National Institute of Genetics establishes a "genetically homogeneous" zebrafish inbred strain — An alternative animal model

A research group led by Associate Professor Noriyoshi Sakai of the National Institute of Genetics and Professor Hiromi Hirata of Aoyama Gakuin University announced that they successfully established a genetically homogeneous zebrafish inbred strain. According to the announcement, the group continued sib-pair mating of the IM strain to produce an inbred strain (currently 50th generation) and now established the inbred Mishima-AB (M-AB) strain (currently 30th generation) via new sib-pair mating with another wild-type*AB strain. The rate of homologous nucleotide sequence differences in the M-AB strain was 0.011%, confirming genetic homogeneity. The new strain allows for high-precision analysis of traits involving many genes, such as behavior and drug response. The results of this research were published in the international academic journal Scientific Reports on March 30.

The zebrafish is a vertebrate model organism that is widely used worldwide. However, inbred strains in which the majority of loci are homozygous have not been developed successfully through genetically homogeneous inbreeding due to an imbalanced sex ratio of offspring and occurrence of harmful traits as a result of inbreeding, with the latter being referred to as inbreeding depression. Moreover, in zebrafish, the sex ratio of offspring is skewed depending on environmental factors, and this is an additional impediment to establishing inbred strains, which is not seen in mice or killifish. The development of genetically homogeneous strains in combination with gynogenetic individuals was investigated, but the same strains became fragile and did not reach sufficient genetic homogeneity.

From this background, the group continued sib-pair mating of the IM strain established by Sakai's research group to develop an inbred strain (now 50th generation) and created a new inbred Mishima-AB (M-AB strain: now 30th generation) strain through sib-pair mating with another wild-type*AB strain. During passaging, multiple pairs of siblings were mated, and the pairs that had the highest egg number and fertility rate and produced offspring with the least abnormality were selected to avoid inbreeding depression. Furthermore, the method of raising the larvae was reviewed. The production of male-biased progeny was successfully avoided by starting the rotifer diet 4 days after fertilization to reduce the population density during the growth process.

Genome sequencing of the established M-AB strain revealed a homologous nucleotide sequence difference rate of 0.011%, showing a sufficient level of genetic homogeneity. Moreover, the M-AB strain was found to be productive and lay robust eggs. Fertilized eggs can undergo genetic engineering. Zebrafish have homologous organs with simpler structures than humans and other mammals and are being studied as a model for human genetic diseases. The availability of genetically homogeneous strains is expected to facilitate the use of zebrafish as an alternative animal model to mice in studies sensitive to individual differences, such as behavior, immunity, drug discovery, and lifestyle-related diseases, thereby improving our understanding of genes and diseases.

Sakai said, "Use of zebrafish as a model organism started more recently compared to mice and rats and had the problem that strains were not well developed. However, strain development is a time-consuming process and is not suitable to the research cycle in which results produced recently are used to obtain research grants, and those grants are then used to produce more results. We could not have achieved the results of this research without the sustainable research environment at the National Institute of Genetics."

Journal Information
Publication: Scientific Reports
Title: Establishment of a zebrafish inbred strain, M-AB, capable of regular breeding and genetic manipulation
DOI: 10.1038/s41598-024-57699-3