Temporal and Concentration Effects of Methanol on Cryopreservation of Zebrafish (Danio rerio) Sperm

Cryopreservation of sperm from the gudgeon, Microphysogobio rapidus (Cyprinidae): Effects of cryoprotectant, diluents, and dilution ratio

We investigated methods for cryopreserving sperm from the endangered gudgeon, Microphysogobio rapidus, by examining the effects of cryoprotective agent (CPA) concentration, diluent, and dilution ratio on post-thaw sperm quality. The quality of frozen sperm was evaluated in terms of motility and kinematic parameters, viability, DNA damage, and fertilization rate. We evaluated methanol, glycerol, dimethyl sulfoxide (DMSO), and ethylene glycol as CPAs. Sperm motility, velocity, and viability were significantly higher when methanol was used as the CPA (p < 0.05). The diluents tested were Ringer's solution, Kurokura's Extender, Common Carp Sperm Extender (CCSE), and buffered sperm motility-inhibiting saline solution (BSMIS); post-thaw motility was highest when Ringer's solution was used as the diluent. Next, various quantities of methanol were combined with Ringer's solution to identify the optimal dose of methanol. The dilution ratios tested ranged from 1:1 to 1:7. Cryopreserved sperm was thawed at 20 °C for 15 s. The use of 10% methanol with Ringer's solution at a dilution ratio of 1:5 resulted in the highest post-thaw sperm motility, viability, and velocity including VAP, VCL, and VSL. Post-thaw sperm showed significantly greater DNA damage than the control (fresh sperm) (p < 0.05). The fertilization rate was highest with fresh sperm (p < 0.05), followed by sperm frozen with 10% methanol + Ringer's solution. We recommend that the best way to preserve sperm in the studied species is to use a combination of Ringer's solution and 10% methanol at a 1:5 dilution ratio. Our findings will facilitate the artificial fertilization of M. rapidus.

Engineered ice-binding protein (FfIBP) shows increased stability and resistance to thermal and chemical denaturation compared to the wildtype

Many polar organisms produce antifreeze proteins (AFPs) and ice-binding proteins (IBPs) to protect themselves from ice formation. As IBPs protect cells and organisms, the potential of IBPs as natural or biological cryoprotective agents (CPAs) for the cryopreservation of animal cells, such as oocytes and sperm, has been explored to increase the recovery rate after freezing-thawing. However, only a few IBPs have shown success in cryopreservation, possibly because of the presence of protein denaturants, such as dimethyl sulfoxide, alcohols, or ethylene glycol, in freezing buffer conditions, rendering the IBPs inactive. Therefore, we investigated the thermal and chemical stability of FfIBP isolated from Antarctic bacteria to assess its suitability as a protein-based impermeable cryoprotectant. A molecular dynamics (MD) simulation identified and generated stability-enhanced mutants (FfIBP_CC1). The results indicated that FfIBP_CC1 displayed enhanced resistance to denaturation at elevated temperatures and chemical concentrations, compared to wildtype FfIBP, and was functional in known CPAs while retaining ice-binding properties. Given that FfIBP shares an overall structure similar to DUF3494 IBPs, which are recognized as the most widespread IBP family, these findings provide important structural information on thermal and chemical stability, which could potentially be applied to other DUF3494 IBPs for future protein engineering.

Effect of type and concentration of cryoprotectant on the motility, viability, and fertility of climbing perch Anabas testudineus Bloch, 1792 (Pisces: Anabantidae) sperm

The climbing perch, Anabas testudineus is a freshwater fish that has economic value in Indonesia. It is cultured in the country, but the breeding technology, specifically sperm storage, is not well developed. Sperm cryopreservation is one of the preservation methods that need to be developed to support fish breeding technology. The type of cryoprotectants and its concentration are species-dependent and determines the success of this approach. Therefore, this study is aimed at determining the optimal type and concentration of cryoprotectant for sperm cryopreservation of A. testudineus. Four separate study series were performed, each of which evaluated one type of cryoprotectant at five concentration levels. The cryoprotectants used were DMSO, methanol, glycerol, and ethanol, and the tested concentrations were 0%, 5%, 10%, 15%, and 20%, which were combined with 5% egg yolks. Each treatment was conducted with three replications. The results showed that the type of cryoprotectant and its concentration significantly affected sperm motility, viability, and fertility of climbing perch (P < 0.05). The best outcome was obtained in DMSO, and methanol at a concentration of 10%, glycerol at 5%, and ethanol at 15%. However, the highest motility, viability, and fertility values were observed at 10% DMSO, indicating it is the best type and concentration for sperm cryopreservation of climbing perch A. testudineus.

Cryopreservation of Roughscale Sole (Clidoderma asperrimum) Sperm: Effects of Cryoprotectant, Diluent, Dilution Ratio, and Thawing Temperature

Simple Summary

The roughscale sole, Clidoderma asperrimum, is found in the East and West Seas of Korea, waters north of Hokkaido in Japan, as well as the East China Sea, the East Pacific, and the Canadian Maritimes. In 2021, this fish was categorized as an endangered species. Thus, there is a need to maintain gametes by freezing sperm. This study investigated the impacts of the cryoprotective agent, diluent, dilution ratio, and thawing temperature on the cryopreservation of fish sperm. In this investigation, sperm dilution 1:1 with a mixture of 10% dimethyl sulfoxide + Stein’s solution and thawing at 10 °C provided the most effective DNA damage prevention. These results support the development of a roughscale sole sperm cryopreservation procedure.

Abstract

The roughscale sole, Clidoderma asperrimum is categorized as an endangered species. Sperm freezing is essential for preserving gametes. This study examined the CPA concentration, diluent, dilution ratio, and thawing temperature to design a sperm cryopreservation protocol for roughscale sole. The variables examined included sperm motility and kinematics, cell survival, fertilization, and DNA fragmentation. Sperm motility parameters were assessed via computer-assisted sperm analysis using a CEROS II instrument. Cell survival rate and DNA damage were assessed using the Cell Counting Kit-8 and single-cell gel electrophoresis assay, respectively. Sperm preservation was tested using several CPAs, including ethylene glycol, dimethyl sulfoxide (DMSO), glycerol, propylene glycol, and methanol. The diluents tested were 300 mM sucrose, 300 mM glucose, Stein’s solution, Ringer’s solution, and Hank’s solution. The optimal conditions for sperm cryopreservation were 10% DMSO + Stein’s solution. After thawing, sperm motility was highest with a 1:1 dilution ratio (sperm to CPA + diluent), at 69.20 ± 0.32%; thawing at 10 °C was optimal for post-thaw motility (72.03 ± 0.95%). The highest fertilization rate (40.00 ± 1.22%) was obtained using DMSO. The fresh sperm had the lowest tail DNA, followed by 10% DMSO + Stein’s solution. The developed cryopreservation methods can be used in roughscale sole hatcheries.

Is catalase an effective additive to alleviate oxidative stress during cryopreservation of zebrafish sperm at the repository level?

The goal of this study was to investigate whether supplementation of cryoprotective medium with catalase (CAT), an antioxidation enzyme, is efficient for zebrafish sperm cryopreservation from the viewpoint of high-throughput genetic repository operations. Three cryoprotectants (10%, v/v), dimethylacetamide (DMA), dimethylformamide (DMF), and methanol were used. The objectives were to evaluate the effects of CAT on sperm motility, plasma membrane integrity, and concentration for: 1) fresh sperm at equilibration up to 60 min; 2) post-thaw sperm after cooling at 10, 20, and 40 °C/min), and 3) post-thaw fertilization and embryo survival rates. Catalase addition did not improve sperm motility, regardless of the cryoprotectants added. After 10-min exposure to DMA or methanol, membrane integrity was significantly decreased (70-75%) compared to controls. With catalase, sperm cells maintained membrane integrity and after 50 min equilibration, cell concentrations were maintained with CAT compared to cryoprotectant-only test groups. However, after cryopreservation and thawing, CAT did not affect the outcome of motility, membrane integrity, cell concentration, fertilization, or embryo survival assays. Analysis of cooling rates also indicated that CAT did not affect 3-hpf fertilization or 24-hpf survival rates. Overall, addition of CAT could provide some protection of sperm from oxidative stress before freezing, but not after thawing. We propose that decisions concerning routine use of CAT for repositories, especially those handling tens of thousands of frozen samples per year, would depend on whether efficient high-throughput operation, or specific research questions are programmatic goals.

Development of an open hardware 3-D printed conveyor device for continuous cryopreservation of non-batched samples

A great challenge among communities participating in germplasm repository development is to obtain suitable cryopreservation equipment and devices. Commercial programmable freezers are costly and thus unaffordable to many users. Self-made devices have substantial variability among users, resulting in few opportunities for standardization across communities. The development of open hardware with the increasing accessibility of three-dimensional (3-D) printing offers rapid prototyping and easy fabrication of devices by users around the world at low cost. The present study explored the feasibility of developing operational prototypes of 3-D printed motorized cryopreservation devices for continuous freezing of non-batched samples. A controlled cooling conveyor device (CCCD) was designed and fabricated to cryopreserve sperm samples in straws that were loaded onto chain links suspended over liquid nitrogen held in a Styrofoam box. Cooling rates of 5 to 34 °C/min for 0.5-ml French straws were produced by adjusting the height of conveyor chains, slopes, and liquid nitrogen mass. The plunge temperature (-47 °C to -61 °C) was controlled by adjustment of conveyor speed. The cooling curves from the CCCD were comparable to a commercial programmable freezer. There were no significant differences in post-thaw motility of sperm from ornamental (Koi) common carp (Cyprinus carpio) among samples frozen with the CCCD and those frozen with a commercial programmable freezer. The post-thaw sperm motility was consistent among samples frozen in the CCCD across a 15-min time span. The CCCD prototypes in the present study proved to be feasible and functional as low-cost, customizable, portable, and yet standardizable options for freezing of individual (non-batched) samples. Additional design alternatives are proposed to facilitate further adaptation and development by diverse user communities.

A 3D Printed Vitrification Device for Storage in Cryopreservation Vials

Sperm cryopreservation by vitrification is a promising approach for small-bodied animals such as zebrafish (Danio rerio). However, most vitrification tools adopted in aquatic research were initially designed for applications other than sperm (such as human embryo freezing) and, thus, pose challenges for adoption to sperm vitrification. Three-dimensional (3D) printing combined with open hardware sharing is an emerging strategy to address challenges in the development of cryopreservation tools. The goal of this study was to develop a 3D printed Vitrification Device for Cryo-Vials (VDCV) that can be integrated with the existing vial storage systems. The VDCV combined the vitrification and handling components to achieve functions of sample handling, vitrification, storage, and identification. The vitrification component featured a base, a stem, and a loop. A total of 36 configurations with various loop lengths (8, 10, and 12 mm); loop widths (2.0, 2.5, 3.0, and 3.5 mm); and support structures (open, transverse, and axial) of the VDCD prototypes were designed, fabricated, and tested. Device handling orientations (horizontal and vertical holding angles prior to and during freezing) were also investigated. Computer simulations estimated that the cooling rate of the samples ranged from 0.6-1.5 × 10⁵ °C/min in all the configurations. Prior to freezing, loops with axial supports produced a minimum of 92% film retention. The overall trends of full vitrification occurrence were observed: horizontal plunging > vertical plunging, and axial support > transverse support and open loop. A loop length of 8 mm had the highest overall vitrification occurrence (86-100%). No significant differences (p = 0.6584) were shown in a volume capacity (5.7-6.0 μL) among the three supporting configurations. A single unit of VDCV can provide loading efficiencies of about 6 × 10⁷ sperm/vial, pooling of samples from 3-6 males/vial, and fertilization for 1800 eggs/vial. The VDCV are low-cost (<$0.5 material cost per unit) and can be customized, standardized, securely labeled, and efficiently stored. The prototypes can be accessed by user communities through open-fabrication file sharing and fabricated with consumer-level 3D printers, thus facilitating community-level standardization.