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Abstract: Proteins that possess a chromo domain are well‐known for their roles in heterochromatin assembly and maintenance. The Heterochromatin Protein 1 (HP1) family, with a chromo domain and carboxy‐terminal chromo shadow domain, targets heterochromatin through interaction with histone H3 methylated on lysine 9 (H3K9me2/3). The structural and functional diversity of these proteins observed in both fission yeast and metazoans correlate with chromatin specialization. To expand these studies, we examined chromo domain proteins in the ciliate Tetrahymena thermophila, which has functionally diverse and developmentally regulated heterochromatin domains. We identified thirteen proteins similar to HP1. Together they possess only a fraction of the possible chromo domain subtypes and most lack a recognizable chromo shadow domain. Using fluorescence microscopy to track chromatin localization of tagged proteins through the life cycle, we show evidence that in T. thermophila this family has diversified with biological roles in RNAi‐directed DNA elimination, germline genome structure, and somatic heterochromatin. Those proteins with H3K27me3 binding sequence characteristics localize to chromatin in mature nuclei, whereas those with H3K9me2/3 binding characteristics localize to developing nuclei undergoing DNA elimination. Findings point to an expanded and diversified family of chromo domain proteins that parallels heterochromatin diversity in ciliates. [ABSTRACT FROM AUTHOR]

Primordial germ cell 7 (PGC7), a maternal factor essential for early development, plays a critical role in the regulation of DNA methylation, transcriptional repression, chromatin condensation, and cell division and the maintenance of cell pluripotentiality. Despite the fundamental roles of PGC7 in these cellular processes, only a few molecular and functional interactions of PGC7 have been reported. Here, a streptavidin-biotin affinity purification technique combined with LC-MS/MS was used to analyze potential proteins that interact with PGC7. In total, 291 potential PGC7-interacting proteins were identified. Through an in-depth bioinformatic analysis of potential interactors, we linked PGC7 to critical cellular processes including translation, RNA processing, cell cycle, and regulation of heterochromatin structure. To better understand the functional interactions of PGC7 with its potential interactors, we constructed a protein-protein interaction network using the STRING database. In addition, we discussed in detail the interactions between PGC7 and some of its newly validated partners. The identification of these potential interactors of PGC7 expands our knowledge on the PGC7 interactome and provides a valuable resource for understanding the diverse functions of this protein.