title: VASA expression suggests shared germ line dynamics in bivalve molluscs.
abstract: Germ line segregation can occur during embryogenesis or after embryogenesis completion, with multipotent cells able to give rise to both germ and somatic cells in the developing juvenile or even in adulthood. These undifferentiated cells, in some animals, are self-renewing stem cells. In all these cell lineages, the same set of genes, among which vasa, appears to be expressed. We traced VASA expression during the peculiar gonad rebuilding of bivalves to verify its presence from undifferentiated germ cells to mature gametes in an animal taxon in which the mechanism of germ line establishment is still under investigation. We utilized antibodies produced against VASPH, VASA homolog of Ruditapes philippinarum (Subclass Heterodonta), to compare the known expression pattern of R. philippinarum to two species of the Subclass Pteriomorphia, Anadara kagoshimensis and Crassostrea gigas, and another species of the Subclass Heterodonta, Mya arenaria. The immunohistological data obtained support a conserved mechanism of proliferation of "primordial stem cells" among the simple columnar epithelium of the gut, as well as in the connective tissue, contributing to the seasonal gonad reconstitution. Given the taxonomic separation of the analyzed species, we suggest that the process could be shared in bivalve molluscs. The presence of germ cell precursors in the gut epithelium appears to be a feature in common with model organisms, such as mouse, fruit fly, and human. Thus, the comparative study of germ line establishment can add details on bivalve development, but can also help to clarify the role that VASA plays during germ cell specification.
authors.affiliation: Department of Scienze Biologiche, Geologiche ed Ambientali, University of Bologna, Via Selmi 3, 40126, Bologna, Italy. liliana.milani@unibo.it.
authors.forename: Liliana
authors.identifier: http://orcid.org/0000-0001-5052-2075
authors.initials: L
authors.lastname: Milani
authors.affiliation: Department of Scienze Biologiche, Geologiche ed Ambientali, University of Bologna, Via Selmi 3, 40126, Bologna, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Pecci
authors.affiliation: Department of Scienze Biologiche, Geologiche ed Ambientali, University of Bologna, Via Selmi 3, 40126, Bologna, Italy.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Ghiselli
authors.affiliation: Department of Scienze Biologiche, Geologiche ed Ambientali, University of Bologna, Via Selmi 3, 40126, Bologna, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Passamonti
authors.affiliation: Department of Scienze Biologiche, Geologiche ed Ambientali, University of Bologna, Via Selmi 3, 40126, Bologna, Italy.
authors.forename: Simone
authors.initials: S
authors.lastname: Bettini
authors.affiliation: Department of Scienze Biologiche, Geologiche ed Ambientali, University of Bologna, Via Selmi 3, 40126, Bologna, Italy.
authors.forename: Valeria
authors.initials: V
authors.lastname: Franceschini
authors.affiliation: Department of Scienze Biologiche, Geologiche ed Ambientali, University of Bologna, Via Selmi 3, 40126, Bologna, Italy.
authors.forename: Maria Gabriella
authors.initials: MG
authors.lastname: Maurizii
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D049872:Bivalvia / Q000166:cytology / Q000378:metabolism*; D053487:DEAD-box RNA Helicases / Q000235:genetics* / Q000378:metabolism; D005854:Germ Cells / Q000166:cytology / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D053487:DEAD-box RNA Helicases
keywords: Anadara kagoshimensis; Crassostrea gigas; Gonads; Immunohistochemistry; Multipotent cells; Mya arenaria