Ciliary Signalling and Mechanotransduction in the Pathophysiology of Craniosynostosis

Craniosynostosis (CS) is the second most prevalent inborn craniofacial malformation; it results from the premature fusion of cranial sutures and leads to dimorphisms of variable severity. CS is clinically heterogeneous, as it can be either a sporadic isolated defect, more frequently, or part of a syndromic phenotype with mendelian inheritance. The genetic basis of CS is also extremely heterogeneous, with nearly a hundred genes associated so far, mostly mutated in syndromic forms. Several genes can be categorised within partially overlapping pathways, including those causing defects of the primary cilium. The primary cilium is a cellular antenna serving as a signalling hub implicated in mechanotransduction, housing key molecular signals expressed on the ciliary membrane and in the cilioplasm. This mechanical property mediated by the primary cilium may also represent a cue to understand the pathophysiology of non-syndromic CS. In this review, we aimed to highlight the implication of the primary cilium components and active signalling in CS pathophysiology, dissecting their biological functions in craniofacial development and in suture biomechanics. Through an in-depth revision of the literature and computational annotation of disease-associated genes we categorised 18 ciliary genes involved in CS aetiology. Interestingly, a prevalent implication of midline sutures is observed in CS ciliopathies, possibly explained by the specific neural crest origin of the frontal bone.

Computational annotation of miRNA transcription start sites

Motivation MicroRNAs (miRNAs) are small noncoding RNAs that play important roles in gene regulation and phenotype development. The identification of miRNA transcription start sites (TSSs) is critical to understand the functional roles of miRNA genes and their transcriptional regulation. Unlike protein-coding genes, miRNA TSSs are not directly detectable from conventional RNA-Seq experiments due to miRNA-specific process of biogenesis. In the past decade, large-scale genome-wide TSS-Seq and transcription activation marker profiling data have become available, based on which, many computational methods have been developed. These methods have greatly advanced genome-wide miRNA TSS annotation. Results In this study, we summarized recent computational methods and their results on miRNA TSS annotation. We collected and performed a comparative analysis of miRNA TSS annotations from 14 representative studies. We further compiled a robust set of miRNA TSSs (RSmirT) that are supported by multiple studies. Integrative genomic and epigenomic data analysis on RSmirT revealed the genomic and epigenomic features of miRNA TSSs as well as their relations to protein-coding and long non-coding genes. Contact [email protected], [email protected]

Cicada endosymbionts contain tRNAs that are processed despite having genomes that lack tRNA processing activities

Gene loss and genome reduction are defining characteristics of nutritional endosymbiotic bacteria. In extreme cases, even essential genes related to core cellular processes such as replication, transcription, and translation are lost from endosymbiont genomes. Computational predictions on the genomes of the two bacterial symbionts of the cicadaDiceroprocta semicincta, “CandidatusHodgkinia cicadicola” (Alphaproteobacteria) and “Ca. Sulcia muelleri” (Betaproteobacteria), find only 26 and 16 tRNA, and 15 and 10 aminoacyl tRNA synthetase genes, respectively. Furthermore, the original “Ca.Hodgkinia” genome annotation is missing several essential genes involved in tRNA processing, such as RNase P and CCA tRNA nucleotidyltransferase, as well as several RNA editing enzymes required for tRNA maturation. How “Ca. Sulcia” and “Ca. Hodgkinia” preform basic translation-related processes without these genes remains unknown. Here, by sequencing eukaryotic mRNA and total small RNA, we show that the limited tRNA set predicted by computational annotation of “Ca. Sulcia” and “Ca. Hodgkinia” is likely correct. Furthermore, we show that despite the absence of genes encoding tRNA processing activities in the symbiont genomes, symbiont tRNAs have correctly processed 5’ and 3’ ends, and seem to undergo nucleotide modification. Surprisingly, we find that most “Ca. Hodgkinia”and “Ca. Sulcia” tRNAs exist as tRNA halves. Finally, and in contrast with other related insects, we show that cicadas have experienced little horizontal gene transfer that might complement the activities missing from the endosymbiont genomes. We conclude that “Ca. Sulcia” and “Ca. Hodgkinia” tRNAs likely function in bacterial translation, but require host-encoded enzymes to do so.