Loss of activity mutations in phospholipase C zeta (PLCζ) abolishes calcium oscillatory ability of human recombinant protein in mouse oocytes.
BACKGROUND
Mammalian oocyte activation occurs via a series of intracellular calcium (Ca(2+)) oscillations thought to be induced by a sperm-specific phospholipase C zeta (PLCζ). There is now strong evidence to indicate that certain types of human male infertility are caused by failure of the sperm to activate the oocyte in an appropriate manner. Molecular analysis of the PLCζ gene of a male patient with oocyte activation deficiency has previously identified a point mutation causing a histidine to proline substitution at PLCζ residue 398 (PLCζ(H398P)), leading to abnormal Ca(2+) release profiles and reduced oocyte activation efficiency.


RESULTS
In the present study, we used HEK293T cells to produce recombinant human wild-type PLCζ (PLCζ(WT)) protein which, upon microinjection into mouse oocytes, induced Ca(2+) oscillations characteristic of oocyte activation. Injection of recombinant PLCζ(H398P) was unable to elicit Ca(2+) oscillations in mouse oocytes. Loss of activity mutations, such as PLCζ(H398P) and an artificially induced frameshift mutation (PLCζ(ΔYC2)) did not affect Ca(2+) release when over-expressed in HEK293T cells, whereas PLCζ(WT) inhibited adenosine triphosphate-activated Ca(2+) release. Confocal imaging of fluorescently tagged PLCζ isoforms in HEK293T cells suggested a cytoplasmic pattern of localization, while quantitative analysis of fluorescence levels showed that PLCζ(WT) > PLCζ(H398P) > PLCζ(ΔYC2), indicating that loss of activity mutations may lead to protein instability. This was further indicated by the low proportion of sperm and the lower levels of total PLCζ immunofluorescence from the patient exhibiting PLCζ(H398P) compared with fertile controls.


CONCLUSIONS
We demonstrate, for the first time, the production of active recombinant human PLCζ protein which retained the ability to elicit characteristic Ca(2+) oscillations in mouse oocytes, an ability which was eliminated by an infertility-linked mutation. These findings advance our understanding of PLCζ, and provide a critical step forward in obtaining purified PLCζ protein as a potential therapeutic agent for oocyte activation deficiency.
Nuffield Department of Obstetrics and Gynaecology, Level 3, Women's Centre, John Radcliffe Hospital, Headington,Oxford OX3 9DU, UK. kevin.coward@obs-gyn.ox.ac.uk
Junaid
J
Kashir
Celine
C
Jones
Hoi Chang
HC
Lee
Katja
K
Rietdorf
Dimitra
D
Nikiforaki
Claire
C
Durrans
Margarida
M
Ruas
Sze Tian
ST
Tee
Bjorn
B
Heindryckx
Antony
A
Galione
Petra
P
De Sutter
Rafael A
RA
Fissore
John
J
Parrington
Kevin
K
Coward
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005260:Female; D005455:Fluorescent Antibody Technique; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D051379:Mice; D009154:Mutation; D009865:Oocytes / Q000378:metabolism*; D054801:Phosphoinositide Phospholipase C / Q000235:genetics*; D011994:Recombinant Proteins / Q000378:metabolism; D013084:Sperm-Ovum Interactions; D013094:Spermatozoa / Q000378:metabolism
D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; C499235:PLCZ1 protein, human; D054801:Phosphoinositide Phospholipase C; D002118:Calcium