Mb1-iCre Mice

Catalog Number: C001552

Strain Name: C57BL/6JCya-Cd79a^em2(iCre)/Cya

Genetic Background: C57BL/6JCya

Expected Expression Tissues/Cells: Lymphoid B Cells (Higher activity in the early developmental stages)

Strain Description

The MB1 gene, CD79a, is critical in the immune system. It encodes the Ig-α protein, a key component of the B cell antigen receptor complex. Ig-α non-covalently binds with surface immunoglobulin (Ig) and Ig-β, facilitating the expression function of the B cell antigen receptor. This gene is expressed early in B cell development, even before the V(D)J recombination occurs at the IgH locus. The CD79a gene is primarily expressed in lymphoid germinal centers and subgroups of peripheral immune cells, with notable cytoplasmic expression. CD79a and CD79b together form the B cell receptor (BCR) complex, which serves as an identity tag for B cells, recognizing specific antigens and initiating humoral immune responses. Mutations in the CD79a gene can lead to various immunodeficiencies, including X-linked agammaglobulinemia, characterized by a lack of mature B cells and antibodies. Moreover, CD79a is expressed in some malignant B cell tumors, making it a potential target for diagnosis and treatment.

Mb1-iCre mice were generated by integrating a codon-optimized Cre recombinase gene (iCre) expression cassette, which has higher recombination activity, into the endogenous Cd79a gene in the mouse, driving its specific expression. This strategy disrupts the expression of the mouse endogenous Cd79a gene. When bred with mice containing the loxP site-flanked sequence, Cre recombinase-mediated deletion of the flanked sequence is estimated to occur in the lymphoid B cells of the offspring mice, with a predicted high level of Cre recombinase activity in the early development of B cells.

Strain Strategy

Exon 1 of the mouse Cd79a gene was truncated to remove the ATG start codon, and patial exon 2 plus patial intron 3 was replaced with the "Kozak-iCre-SV40 late pA" cassette.

Validation Data

a. Method

Mb1-iCre mice were crossed with Rosa26-LSL-tdTomato mice, which conditionally express a red fluorescent protein (tdTomato), to generate double-heterozygous offspring. In the offspring, deletion of the loxP-stop-loxP (LSL) cassette by Cre recombinase leads to tdTomato protein expression in Cre-positive cells. When the offspring mice reach 7 weeks of age, collect peripheral blood, spleen, and bone marrow tissues. Use flow cytometry (FACS) to detect tdTomato protein expression and determine Cre recombinase expression.

b. Group

Cre+: Mb1-iCre[KI/+];ROSA26-LSL-tdTomato[CKI/+];

Cre-: ROSA26-LSL-tdTomato[CKI/+].

c. Result

1) Expression of Cre recombinase in the lymphoid B cells

Figure 1. Expression of Cre recombinase in lymphoid B cells (mCD45+mCD19+) from peripheral blood (PB), spleen, and bone marrow (BM). FACS results show strong tdTomato expression in peripheral blood lymphoid B cells of Cre+ mice, with a recombination efficiency of over 98%. tdTomato expression was also detected in spleen lymphoid B cells, with a recombination efficiency of around 80%, and in bone marrow lymphoid B cells, with a recombination efficiency between 76.93% and 80.66%. In the control group (Cre-), tdTomato signals were almost undetectable in peripheral blood, spleen, and bone marrow.

2) Expression of Cre recombinase in the lymphoid T cells

Figure 2. Expression of Cre recombinase in lymphoid T cells (mCD45+mCD3+) from peripheral blood (PB), spleen, and bone marrow (BM). FACS results show that in Cre+ mice, tdTomato signals were detected in only 1.89%-2.21% of peripheral blood lymphoid T cells, 2.49%-3.72% of spleen lymphoid T cells, and no significant CD3+ T cell population in bone marrow. In the control group (Cre-), tdTomato signals were almost undetectable in peripheral blood, spleen, and bone marrow.

d. Summary

In Mb1-iCre mice, Cre recombinase expression is primarily concentrated in the lymphoid B cells. This model can be used for tissue-specific research targeting lymphoid B cells with good expression specificity.

Announcement

1. The insertion site of the Cre recombinase gene expression cassette in this strain is located on chromosome 7. Please avoid breeding with gene-edited mice targeting genes on the same chromosome as the Cre mouse when conducting mating.

2. The Cd79a gene expression was disrupted during the construction, homozygous Mb1-iCre mice may exhibit arrested development of B cells at the pro-B cell stage due to diminished signaling of the B cell receptor.