Near-infrared (NIR) fluorescence imaging is a noninvasive technique that provides numerous advantages for the real-time in vivo monitoring of biological information in living subjects without the use of ionizing radiation. Near-infrared fluorescent (NIRF) dyes are widely used as fluorescent imaging probes. These fluorescent dyes remarkably decrease the interference caused by the self-absorption of substances and autofluorescence, increase detection selectivity and sensitivity, and reduce damage to the human body. Thus, they are beneficial for bioassays. Indole heptamethine cyanine dyes are widely investigated in the field of near-infrared fluorescence imaging. They are mainly composed of indole heterocyclics, heptamethine chains, and N-substituent side chains. With indole heptamethine cyanine dyes as the parent, introducing reactive groups to the parent compounds or changing their structures can make fluorescent probes have different functions like labeling protein and tumor, detecting intracellular metal cations, which has become the hotspot in the field of fluorescence imaging of biological research. Therefore, this study reviewed the applications of indole heptamethine cyanine fluorescent probes to metal cation detection, pH, molecules, tumor imaging, and protein in vivo. The distribution, imaging results, and metabolism of the probes in vivo and in vitro were described. The biological application trends and existing problems of fluorescent probes were discussed.

Bardet-Biedl syndrome (BBS) is a ciliopathy caused by defects in the assembly or distribution of the BBSome, a conserved protein complex. The BBSome cycles via intraflagellar transport (IFT) through cilia to transport signaling proteins. How the BBSome is recruited to the basal body for binding to IFT trains for ciliary entry remains unknown. Here, we show that the Rab-like 5 GTPase IFT22 regulates basal body targeting of the BBSome in Chlamydomonas reinhardtii. Our functional, biochemical and single particle in vivo imaging assays show that IFT22 is an active GTPase with low intrinsic GTPase activity. IFT22 is part of the IFT-B1 subcomplex but is not required for ciliary assembly. Independent of its association to IFT-B1, IFT22 binds and stabilizes the Arf-like 6 GTPase BBS3, a BBS protein that is not part of the BBSome. IFT22/BBS3 associates with the BBSome through an interaction between BBS3 and the BBSome. When both IFT22 and BBS3 are in their guanosine triphosphate (GTP)-bound states they recruit the BBSome to the basal body for coupling with the IFT-B1 subcomplex. The GTP-bound BBS3 likely remains to be associated with the BBSome upon ciliary entry. In contrast, IFT22 is not required for the transport of BBSomes in cilia, indicating that the BBSome is transferred from IFT22 to the IFT trains at the ciliary base. In summary, our data propose that nucleotide-dependent recruitment of the BBSome to the basal body by IFT22 regulates BBSome entry into cilia. Significance Bardet-Biedl syndrome (BBS) is a rare human ciliopathy associated with blindness, obesity, and kidney anomalies. It is caused by defects in the assembly or transport of the BBSome, a conserved octamer of BBS proteins, which assists intraflagellar transport (IFT) with the removal of signaling proteins from cilia. Here, we show that the GTPase component of IFT-B1, IFT22, autonomous of IFT-B1 association, binds and stabilizes BBS3 in the cell body. When both are in their GTP-bound state, IFT22 and BBS3 recruit the BBSome to the basal body for loading onto the IFT machinery for ciliary entry. IFT22 recruits the BBSome to the basal body through BBS3 in a nucleotide-dependent manner providing a regulatory mechanism for BBSome entry into the cilium.