Isolation of a highly pure archeocyte fraction from the fresh-water spongeEphydatia fluviatilis

Whole-Body Regeneration in Sponges: Diversity, Fine Mechanisms, and Future Prospects

While virtually all animals show certain abilities for regeneration after an injury, these abilities vary greatly among metazoans. Porifera (Sponges) is basal metazoans characterized by a wide variety of different regenerative processes, including whole-body regeneration (WBR). Considering phylogenetic position and unique body organization, sponges are highly promising models, as they can shed light on the origin and early evolution of regeneration in general and WBR in particular. The present review summarizes available data on the morphogenetic and cellular mechanisms accompanying different types of WBR in sponges. Sponges show a high diversity of WBR, which principally could be divided into (1) WBR from a body fragment and (2) WBR by aggregation of dissociated cells. Sponges belonging to different phylogenetic clades and even to different species and/or differing in the anatomical structure undergo different morphogeneses after similar operations. A common characteristic feature of WBR in sponges is the instability of the main body axis: a change of the organism polarity is described during all types of WBR. The cellular mechanisms of WBR are different across sponge classes, while cell dedifferentiations and transdifferentiations are involved in regeneration processes in all sponges. Data considering molecular regulation of WBR in sponges are extremely scarce. However, the possibility to achieve various types of WBR ensured by common morphogenetic and cellular basis in a single species makes sponges highly accessible for future comprehensive physiological, biochemical, and molecular studies of regeneration processes.

Drosophila as a Genetic Model for Hematopoiesis

In this FlyBook chapter, we present a survey of the current literature on the development of the hematopoietic system in Drosophila The Drosophila blood system consists entirely of cells that function in innate immunity, tissue integrity, wound healing, and various forms of stress response, and are therefore functionally similar to myeloid cells in mammals. The primary cell types are specialized for phagocytic, melanization, and encapsulation functions. As in mammalian systems, multiple sites of hematopoiesis are evident in Drosophila and the mechanisms involved in this process employ many of the same molecular strategies that exemplify blood development in humans. Drosophila blood progenitors respond to internal and external stress by coopting developmental pathways that involve both local and systemic signals. An important goal of these Drosophila studies is to develop the tools and mechanisms critical to further our understanding of human hematopoiesis during homeostasis and dysfunction.

MicroRNA expression during demosponge dissociation, reaggregation, and differentiation and a evolutionarily conserved demosponge miRNA expression profile

Demosponges share eight orthologous microRNAs (miRNAs), with none in common with Bilateria. Biological functions of these demosponge miRNAs are unknown. Bilaterian miRNAs are key regulators of cellular processes including cell cycle, differentiation, and metabolism. Resolving if demosponge miRNAs participate in such biological functions will provide clues whether these functions are convergent, evidence on the mode of evolution of cellular developmental processes. Here, a quantitative PCR (qPCR) assay was developed and used to test for differential miRNA expression during dissociation and reaggregation in Spongosorites, compare expression profiles between choanosome and cortex in Spongosorites, and compare undifferentiated gemmules to differentiated juveniles in Ephydatia. During Spongosorites dissociation and reaggregation, miRNA expression showed a global decrease in expression across a range of reaggregating cell densities. miRNA differential response could be related to various general cellular responses, potentially related to nutrient-poor conditions of the minimal artificial seawater media, stress response from tissue dissociation, or loss of cell-cell or cell-matrix contact. In Ephydatia, overall increase in miRNA expression in gemmule-hatched stage 4/5 juveniles relative to gemmules is observed, indicating that increased miRNA expression may be related to increased cellular activity such as migration, cell cycle, and/or differentiation. Observed differential miRNA expression of miRNA during dissociation in Spongosorites (lowered global expression), and during activation, and differentiation of Ephydatia gemmules (increased global expression) could indicate that miRNA expression is associated with cell cycle, differentiation, or metabolism pathways. Interspecies comparison was performed, results indicating that orthologous miRNAs share similar relative expression pattern between the four species tested (Spongosorites, Cinachyrella, Haliclona, and Ephydatia), demonstrating and evolutionarily conserved miRNA expression profile across Demospongia. While these results do not elucidate specific molecular and cellular pathways, together they provide a broad survey of miRNA expression in demosponge systems.

The stem cell system in demosponges: suggested involvement of two types of cells: archeocytes (active stem cells) and choanocytes (food-entrapping flagellated cells)

Major questions about stem cell systems include what type(s) of stem cells are involved (unipotent/totipotent/pluripotent/multipotent stem cells) and how the self-renewal and differentiation of stem cells are regulated. Sponges, the sister group of all other animals and probably the earliest branching multicellular lineage of extant animals, are thought to possess totipotent stem cells. This review introduces what is known about the stem cells in sponges based on histological studies and also on recent molecular biological studies that have started to reveal the molecular and cellular mechanisms of the stem cell system in sponges (mainly in demosponges). The currently proposed model of the stem cell system in demosponges is described, and the possible applicability of this model to other classes of sponges is discussed. Finally, a possible scenario of the evolution of stem cells, including how migrating stem cells arose in the urmetazoan (the last common ancestor of metazoans) and the evolutionary origin of germ line cells in the urbilaterian (the last common ancestor of bilaterians), are discussed.

Cultivation of sponges, sponge cells and symbionts: achievements and future prospects

Marine sponges are a rich source of bioactive compounds with pharmaceutical potential. Since biological production is one option to supply materials for early drug development, the main challenge is to establish generic techniques for small-scale production of marine organisms. We analysed the state of the art for cultivation of whole sponges, sponge cells and sponge symbionts. To date, cultivation of whole sponges has been most successful in situ; however, optimal conditions are species specific. The establishment of sponge cell lines has been limited by the inability to obtain an axenic inoculum as well as the lack of knowledge on nutritional requirements in vitro. Approaches to overcome these bottlenecks, including transformation of sponge cells and using media based on yolk, are elaborated. Although a number of bioactive metabolite-producing microorganisms have been isolated from sponges, and it has been suggested that the source of most sponge-derived bioactive compounds is microbial symbionts, cultivation of sponge-specific microorganisms has had limited success. The current genomics revolution provides novel approaches to cultivate these microorganisms.

The stem cell system in demosponges: insights into the origin of somatic stem cells

The stem cell system is one of the unique systems that have evolved only in multicellular organisms. Major questions about this system include what type(s) of stem cells are involved (pluri-, multi- or uni-potent stem cells), and how the self-renewal and differentiation of stem cells are regulated. To understand the origin of the stem cell system in metazoans and to get insights into the ancestral stem cell itself, it is important to discover the molecular and cellular mechanisms of the stem cell system in sponges (Porifera), the evolutionarily oldest extant metazoans. Histological studies here provided a body of evidence that archeocytes are the stem cells in sponges, and recent molecular studies of sponges, especially the finding of the expression of Piwi homologues in archeocytes and choanocytes in a freshwater sponge, Ephydatia fluviatilis, have provided critical insights into the stem cell system in demosponges. Here I introduce archeocytes and discuss (i) modes of archeocyte differentiation, (ii) our current model of the stem cell system in sponges composed of both archeocytes and choanocytes based on our molecular analysis and previous microscopic studies suggesting the maintenance of pluripotency in choanocytes, (iii) the inference that the Piwi and piRNA function in maintaining stem cells (which also give rise to gametes) may have already been achieved in the ancestral metazoan, and (iv) possible hypotheses about how the migrating stem cells arose in the urmetazoan (protometazoan) and about the evolutionary origin of germline cells in the urbilaterian (protobilaterian).

Biology of the Porifera: cell culture

The discovery that dissociated sponge cells will reaggregate to form a functional organism was the basis for the establishment of sponge cell cultures that have been used as a model for the study of fundamental processes in developmental biology and immunology. More recent is the discovery of unique bioactive compounds in marine sponges, and the feasibility of in vitro production of these chemicals is being evaluated. Techniques are well established for cell dissociation; development of several nutrient media formulations has resulted in improvements in viability and cell division; and molecular approaches to identification of genes responsible for regulation of cell cycling may provide unique perspectives in culture optimization. The use of novel substrates for immobilization of cells offers alternatives for proliferation and scale-up. All of these results support the potential for development of a model system for the study of basic metabolic processes involved in cell differentiation, as well as an in vitro production system for sponge-derived bioactive compounds. Perhaps more important, however, is the development of cell lines of these "simple" metazoans to facilitate basic cell physiology and molecular biology research that may be applied to understanding more complex metazoan systems, including humans.

Temporal and spatial expression of EmH-3, a homeobox-containing gene isolated from the freshwater sponge Ephydatia muelleri

Homeoboxes have been particularly valuable in identifying genes involved in development. This prompted us to look for homeobox-containing genes in sponges, the most primitive metazoans, and to explore the potential role of these genes in their development. Using the reverse transcription polymerase reaction (RT-PCR), we analyzed the expression of EmH-3 homeobox-containing gene at different stages of development, and in different cell-type populations. The patterns of EmH-3 expression show that this gene is expressed differentially in the course of development and in a cell-type specific manner. The level of transcripts increases from undetectable levels in resting gemmules to higher levels at the moment of hatching and throughout the sponge's life. EmH-3 is strongly expressed in the pluripotent archaeocytes, whether isolated from fully differentiated sponges (adult archaeocytes) or from HU-treated sponges (embryonic archaeocytes). Conversely, in differentiated cells such as pinacocytes and choanocytes, EmH-3 expression is very weak and similar to that found in the resting gemmules. On the other hand, another freshwater sponge homeobox-containing gene, prox1 from Ephydatia fluviatilis is expressed almost at the same level at all stages of development and in all the investigated cell populations. Together, these results suggest that EmH-3 plays a role in cell determination and/or differentiation. In particular EmH-3 would determine which archaeocytes will multiply and undergo differentiation and which ones will remain undifferentiated.

Ultrastructural study of differentiation processes during aggregation of purified sponge archaeocytes

Archaeocytes from the spongeEphydatia fluviatilis were dissociated and then isolated on Ficoll density gradients. Their aggregation and reconstitution processes were studied by transmission electron microscopy to determine their capabilities for differentiation.Archaeocyte aggregates follow a well defined sequence of differentiation to generate the characteristic structures of a sponge. Pinacoderm is the first structure to be regenerated and appears progressively at the surface of the 12 h aggregates. Pinacocytes which have differentiated in archaeocyte aggregates are identical to native ones except that the nucleolus remains in most cells. The choanocytes appear only after 24 h by a two step process. First, small cells (choanoblasts) are formed from archaeocytes by mitosis. These cells then transform into fully differentiated choanocytes possessing collars and flagella. The early choanocyte chambers are small, irregular and randomly dispersed in the aggregates. Finally, collencytes and sclerocytes begin to appear just before the aggregates spread on the substrate.The differentiation of a suspension of pure archaeocytes is a unique model system to study sponge cell differentiation and has allowed us to demonstrate that archaeocytes isolated from developed sponges maintain the capacity to differentiate even though this capacity is not usually expressed.