Cryopreservation of Hydractinia symbiolongicarpus Sperm to Support Community-Based Repository Development for Preservation of Genetic Resources

Simple Summary Hydractinia symbiolongicarpus is an emerging model organism in which cutting-edge genomic tools and resources are being developed for use in a growing number of research fields. One limitation of this model system is the lack of long-term storage for genetic resources. In this study, approaches for Hydractinia sperm cryopreservation were established for the first time. Open hardware and 3-D printing were used to facilitate animal husbandry, sperm handling, and cryopreservation. Hydractinia sperm at a concentration of 2 x 10(7) cells/mL stored at 4 degrees C for as long as 6 d were able to achieve 50% fertilization rate. A fertilization rate of 41-69% was observed using sperm equilibrated with 5, 10, or 15% (v/v) cryoprotectant (dimethyl sulfoxide or methanol) for 20 min, cooled at a rate of 5, 10, or 20 degrees C/min from 4 degrees C to -80 degrees C, at a cell concentration of 1 x 10(8) sperm/mL, in 0.25 mL French straws. Establishing repository capabilities for the Hydractinia research community will be essential for future development, maintenance, protection, and distribution of genetic resources. More broadly, these generalizable approaches can be used as a model to develop germplasm repositories for other cnidarian species. Hydractinia symbiolongicarpus is an emerging model organism in which cutting-edge genomic tools and resources are being developed for use in a growing number of research fields. One limitation of this model system is the lack of long-term storage for genetic resources. The goal of this study was to establish a generalizable cryopreservation approach for Hydractinia that would support future repository development for other cnidarian species. Specific objectives were to: (1) characterize basic parameters related to sperm quality; (2) develop a generalizable approach for sperm collection; (3) assess the feasibility of in vitro fertilization (IVF) with sperm after refrigerated storage; (4) assess the feasibility of IVF with sperm cryopreserved with various sperm concentrations; (5) evaluate feasibility of cryopreservation with various freezing conditions, and (6) explore the feasibility of cryopreservation by use of a 3-D printed open-hardware (CryoKit) device. Animal husbandry and sperm collection were facilitated by use of 3-D printed open hardware. Hydractinia sperm at a concentration of 2 x 10(7) cells/mL stored at 4 degrees C for 6 d were able to achieve 50% fertilization rate. It appeared that relatively higher sperm concentration (>5 x 10(7) cells/mL) for cryopreservation could promote fertilization. A fertilization rate of 41-69% was observed using sperm equilibrated with 5, 10, or 15% (v/v) cryoprotectant (dimethyl sulfoxide or methanol) for 20 min, cooled at a rate of 5, 10, or 20 degrees C/min from 4 degrees C to -80 degrees C, at a cell concentration of 10(8)/mL, in 0.25 mL French straws. Samples cryopreserved with the CryoKit produced a fertilization rate of 72-82%. Establishing repository capabilities for the Hydractinia research community will be essential for future development, maintenance, protection, and distribution of genetic resources. More broadly, these generalizable approaches can be used as a model to develop germplasm repositories for other cnidarian species.