Ski3/TTC37 deficiency associated with trichohepatoenteric syndrome causes mitochondrial dysfunction in Drosophila

SKI complex: A multifaceted cytoplasmic RNA exosome cofactor in mRNA metabolism with links to disease, developmental processes, and antiviral responses

RNA stability and quality control are integral parts of gene expression regulation. A key factor shaping eukaryotic transcriptomes, mainly via 3'-5' exoribonucleolytic trimming or degradation of diverse transcripts in nuclear and cytoplasmic compartments, is the RNA exosome. Precise exosome targeting to various RNA molecules requires strict collaboration with specialized auxiliary factors, which facilitate interactions with its substrates. The predominant class of cytoplasmic RNA targeted by the exosome are protein-coding transcripts, which are carefully scrutinized for errors during translation. Normal, functional mRNAs are turned over following protein synthesis by the exosome or by Xrn1 5'-3'-exonuclease, acting in concert with Dcp1/2 decapping complex. In turn, aberrant transcripts are eliminated by dedicated surveillance pathways, triggered whenever ribosome translocation is impaired. Cytoplasmic 3'-5' mRNA decay and surveillance are dependent on the tight cooperation between the exosome and its evolutionary conserved co-factor-the SKI (superkiller) complex (SKIc). Here, we summarize recent findings from structural, biochemical, and functional studies of SKIc roles in controlling cytoplasmic RNA metabolism, including links to various cellular processes. Mechanism of SKIc action is illuminated by presentation of its spatial structure and details of its interactions with exosome and ribosome. Furthermore, contribution of SKIc and exosome to various mRNA decay pathways, usually converging on recycling of ribosomal subunits, is delineated. A crucial physiological role of SKIc is emphasized by describing association between its dysfunction and devastating human disease-a trichohepatoenteric syndrome (THES). Eventually, we discuss SKIc functions in the regulation of antiviral defense systems, cell signaling and developmental transitions, emerging from interdisciplinary investigations. This article is categorized under: RNA Turnover and Surveillance > Turnover/Surveillance Mechanisms RNA Turnover and Surveillance > Regulation of RNA Stability RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes.

Novel TTC37 mutations in a patient with Trichohepatoenteric syndrome: a case report and literature review

BACKGROUND

Trichohepatoenteric syndrome (THES) is a rare autosomal recessive genetic disease caused by pathogenic mutations in TTC37 or SKIV2L gene. The presentation is variable, including intractable diarrhea, woolly hair abnormality, immune dysfunction, intrauterine growth restriction (IUGR), facial dysmorphism, and sometimes liver and skin abnormalities. Although four Chinese children affected with THES syndrome 1 have been described in Singapore, Taiwan (China) and Malaysia, to our knowledge, this is the first report of a patient with THES in Mainland China, harboring classical platelets features, clinical course, and novel mutations in TTC37 gene.

CASE DESCRIPTION

The male infant had symmetrical IUGR, and was born at 37⁺¹ weeks with a birth weight of 1,480 g. He presented with feeding difficulties and vomiting from the 12^th day after birth during the stay in neonatal intensive care unit, and had excessive diarrhea from the 21st day after birth. From the 35^th day after birth, even slightly hypotonic oral rehydration solution caused watery stools. The blood glucose level was lower than 3.3 mmol/L even when the glucose infusion rate was up to 14 mg/kg/min on the parenteral alone, which has not been reported in previous literature. Normal α-granules were observed occasionally in THES platelets. Whole-exome sequencing analysis identified compound heterozygous mutations (c.4130C > G: p.S1377X) and (Exon11-13 del) in the TTC37 gene, which had been inherited from his father and mother, respectively. To our knowledge, the above mutations have not been described in any database or previous literature. Total parenteral nutrition was employed as mainstay of therapy, and hydrocortisone (1 mg/kg/dose, every 4 hours) was used to maintain blood glucose levels. The patient's final prognosis was poor after discharged from the hospital.

CONCLUSIONS

This case presented with mild platelet abnormality and intractable hypoglycemia, which extends the known mutation and phenotype of THES. The clinical features of Chinese patient are consistent with other ethnicity. Molecular diagnosis is useful for patients with unexplained intractable diarrhea, which puts an end to a long diagnostic odyssey.