title: Germ cell proliferation and cluster behavior in ovarioles of Sialis flavilatera (Megaloptera: Sialidae) during larval growth.
abstract: Telotrophic meroistic insect ovaries are assigned to four different types. The Sialis type is found in Sialidae (Megaloptera), Raphidioptera and a coleopteran subgroup (Myxophaga: Hydroscaphidae). King and Büning (1985) proposed a hypothetical model for the development of this ovariole type; however, a detailed description of ovarian development in Sialis was missing so far. Using light and electron microscopy, we investigated developing ovaries of Sialis flavilatera starting in the 10th month of the biennial larval phase until adulthood. At least from the 10th month onwards, a Sialis ovariole anlage contains a single germ cell syncytium, whose growth is promoted by a mitotic cell population maintained in its anterior compartment. The stem-like, dividing germ cells form synchronous sub-clusters consisting of 2-16 cystocytes, which are spatially arranged in bigger rosettes that stay connected to each other via cytoplasmic tubes. Within individual rosettes, cells communicate by centrally gathering intercellular bridges. Following each round of cystocyte division and subsequent rosette formation, plasma membrane wrinkles sprout near newborn bridges, elongate, and interdigitate with the preexisting membrane tubes. In this way the membrane labyrinth emerges and grows. Germ cells leaving the proliferation zone posteriorly enter meiotic prophase. Hypotheses on the phylogenetic origin of this ovary type are discussed in the light of our results.
authors.affiliation: Biology Department, Developmental Biology Unit, University of Erlangen-Nuremberg, Staudtstr. 5, D-91058 Erlangen, Germany. Electronic address: ralph.ruebsam@fau.de.
authors.forename: Ralph
authors.initials: R
authors.lastname: Rübsam
authors.affiliation: Artemisstr. 34, D-13469 Berlin, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Büning
mesh_terms: D000818:Animals; D049109:Cell Proliferation; D005260:Female; D005854:Germ Cells / Q000166:cytology / Q000254:growth & development / Q000648:ultrastructure; D007313:Insecta / Q000166:cytology* / Q000254:growth & development* / Q000648:ultrastructure; D007814:Larva / Q000166:cytology / Q000254:growth & development / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D010053:Ovary / Q000166:cytology / Q000254:growth & development / Q000648:ultrastructure
keywords: Germ cell cluster; Insect ovary; Phylogeny; Stem cell; Syncytium; Ultrastructure