The H2B-Medium-FT knock-in allele carries a chromatin-associated blue to red fluorescent timer under the control of tetO, a tetracycline-responsive regulatory element, and CMV inserted into the endogenous Hprt1 locus on the X chromosome. The strain also carries the Gt(ROSA)26Sortm1(rtTA*M2)Jae allele, providing inducible widespread expression of the H2B-FT reporter. H2B-FT is a fluorescent timer (FT) that shifts from blue (fast cycling cells) to red (mature, stable cells) fused to human histone (H2B.J or H2BC9), which directs the FT signal to the chromatin. The blue/red ratio decreases as the cell cycle lengthens or slows and can be used to track cell cycling rates. Of the three kinetic variants of the FT protein, Medium-FT has the middle range of blue/red ratio and a medium blue to red conversion time. Females heterozygous and males hemizygous for the Hprt1tm1(tetO/CMV-H2BC9/mediumFT)Sguo allele (which is X-linked), and homozygous for the Gt(ROSA)26Sortm1.1(rtTA*M2)Jae allele are viable and fertile. This strain may be useful in studies of cell cycle dynamics.

Widespread doxycycline-mediated, reversible expression of the blue to red fluorescent timer fused to human histone (H2B-Medium FT) in this X-linked Hprt1 (hypoxanthine guanine phosphoribosyl transferase 1) mutant strain is regulated by a tetracycline operator (tetO). This strain maybe used to distinguish between fast-cycling (blue) and slow-cycling cells (red).

This strain is hosted by NIH's MMRRC, which partners with JAX for the distribution of this and other strains. For additional information and to purchase, please visit the MMRRC site.