Novel TONSL variants cause SPONASTRIME dysplasia and associate with spontaneous chromosome breaks, defective cell proliferation and apoptosis

Dental and craniofacial manifestations in sponastrime dysplasia - An observational study

Sponastrime dysplasia is an extremely rare autosomal recessive spondyloepimetaphyseal dysplasia characterized by short stature, midface hypoplasia, nasal alterations, and dental anomalies. This is, to date, the first comprehensive report on oral and craniofacial findings, and on subjective oral health-related quality of life as clinically and radiologically examined in two adults with sponastrime dysplasia. Both subjects had typical features of sponastrime dysplasia with disproportionate short stature, hypertelorism and midface hypoplasia, and variants in the TONSL gene. One had a severe phenotype (adult height 91 cm), whereas the other exhibited moderate severity (adult height 135 cm). The notable variation in the disorder severity was also expressed in dental manifestations. Dentin dysplasia type I-like abnormalities were seen in tooth eruption and morphology. Dental roots were shortened in both individuals. The individual with severe growth failure had lost several permanent teeth and reported a moderate level of discomfort and impairment due to oral health issues, as evaluated with the Oral Health Impact Profile questionnaire. In contrast, the other individual had a full permanent dentition and minimal negative impact on oral health-related quality of life. Both had short jaw lengths and face height. The anteroposterior jaw relationships were normal. The jaws of the individual with a severe phenotype were retrognathic in relation to the skull base. Both had prominent forehead. Due to significant craniofacial and dental involvement, individuals with sponastrime dysplasia should be regularly followed by a multidisciplinary medical team including a dentist, to maintain individuals' oral health and oral health-related quality of life.

TONSOKU is required for the maintenance of repressive chromatin modifications in Arabidopsis

The stability of eukaryotic genomes relies on the faithful transmission of DNA sequences and the maintenance of chromatin states through DNA replication. Plant TONSOKU (TSK) and its animal ortholog TONSOKU-like (TONSL) act as readers for newly synthesized histones and preserve DNA integrity via facilitating DNA repair at post-replicative chromatin. However, whether TSK/TONSL regulate the maintenance of chromatin states remains elusive. Here, we show that TSK is dispensable for global histone and nucleosome accumulation but necessary for maintaining repressive chromatin modifications, including H3K9me2, H2A.W, H3K27me3, and DNA methylation. TSK physically interacts with H3K9 methyltransferases and Polycomb proteins. Moreover, TSK mutation strongly enhances defects in Polycomb pathway mutants. TSK is intended to only associate with nascent chromatin until it starts to mature. We propose that TSK ensures the preservation of chromatin states by supporting the recruitment of chromatin modifiers to post-replicative chromatin in a critical short window of time following DNA replication.

The Role of the TSK/TONSL-H3.1 Pathway in Maintaining Genome Stability in Multicellular Eukaryotes

Replication-dependent histone H3.1 and replication-independent histone H3.3 are nearly identical proteins in most multicellular eukaryotes. The N-terminal tails of these H3 variants, where the majority of histone post-translational modifications are made, typically differ by only one amino acid. Despite extensive sequence similarity with H3.3, the H3.1 variant has been hypothesized to play unique roles in cells, as it is specifically expressed and inserted into chromatin during DNA replication. However, identifying a function that is unique to H3.1 during replication has remained elusive. In this review, we discuss recent findings regarding the involvement of the H3.1 variant in regulating the TSK/TONSL-mediated resolution of stalled or broken replication forks. Uncovering this new function for the H3.1 variant has been made possible by the identification of the first proteins containing domains that can selectively bind or modify the H3.1 variant. The functional characterization of H3-variant-specific readers and writers reveals another layer of chromatin-based information regulating transcription, DNA replication, and DNA repair.