Meeting Abstract

13.1  Jan. 4  Reversed polarity budding in the basal bilaterian Convolutriloba retrogemma (Acoelomorpha: Acoela) SIKES, James M.*; BELY, Alexa E.; University of Maryland jsikes@umd.edu

The acoel Convolutriloba retrogemma reproduces by a remarkable budding process in which two posterior buds are formed that have a reversed A/P polarity relative to the parent. To investigate the evolution and development of this process, we have investigated the phylogenetic context of this mode of asexual reproduction, performed regeneration experiments on budding worms, and characterized patterns of cell division, muscle fiber dynamics, and gene expression during the budding process. 18S rDNA and COI gene sequence data reveal that C. retrogemma is most closely related to another Convolutriloba species (C. longifissura) that reproduces by two orthogonal divisions, a first one transverse and a second longitudinal. Interestingly, based on the phylogenetic placement of a recently discovered species that also reproduces by forming buds like C. retrogemma, it appears that reversed polarity budding has independently evolved at least twice within this group. Regeneration exeriments in which posterior buds are cut off from the parent at different axial positions demonstrate that the zone of A/P axis reversal occurs at the site of bud initiation. Studies of cell division (as revealed by BrdU labeling of S-phase cells) and muscle filaments (as revealed by phalloidin studies of F-actin) reveal that posterior buds extend via an anterior growth zone and that muscle fibers may be continuous across the parent and bud. To investigate gene expression during the budding process, we have cloned members of the anterior, central, and posterior classes of Hox genes as well as homologs of orthodenticle, an anterior patterning gene. RT-PCR results suggest that both anterior markers are upregulated during budding and attempts to characterize the spatio-temporal expression of these genes are currently underway.