Transfection of Sponge Cells and Intracellular Localization of Cancer-Related MYC, RRAS2, and DRG1 Proteins

The determination of the protein's intracellular localization is essential for understanding its biological function. Protein localization studies are mainly performed on primary and secondary vertebrate cell lines for which most protocols have been optimized. In spite of experimental difficulties, studies on invertebrate cells, including basal Metazoa, have greatly advanced. In recent years, the interest in studying human diseases from an evolutionary perspective has significantly increased. Sponges, placed at the base of the animal tree, are simple animals without true tissues and organs but with a complex genome containing many genes whose human homologs have been implicated in human diseases, including cancer. Therefore, sponges are an innovative model for elucidating the fundamental role of the proteins involved in cancer. In this study, we overexpressed human cancer-related proteins and their sponge homologs in human cancer cells, human fibroblasts, and sponge cells. We demonstrated that human and sponge MYC proteins localize in the nucleus, the RRAS2 in the plasma membrane, the membranes of the endolysosomal vesicles, and the DRG1 in the cell's cytosol. Despite the very low transfection efficiency of sponge cells, we observed an identical localization of human proteins and their sponge homologs, indicating their similar cellular functions.

DNA Repair Repertoire of the Enigmatic Hydra

Since its discovery by Abraham Trembley in 1744, hydra has been a popular research organism. Features like spectacular regeneration capacity, peculiar tissue dynamics, continuous pattern formation, unique evolutionary position, and an apparent lack of organismal senescence make hydra an intriguing animal to study. While a large body of work has taken place, particularly in the domain of evolutionary developmental biology of hydra, in recent years, the focus has shifted to molecular mechanisms underlying various phenomena. DNA repair is a fundamental cellular process that helps to maintain integrity of the genome through multiple repair pathways found across taxa, from archaea to higher animals. DNA repair capacity and senescence are known to be closely associated, with mutations in several repair pathways leading to premature ageing phenotypes. Analysis of DNA repair in an animal like hydra could offer clues into several aspects including hydra’s purported lack of organismal ageing, evolution of DNA repair systems in metazoa, and alternative functions of repair proteins. We review here the different DNA repair mechanisms known so far in hydra. Hydra genes from various DNA repair pathways show very high similarity with their vertebrate orthologues, indicating conservation at the level of sequence, structure, and function. Notably, most hydra repair genes are more similar to deuterostome counterparts than to common model invertebrates, hinting at ancient evolutionary origins of repair pathways and further highlighting the relevance of organisms like hydra as model systems. It appears that hydra has the full repertoire of DNA repair pathways, which are employed in stress as well as normal physiological conditions and may have a link with its observed lack of senescence. The close correspondence of hydra repair genes with higher vertebrates further demonstrates the need for deeper studies of various repair components, their interconnections, and functions in this early metazoan.

More than just orphans: are taxonomically-restricted genes important in evolution?

Comparative genome analyses indicate that every taxonomic group so far studied contains 10-20% of genes that lack recognizable homologs in other species. Do such 'orphan' or 'taxonomically-restricted' genes comprise spurious, non-functional ORFs, or does their presence reflect important evolutionary processes? Recent studies in basal metazoans such as Nematostella, Acropora and Hydra have shed light on the function of these genes, and now indicate that they are involved in important species-specific adaptive processes. Here we focus on evidence from Hydra suggesting that taxonomically-restricted genes play a role in the creation of phylum-specific novelties such as cnidocytes, in the generation of morphological diversity, and in the innate defence system. We propose that taxon-specific genes drive morphological specification, enabling organisms to adapt to changing conditions.

The diversity of C-type lectins in the genome of a basal metazoan, Nematostella vectensis

C-type lectins (CTLs) are involved in cell-cell adhesion, recognition, and innate immunity in higher vertebrates, but little is known about CTLs in basal metazoans. The recent sequencing of the cnidarian Nematostella vectensis genome allowed us to explore the CTL-like gene family at the base of metazoan evolution. Sixty-seven predicted CTLs, with a total of 92 putative C-type lectin domains (CTLDs), were classified according to number of CTLDs present and their association with other protein domains in the CTL. Conserved residues in the glycan-binding pocket suggest that approximately half of the CTLDs retain glycan-binding function. Phylogenetic analysis of N. vectensis CTLDs with respect to other model invertebrates and humans indicates N. vectensis CTLD sequences more closely resemble vertebrate CTLDs. This study provides a N. vectensis CTL database that can be used for further research on the evolution of cnidarian CTLs and the role of CTLs in cnidarian innate immunity.

Morphogenesis by coupled regulatory networks: reliable control of positional information and proportion regulation

Based on a non-equilibrium mechanism for spatial pattern formation we study how position information can be controlled by locally coupled discrete dynamical networks, similar to gene regulation networks of cells in a developing multicellular organism. As an example we study the developmental problems of domain formation and proportion regulation in the presence of noise, as well as in the presence of cell flow. We find that networks that solve this task exhibit a hierarchical structure of information processing and are of similar complexity as developmental circuits of living cells. Proportion regulation is scalable with system size and leads to sharp, precisely localized boundaries of gene expression domains, even for large numbers of cells. A detailed analysis of noise-induced dynamics, using a mean-field approximation, shows that noise in gene expression states stabilizes (rather than disrupts) the spatial pattern in the presence of cell movements, both for stationary as well as growing systems. Finally, we discuss how this mechanism could be realized in the highly dynamic environment of growing tissues in multicellular organisms.

Characterization of taxonomically restricted genes in a phylum-restricted cell type

BACKGROUND

Despite decades of research, the molecular mechanisms responsible for the evolution of morphological diversity remain poorly understood. While current models assume that species-specific morphologies are governed by differential use of conserved genetic regulatory circuits, it is debated whether non-conserved taxonomically restricted genes are also involved in making taxonomically relevant structures. The genomic resources available in Hydra, a member of the early branching animal phylum Cnidaria, provide a unique opportunity to study the molecular evolution of morphological novelties such as the nematocyte, a cell type characteristic of, and unique to, Cnidaria.

RESULTS

We have identified nematocyte-specific genes by suppression subtractive hybridization and find that a considerable portion has no homologues to any sequences in animals outside Hydra. By analyzing the transcripts of these taxonomically restricted genes and mining of the Hydra magnipapillata genome, we find unexpected complexity in gene structure and transcript processing. Transgenic Hydra expressing the green fluorescent protein reporter under control of one of the taxonomically restricted gene promoters recapitulate faithfully the described expression pattern, indicating that promoters of taxonomically restricted genes contain all elements essential for spatial and temporal control mechanisms. Surprisingly, phylogenetic footprinting of this promoter did not reveal any conserved cis-regulatory elements.

CONCLUSIONS

Our findings suggest that taxonomically restricted genes are involved in the evolution of morphological novelties such as the cnidarian nematocyte. The transcriptional regulatory network controlling taxonomically restricted gene expression may contain not yet characterized transcription factors or cis-regulatory elements.

Molecular phylogenetics in Hydra, a classical model in evolutionary developmental biology

Among the earliest diverging animal phyla are the Cnidaria. Freshwater polyps of the genus Hydra (Cnidaria, Hydrozoa) have long been of general interest because different species of Hydra reveal fundamental principles that underlie development, differentiation, regeneration and also symbiosis. The phylogenetic relationships among the Hydra species most commonly used in current research are not resolved yet. Here we estimate the phylogenetic relations among eight scientifically important members of the genus Hydra with molecular data from two nuclear (18S rDNA, 28S rDNA) and two mitochondrial (16S rRNA, cytochrome oxidase subunit I (COI)) genes. The phylogenetic trees obtained by maximum parsimony (MP), maximum likelihood (ML) and Bayesian inference (BI) methods were generally compatible with present morphological classification patterns. However, the present analysis also bears on several long-standing questions about Hydra systematics and reveals some characteristics of the phylogenetic relationships of this genus that were unknown so far. It indicates that Hydra viridissima, the only species in Hydra, which contains symbiotic algae, might be considered as the sister group to all other species within this genus. Analyses of both nuclear and mitochondrial sequences support the view that Hydra oligactis and Hydra circumcincta are sisters to all other Hydra species. Unexpectedly, we also find that in contrast to its initial description, the strain used for making transgenic Hydra, Hydra vulgaris (strain AEP) is more closely related to Hydra carnea than to other species of Hydra.

Hydra molecular network reaches criticality at the symmetry-breaking axis-defining moment

We study biological, multicellular symmetry breaking on a hollow cell sphere as it occurs during hydra regeneration from a random cell aggregate. We show that even a weak temperature gradient directs the axis of the regenerating animal--but only if it is applied during the symmetry-breaking moment. We observe that the spatial distribution of the early expressed, head-specific gene ks1 has become scale-free and fractal at that point. We suggest the self-organized critical state to reflect long range signaling, which is required for axis definition and arises from cell next-neighbor communication.

Why polyps regenerate and we don't: towards a cellular and molecular framework for Hydra regeneration

The basis for Hydra's enormous regeneration capacity is the "stem cellness" of its epithelium which continuously undergoes self-renewing mitotic divisions and also has the option to follow differentiation pathways. Now, emerging molecular tools have shed light on the molecular processes controlling these pathways. In this review I discuss how the modular tissue architecture may allow continuous replacement of cells in Hydra. I also describe the discovery and regulation of factors controlling the transition from self-renewing epithelial stem cells to differentiated cells.

Activities of the protein kinases STK, PI3K, MEK, and ERK are required for the development of the head organizer in Hydra magnipapillata

The development of the hydra's head and its hypostome has been studied at the molecular level. Many genes have been cloned from hydra as potential candidates that control the development of its head. Much work was performed on the mechanisms controlling expression of these genes in the position-dependent manner. Moreover, there have been data to support the involvement of three main signaling pathways that involve PKC, SRC, and PI3K kinases in the regulation of the head formation and in the expression of several head-specific genes. In this report, we present data supporting the participation of these three signaling pathways on the development of the hypostome. We used grafting experiments and inhibitors of the specific kinases to show the participation of these enzymes in hypostome formation. From our results, we postulate that these signal transduction pathways regulate the very early stages of the head development, most likely at the point when the cells start to differentiate to form the head organizer.

Genome sizes and chromosomes in the basal metazoan Hydra

Hydras belong to one of the earliest eumetazoan animal groups, but to date very little is known about their genome sizes, gene numbers, and chromosomes. Here we provide genome size estimates and corresponding karyotypes for five Hydra species. Nuclear DNA contents were assessed by slide-based Feulgen microphotometry. Hydra oligactis possesses the largest genome of 1450 Mbp, followed by similar 1 C capacities in H. carnea (1350 Mbp), H. vulgaris (1250 Mpb) and H. circumcincta (1150 Mbp). The smallest genome of 380 Mbp was determined in H. viridissima. While the number of chromosomes is identical in all five Hydra species (2n = 30), the size of the chromosomes is strictly correlated to the size of the genome, with H. viridissima having conspicuously small chromosomes. The taxonomic and evolutionary significance of the C-value and chromosomal size variation in this ancient group of metazoans as well as its impact on genomic organization and forthcoming genome projects are discussed.

Discovery of genes expressed in Hydra embryogenesis

Hydra's remarkable capacity to regenerate, to proliferate asexually by budding, and to form a pattern de novo from aggregates allows studying complex cellular and molecular processes typical for embryonic development. The underlying assumption is that patterning in adult hydra tissue relies on factors and genes which are active also during early embryogenesis. Previously, we reported that in Hydra the timing of expression of conserved regulatory genes, known to be involved in adult patterning, differs greatly in adults and embryos (Fröbius, A.C., Genikhovich, G., Kürn, U., Anton-Erxleben, F. and Bosch, T.C.G., 2003. Expression of developmental genes during early embryogenesis of Hydra. Dev. Genes Evol. 213, 445-455). Here, we describe an unbiased screening strategy to identify genes that are relevant to Hydra vulgaris embryogenesis. The approach yielded two sets of differentially expressed genes: one set was expressed exclusively or nearly exclusively in the embryos, while the second set was upregulated in embryos in comparison to adult polyps. Many of the genes identified in hydra embryos had no matches in the database. Among the conserved genes upregulated in embryos is the Hydra orthologue of Embryonic Ectoderm Development (HyEED). The expression pattern of HyEED in developing embryos suggests that interstitial stem cells in Hydra originate in the endoderm. Importantly, the observations uncover previously unknown differences in genes expressed by embryos and polyps and indicate that not only the timing of expression of developmental genes but also the genetic context is different in Hydra embryos compared to adults.

Maintenance of ancestral complexity and non-metazoan genes in two basal cnidarians

Cnidarians are among the simplest extant animals; however EST analyses reveal that they have a remarkably high level of genetic complexity. In this article, we show that the full diversity of metazoan signaling pathways is represented in this phylum, as are antagonists previously known only in chordates. Many of the cnidarian ESTs match genes previously known only in non-animal kingdoms. At least some of these represent ancient genes lost by all bilaterians examined so far, rather than genes gained by recent lateral gene transfer.

Control of foot differentiation in Hydra: Phylogenetic footprinting indicates interaction of head, bud and foot patterning systems

Homeodomain transcription factor CnNK-2 seems to play a major role in foot formation in Hydra. Recently, we reported in vitro evidence indicating that CnNK-2 has autoregulatory features and regulates expression of the morphogenetic peptide pedibin. We proposed that CnNK-2 and pedibin synergistically orchestrate foot differentiation processes. Here, we further analyzed the regulatory network controlling foot formation in Hydra. By phylogenetic footprinting we compared the CnNK-2 5'-flanking sequence from two closely related species, Hydra vulgaris and Hydra oligactis. Unexpectedly, we detected a highly conserved binding site for HNF-3beta, a vertebrate Forkhead transcription factor, in the CnNK-2 5'-flanking region. The Hydra HNF-3beta homolog budhead is predominantly expressed in the apical region of the body column and early during budding. Budhead is absent from tissue expressing CnNK-2 and thought to be involved in determining tissue for head differentiation. By electrophoretic mobility shift assays we demonstrate an in vitro interaction between recombinant budhead protein and the interspecific conserved HNF-3beta binding motif in the CnNK-2 5'-flanking region. Our results strengthen the view of CnNK-2 as an important regulator during foot patterning processes. Furtheron, they point to budhead as a candidate for a transcriptional regulator of CnNK-2 and to an interaction of foot and head patterning processes in Hydra on the molecular level.

Ultraviolet irradiation initiates ectopic foot formation in regenerating hydra and promotes budding

We have studied the effects of ultraviolet-C (UVC) and Ultraviolet-B (UVB) on growth and pattern formation in Pelmatohydra oligactis. UVC brings about a significant increase in budding in intact hydra while UVB does not exhibit such an effect. Excessive budding could be a response for survival at wavelengths that damage biological tissues. If the head or base piece of a bisected hydra is irradiated and recombined with the unirradiated missing part, regeneration proceeds normally indicating that exposure of a body part with either an intact head or foot to UVC does not influence pattern formation. Most significantly, in the middle piece, but not in the head or the base piece of a trisected hydra, UVC leads to initiation of ectopic feet formation in almost one third of the cases. Thus, UV irradiation interferes with pattern formation in regenerating hydra, possibly by changing positional values, and promotes budding in intact hydra. This is the first report on induction of ectopic feet formation by UV in regenerating hydra and opens up the possibility of using UV irradiation as a tool to understand pattern formation in the enigmatic hydra.

Ancient signals: peptides and the interpretation of positional information in ancestral metazoans

Understanding the 'tool kit' that builds the most fundamental aspects of animal complexity requires data from the basal animals. Among the earliest diverging animal phyla are the Cnidaria which are the first in having a defined body plan including an axis, a nervous system and a tissue layer construction. Here I revise our understanding of patterning mechanism in cnidarians with special emphasis on the nature of positional signals in Hydra as perhaps the best studied model organism within this phylum. I show that (i) peptides play a major role as positional signals and in cell-cell communication; (ii) that intracellular signalling pathways in Hydra leading to activation of target genes are shared with all multicellular animals; (iii) that homeobox genes translate the positional signals; and (iv) that the signals are integrated by a complex genetic regulatory machinery that includes both novel cis regulatory elements as well as taxon specific target genes. On the basis of these results I present a model for the regulatory interactions required for axis formation in Hydra.

A Dickkopf- 3-related gene is expressed in differentiating nematocytes in the basal metazoan Hydra

In vertebrate development the Dickkopf protein family carries out multiple functions and is represented by at least four different genes with distinct biological activities. In invertebrates such as Drosophila and Caenorhabditis, Dickkopf genes have so far not been identified. Here we describe the identification and characterization of a Dickkopf gene with a deduced amino acid sequence closely related to that of chicken Dkk-3 in the basal metazoan Hydra. HyDkk-3 appears to be the only Dickkopf gene in Hydra. The gene is expressed in the gastric region in nematocytes at a late differentiation stage. In silico searches of EST and genome databases indicated the absence of Dkk genes from the protostomes Drosophila and Caenorhabditis, whereas within the deuterostomes, a Dkk-3 gene could be identified in the genome of the urochordate Ciona intestinalis. The results indicate that at an early stage of evolution of multicellularity Dickkopf proteins have already played important roles as developmental signals. They also suggest that vertebrate Dkk-1, 2 and 4 may have originated from a common ancestor gene of Dkk-3.

Control of foot differentiation in Hydra: in vitro evidence that the NK-2 homeobox factor CnNK-2 autoregulates its own expression and uses pedibin as target gene

The foot of the simple metazoan Hydra is a highly dynamic body region of constant tissue movement, cell proliferation, determination and differentiation. Previously, two genes have been shown to participate in the development and differentiation of this body region: homeodomain factor CnNK-2 and signal peptide pedibin [Dev. Biol. 180 (1996) 473; Development 126 (1999) 517; Development 122 (1996) 1941; Mech. Dev. 106 (2001) 37]. CnNk-2 functions as transcriptional regulator and is responsive to changes in the positional value while the secreted peptide pedibin serves as "extrinsic" positional signal. Exposure of polyps to pedibin increases the spatial domain of CnNK-2 expression towards the gastric region, indicating that positional signals are integrated at the cis-regulatory region of CnNK-2. In the present study, to elucidate the molecular basis of the interaction of CnNK-2 and pedibin, we characterized the 5' regulatory regions of both genes. Within the CnNK-2 5' upstream region, electrophoretic mobility shift assays showed that putative NK-2 binding motifs are specifically bound by both nuclear protein from Hydra foot and by recombinant CnNK-2, suggesting that CnNK-2 might autoregulate its own expression. This is the first indication for an autoregulatory circuit in Hydra. In addition, we also identified NK-2 binding sites in the cis-regulatory region of the pedibin gene, indicating that this gene is one of the targets of the transcription factor CnNK-2. On the basis of these results, we present a model for the regulatory interactions required for patterning the basal end of the single axis in Hydra which postulates that CnNK-2 together with pedibin orchestrates foot specific differentiation.

What's new in cnidarian biology?

This introduction to the following collection of eight review articles on aspects of cnidarian biology looks at reasons why people study these animals, their economic importance, and their conceptual interest as highlighted in the reviews.

In vivo electroporation for genetic manipulations of whole Hydra polyps

In vivo electroporation is used to study gene regulation and gene function in the freshwater polyp Hydra. Although this approach has been used successfully by several investigators, efficacy and handling continue to present a problem. Here we show technical aspects of in vivo electroporation for introducing fluorescent dyes, plasmid DNA and double stranded RNA into Hydra polyps. We describe the fundamentals of the electroporation delivery system, discuss recent studies where this approach has been used successfully, compare it to alternative transfection methods such as lipofection, and identify future directions.