Microtubule-associated protein 1B is implicated in stem cell commitment and nervous system regeneration in planarians.

Microtubule-associated 1B (MAP1B) proteins are expressed at the nervous system level where they control cytoskeleton activity and regulate neurotransmitter release. Here, we report about the identification of a planarian MAP1B factor (DjMap1B) that is enriched in cephalic ganglia and longitudinal nerve cords but not in neoblasts, the plentiful population of adult stem cells present in planarians, thanks to which these animals can continuously cell turnover and regenerate any lost body parts. DjMap1B knockdown induces morphological anomalies in the nervous system and affects neoblast commitment. Our data put forward a correlation between a MAP1B factor and stem cells and suggest a function of the nervous system in non-cell autonomous control of planarian stem cells.

Insight into stem cell regulation from sub-lethally irradiated worms.

Despite the significant advances in the comprehension of stem cell control network, the nature of extrinsic signals regulating their dynamic remains to be understood. In this paper, we take advantage of the stem cell repopulation process that follows low-dose X-ray treatment in planarians to identify genes, preferentially enriched in differentiated cells, whose expression is activated during the process. Genetic silencing of some of them impaired the stem cell repopulation, suggesting a tight extrinsic control of stem cell activity.

Putrescine independent wound response phenotype is produced by ODC-like RNAi in planarians.

Despite increasing evidence indicates polyamines as a convergence point for signaling pathways, including cell growth and differentiation, a unifying concept to interpret their role is still missing. The activity of ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis, is tightly regulated by a complex molecular machinery, and the demonstration of the existence of multiple ODC paralogs, lacking decarboxylation activity, suggests additional layers of complexity to the intricate ODC regulatory pathway. Because of their extraordinary regenerative abilities and abundance of stem cells, planarians have potential to contribute to our understanding of polyamine function in an in vivo context. We undertook a study on ODC function in planarians and we found six planarian ODCs (ODC1-6). Five out of six ODC homologs carry substitutions of key aminoacids for enzymatic activity, which makes them theoretically unable to decarboxylate ornithine. Silencing of ODC5 and 6 produced a complex phenotype, by prompting animals to an aberrant response, following chronic injury without tissue removal. Phenotype is neither rescued by putrescine, nor mimicked by difluoromethylornithine treatment. Moreover, the co-silencing of other genes of the ODC regulatory pathway did not modulate phenotype outcome or severity, thus suggesting that the function/s of these ODC-like proteins might be unrelated to decarboxylase activity and putrescine production.

Prohibitin 2 regulates cell proliferation and mitochondrial cristae morphogenesis in planarian stem cells.

Prohibitins are pleiotropic proteins, whose multiple roles are emerging as key elements in the regulation of cell survival and proliferation. Indeed, prohibitins interact with several intracellular proteins strategically involved in the regulation of cell cycle progression in response to extracellular growth signals. Prohibitins also have regulatory functions in mitochondrial fusion and cristae morphogenesis, phenomena related to the ability of self-renewing embryonic stem cells to undergo differentiation, during which mitochondria develop numerous cristae, increase in number, and generate an extensive reticular network. We recently identified a Prohibitin 2 homolog (DjPhb2) that is expressed in adult stem cells (neoblasts) of planarians, a well-known model system for in vivo studies on stem cells and tissue regeneration. Here, we show that in DjPhb2 silenced planarians, most proliferating cells disappear, with the exception of a subpopulation of neoblasts localized along the dorsal body midline. Neoblast depletion impairs regeneration and, finally, leads animals to death. Our in vivo findings demonstrate that prohibitin 2 plays an important role in regulating stem cell biology, being involved in both the control of cell cycle progression and mitochondrial cristae morphogenesis.

Ultrastructural and cytochemical aspects of the germarium and the vitellarium in Syndesmis patagonica (Platyhelminthes, Rhabdocoela, Umagillidae).

The cytoarchitecture of the female gonad of the endosymbiont umagillid Syndesmis patagonica has been investigated using electron microscopy and cytochemical techniques. The female gonad consists of paired germaria and vitellaria located behind the pharynx in the mid-posterior region of the body. Both the germaria and the vitellaria are enveloped by an outer extracellular lamina and an inner sheath of accessory cells which contribute to the extracellular lamina. Oocyte maturation occurs completely during the prophase of the first meiotic division. Oocyte differentiation is characterized by the appearance of chromatoid bodies and the development of endoplasmic reticulum and Golgi complexes. These organelles appear to be involved in the production of round granules, about 2-2.5 µm in diameter, with a homogeneous electron-dense core surrounded by a granular component and a translucent halo delimited by a membrane. These egg granules migrate to the periphery of mature oocytes, are positive to the cytochemical test for polyphenol detection, are unaffected by protease and have been interpreted as eggshell granules. The mature oocytes also contain a small number of yolk granules, lipid droplets, and glycogen particles scattered throughout the ooplasm. The vitellaria are branched organs composed of vitelline follicles with vitellocytes at different stages of maturation. Developing vitellocytes contain well-developed rough endoplasmic reticulum and small Golgi complexes involved in the production of eggshell and yolk globules. Eggshell globules are round, measure 4-5 µm in diameter, and have a mosaic-like patterned content which contains polyphenols. The yolk globules, 2-3 µm in diameter, show a homogeneous protein content of medium electron density, devoid of polyphenols, and completely digested by protease. The mature vitellocytes also contain glycogen as further reserve material. The presence of polyphenolic eggshell granules in the oocytes and of polyphenolic eggshell globules with a mosaic-like pattern in the vitellocytes have been considered apomorphic features of the Rhabdocoela + Prolecithophora.

The female gonad in two species of Microplana (Platyhelminthes, Tricladida, Rhynchodemidae): ultrastructural and cytochemical investigations.

The female gonad of the land planarians Microplana scharffi and Microplana terrestris consists of two small germaria located ventrally in the anterior third of the body and of two ventro-lateral rows of oblong vitelline follicles distributed between the intestinal pouches. Both these structures are enveloped by a tunica composed of an outer extracellular lamina and an inner sheath of accessory cells. Oocyte maturation is characterized by the appearance of chromatoid bodies and the development of endoplasmic reticulum and Golgi complexes. These organelles appear to be correlated with the production of egg granules with a fenestrated/granular content of medium electron density, about 4-5 mum in diameter, which remain dispersed in the ooplasm of mature oocytes. On the basis of cytochemical tests showing their glycoprotein composition, and their localization in mature oocytes, these egg granules have been interpreted as yolk. In the vitelline follicles, vitellocytes show the typical features of secretory cells with well-developed rough endoplasmic reticulum and Golgi complexes involved in the production of eggshell globules and yolk. The eggshell globules, which appear to arise from repeated coalescences of two types of Golgi-derived vesicles, contain polyphenols and, when completely mature, they measure about 1-1,2 mum in diameter and show a meandering/concentric content pattern as is typical of the situation observed in most Proseriata and Tricladida. Mature vitellocytes also contain a large amount of glycogen and lipids as further reserve material. On the basis of the ultrastructural features of the female gonad and in relation to the current literature the two species of rhynchodemids investigated appear to be closely related to the freshwater planarians belonging to the family Dugesiidae.

Ultrastructural and cytochemical aspects of the female gonad of Geoplana burmeisteri (Platyhelminthes, Tricladida, Terricola).

The ultrastructure of the female gonad of the land planarian Geoplana burmeisteri was investigated by means of electron microscopy and cytochemical techniques. It consists of two small germaria located ventral to the intestine and of two irregular, lateral rows of vitelline follicles, both enveloped by a tunica composed of an extracellular lamina and an inner sheath of accessory cells. Accessory cell projections completely surround developing oocytes and vitellocytes. The main feature of oocyte maturation is the appearance of chromatoid bodies and the development of the rough endoplasmic reticulum (RER) and Golgi complexes. These organelles appear to be correlated with the production of egg inclusions of medium electron density, about 1.5-1.8 microm in diameter, which remain scattered in the ooplasm of mature oocytes. On the basis of cytochemical tests demonstrating their glycoprotein composition, these inclusions were interpreted as residual yolk globules. Vitellocytes are typical secretory cells with well-developed RER and Golgi complexes that are mainly involved in the production of yolk globules and eggshell globules, respectively. Eggshell globules appear to arise from repeated coalescence of small Golgi-derived vesicles and, at an intermediate stage of maturation, show a multigranular pattern. Later, after vesicle fusion, they reach a diameter of 1.3-1.6 microm when completely mature and show a meandering/concentric pattern, as is typical of the situation seen in most Proseriata and Tricladida. The content of yolk globules is completely digested by pronase, while the content of eggshell globules is unaffected. Mature vitellocytes contain, in addition, a large quantity of glycogen and lipid droplets as further reserve material. On the basis of the ultrastructural characteristics of the female gonad described above and in relation to the current literature, we conclude that G. burmeisteri appears to be more closely related to the freshwater triclads, in particular to members of the Dugesiidae, than to the marine triclads.