Abstract
Sperm glycocalyx and plasma membrane undergo outstanding modifications during fertilization. However, it is unclear how in vitro capacitation time and acrosome reaction affect the specific location of boar sperm glycoconjugates. This study aimed to identify lectin binding patterns and to describe the sequential changes during different in vitro capacitation times (1 and 4 h) and acrosome reaction in boar spermatozoa. With Aleuria aurantia agglutinin (AAA), most uncapacitated cells were labelled in the postacrosomal region. Nevertheless, after 1 h of in vitro capacitation and the acrosome reaction, most AAA binding sites were in the acrosomal region. With Concanavalin A (ConA), most sperm were labeled in the postacrosomal region before and after capacitation. After the acrosome reaction induction, this pattern changed to a highly stained acrosomal and postacrosomal regions. Peanut agglutinin (PNA) binding sites were in the acrosomal region in uncapacitated and capacitated sperm. In acrosome reacted sperm after 4h capacitation, the most frequent pattern showed remaining positive labeling in the central area of the head. With Pisum sativum agglutinin (PSA), most uncapacitated cells showed a postacrosomal region staining. Nevertheless, faint stained all over the head and highly acrosomal region labelling was observed in the major part of capacitated and acrosome reacted sperm respectively. With Wheat germ agglutinin (WGA), the most representative pattern in uncapacitated, capacitated and acrosome reacted sperm was labelled in the acrosomal region. Regarding capacitation time, the most significant changes in the most representative pattern were observed in acrosome reacted spermatozoa after 4 h of in vitro capacitation. Highlights Lectins allow detailed descriptions of eight different populations in boar sperm. Changes in lectin binding patterns during capacitation are time dependent. Lectin binding patterns significantly change after 4 h of in vitro capacitation.
Highlights
Mammalian spermatozoa are unable to fertilise an oocyte when ejaculated
Lectin binding patterns observed on sperm were the following: Pattern 1 (P1): Highly stained acrosomal region (AAc) with maximum fluorescence in apical ridge (ApR); Pattern 2 (P2): Faint stained all over the head; Pattern 3 (P3): Highly stained AAc and anterior (PAcA) and posterior postacrosomal region (PAcP) with no labelling in the equatorial segment (EqS); Pattern 4 (P4): labelling in the postacrosomal region (PAcA þ PAcP); Pattern 5 (P5): Highly stained AAc and faint labelling in EqS and PAcP with a non-labelled PAcA; Pattern 6 (P6): Highly stained EqS; Pattern 7 (P7): Stained AAc with maximum fluorescence at the end of AAc; Pattern 8 (P8): faint labelling in EqS
We detected a significant increase of P1 after 1 and 4 h capacitation compared to uncapacitated spermatozoa
Summary
Mammalian spermatozoa are unable to fertilise an oocyte when ejaculated They must undergo epididymal maturation, capacitation and acrosome reaction to achieve oocyte fertilisation (Okabe 2013). Sperm capacitation was first reported independently by Chang (1951) and Austin (1952) It is a gradual and multi-step process that occurs during the sperm sequential journey along the female genital tract in vivo (Yanagimachi 1994; Gervasi and Visconti 2016; Stival et al 2016). This process has been successfully reproduced in vitro by incubation in a chemically defined medium in many species (Edwards 1969; Rath et al 1999; Albarracın et al 2004; Agarwal et al 2017). Acrosome reaction is characterised as multiple fusions of the plasma membrane with the outer acrosomal membrane and the release of acrosomal contents including hydrolytic enzymes by exocytosis that
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