TABLE 1.

Tracing neural progenitors and/or their progeny in the adult zebrafish telencephalon.

Method	Principle	Output (and limitations)	Princeps publications
Thymidine analogs	These compounds (BrdU, CldU, EdU) incorporate into the DNA of cycling cells during the S phase. They are revealed by immuno-histochemistry or click-chemistry.	Labeling of dividing cells only (thus low efficiency to label dormant cells). Identification of the progeny cells becoming post-mitotic or dividing infrequently post-labeling (dilution of the label at each division round, so rapidly dividing progeny cells are lost). Detection of cells dividing infrequently, when detected together with a proliferation marker (PCNA, MCM proteins) after a chase (“label retention assay”).	Adolf et al., 2006; Grandel et al., 2006; Pellegrini et al., 2007
Retroviruses	Cells with ventricular contact are infected upon intra-ventricular injection of the viral suspension. Following infection, the genetic material carried by the virus is reverse transcribed and integrates into the host cell genome.	Integration into dividing cells for simple retroviruses, and into non-dividing cells as well for lentiviruses, the genetic material of which can cross nuclear pores. Permanent labeling of the progenitor and its progeny. Cell specificity of expression can be achieved using specific promoters.	Rothenaigner et al., 2011
DNA electroporation or lipofection	Cells with ventricular contact are targeted upon intra-ventricular injection of the virus suspension and electroporation. DNA remains episomal.	Cell specificity of expression can be achieved using specific promoters. Labeling is transmitted to progeny cells but is a priori not permanent. Bias toward targeting cells with a large apical surface.	Chapouton et al., 2010; Alunni et al., 2013
Conditional Cre-lox-mediated genetic tracing	Double transgenic animals (driver-reporter) are used. Expression of Cre-ER is driven from the driver transgene by neural progenitor-specific promoters, and nuclear translocation is temporally controlled by tamoxifen treatment. It recombines the reporter transgene at LoxP sites to express a reporter, usually driven by a ubiquitous promoter.	Cell specificity of the recombination is achieved using specific promoters (so far: her4.1; gfap; nestin); these promoters may not recapitulate the endogenous pattern in all lines, and need to drive strong expression for recombination to be efficient. Labeling is permanent in the progenitor and all its progeny cells. Various extents of recombination can be used (from clonal to full).	Kroehne et al., 2011
Tet-rtTA-mediated genetic tracing	Double transgenic animals (driver-reporter) are used. Expression of Tet is driven from the driver transgene by neural progenitor-specific promoters, and its activity is temporally controlled by doxycylin treatment. It then activates the reporter transgene.	Cell specificity of induction is achieved using specific promoters (so far: her4.1). Labeling is transient in the progenitor following arrest of the doxycycline treatment. If the reporter protein is fused with a histone (e.g., H2B), it will be diluted in the progenitor cell upon division, but stably maintained in post-mitotic cells generated soon after induction, hence also serving as a birth dating method; like with thymidine analogs, rapidly dividing progeny cells will be lost by label dilution. Various extents of induction can be used (from clonal to full); full inductions can also be used to track non-dividing progenitor cells that retain the label (although with caution, as expression levels at induction may be variable).	Furlan et al., 2017
Intravital imaging	2P: Semi-transparent adult animals (casper or nacre) are used, anesthetized and imaged using 2P microscopy. Progenitor cells are tracked using specific transgenic reporter backgrounds or following reporter electroporation. 3P: transgenic casper adults are used, anesthetized and imaged using 3P microscopy.	Individual progenitor cells can be tracked over some weeks. Tracking of progeny cells is transient as they leave the progenitor niche to reach deep parenchymal areas. Only applicable so far to the dorsal-most pallial areas (Da, Dm). Individual progenitors can be imaged, as well as cells located much deeper in the parenchyma (at least 200 mm below the NSC layer), e.g., neurons. Howerver the method has not been used yet for repetitive imaging.	Barbosa et al., 2015a; Dray et al., 2015; Guesmi et al., 2018