reaggregation of marine sponges' cells helped the scientists to come closer to understanding of the origin and early evolution of multicellular animals.The work was published in Journal of Experimental Zoology Part A: Ecological Genetics and Physiology.

Andrey Lavrov and Igor Kosevich, MSU biologists, researched the ability of the cells of marine sponges (Porifera) to reaggregation - a process, during which the artificially separated sponge cells reaggregate and build multicellular aggregates of varying types.

Marine sponges are the most ancient group of multicellular animalsliving on Earth. The structure of adult sponges is quite simple: they lack internal organs, digestion, nervous and muscular system. Though, sponges show a unique set of features, uncommon for the rest of the fauna. A high plasticity of the tissue is their definingcharacteristic that enables a constant reconstructionof a sponge's organism. This allows adaptation to the changing environment.

One of the manifestations of this plasticity is an ability to reaggregate after a dissociation of tissues. 'Reaggregation of cells represents a prospective model system allowing a research ofsponge tissues functioningunder a laboratory control,' - tells Andrey Lavrov, junior researcher in Department of Invertebrate Zoology, Faculty of Biology, MSU.

During the research Andrey Lavrov and Igor Kosevich experimented with cultures of the sponges'cells under a laboratory surveillance. The scientists described the process of cell suspension obtaining: 'To split a cell two main methods of tissues dissociation are used: the chemical one and the mechanical one. In case of mechanical dissociation animal's tissues are wiped through a gauze which leads to splitting into separate cells and small groups of cells. Under chemical dissociation sponges tissues are exposed to in calcium- and magnesium-free seawater containing a chelating agent EDTA. That leads to malfunction of the intercellular contacts and splitting a tissue into cells. Concentrated suspensions of sponge cells are put into Petri dish. In that temporary cell cultures the process of reaggregation further takes place.'

During reaggregation process multicellular aggregates form in the cell cultures. On the initial stages all cells in the aggregates have a spherical shape, then the surface cells acquire a T-shape, and the inner cells - an amoeboid shape. Structure of these multicellular aggregates were studied under light microscope and also under scanning and transmission electron microscopy in the Interdepartmental laboratory of electronic microscopy (ILEM) of the MSU biological faculty.

'In a number of cases such multicellular aggregates are able to the progressive development that may end up with a full reconstructionof an animal's initialorganization. The main result of our study is a detailed description of the cell reaggregation process dynamics, and also of the structure of multicellular aggregates of the marine sponges belonging to the Demospongiae class,' - explains Andrey Lavrov.

The detailed research of functioning of sponge tissues brings the scientists closer to understanding of the general functioning of multicellular organisms and processes that led to the transition from unicellular to multicellular forms of life. Apart from that, the research has a practical use: long-term cultures of multicellular aggregates, forming during the reaggregation process, may become a basis for producing biologically active substances used in pharmaceutics and cosmetics.