TDRD6 mediates early steps of spliceosome maturation in primary spermatocytes

Very little is known about splicing and its regulation in germ cells, particularly during meiosis. This paper describes the role of a male germ cell-specific protein, Tudor containing protein 6 (TDRD6), in assembly of the spliceosome in spermatocytes. We show that in spermatocytes, TDRD6 interacts with the key protein methyl transferase of the splicing pathway PRMT5. PRMT5 methylates arginines in substrate proteins. In a methylation dependent manner, TDRD6 also associates with spliceosomal core protein SmB in the absence of RNA, thus before an RNP-type spliceosome has been assembled. In Tdrd6-/- primary spermatocytes, PRMT5''s association with SmB and the arginine dimethylation of SmB are much reduced. Abrogation of arginine methylation impaired the assembly of spliceosomes and the presence of the spliceosomal RNA U5 is aberrantly increased. These deficiencies in spliceosome maturation correlated with decreased numbers of Cajal bodies and gems involved in later stages, i.e. nuclear snRNP maturation. To reveal functional consequences of these deficiencies, transcriptome analysis of primary spermatocytes showed high numbers of splicing defects such as aberrant usage of intron and exons as well as aberrant representation of splice junctions upon TDRD6 loss. This study reveals a novel function of TDRD6 in spliceosome maturation and mRNA splicing in spermatocytes. Overall design: Examination of splicing defects in isolated diplotene cells of 20dpp Tdrd6-/- vs. Tdrd6+/- testes pooled from at least 4 mice by deep sequencing in duplicate using Illumina® HiSeq 2500.

16

Akpınar M, Lesche M, Fanourgakis G, Fu J, Anastassiadis K, Dahl A, Jessberger R