Irmeli Palmberg

Stem cells in microturbellarians

SummaryA combination of microscopical, immunocytochemical, and autoradiographic techniques were employed to study stem cells and their fates during asexual reproduction and regeneration in two microturbellarians,Microstomum lineare (Macrostomida) andStenostomum leucops (Catenulida). Special attention was paid to the development of the immunoreactivity (IR) to FMRF/RF-amide and 5-HT in differentiating nerve cells.Asexual reproduction inM. lineare andS. leucops occurs by paratomy, i.e., fragmentation after completed differentiation of the new organs. Regeneration, on the other hand, involves a combination of morphallactic and epimorphic processes without the formation of a regeneration blastema. The only cells incorporating tritiated thymidine ([3H]T) were the mesenchymal and gastrodermal neoblasts, which proliferate continuously replenishing the population of stem cells available for growth, asexual reproduction and regeneration. These proliferative cells occurred in two ultrastructurally different forms, differing from each other only by the presence or absence of ciliar basal bodies in the cytoplasm. Few differentiated cells were labeled in the head piece after completed regeneration. A greater amount of labeled differentiated cells were, however, observed postpharyngeally in the first zooid as well as in zooids having developed during the same time (i.e., 20–45 h after the treatment with [3H]T). Furthermore, many labeled cells were still undifferentiated at that time or just in the beginning of the differentiation process. It can therefore be concluded that neoblasts function both as reserve cells and as functional stem cells for all differentiated cell types in these worms. IR to FMRF/RF-amide neuropeptides was not observed in nerve cells differentiating from neoblasts until the occurrence of dense-core vesicles in their cytoplasm. Due to methodological difficulties only weak or no IR to 5-HT could be traced in the nervous system of the asexual and regenerating worms.

The nervous system of Microstomum lineare (Turbellaria, Macrostomida)

SummaryThe nervous system (NS) of Microstomum lineare (Turbellaria, Macrostomida) was studied by electron and light microscopy, combined with fluorescence histochemistry (Falck-Hillarp method for biogenic monoamines). The NS is primitively organized, with a bilobed brain, two lateral nerve cords lacking commissures, and peripheral nerve cells scattered along the nerve cords. The stomatogastric NS, with a pharyngeal nerve ring, is joined to the central NS by a pair of connective ganglia. A green fluorescence in all parts of the NS indicates catecholaminergic neurons as the dominant neuron type.Ultrastructurally, two types of neurons were identified on the basis of their vesicle content: 1. Aminergic (catecholaminergic) neurons containing densecore vesicles of varying electron-density and size, i.e., small dense-core vesicles (diameter 50–100 nm), vesicles with a highly electron-dense core (60–140 nm), and vesicles with an eccentric dense-core. 2. Presumed peptidergic neuro-secretory neurons containing large granular vesicles (diameter about 200 nm) in the stomatogastric NS and peripheral parts of the central NS. In light microscopy, paraldehyde-thionin stained neurons were observed in the same areas.

Cell migration and differentiation during wound healing and regeneration in Microstomum lineare (Turbellaria)

Using transmission electron microscopy and serial sections with light-microscopic autoradiography, I have investigated the ultrastructure of wound healing, the distribution of cells preparing for proliferation, and the fates of cells labelled with exogenous tritiated thymidine ([3H]T) in Microstomum lineare undergoing wound healing and regeneration. Immediately after decapitation the open wound was reduced to a minimum by strong contraction of circular muscle fibers. The wound epidermis was cellular, consisting of thin parts of epidermal cells from the epidermis around the wound. These epidermal cells maintained close adhesive contact with one another through zonulae adherentes and septate junctions. No proliferating cells were found in the old epidermis. The only cells taking up [3H]T were mesenchymal and gastrodermal neoblasts which proliferated and migrated towards the surface. The final epidermis was formed by conjunction of the wound epidermis and newly differentiated epidermal cells. Regeneration in Microstomum, in contrast to that of planarians, occurs mainly by morphallaxis, without the formation of a regeneration blastema, but also through continuous cell proliferation, migration, and differentiation.

Asexual reproduction in Microstomum lineare (Turbellaria). I. An autoradiographic and ultrastructural study

The distribution of cells preparing for proliferation during asexual reproduction by paratomy in Microstomum lineare (Turbellaria) was investigated using the technique of exogenous tritiated thymidine ([3H]T) labelling and routine electron microscopy. The subsequent fates of labelled cells in developing and mature zooids were followed by fixing tissues at various intervals. The only labelled cells are mesenchymal and gastrodermal neoblasts, occurring along the whole worm without any special growth zones or axial gradient. Organ primordia develop as a result of locally dividing as well as of migrating cells.

Differentiation during asexual reproduction and regeneration in a microturbellarian

Autoradiography, immunocytochemistry, and microscopy were employed to study stem cells and their fates in experimentally decapitated and in asexually reproducing specimens of Microstomum lineare (O. F. Müller). Differentiation of the nervous system in developing zooids was monitored by the appearance of immunoreactivity to the neuropeptide FMRF/RF-amide and to the biogenic amine 5-HT. Labelling with [3HH]T (tritiated thymidine) provided a means to follow the proliferation of stem cells and their differentiation into nerve and other cell types both in the regenerating head end and in more posterior zooids produced by asexual reproduction. Initiation of development of a new zooid was characterized by immunoreactivity for 5-HT in the postpharyngeal commissure and in a cell group at its branching point with the parental lateral nerve cords; initiation of regeneration, on the other hand, was characterized by increased immunoreactivity for FMRF/RF-amide in the cut nerve ends. Antigenicity to FMRF/RF-amide antibody appeared before that to 5-HT in the developing brain as well as in the pharyngeal plexus. FMRF/RF-amide-positive neurons were not, however, found among differentiating nerve cells until dense-core vesicles appeared in their cytoplasm. The only cells incorporating tritiated thymidine ([3H]T) were neoblasts in the mesenchyme and gastrodermis, which proliferate continuously, replenishing the population of stem cells available for growth, asexual reproduction, and regeneration. Two forms of the proliferative cells arose, one with and one without ciliary basal bodies in the cytoplasm. Even in completely regenerated specimens there were many labelled undifferentiated cells (i.e., 20–45 h after exposure to [3H]T). I propose that neoblasts function both as stem cells for all differentiated cell types and as reserve cells with a determined life time.

Ultrastructure of epidermal eyespots of Microstomum lineare (Turbellaria, macrostomida)

SummaryThe eyespots of Microstomum lineare were studied by electron microscopy, light microscopy, and fluorescence microscopy. Each eyespot consists of two ciliary photoreceptor cells shielded by pigment cells and additional sensory cells. The photoreceptor cells are characterized by a distal intracellular cavity lined with 50–100 interwoven cilia. The other sensory cells are of two ultrastructurally different types, one with long cilia predominating and the other with balloonlike cilia. The pigment cells, which envelop processes of the sensory cells, contain pigment vacuoles varying in size and content and give a bright red fluorescence by the Falck-Hillarp method. The eyespots are suggested to perform a dual function as photoreceptors and chemoreceptors. The evolutionary significance of ciliary photoreceptors in Turbellaria is discussed.

Asexual reproduction in Microstomum lineare (Turbellaria). II: The nervous system in the division zone

The innervation of the division zone in the asexually reproducing Microstomum lineare (Turbellaria) was studied by light and electron microscopy. Nerve fibres presumed to be peptidergic form a circumferential belt and longitudinal nerve fibres and nerve swellings join the circumferential belt from opposite directions. Peptidergic nervous influence on asexual reproduction by paratomy is indicated by (1) synaptoids and (2) omega-shaped configurations. These release sites are observed at muscles of the division zone and in the vicinity of neoblast cells.

Higher Education Students' Perceptions of Environmental Issues and Media Coverage.

Abstract This study aims to find higher education students’ perceptions about environmental issues and how the perceptions are related to perceptions of media coverage. This study investigates higher education students’ perceptions of the seriousness of environmental issues and their relation to perceptions of media coverage. Higher education students perceived a global problem, lack of clean water, as most serious environmental problem. Media has had an effect on students’ perceptions on environmental issues: when students perceived the problem as serious they also perceived the information in media concerning it appropriate. Students perceived that the media underestimate and obscure some environmental problems such as biological diversity and global warming. It was concluded that higher education educators need more knowledge of students’, future decision makers’ concerns and perceptions about environmental issues to develop more effective teaching practices in higher education. Through education environmental issues literacy, which is a precursor for engaged protection of the environment, can be fostered. This study offers some insights into higher education students’ perceptions of the media’s role in environmental issues.

Environmental Issues in the Media--Students' Perceptions in the Three Nordic-Baltic Countries.

Abstract The media, as a source of information, is supposed to have a significant role in effecting peopleís environmental knowledge and attitudes. The purpose of this study was to find studentsí perceptions of environmental issues as presented in the media and how students in Finland, Lithuania and Sweden used these media sources in the matters related to environmental issues. The most important source of environmental knowledge was found to be the Internet, followed by newspapers, television, school and education. In their own lives, students discussed environmental issues every day and, to some extent, in social media, discussion forums and blogs. In Finland, newspapers represented the most important source of environmental knowledge; in Lithuania, environmental organisations were the most prevalent, and, in Sweden, it was in a school or educational context. Based on these results, it was concluded that, in order to reach both genders of students in different countries and to more greatly benefit from all sources of information, a variety of media should be used in education for sustainability.

Nordic Student Teachers’ Views on the Importance of Species and Species Identification

ABSTRACT People’s knowledge about nature, their interest in nature, their nature experiences, and their values and emotions regarding nature are factors that promote people’s positive views on environmental issues and sustainability. Knowing the variation and patterns in teachers’ and student teachers’ views is an essential step in considering the ways in which sustainability might be interpreted and enacted in schools and in teacher education. The aim of this study is to analyze student teachers’ views on the importance of species and species identification in general and as a part of their professional development regarding their understanding of biodiversity and sustainability. A total of 426 student teachers in Finland, Norway, and Sweden answered a questionnaire consisting of fixed and open-ended questions. Mixed methods were used: t test and analysis of variance for quantitative data and inductive and deductive, model-based content analysis for qualitative data. According to the majority of student teachers (85%), both species identification and biodiversity are important for sustainability; species identification in general was important to 58% of them. Their statements about importance contained mostly ecological views (46%), followed by emotional (17%), educational (16%), and utilitarian (11%) views. The remainder of the student teachers’ statements (10%) contained negativistic or indifferent views. The reasons for the low percentage of educational views are discussed. The implications of the results for teacher education worldwide are emphasized, especially the importance of those teaching methods that have the potential to increase student teachers’ understanding of sustainability.