PSVI-7 - snoRNA dysregulated expression and potential roles in bovine sub-clinical mastitis due to Staphylococcus chromogenes

Abstract: Staphylococcus chromogenes (SC), a frequent non-aureus staphylococcus on Canadian herds causes both clinical and subclinical forms of mastitis and contributes to huge economic losses on Canadian farms. However, little research attention has been directed to uncovering the molecular mechanisms underlying SC mastitis pathogenesis, including the roles of small nucleolar RNAs (snoRNAs). SnoRNAs function to regulate host ribosomal RNAs (rRNAs) biogenesis and processing, and are known to play regulatory functions in several human diseases but no study has examined their regulatory functions in bovine mastitis. To understand the regulatory roles of snoRNAs in cows with SC subclinical mastitis, the snoRNA transcriptome of milk somatic cells from three SC infected cows (positive for SC only, have high somatic cell counts [SCC ≥350,000 cells/mL] for ≥3 months consecutively, only one positive udder sampled), and four healthy cows (low SCC [< 100,000 cells/mL] for ≥3 months consecutively, compositive sample of all quarters) was characterized by sequencing and bioinformatics analysis. Among 232 known snoRNAs found in the samples, 33 were differentially expressed (DE) (14 downregulated and 19 upregulated) (FDR< 0.05). Out of these, SnoRA3/snoRA45 (upregulated) belongs to H/ACA snoRNA box type while SNORD14 (downregulated) belongs to C/D box snoRNA box type. According to RNAsnoop analysis, SnoRA3/snoRA45 interacted with 18S-1667 rRNA (minimum free energy (MFE) = -36Kcal/Mol) while SNORD14 interacted with 28S-3926 rRNA (MFE = -15.40Kcal/Mol). The observed strong MFE suggests that SnoRA3/snoRA45 and SNORD14 might potentially participate in rRNA modifications which could affect important functional sites of the ribosome with implications on the pathogenesis of bovine SC mastitis. SnoRA3/snoRA45 have been reported to guide site specific pseudouridylation of rRNA by upregulating the ribosomal pathway as well as play important roles in cell cycle progression in human. SNORD14 is expressed from the intron of its host gene RPS13, which is a ribosomal protein involved in protein biosynthesis. Also, SNORD14 has been shown to be potentially involved in intracellular protein transport and positive regulation of MAPK cascade. Our results suggest that the DE snoRNAs could potentially regulate the host rRNA biogenesis and processing in response to mastitis due to SC. To the best of our knowledge, this is the first study to report dysregulated snoRNA expression and potential involvement in bovine SC subclinical mastitis.