…”

“…These oocytes could not be fertilized by in vitro fertilization (IVF) techniques, but they were fertilized by intracytoplasmic sperm injection (ICSI) [ 75 ], which suggests that ZP2 is involved in sperm interaction and is essential for fertilization. In other studies, ZP3 mutations, which induce zona free-oocytes [ 72 , 73 ] or EFS were described [ 73 , 76 ]. These mutations could impede ZP assembly, inducing oocyte degeneration and empty COCs [ 73 , 76 ].…”

“…In other studies, ZP3 mutations, which induce zona free-oocytes [ 72 , 73 ] or EFS were described [ 73 , 76 ]. These mutations could impede ZP assembly, inducing oocyte degeneration and empty COCs [ 73 , 76 ]. In relation to ZP4 , Wei et al, described some infertile patients with a thin and irregular ZP and identified some ZP4 mutations; the authors proposing ICSI as a good strategy for fertilizing the oocytes [ 77 ].…”