BDF6 Deficiency Severely Compromises Intracellular Amastigote Development and Infectivity of Trypanosoma cruzi

Trypanosoma cruzi, the causative agent of Chagas disease, relies on complex gene regulatory mechanisms to adapt to its diverse host environments. In recent years, it has been established that epigenetics plays an essential role in these mechanisms via the regulation of chromatin structure. Bromodomain-containing factors (BDFs), known for recognizing acetylated lysines on histones, have emerged as key factors in chromatin remodeling complexes. Among the eight predicted BDFs in T. cruzi, BDF6 is part of a TINTIN-like complex with MRGx and MRGBP, homologous to components of the NuA4/TIP60 chromatin remodeling complex. We generated knockout (KO) parasites for the bdf6 gene using CRISPR/Cas9 gene editing. BDF6 KO epimastigotes exhibit normal morphology but decreased size and growth, and the resulting metacyclic trypomastigotes displayed drastically reduced infectivity. Strikingly, once inside host cells, KO parasites differentiated into amastigotes but failed to replicate. This intracellular arrest was reversed by episomal complementation of BDF6. Consistently, KO parasites also exhibited impaired infectivity in mice, a defect that was also rescued in the addback parasite lines. Our findings highlight BDF6 as a critical regulator of intracellular parasite development, operating in stages beyond epimastigotes where epigenetic plasticity is essential for host adaptation. This striking stage-specific phenotype of BDF6 KO underscores its functional importance and highlights the relevance of epigenetic regulators along T. cruzi life cycle.