Evaporative drying of mouse spermatozoa

Reproductive technologies for the generation and maintenance of valuable animal strains

Many types of mutant and genetically engineered strains have been produced in various animal species. Their numbers have dramatically increased in recent years, with new strains being rapidly produced using genome editing techniques. In the rat, it has been difficult to produce knockout and knock-in strains because the establishment of stem cells has been insufficient. However, a large number of knockout and knock-in strains can currently be produced using genome editing techniques, including zinc-finger nuclease (ZFN), transcription activator-like effector nuclease (TALEN), and the clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein 9 (Cas9) system. Microinjection technique has also contributed widely to the production of various kinds of genome edited animal strains. A novel electroporation method, the “Technique for Animal Knockout system by Electroporation (TAKE)” method, is a simple and highly efficient tool that has accelerated the production of new strains. Gamete preservation is extremely useful for maintaining large numbers of these valuable strains as genetic resources in the long term. These reproductive technologies, including microinjection, TAKE method, and gamete preservation, strongly support biomedical research and the bio-resource banking of animal models. In this review, we introduce the latest reproductive technologies used for the production of genetically engineered animals, especially rats, using genome editing techniques and the efficient maintenance of valuable strains as genetic resources. These technologies can also be applied to other laboratory animals, including mice, and domestic and wild animal species.

Sperm freeze-drying and micro-insemination for biobanking and maintenance of genetic diversity in mammals

Breeding by natural mating is ideal for maintaining animal populations. However, the lack of breeding space resulting from an increased number of strains and the decline in fertility caused by inbreeding inhibits the reproduction of subsequent generations. Reproductive technologies, such as gamete preservation and artificial fertilisation, have been developed to overcome these problems. These approaches efficiently produce offspring of laboratory, domestic and wild animals, and can also be used to treat human infertility. Gamete preservation using sperm contributes to improvements in reproductive systems and enables the use of smaller breeding spaces. Although cryopreservation with liquid nitrogen has been used to preserve spermatozoa, freeze-drying without liquid nitrogen, a novel method, facilitates long-term storage of spermatozoa. This method has recently been applied to maintain animal strains. Micro-insemination techniques, such as intracytoplasmic sperm injection (ICSI), are exceptional for improving assisted reproduction. ICSI can be used to fertilise oocytes, even with immotile and immature spermatozoa that are unsuitable for AI and IVF. Reproductive technologies provide a substantial advantage for biobanking and maintaining the genetic diversity of laboratory, domestic and wild animals. This review covers the latest method of sperm freeze-drying and micro-insemination, and future possibilities for maintaining animal strains and populations.

Simple gamete preservation and artificial reproduction of mammals using micro-insemination techniques

Assisted reproductive technology (ART) has been applied in various procedures as an effective breeding method in experimental, domestic, and wild animals, and for the treatment of human infertility. Micro-insemination techniques such as intracytoplasmic injection of spermatozoa and spermatids are now routinely used ART tools. With these techniques, even immotile and immature sperm cells can be employed as donors for producing the next generation. Gamete preservation, another ART tool, has contributed to reproductive regulation, worldwide transportation, and disease protection of animal strains, and the preserved gametes have been effectively used for the production of offspring. ART is now an indispensable tool in mammalian reproduction. This review covers the latest ART tools, with a particular emphasis on micro-insemination and gamete preservation, and discusses the future direction of mammalian artificial reproductive technology.