Espn, as a transcription factor, is an infection-dependent regulator of the ESX-1 system in M. marinum. The ESX-1 secretion system is crucial for mycobacteria as it enables disruption of the macrophage phagosome during infection, access to the cytoplasm, and regulation of widespread gene expression in the mycobacterial cell [1].

In M. marinum, under laboratory conditions, EspN's activity is masked by the EspM repressor. However, during infection, EspN is critical. In the absence of EspM, EspN is required for ESX-1 function as it activates the expression of the whiB6 transcription factor gene, specific ESX-1 substrate, and secretory component genes. It is also essential for M. marinum growth within and cytolysis of macrophages, as well as for disease burden in a zebrafish larval model of infection [1].

In conclusion, EspN is a key infection-dependent regulator of the ESX-1 transcriptional network in M. marinum. Its study, especially through models like the zebrafish larval model of infection, reveals its importance in mycobacterial pathogenesis, highlighting its significance in understanding the mechanisms of mycobacterial-host interactions during infection.

References:

1. Nicholson, Kathleen R, Cronin, Rachel M, Menon, Aruna R, Tobin, David M, Champion, Patricia A. 2023. The EspN transcription factor is an infection-dependent regulator of the ESX-1 system in M. marinum. In bioRxiv : the preprint server for biology, , . doi:10.1101/2023.02.15.528779. https://pubmed.ncbi.nlm.nih.gov/36824794/