Alternative catalytic residues in the active site of Esco acetyltransferases.

Cohesin is a protein complex whose core subunits, Smc1, Smc3, Scc1, and SA1/SA2 form a ring-like structure encircling the DNA. Cohesins play a key role in the expression, repair, and segregation of eukaryotic genomes. Following a catalytic mechanism that is insufficiently understood, Esco1 and Esco2 acetyltransferases acetylate the cohesin subunit Smc3, thereby inducing stabilization of cohesin on DNA. As a prerequisite for structure-guided investigation of enzymatic activity, we determine here the crystal structure of the mouse Esco2/CoA complex at 1.8 Šresolution. We reconstitute cohesin as tri- or tetrameric assemblies and use those as physiologically-relevant substrates for enzymatic assays in vitro. Furthermore, we employ cell-based complementation studies in mouse embryonic fibroblast deficient for Esco1 and Esco2, as a means to identify catalytically-important residues in vivo. These analyses demonstrate that D567/S566 and E491/S527, located on opposite sides of the murine Esco2 active site cleft, are critical for catalysis. Our experiments support a catalytic mechanism of acetylation where residues D567 and E491 are general bases that deprotonate the ε-amino group of lysine substrate, also involving two nearby serine residues - S566 and S527- that possess a proton relay function.

Meiotic sex chromosome cohesion and autosomal synapsis are supported by Esco2.

In mitotic cells, establishment of sister chromatid cohesion requires acetylation of the cohesin subunit SMC3 (acSMC3) by ESCO1 and/or ESCO2. Meiotic cohesin plays additional but poorly understood roles in the formation of chromosome axial elements (AEs) and synaptonemal complexes. Here, we show that levels of ESCO2, acSMC3, and the pro-cohesion factor sororin increase on meiotic chromosomes as homologs synapse. These proteins are less abundant on the largely unsynapsed sex chromosomes, whose sister chromatid cohesion appears weaker throughout the meiotic prophase. Using three distinct conditional Esco2 knockout mouse strains, we demonstrate that ESCO2 is essential for male gametogenesis. Partial depletion of ESCO2 in prophase I spermatocytes delays chromosome synapsis and further weakens cohesion along sex chromosomes, which show extensive separation of AEs into single chromatids. Unsynapsed regions of autosomes are associated with the sex chromatin and also display split AEs. This study provides the first evidence for a specific role of ESCO2 in mammalian meiosis, identifies a particular ESCO2 dependence of sex chromosome cohesion and suggests support of autosomal synapsis by acSMC3-stabilized cohesion.

Mice lacking the cerebral cortex develop normal song: insights into the foundations of vocal learning.

Mouse models play an increasingly important role in the identification and functional assessment of speech-associated genes, with a focus on genes involved in vocal production, and possibly vocal learning. Moreover, mice reportedly show direct projections from the cortex to brainstem vocal motor neurons, implying a degree of volitional control over vocal output. Yet, deaf mice did not reveal differences in call structures compared to their littermates, suggesting that auditory input is not a prerequisite for the development of species-specific sounds. To elucidate the importance of cortical structures for the development of mouse ultrasonic vocalizations (USVs) in more detail, we studied Emx1-CRE;Esco2(fl/fl) mice, which lack the hippocampus and large parts of the cortex. We conducted acoustic analyses of the USVs of 28 pups during short-term isolation and 23 adult males during courtship encounters. We found no significant differences in the vocalizations of Emx1-CRE;Esco2(fl/fl) mice, and only minor differences in call type usage in adult mice, compared to control littermates. Our findings question the notion that cortical structures are necessary for the production of mouse USVs. Thus, mice might be less suitable to study the mechanisms supporting vocal learning than previously assumed, despite their value for studying the genetic foundations of neurodevelopment more generally.

The non-redundant function of cohesin acetyltransferase Esco2: some answers and new questions.

Cohesin and cohesin regulatory proteins function in an essential pathway enabling proper cohesion and segregation of sister chromatids. Additionally, these proteins are involved in double-strand break (DSB) repair and transcriptional regulation. Mutations in Establishment of cohesion 1 homolog 2 (Esco2), an evolutionary conserved cohesin acetyltransferase, are the cause of Roberts syndrome (RBS), a human congenital disorder. To explore the mechanism by which the deficiency in Esco2 affects cohesin's functions, we generated a mouse harboring a conditional Esco2 allele. To our surprise and in marked contrast to RBS, mouse Esco2 turns out to be a cell viability factor, the absence of which results in severe chromosome segregation defects and apoptosis. We found that the acetylation of the cohesin subunit Smc3 is significantly reduced in Esco2-deficient cells resulting in a marked reduction of Sororin recruitment to several, but not all cohesin bound loci. Here, we provide evidence that Esco2 is also required for DSB repair, which is consistent with previous studies in RBS cells.

Cohesin acetyltransferase Esco2 is a cell viability factor and is required for cohesion in pericentric heterochromatin.

Sister chromatid cohesion, mediated by cohesin and regulated by Sororin, is essential for chromosome segregation. In mammalian cells, cohesion establishment and Sororin recruitment to chromatin-bound cohesin depends on the acetyltransferases Esco1 and Esco2. Mutations in Esco2 cause Roberts syndrome, a developmental disease in which mitotic chromosomes have a 'railroad' track morphology. Here, we show that Esco2 deficiency leads to termination of mouse development at pre- and post-implantation stages, indicating that Esco2 functions non-redundantly with Esco1. Esco2 is transiently expressed during S-phase when it localizes to pericentric heterochromatin (PCH). In interphase, Esco2 depletion leads to a reduction in cohesin acetylation and Sororin recruitment to chromatin. In early mitosis, Esco2 deficiency causes changes in the chromosomal localization of cohesin and its protector Sgo1. Our results suggest that Esco2 is needed for cohesin acetylation in PCH and that this modification is required for the proper distribution of cohesin on mitotic chromosomes and for centromeric cohesion.