Induction of gynogenesis and effects of ultraviolet irradiation on ultrastructure of sperm of the Zhikong scallop Chlamys farreri

Abstract

Effects of ultraviolet (UV) irradiation on genetic inactivation and ultrastructure of sperm were examined in the scallop Chlamys farreri . UV irradiation of sperm for 30 s at a UV intensity of 256 erg/mm 2 per s was the optimum dose to achieve haploid gynogenesis on the basis of observations on rate of cleaved eggs, chromosome constitutions and flow cytometry analysis of the larvae. The rates of cleaved eggs and development of D-shaped larvae decreased with increasing irradiation time, while the survival rate of trochophore larvae improved at UV exposure longer than 20 s, suggesting the presence of a 'Hertwig effect' in the gynogenesis of C. farreri. Electron microscopy showed clear destruction of the acrosome, cytoplasmic membrane, nuclear envelope, mitochondrial cristae, and flagellum in the UV-irradiated sperm. Moreover, an irradiation duration of 30 s caused decondensation of sperm chromatin. Abnormalities in these structures might affect the ability of sperm to fertilize the eggs.

Induction of gynogenetic diploids and cytological studies in the zhikong scallop,Chlamys farreri

“…Instead, the male pronucleus became a dense chromatin body which did not participate in karyokinesis. These results are fundamentally identical to cytological observations of gynogenetic haploid scallop zygotes (Pan et al 2004), indicating that CB and 6-DMAP treatments did not affect the behavior of the UV-irradiated sperm nucleus during meiosis and cleavage.…”

“…During insemination and treatment, the water temperature was maintained at 20 • C. The procedures following the UV-irradiation of the sperm were performed in the absence of visible light to prevent the possible photoreactivation of the sperm's DNA (Ijiri and Egami 1980). The starting time of the 6-DMAP and CB treatments was based on cytological observation (Pan et al 2004). CB and 6-DMAP concentrations were based on previous papers (Lu and Wang 1992;Yang et al 1997;Yang et al 1999).…”

Sperm nuclear expansion and meiotic maturation in normal and gynogenetic eggs of the scallop, Chlamys farreri

“…The dish was placed on a recipro shaker (Guohua Inc., Changzhou, China) 15 cm below an 15 W UV germicidal light (Toshiba GL15, 254 nm of UV wave length; Toshiba Inc. Tokyo, Japan) which provided an UV intensity of 2561 µWcm -2 s -1 as measured by a digital radiometer (Model 97503-00; Cole-Parmer Inc., USA). The sperm suspension in petri dish was exposed to the UV light for 30 s. This irradiation duration is the optimum dose for inducing haploid gynogenesis in this species (Pan et al, 2004). Both the treated sperm and the untreated sperm (control) were mixed separately with a suspension of eggs, and the eggs were then allowed to develop at 20℃.…”