title: Studies on cryoprotectant toxicity to zebrafish (Danio rerio) oocytes.
abstract: Cryopreservation of fish germ cells is an important measure in conservation of fish genetic material. Although investigations on cryopreservation of fish sperm and embryos have been carried out extensively, cryopreservation of fish oocytes has not been studied systematically. In the present study the toxicity of cryoprotectants to zebrafish (Danio rerio) oocytes was investigated. Commonly used cryoprotectants dimethyl sulfoxide (DMSO), methanol, ethylene glycol (EG), propylene glycol (PG), sucrose and glucose were studied. Stage III (vitellogenic), stage IV (maturation) and stage V (mature egg) zebrafish oocytes were incubated in Hank's medium containing different concentrations of cryoprotectants (0.25-4M) for 30 min at room temperature. Three different tests were used to assess oocyte viability: trypan blue (TB) staining, thiazolyl blue (MTT) staining and in vitro maturation followed by observation of germinal vesicle breakdown (GVBD). Results showed that the toxic effect of cryoprotectant on oocytes generally increased with increasing concentration. MTT test was shown to be the least sensitive testing method and gave poor correlation to subsequent GVBD results. Sensitivity of vital tests increases in the order of MTT, TB and GVBD. GVBD test showed that cryoprotectant toxicity to stage III zebrafish oocytes increased in the order of methanol, PG, DMSO, EG, glucose and sucrose. No Observed Effect Concentrations (NOECs) for stage III oocytes were 2M, 1M, 1M, 0.5M, less than 0.25M and less than 0.25M for methanol, PG, DMSO, EG, glucose and sucrose respectively. TB test also showed that the toxicity of tested cryoprotectants increased in the same order. The sensitivity of oocytes to cryoprotectants appeared to increase with development stage with stage V oocytes being the most sensitive.
authors.affiliation: Luton Institute of Research in the Applied Natural Sciences, The Spires, 2 Adelaide Street, Luton LU1 5DU, Bedfordshire, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Plachinta
authors.forename: T
authors.initials: T
authors.lastname: Zhang
authors.forename: D M
authors.initials: DM
authors.lastname: Rawson
mesh_terms: D000438:Alcohols / Q000633:toxicity; D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D015925:Cryopreservation; D003451:Cryoprotective Agents / Q000633:toxicity*; D004121:Dimethyl Sulfoxide / Q000633:toxicity; D005260:Female; D005947:Glucose / Q000633:toxicity; D009865:Oocytes / Q000187:drug effects*; D013395:Sucrose / Q000633:toxicity; D015027:Zebrafish
chemical_list: D000438:Alcohols; D003451:Cryoprotective Agents; D013395:Sucrose; D005947:Glucose; D004121:Dimethyl Sulfoxide