JAX® GEMM® Strains: Update on Nomenclature Changes for Congenic Mutant Strains

JAX® Bulletin #4
May 23, 2000

A large number of JAX® GEMM® strains (Genetically Engineered & Mutant Mice) are congenic strains. Congenic strains are produced by transferring a mutation from one genetic background to a specific inbred strain through repeated backcrossing. The congenic strain and the inbred partner are expected to be identical at all loci except for the transferred locus and a linked segment of chromosome. The size of the segment and the possibility of transferred alleles on other chromosomes depend on the number of backcross generations.

A strain is considered fully congenic after ten generations of backcrossing (N10). However, strains carrying mutations that have been backcrossed onto the background strain for at least five, but fewer than ten generations are considered incipient congenic strains and may be useful in a variety of research areas.

Most strain names for congenic mice carrying spontaneous and targeted mutations, as well as for a few strains congenic for histocompatibility loci, have not followed standard congenic nomenclature for historical reasons. In response to concerns from the scientific community about the origins of genetic mutations and differences in phenotype due to genetic background effects, the International Committee on Standardized Genetic Nomenclature for Mice and The Jackson Laboratory made a commitment to correct these inconsistencies.

Effective June 1, 2000, a large number of JAX® Mice strain names will change to indicate the mutation?s strain of origin. Strains are listed by their new names, with former names indicated below the new name, in the JAX® Mice 2000 Catalog and in the JAX® Mice Database. Examples of these name changes are provided below. Congenic nomenclature is adopted once a strain has reached the fifth generation of backcrossing (N5) although a strain is not considered fully congenic until N10. The decision was made not to change the nomenclature of some strains that carry multiple alleles derived from different origins, either because of the way the strain was generated or because the nomenclature would cause additional confusion. Additional information on the origins of transgenes and genetic mutations may be found through the JAX® Mice Database by conducting a search using the gene symbol or stock number of interest.

For more information about congenic nomenclature please refer to the nomenclature guidelines on the JAX® Mice Website. For assistance with these nomenclature changes contact Technical Information Services at tel: 800-422-6423 or 207-288-5845, fax: 207-288-6150.

Examples of Nomenclature Changes

Congenic strain names

Example 1.

STRAIN NAME

B6.129P2-Tcrbtm1Mom
FORMER NAME: C57BL/6J-Tcrbtm1Mom

STOCK NUMBER

002118

TYPE

Targeted Mutation Congenic

CONTROL

C57BL/6J 000664

BACKGROUND STRAIN

C57BL/6J

DONOR STRAIN

129P2 via E14TG2a ES cell line

GENERATION

N12F15

Note: This strain name should not be confused with that of a mutation maintained on a mixed B6;129P genetic background, where the strain abbreviations in the name are separated by a semicolon rather than a period (see Example 5). We have included additional information (strain type, control information, background and donor strains, and generation number) in the congenic strain detail both in our printed literature and on our Web site to more clearly delineate the genetic background.

Example 2.

STRAIN NAME

B6Ei.Cg-Atp7aMo-blo
FORMER NAME: C57BL/6JEi-Atp7aMo-blo

STOCK NUMBER

002044

TYPE

Spontaneous Mutation Congenic

CONTROL

Wildtype from the colony

BACKGROUND STRAIN

C57BL/6JEi

DONOR STRAIN

Oak Ridge stock

GENERATION

N69F1

Note: The Cg (for congenic) is used when there are multiple donor strains or the donor strain is of mixed genetic background.

Example 3.

STRAIN NAME

BKS.Cg-m +/+ Leprdb
FORMER NAME: C57BLKS/J-m +/+ Leprdb

STOCK NUMBER

000642

TYPE

Spontaneous Mutation Congenic

CONTROL

C57BLKS/J 000662

BACKGROUND STRAIN

C57BLKS/J

DONOR STRAIN

Leprdb, C57BLKS; m, DBA/J

GENERATION

N?F82

Note: In this example, the Cg is used to avoid suggesting that both mutations arose on DBA/J while showing that the misty (m) coat color marker and the diabetes (Leprdb) mutation are maintained in repulsion.

Example 4.

STRAIN NAME

C.129P2(B6)-Il2tm1Hor
FORMER NAME: BALB/c-Il2tm1Hor

STOCK NUMBER

002229

TYPE

Targeted Mutation Congenic

CONTROL

BALB/cJ 000651; Wildtype from the colony

BACKGROUND STRAIN

BALB/c

DONOR STRAIN

B6;129P-Il2tm1Hor

GENERATION

N10F9+

Note: Additional contributing genetic material may be included in parentheses following the donor strain. In this example, a targeted mutation has been transferred from a mixed B6;129P background to a third inbred strain. The genomic region flanking the targeted gene is 129P2-like because of the origin of the ES cell line, but an unknown amount of the strain?s genome may be of C57BL/6 origin. The amount of donor strain DNA, both linked and unlinked to the differential locus, decreases with increasing generations of backcrossing.

Strain with a mutation carried on a mixed genetic background

Example 5.

STRAIN NAME

B6;129P-Tcrbtm1Mom

STOCK NUMBER

002117

TYPE

Targeted Mutation

CONTROL

B6129PF2 100903

Note: This is not a congenic, but rather a mixture of C57BL/6 and 129P2 (from ES cell line) and so is segregating alleles from these two strains. The comma between strain abbreviations was replaced with a semicolon to make a clearer distinction from the period in congenic nomenclature.

Strain with nomenclature that did not change, but that carries alleles from different origins

Example 6.

STRAIN NAME

C57BL/6J-Igha Thy1a Gpi1a

STOCK NUMBER

001317

TYPE

Non-Histocompatibility
Allogantigens and Other Cellular
Marker Congenic

Note: This strain was made by mating together, not backcrossing, three individual congenic strains carrying differential alleles already on a C57BL/6J genetic background (B6.C-Igha, B6.PL-Thy1a, and B6.CAST-Gpi1).