Description

In fixed samples, chromatin is most often visualized by using a fluorescent DNA-binding dye like DAPI, which emits blue light (Kapuscinski 1995). In live fluorescence microscopy, however, a fluorescently tagged histone is often used instead. Histones form nucleosomes to package chromatin, and are involved in the organization of the genome (Chen et al. 2021). Most frequently, histones are fused to red or green fluorescent proteins, though the use of a blue or cyan fluorescent protein instead would allow for three (or more) channel imaging (Kanda et al. 1998, Das et al. 2003, Ooi et al. 2006).

We sought to generate an endogenously tagged histone line with a blue or cyan fluorescent protein. mTurquoise2 is a relatively recently engineered cyan fluorescent protein with a high quantum yield (Goedhart et al. 2012). Thus, we constructed a HIS-72::mTurquoise2 fluorescent fusion protein using a design similar to that of another group who also tagged HIS-72 (Figure 1A, Dickinson et al. 2013; see Design section). We report similar localization of HIS-72::mTurquoise2 to previously generated HIS-72 fluorescent fusion strains in most nuclei of the animal (Figure 1G). HIS-72::mTurquoise2 shows chromatin labeling in the germline and all stages of the cell cycle in the early embryo (Figure 1B-F). We observed that HIS-72::mTurquoise2 signal is significantly reduced on chromatin during the meiosis I and II divisions as compared with other stages (Figure 1B,C), which is not observed in other exogenously expressed fluorescently tagged histone lines (Bai and Bembenek 2017, Bembenek et al. 2007). This may reflect the role of different histone variants in meiotic chromosome function.

In sum, we have constructed a HIS-72::mTurquoise2 fluorescent fusion strain for use to the C. elegans community.