Mechanisms of oocyte activation in the presence and absence of PLCζ

Thesis

Mammalian oocyte activation is thought to be caused by a sperm borne PLC subtype, called phospholipase C zeta1 (PLCζ). PLCζ RNA and protein microinjection and knockout studies in a mouse model have confirmed its primary role in releasing calcium (Ca2+) in the oocyte at fertilisation. Studies revealed that a few delayed Ca2+ transients can still occur in the oocyte after fertilisation with PLCζ knockout sperm, resulting in a reduced embryo formation rate and increased polyspermy, but otherwise apparently normal development to term, indicating the presence of a secondary factor(s) which can stimulate Ca2+ release in the oocyte. In this study, an attempt was made to identify such a secondary factor(s). In silico analysis of transcriptomic data revealed that mature sperm cells carry transcripts of PLCβ, PLCγ, PLCδ, and PLCζ subtypes. In MII oocytes, PLCβ1, PLCβ3, PLCγ1, and PLCγ2 were reported to be expressed. The mRNA and protein expression analysis showed reorganised expressions in the PLCζ knockout sperm cells. This reorganised expression levels of IP3 generators led to investigate PLC subtypes as potential secondary factors of oocyte activation. Proteomic analysis of PLCζ knockout sperm cells suggested that some proteins showing differential expression that are overexpressed in PLCζ knockout sperm participate in acrosome reaction, fusion and binding of gametes. Pharmacological interventions and Ca2+ dynamics investigations suggest that interference with Gαq (Gq) mediated PLCβ activation has a significant impact on Ca2+ release as well as fertilisation indicators, for both PLCζ knockout and wild type sperm, in distinct ways. Blocking Gq mediated PLCβ activation also blocks secondary Ca2+ transients triggered by PLCζ deficient sperm. Collectively, these data suggest that gametes express a number of PLC isoforms with differential expression in PLCζ knockout sperm, and PLCβ isoforms can act as potential secondary factors during oocyte activation thorough the Gq pathway, in parallel to PLCζ.

Authors: Sahu, RK

• DOI: 10.5287/ora-wv9b79qed
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: sperm; fertilisation; PLCζ; oocyte activation
• Subjects: Pharmacology