title: Identification and characterisation of synaptonemal complex genes in monotremes.
abstract: The platypus and echidna are the only extant species belonging to the clade of monotremata, the most basal mammalian lineage. The platypus is particularly well known for its mix of mammalian and reptilian characteristics and work in recent years has revealed this also extends to the genetic level. Amongst the monotreme specific features is the unique multiple sex chromosome system (5X4Y in the echidna and 5X5Y in the platypus), which forms a chain in meiosis. This raises questions about sex chromosome organisation at meiosis, including whether there has been changes in genes coding for synaptonemal complex proteins which are involved in homologous synapsis. Here we investigate the key structural components of the synaptonemal complex in platypus and echidna, synaptonemal complex proteins 1, 2 and 3 (SYCP1, SYCP2 and SYCP3). SYCP1 and SYCP2 orthologues are present, conserved and expressed in platypus testis. SYCP3 in contrast is highly diverged, but key residues required for self-association are conserved, while those required for tetramer stabilisation and DNA binding are missing. We also discovered a second SYCP3-like gene (SYCP3-like) in the same region. Comparison with the recently published Y-borne SYCP3 amino acid sequences revealed that SYCP3Y is more similar to SYCP3 in other mammals than the monotreme autosomal SYCP3. It is currently unclear if these changes in the SYCP3 gene repertoire are related to meiotic organisation of the extraordinary monotreme sex chromosome system.
authors.affiliation: The Robinson Institute, School of Molecular and Biomedical Science, University of Adelaide, Gate 8 Victoria Drive, Adelaide, South Australia 5005, Australia. Electronic address: aaron.casey@adelaide.edu.au.
authors.forename: Aaron E
authors.initials: AE
authors.lastname: Casey
authors.affiliation: The Robinson Institute, School of Molecular and Biomedical Science, University of Adelaide, Gate 8 Victoria Drive, Adelaide, South Australia 5005, Australia.
authors.forename: Tasman J
authors.initials: TJ
authors.lastname: Daish
authors.affiliation: The Robinson Institute, School of Molecular and Biomedical Science, University of Adelaide, Gate 8 Victoria Drive, Adelaide, South Australia 5005, Australia.
authors.forename: Frank
authors.initials: F
authors.lastname: Grutzner
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D033481:Chromosomes, Mammalian / Q000235:genetics; D019143:Evolution, Molecular; D008297:Male; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D010987:Platypus / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D012730:Sex Chromosomes / Q000235:genetics; D013573:Synaptonemal Complex / Q000235:genetics* / Q000378:metabolism; D004442:Tachyglossidae / Q000235:genetics*; D013737:Testis / Q000378:metabolism
chemical_list: D009687:Nuclear Proteins
keywords: Meiosis; Monotremes; SYCP1; SYCP2; SYCP3; Synaptonemal complex