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Study Question: Does motile sperm organelle morphology examination (MSOME) affect levels and localization patterns of the oocyte activation factor phospholipase C zeta (PLCζ) in globozoospermic sperm with and without an acrosomal bud?, Summary Answer: MSOME identified round-headed globozoospermic sperm with increased levels of PLCζ relative to sperm from the same sample that did not undergo MSOME, and identified novel patterns of PLCζ localization in sperm exhibiting an acrosomal bud., What Is Known Already: Absence or reduction in the level of PLCζ in the sperm head, abnormal localization patterning, or defective functional ability as a result of PLCζ gene mutation, have been linked to certain types of human male factor infertility in which oocyte activation is deficient. It has been determined that a subpopulation of sperm (1%) from a patient exhibiting 100% globozoospermia presented with an acrosome bud upon MSOME. A cycle of intracytoplasmic morphologically selected sperm injection, carried out with sperm exhibiting an acrosomal bud led to pregnancy and birth of a healthy baby boy, without the use of assisted oocyte activation (AOA)., Study Design, Size, Duration: Immunofluorescent analysis of PLCζ in globozoospermic sperm from three patients, before and after MSOME., Participants/materials, Setting, Methods: Quantitative immunofluorescence was used to investigate PLCζ levels and localization patterns in individual sperm (n = 1 patient) identified by MSOME and isolated by micromanipulation, and presenting with and without the acrosomal bud. A secondary aim was to investigate levels and localization patterns of PLCζ in sperm before and after MSOME from two other globozoospermic men., Main Results and the Role of Chance: Non-globozoospermic control sperm exhibited characteristic localization patterns of PLCζ immunofluorescence. Completely round-headed globozoospermic sperm from patients 1-3 were either devoid of PLCζ immunofluorescence, or exhibited an abnormal, punctate, pattern of PLCζ localization. PLCζ immunofluorescence in sperm exhibiting an acrosomal bud was observed in the midpiece with varying fluorescent intensity and was detected in 28.5% of such sperm. The majority of sperm with an acrosomal bud (43.0%) exhibited punctate patterns of PLCζ localization within the sperm head. A further 28.5% of sperm exhibited PLCζ in both the head and the midpiece. Total levels of PLCζ, and the proportions of sperm exhibiting PLCζ immunoreactivity, showed significant variance (P ≤ 0.05) amongst control [45.8 arbitrary units (a.u.) and 95.7%, respectively], non-MSOME-selected (25.9 a.u. and 46.1%, respectively) and MSOME-selected globozoospermic sperm (33.4 a.u. and 65.0%, respectively). Total levels of PLCζ immunofluorescence, and proportions of sperm exhibiting PLCζ immunoreactivity, in control sperm was significantly higher (P≤ 0.05) compared with non-MSOME-selected sperm, but not significantly different from MSOME-selected sperm., Limitations, Reasons for Caution: The low numbers of sperm analysed may not be ideal for conclusive statistical analysis. Evaluation of the effects of MSOME on morphologically normal sperm would confirm conclusions., Wider Implications of the Findings: The present findings provide hope for the future treatment of globozoospermia without the need for AOA, and provide further evidence for the clinical application of PLCζ as a therapeutic and prognostic tool., Study Funding/competing Interest(s): The research described herein was funded by the Nuffield Department of Obstetrics and Gynaecology, University of Oxford. The authors report no conflict of interest.