title: Deviating from the Norm: Peculiarities of Aplysia cf. californica Early Cleavage Compared to Traditional Spiralian Models.
abstract: Spiralia represents one of the main clades of bilaterally symmetrical metazoans (Bilateria). This group is of particular interest due to the remarkable conservation of its early developmental pattern despite of the high diversity of larval and adult body plans. Variations during embryogenesis are considered powerful tools to determine ancestral and derived characters under a phylogenetic framework. By direct observation of embryos cultured in vitro, we analyzed the early cleavage of the euopisthobranchs Aplysia cf. californica. We used tubulin immunocytochemistry to stain mitotic spindles during early cleavages, and followed each division with the aid of an autofluorescent compound inside yolk platelets, which differed from the characteristic pink-brownish pigment of the vegetal cytoplasm in zygotes and early embryos. We found that this species exhibits an unequal cleavage characterized by ooplasmic segregation, oblique inclination of mitotic spindles, and differences in size and positioning of the asters in relation to the cellular cortex. Furthermore, we detected asynchrony in cleavage timing between the two large macromeres C and D, which increases the number of cleavage rounds required to reach a particular cell stage in comparison to other spiralians. Here, we report the presence of a transient and previously undescribed U-shaped embryo in this species. The present detailed description of A. californica early development deviates considerably from stereotypical patterns described in other spiralians. Our observations demonstrate that early spiralian development can be more plastic than previously thought.
authors.affiliation: Laboratorio de Biología del Desarrollo 113, Escuela de Ciencias Biológicas, Pontificia Universidad Católica del Ecuador, Quito, Ecuador.|Centro Nacional de Acuicultura e Investigaciones Marinas, Escuela Politécnica del Litoral, San Pedro, Santa Elena, Ecuador.
authors.forename: Yolanda E
authors.initials: YE
authors.lastname: Chávez-Viteri
authors.affiliation: Centro Nacional de Acuicultura e Investigaciones Marinas, Escuela Politécnica del Litoral, San Pedro, Santa Elena, Ecuador.|Evolutionary Developmental Biology Laboratory, Department of Biological Sciences, Universidad de los Andes, Bogotá, Colombia.|Departamento de Zoologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil.|Instituto Nacional de Ciência e Tecnologia em Estudos Interdisciplinares e Transdisciplinares em Ecologia e Evolução (IN-TREE), Salvador, BA, Brazil.
authors.forename: Federico D
authors.initials: FD
authors.lastname: Brown
authors.affiliation: Laboratorio de Biología del Desarrollo 113, Escuela de Ciencias Biológicas, Pontificia Universidad Católica del Ecuador, Quito, Ecuador.
authors.forename: Oscar D
authors.initials: OD
authors.lastname: Pérez
mesh_terms: D000818:Animals; D001048:Aplysia / Q000196:embryology*; D002455:Cell Division / Q000502:physiology; D019070:Cell Lineage / Q000235:genetics; D007814:Larva / Q000254:growth & development; D008954:Models, Biological; D013045:Species Specificity