Diverse choanocyte behavior during cell reaggregation in Demospongiae and Calcarea
Creators: name: Lavrov, Andrey
name: Kosevich, Igor
Publisher: name: F1000Research
Year: 2017

description: Sponges (phylum Porifera) are one of the most primitive multicellular animals. Sponge organization is simple compared to other Metazoa: sponges lack organs, muscles, nervous and digestive systems. Their body is composed of three parts: outer epitheliums (exo- and basipinacoderm), inner epitheliums (endopinacoderm and choanoderm) and mesohyl (space between epitheliums occupied by wandering cells and ECM).<br><br>Despite simplicity sponges display unique features in their organization. Continuous tissue reorganization is one of them. Such reorganization bases on differentiation plasticity and motility of their cells. Virtually all cells in the sponge body permanently move and many of them are capable for transdifferentiation. Continuous tissue reorganization allows sponges adjusting aquiferous system to certain hydrodynamic conditions, reconstructing somatic tissue after degradation during sexual reproduction, production bodies for asexual reproduction and movement.<br><br>The most outstanding manifestation of sponge anatomical plasticity is cell reaggregation after tissue dissociation. Multicellular aggregates differing in structure are formed in the course of reaggregation ending in certain cases in reconstruction of intact sponge. Sponge cell reaggregation is unique model system to study the cells potencies and behavior in the primitive multicellular organisms.<br><br>We studied cell reaggregation in two Demospongiae species (<i>Halichondria panicea, Halisarca dujardini</i>) and in one Calcarea species (<i>Leucosolenia complicata</i>). All three species show different modes of reaggregation: in <i>L. complicata</i> cell reaggregation ceases at the stage of early primmorphs, in <i>H. panicea</i> – at the stage of primmorphs and only cells of <i>H. dujardini</i> reconstructed intact sponge at 10-12 day post-dissociation (dpd). Using sLCM and TEM we studied behavior of choanocytes during cell reaggregation of these species and found significant differences in choanocyte behavior between demosponge and calcarean species. Choanocytes of <i>L. complicata</i> retain their differentiation during cell reaggregation – we found choanocytes with all their characteristic features in early-stage primmorphs at 6 dpd. On the contrary, in the both demosponge species choanocytes dedifferentiate during cell reaggregation losing flagellums and microvilli collars and becoming indistinguishable from nucleolar amoebocytes in the early-stage primmorphs of these species. In <i>H. dujardini</i> during further development the choanocytes differentiate from population of cells with amoebocyte morphology including both nucleolar amoebocytes of maternal sponge and dedifferentiated choanocytes.<br><br>This study gives first insights into the different behavior of cells during reaggregation in the demosponge and calcarean species. Choanocytes can be easily defined by their structure but further investigation of behavior of other cell types needs elaboration of specific methods of each cell type labelling.