title: A peculiar lamin in a peculiar mammal: Expression of lamin LIII in platypus (Ornithorhynchus anatinus).
abstract: Platypus (Ornithorhynchus anatinus) holds a unique phylogenetic position at the base of the mammalian lineage due to an amalgamation of mammalian and sauropsid-like features. Here we describe the set of four lamin genes for platypus. Lamins are major components of the nuclear lamina, which constitutes a main component of the nucleoskeleton and is involved in a wide range of nuclear functions. Vertebrate evolution was accompanied by an increase in the number of lamin genes from a single gene in their closest relatives, the tunicates and cephalochordates, to four genes in the vertebrate lineage. Of the four genes the LIII gene is characterized by the presence of two alternatively spliced CaaX-encoding exons. In amphibians and fish LIII is the major lamin protein in oocytes and early embryos. The LIII gene is conserved throughout the vertebrate lineage, with the notable exception of marsupials and placental mammals, which have lost the LIII gene. Here we show that platypus has retained an LIII gene, albeit with a significantly altered structure and with a radically different expression pattern. The platypus LIII gene contains only a single CaaX-encoding exon and the head domain together with coil 1a and part of coil1b of the platypus LIII protein is replaced by a novel short non-helical N-terminus. It is expressed exclusively in the testis. These features resemble those of male germ cell-specific lamins in placental mammals, in particular those of lamin C2. Our data suggest (i) that the specific functions of LIII, which it fulfills in all other vertebrates, is no longer required in mammals and (ii) once it had been freed from these functions has undergone structural alterations and has adopted a new functionality in monotremes.
authors.affiliation: Department of Cell Biology, FB2, University of Bremen, P.O. Box 33 04 40, 28334 Bremen, Germany.
authors.forename: Annette
authors.initials: A
authors.lastname: Peter
authors.affiliation: Cellular and Molecular Pharmacology, Louvain Drug Research Institute, Université catholique de Louvain, avenue E. Mounier 73 bte B1.73.05, B-1200 Brussels, Belgium. Electronic address: shaunak.khandekar@uclouvain.be.
authors.forename: Shaunak
authors.initials: S
authors.lastname: Khandekar
authors.affiliation: Research School of Biology, ANU College of Medicine, Biology and Environment, Canberra, Australia. Electronic address: janine.deakin@canberra.edu.au.
authors.forename: Janine E
authors.initials: JE
authors.lastname: Deakin
authors.affiliation: Department of Cell Biology, FB2, University of Bremen, P.O. Box 33 04 40, 28334 Bremen, Germany. Electronic address: stick@uni-bremen.de.
authors.forename: Reimer
authors.initials: R
authors.lastname: Stick
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D034882:Lamins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D009007:Monotremata / Q000235:genetics* / Q000378:metabolism; D009928:Organ Specificity; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D013737:Testis / Q000378:metabolism
chemical_list: D034882:Lamins
keywords: Germ cell-specific lamins; Lamin LIII; Lamin gene evolution; Monotremata; Ornithorhynchus anatinus; Platypus