Abstract
Transgenic mice harboring imaging reporters take full advantage of imaging technologies in studies using living mice. Here, we established a tri-fusion multimodal reporter gene containing fragments from firefly luciferase, enhanced green fluorescent protein, and herpes simplex virus type 1 thymidine kinase and generated tri-fusion reporter Tg mice. Fibroblast growth factor type 1 (FGF1), a multifunctional mitogen to a wide range of tissues, regulates proliferation of neural stem cells of the brain, where FGF1 expression is initiated through activation of the FGF1B (F1B) promoter. The reporter mouse under the control of the human F1B promoter enables visualization in vivo where F1B activity is elevated, including tissues not only in the brain but also in the nasopharynx, skull, spine, and testes, particularly in Leydig cells. Treating Tg mice with the alkylating agent busulfan, which is known to eradicate Leydig cells and disrupt spermatogenesis in mice, eliminated the reporter signals. Restoring Leydig cells recovered reporter expression, indicating that the reporter can be used as a surrogate marker for Leydig cells. The F1B tri-fusion reporter mouse model can be utilized in longitudinal monitoring of the health status of the male reproductive system, such as in studies exploring the toxicity of chemicals to spermatogenesis.
Highlights
Fibroblast growth factor 1 (FGF1), known as acidic fibroblast growth factor, is the universal FGF that can activate all FGF receptors
Compared to the TMIR vector driven by CMV, the F1B-TMIR vector resulted in significantly lower luminescence, indicating a low basal activity associated with the F1B promoter
We explored whether mice with temporary Leydig cell death and recovery of spermatogenesis can be detected by changes in TMIR expression
Summary
Fibroblast growth factor 1 (FGF1), known as acidic fibroblast growth factor, is the universal FGF that can activate all FGF receptors. Expressing SV40 T antigen in transgenic mice under the control of the human F1B promoter (−540 to +31 bp) resulted in a high incidence of tumors at the olfactory bulb, ventral forebrain, subventricular zone, thalamus, striatum, and tegmental area where neural stem/progenitor cells are known to be abundant[24,25]. By using an F1B promoter-driven GFP vector and in Tg mice, GFP-positive neural stem/progenitor cells can be readily isolated from the brains of developing or adult mice[12,26,27]. Limited by the penetrating depth and signal intensity of GFP, F1B-GFP mice were unable to demonstrate whole body F1B promoter activity in vivo. Compared to F1B-GFP mice, F1B-TMIR mice take advantage of in vivo imaging using bioluminescence, PET, and SPECT and enable the discovery of F1B promoter activity in male testes. We demonstrated that F1B-TMIR mice can be used to reveal the disruption of spermatogenesis in male mice
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