Acrosome Reaction in Spermatozoa from the Amphioxus Acrosome Reaction in Branchiostoma belcheri (Cephalochordata, Chordata)

Abstract

The formation of an acrosomal process at acrosomal exocytosis in spermatozoa of the amphioxus was described in the present report for the first time. A non-reacted acrosome was located in front of the nucleus, where a cup-shaped acrosomal vesicle covered a conical accumulation of subacrosomal material. When naturally spawned spermatozoa were treated with a calcium ionophore, ionomycin, the acrosomal vesicle opened at the apex and an acrosomal process was projected. The process exhibited a filamentous structure. The reaction followed the mode typically seen in marine invertebrates. These observations suggest that the features and function of the acrosome of amphioxus, whose position is on the border between invertebrates and vertebrates, reflect their ecological adaptation and phylogenic position.

Protein kinase A activity leads to the extension of the acrosomal process in starfish sperm

“…Among Echinoderms, Crinoidea (crinoids) and sea urchins possess a short AP whereas starfish, Holothuroidea (sea cucumbers), and Ophiuroidea possess long APs (Naruse et al, ). Furthermore, Hemichordata, Cephalochordata, and Ctenophora sperm also form long APs (Colwin & Colwin, ; Morisawa, Mizuta, Kubokawa, Tanaka, & Morisawa, ). Therefore, how actin polymerization of PKA substrates occurs may be conserved in many species; we predict that PKAS1 orthologs function in their sperm as well.…”

Semen evaluation: methodological advancements in sperm quality-specific fertility assessment

“…In humans, the PR of sperm is mainly affected by thiols of flagellar proteins such as outer dense fiber protein 1, which are oxidized to form disulfides during epididymal transit and the sperm attains motility [ 53 ]. In animals, with external fertilization, usually, the exposure of sperm to the fertilization medium results in hypotonic shock that induces activation of motile function [ 54 , 55 ]. In mammals, cAMP signaling pathways and adenylyl cyclase are associated with progressive sperm motility [ 56 , 57 ].…”

Cephalochordata

“…A second polar body is produced and groups of maternal chromosomes migrate to one side of the animal pole until the sperm nucleus migrates to them and a zygote nucleus is formed. The sperm has a fl agellum, a round head, a single mitochondrion, and an acrosomal granule (Baccetti et al 1972 ) that undergoes exocytosis, producing a long acrosomal tubule (Morisawa et al 2004 ) that fuses with the egg (Holland and Holland 1992 ). Sperm/egg fusion follows the model of most other invertebrates having sperm with an acrosomal granule (Holland and Holland 1992 ).…”