The Need for a Framework Addressing the Temporal Aspects of Fish Sperm Motility Leading to Community-Level Standardization

Advancing nuclear transfer cloning in zebrafish (Danio rerio) into a translational pathway using interdisciplinary tools

The Zebrafish International Resource Center (ZIRC) is an NIH-funded national stock center and germplasm repository that maintains and distributes genetically modified and wild-type zebrafish (Danio rerio) lines to the biomedical research community. The ZIRC and its community would benefit from incorporating somatic cell nuclear transfer (SCNT) cloning which would allow the preservation of diploid genomes. The goal of this study was to advance a zebrafish SCNT cloning protocol into a reproducible community-level pathway by use of process mapping and simulation modeling approaches to address training requirements, process constraints, and quality management gaps. Training, for most steps in the SCNT protocol, could be completed within two months; however, steps that involved micromanipulation of eggs required more than four months of training. Dechorionation of embryos and egg micromanipulation were identified as major constraints because the processes were performed manually and required advanced operator manual skills. Chemical dechorionation and microfluidic devices to aid micromanipulation were identified as ways to eliminate these constraints. Finally, quality control steps to record the initial quality of collected germplasm were recommended to prevent production defects and harmonize the SCNT pathway across multiple facilities. By beginning to enhance the reproducibility of the SCNT cloning pathway, this technique can be implemented across zebrafish research facilities and facilities that work with other biomedical models.

Enhancing evaluation of bull fertility through multivariate analysis of sperm

Computer-assisted sperm analysis (CASA) has become the predominant tool for assessing bull semen in artificial insemination programs. Despite such popularity CASA's ability to predict fertility has been limited, especially when emphasis is based upon single motion characteristics. Our hypothesis is that numerical sets of CASA measures provide a more effective method to differentiate the potential fertilization capacity of bulls and that bulls can be clustered based upon sets of CASA measures. Therefore, we used CASA to evaluate frozen-thawed semen samples from 307 Holstein and 152 Jersey bulls sourced from USDA-ARS's National Animal Germplasm Program gene bank. Sperm was evaluated immediately after thawing and 30 min later. We evaluated sperm kinetic and morphometric means and variances to capture the structure of CASA data in relation to various sources of variation. These data were subjected to univariate and multivariate statistical methods to investigate animal and management factors affecting sperm characteristics measured by CASA. Clustering with K-means identified 4 clusters of bulls based upon each cluster's set of CASA parameters after thawing. There was little overlap among clusters for sets of CASA measures. At the extremes, bull cluster 1 (BC1, n = 180) and BC3 (n = 101) had different sire conception rates (SCR) -0.07 vs -1.29, respectively and sets of CASA measures. Interestingly, BC2 had CASA measures that could be perceived as negative, e.g., cell size at 8.18mm2 vs 6.37mm2 for BC4 and total motility of 29.7% vs 48.7% for BC3, but SCR for BC2 was higher (-0.79) than BC3 (-1.29). Despite such discrepancies for some BC2 CASA values it appears the potentially negative effects were offset by the levels of other CASA values. Our findings suggest improved approaches for using CASA could lie in evaluating multiple CASA measures as sets within specific numerical ranges rather than as independent measures.

Transitioning from a research protocol to a scalable applied pathway for Xenopus laevis sperm cryopreservation at a national stock center: The effect of cryoprotectants

Sperm cryopreservation is a critical tool for safeguarding and managing valuable genetic resources. Protocols for cryopreservation of Xenopus laevis sperm were available but lacking sperm quality evaluation and scalability and the outcomes were inconsistent. The goal of this study was to begin developing a center-level cryopreservation pathway for this species by integrating French straws as containers that would facilitate germplasm repository development. The objectives were to analyze the effect of: (1) three sperm concentrations (33, 50, and 100 × 106 sperm/mL) on post-thaw fertilization, (2) three final concentrations (2.5%, 5%, and 10%) of dimethyl sulfoxide, methanol, and dimethylformamide (DMFA) on sperm membrane integrity of fresh and frozen samples, (3) two concentrations (5% and 10%) of DMFA with and without 5% sucrose at four cooling rates (5, 10, 20, and 40°C/min) on sperm membrane integrity and motility, and (4) egg exposure to different concentrations of DMFA on fertilization. Few differences in sperm viability were found among fresh samples incubated in cryoprotectants, but thawed samples frozen in methanol or DMFA presented higher membrane integrity. Samples frozen in 10% DMFA at 20°C/min showed higher membrane integrity (60 ± 7%) than other DMFA concentrations and cooling rates, and the same total motility (30 ± 7%) as at 10°C/min. Higher DMFA concentrations (10%-13%) were detrimental for embryo development compared to lower concentrations (<6%). This study provided a reliable protocol for sperm cryopreservation in Xenopus laevis to yield an application pathway with potential for high throughput that can be used as a roadmap for work with other species.

A Modified-Herringbone Micromixer for Assessing Zebrafish Sperm (MAGS)

Sperm motility analysis of aquatic model species is important yet challenging due to the small sample volume, the necessity to activate with water, and the short duration of motility. To achieve standardization of sperm activation, microfluidic mixers have shown improved reproducibility over activation by hand, but challenges remain in optimizing and simplifying the use of these microdevices for greater adoption. The device described herein incorporates a novel micromixer geometry that aligns two sperm inlet streams with modified herringbone structures that split and recombine the sample at a 1:6 dilution with water to achieve rapid and consistent initiation of motility. The polydimethylsiloxane (PDMS) chip can be operated in a positive or negative pressure configuration, allowing a simple micropipettor to draw samples into the chip and rapidly stop the flow. The device was optimized to not only activate zebrafish sperm but also enables practical use with standard computer-assisted sperm analysis (CASA) systems. The micromixer geometry could be modified for other aquatic species with differing cell sizes and adopted for an open hardware approach using 3D resin printing where users could revise, fabricate, and share designs to improve standardization and reproducibility across laboratories and repositories.

Initial assessment of the toxicologic effects of leachates from 3-dimensional (3-D) printed objects on sperm quality in two model fish species

The use of 3-dimensional (3-D) printing is gaining popularity in life sciences and driving innovation in fields including aquatic sperm cryopreservation. Yet, little is known about the effects leachates from these objects may have on biological systems. In this study, we investigated if exposure to leachates from 3-D printed objects fabricated from different photo-curable resins could affect sperm quality in two model fish species, zebrafish (Danio rerio) and goldfish (Carassius auratus). Leachates were collected following contact periods of 10 min and 22 h with objects manufactured using a mask LCD resin printer and three different commercially available resins (i.e., standard, eco-friendly, and impact-resistant). Sperm cells were exposed to the leachates for 18 min, and parameters related to sperm motility, cell count, and membrane integrity were evaluated. All experiments were blinded. Leachate originating from contact with impact-resistant resin for 10 min significantly reduced the cell count of zebrafish sperm, while leachate originating from contact with standard resin for 22 h significantly increased the beat cross frequency of goldfish sperm. The changes were not observed across species and no adverse effects were recorded in percent motility, velocity, amplitude of lateral head movement, or membrane integrity of sperm. Our findings demonstrate that exposure to leachates from certain 3-D printed resins can affect sperm quality, while other resins may support sperm quality evaluation. Further investigations are warranted to assess other parameters, effects, and their biological relevance for a variety of aquatic species.

A 3-D printed vitrification device integrated with French straws

The goal of this work was to develop prototypes of open-hardware vitrification devices for sperm cryopreservation that can be integrated with existing straw platforms. The open-hardware Vitrification Device for French Straws (VD-FS) is low-cost, customizable, 3-D printable, standardized, and allows long-term sample storage and identification. The feasibility was shown for vitrifying and storing samples with multiple configurations. The results can be improved by design alternation and evaluation of various vitrification solutions. This is the first complete open-hardware vitrification device that can be integrated with existing French-straw storage systems, providing a foundation for future community-level modifications and improvements.