Acrosome reaction in spermatozoa from hagfish (Agnatha) Eptatretus burgeri and Eptatretus stouti: Acrosomal exocytosis and identification of filamentous actin

Abstract

Spermatozoa of the hagfishes Eptatretus burgeri and Eptatretus stouti , caught in the sea near Japan and North America, respectively, were found to undergo the acrosome reaction, which resulted in the formation of an acrosomal process with a filamentous core. The acrosomal region of spermatozoa of E. stouti exhibited immunofluorescent labeling using an actin antibody. The midpiece also labeled with the antibody. The acrosomal region showed a similar labeling pattern when sperm were probed with tetramethylrhodamine isothyocyanate (TRITC)-phalloidin; the midpiece did not label. Following induction of the acrosome reaction with the calcium (Ca 2+ ) ionophore ionomycin, TRITC-phalloidin labeling was more intense in the acrosomal region, suggesting that the polymerization of actin occurs during formation of the acrosomal process, as seen in many invertebrates. The potential for sperm to undergo acrosomal exocytosis was already acquired by late spermatids. During acrosomal exocytosis, the outer acrosomal membrane and the overlying plasma membrane disappeared and were replaced by an array of vesicles; these resembled an early stage of the acrosome reaction in spermatozoa of higher vertebrates in which no formation of an acrosomal process occurs. It is phylogenetically interesting that such phenomena occur in spermatozoa of hagfish, a primitive vertebrate positioning between invertebrates and high vertebrates.

Potential role of the acrosome of sturgeon spermatozoa in the fertilization process

“…Sturgeons, tunicate, lampreys, hagfish ( Eptatretus burgeri and E. stouti ) etc. (Cherr and Clark, 1984; Dettlaff et al., 1993; Kille, 1960; Morisawa, 1999; Morisawa and Cherr, 2002; Psenicka et al., 2010) are reported to possess spermatozoa that form fertilization filaments during the acrosome reaction, but only sturgeon eggs provide free entrance for spermatozoon. The latter eggs possess tens micropyles that could be advantageous for spermatozoa, but contrariwise offer a risk of polyspermy, which is usually lethal for embryos (Jaffe and Gould, 1985).…”

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

“…Spermatozoa of the sturgeon, Acipenser transmontanus , also form acrosomal processes, which appear to originate from the nuclear channels and the subacrosomal region (Cherr and Clark, 1982). Recent studies in hagfish, a member of the most primitive vertebrate group, showed an acrosome reaction with intermediate features between the mode in invertebrates and the one in vertebrates: an acrosomal process containing actin projects, deriving from the amorphous subacrosomal material, and the alignment of vesicles appears (Morisawa, 1999;Morisawa and Cherr, 2002). These aspects suggest that the mode of acrosome reaction is complicated in organisms on the border between invertebrates and vertebrates.…”

A Review on Environmental Contaminants-Related Fertility Threat in Male Fishes: Effects and Possible Mechanisms of Action Learned from Wildlife and Laboratory Studies

“…The distal centriole forms the basal body of the axoneme. Sperm is acrosomeless in teleostean fishes, while it possesses acrosome in primitive fishes, including hagfish and sturgeons [45,46]. Sperm morphology in primitive (chondrostei) and bony (teleostei) fishes.…”

“…These suggest that alternations in the size of sperm head and length of flagellum can result in diminished fertility by affecting sperm penetration into the oocytes or sperm motility performance. Various microscopic techniques including scanning and electron microscopy are valuable methods to assess sperm morphology [43,45,92].…”