Rules for Nomenclature of Medaka Strains

Definitions of and nomenclature for medaka strains (Version 1)

   Here we propose rules of nomenclature for medaka strains in order to standardize the medaka resource. This nomenclature is derived from the naming conventions utilized for mice described in “Genetic control of laboratory animals” (Softscience Inc., Tokyo, 1983), “Mouse laboratory manual” (Springer, Tokyo, 2003) and elsewhere. While this classification system is sufficient for existing medaka strains, as new strains are developed a revised version of these guidelines must be developed, discussed, and implemented. The deputy director of the Tokyo Metropolitan Institute of Medical Science, Dr. Hiromichi Yonekawa, has approved this proposal.    Medaka strains meet the following criteria: they exhibit stable genetic traits that are maintained uniformly in each individual and these genetic traits are inherited in successive generations. Medaka strains are categorized as follows: I, inbred strains and their derivative strains; II, mutant strains; III, transgenic strains; and IV, closed colonies.

I. Inbred strains and their derivative strains

1)Inbred strains (inbred strain)

   Inbred strains are established by sister-brother mating (sib mating) for more than 20 successive filial generations (F20). An established inbred strain must be maintained with specific types of inbreeding (predominantly sister-brother mating). An accurate mating record should be kept and genetic monitoring of each inbred strain is desirable.
    Each inbred strain is named with three or four capital letters without any additional symbols.

Examples : HNI inbred strain , Hd-rRII1 inbred strain

   Subsequently, if an inbred strain is maintained by mass mating, fish obtained within the first three generations of the mass population breeding are regarded as constituents of an inbred strain.

   However, after four or more generations, fish in the mass population are referred to as from a closed colony rather than from an inbred strain.

Example in this case: HNI closed colony

2)Inbred substrains (inbred sublines)

   When a sister-brother pair of an established inbred strain is transferred to another institute, the strain obtained after brother-sister mating in 15 or more successive generations in the new institute is regarded as an inbred substrain. The inbred substrain is named with the original inbred strain followed by a slash(/) and the name of the institute that developed it (abbreviations can be used).

Examples : HO5/NAGOYA inbred substrain

3)Coisogenic strains

   Coisogenic strains are the inbred strains that differ at only a single locus through mutation occurring in that strain. Coisogenic strains should be designated by the strain name followed by a hyphen and the gene symbol of the differential allele, in italics..

Examples : Hd-rR- r/r coisogenic strain

4)Congenic strains

   When a specific gene is introduced into an inbred strain by backcrossing (generally repeated for eight or more generations), the obtained strains are called a congenic strain. Congenic strains are designated by a symbol of three parts. The symbol of the recipient strain is separated by a period from a symbol of the donor strain, this being the strain in which the allele or mutation originated. A hyphen then separates the strain name from the symbol (in italics) of the differential allele(s) introduced from the donor strain.

Examples : Hd-rR.HNI- DMY congenic strain

II.Mutant strains

   A mutant strain has a gene mutation and is named with the symbol or tentative symbol of the mutated gene. Strains generated by ENU mutagenesis are named ENU followed by the gene symbol in parentheses. A strain with a radiation-induced mutation is named RAD followed by the gene symbol in parentheses. If there are two or more alleles for mutant strain, the alleles are numbered chronologically starting with the first allele discovered. If the strain containing a mutation needs to be indicated, the name of the strain is placed first and the subsequent symbols are hyphenated.

Examples : Da/Da mutant strain , ENU(311A) mutant strain , RAD( ut ) mutant strain , RAD( ut ) 2 mutant strain, d-rR-ENU( b ) mutant strain

III. Transgenic strains


A transgenic strain harbors a foreign gene or DNA construct. A transgenic strain is named Tg followed by the symbol of the foreign gene in parentheses. If there are two or more similar transgenic lines, the lines are numbered chronologically after the parenthesis. The second line developed is numbered “2” and so forth. If the host strain needs to be indicated, the name of the host strain is placed first and the subsequent symbols are hyphenated.

Examples : Tg(olvas-GFP) transgenic strain , d-rR-Tg(olvas-GFP)2 transgenic strain

IV. Closed colonies

   A closed colony is a population of medaka that maintained without introducing broodstock from another source. A closed colony is named with the symbol indicating its characteristic or the name of the origin place and the phrase “closed colony.”

Examples : Higashidori closed colonies , HNI closed colony

If you have any further questions please contact the NBRP Medaka core
Kiyoshi Naruse
National Institute for Basic Biology,
Laboratory of Bioresources,
Nishigonaka 38, Myodaiji, Okazaki 444-8585, Aichi, Japan
TEL/FAX: 0564-55-7580