title: Amelotin Gene Structure and Expression during Enamel Formation in the Opossum Monodelphis domestica.
abstract: Amelotin (AMTN) is an ameloblast-secreted protein that belongs to the secretory calcium-binding phosphoprotein family, which also includes the enamel matrix proteins amelogenin, ameloblastin and enamelin. Although AMTN is supposed to play an important role in enamel formation, data were long limited to the rodents, in which it is expressed during the maturation stage. Recent comparative studies in sauropsids and amphibians revealed that (i) AMTN was expressed earlier, i.e. as soon as ameloblasts are depositing the enamel matrix, and (ii) AMTN structure was different, a change which mostly resulted from an intraexonic splicing in the large exon 8 of an ancestral mammal. The present study was performed to know whether the differences in AMTN structure and expression in rodents compared to non-mammalian tetrapods dated back to an early ancestral mammal or were acquired later in mammalian evolution. We sequenced, assembled and screened the jaw transcriptome of a neonate opossum Monodelphis domestica, a marsupial. We found two AMTN transcripts. Variant 1, representing 70.8% of AMTN transcripts, displayed the structure known in rodents, whereas variant 2 (29.2%) exhibited the nonmammalian tetrapod structure. Then, we studied AMTN expression during amelogenesis in a neonate specimen. We obtained similar data as those reported in rodents. These findings indicate that more than 180 million years ago, before the divergence of marsupials and placentals, changes occurred in AMTN function and structure. The spatiotemporal expression was delayed to the maturation stage of amelogenesis and the intraexonic splicing gave rise to isoform 1, encoded by variant 1 and lacking the RGD motif. The ancestral isoform 2, housing the RGD, was initially conserved, as demonstrated here in a marsupial, then secondarily lost in the placental lineages. These findings bring new elements towards our understanding of the non-prismatic to prismatic enamel transition that occurred at the onset of mammals.
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, Institut de Biologie Paris-Seine (IBPS), UMR7138, 75005 Paris, France; CNRS, IBPS, UMR7138, 75005 Paris, France.
authors.forename: Barbara
authors.initials: B
authors.lastname: Gasse
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, Institut de Biologie Paris-Seine (IBPS), UMR7138, 75005 Paris, France; CNRS, IBPS, UMR7138, 75005 Paris, France; Sorbonne Universités, UPMC Univ Paris 06, Station Biologique de Roscoff, Plateforme ABiMS (Analyses and Bioinformatics for Marine Science), 29680 Roscoff, France.
authors.forename: Xi
authors.initials: X
authors.lastname: Liu
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, Station Biologique de Roscoff, Plateforme ABiMS (Analyses and Bioinformatics for Marine Science), 29680 Roscoff, France.
authors.forename: Erwan
authors.initials: E
authors.lastname: Corre
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, Institut de Biologie Paris-Seine (IBPS), UMR7138, 75005 Paris, France; CNRS, IBPS, UMR7138, 75005 Paris, France.
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Sire
mesh_terms: D000566:Amelogenesis / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D000831:Animals, Newborn; D003743:Dental Enamel / Q000254:growth & development* / Q000378:metabolism*; D003746:Dental Enamel Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D008969:Molecular Sequence Data; D048309:Monodelphis / Q000235:genetics* / Q000254:growth & development; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D003746:Dental Enamel Proteins; D012333:RNA, Messenger