Oocyte activation ability correlates with head flatness and presence of perinuclear theca substance in human and mouse sperm

Abstract

BACKGROUNDRecent studies indicate that round-headed sperm cannot activate oocytes and lack the postacrosomal sheath (PAS) or perinuclear theca (PT), although normal flat-headed sperm can activate oocytes and do have PAS (PT). In this study, we investigated how oocyte activation ability correlates with sperm head morphology (round and flat) and the presence of PT, by studying MN13, a representative molecule of the PT.METHODSWe analyzed sperm with flat and round heads from infertile patients with globozoospermia (n = 1) and teratozoospermia (n = 1), and also from GOPC-/- mice, an animal model of human globozoospermia. Differential interference contrast image analysis, immunocytochemistry with MN13 antibody, transmission electron microscopy and an oocyte activation assay (assessing pronucleus formation) with ICSI were used.RESULTSFlat-headed (control) sperm from both a healthy fertile volunteer man and wild-type mice had MN13 and PAS (PT). Flat-headed sperm (<5 of the population) from GOPC-/- mice also had both MN13 and PAS (PT), and they showed high oocyte activation ability. In contrast, round-headed sperm from a globozoospermia patient (100) and GOPC-/- mice (>95 of the population) had neither MN13, nor PAS (PT), nor oocyte activation ability. Oocyte activation was higher in flat- versus round-headed sperm from GOPC -/- mice (P < 0.05).CONCLUSIONSOocyte activation ability may be related to sperm head flatness and presence of MN13 and PAS (PT) in human and mouse sperm. This information is a first step towards the possibility of selecting good-quality sperm with high oocyte activation ability for ICSI.