Planaria

Sistem saraf adalah sistem yang berfungsi untuk membuat organisme menjadi terbiasa terhadap lingkungannya dan merangsang organisme agar menyesuaikan diri secara menguntungkan terhadap lingkungan. Sistem saraf juga berperan dalam mengatur lingkungan dalam dan menjadi tempat penyimpanan (penimbunan) informasi, memori dan recall (Team Teaching Struktur Hewan, 2014).
Sistem saraf pada makhluk hidup memiliki beberapa perbedaan antara satu dengan yang lain. Misalnya saja antara hewan vertebrata dan hewan invertebrata. Pada hewan invertebrata yang sudah memiliki sistem saraf tentu strukturnya jauh lebih sederhana dibandingkan dengan sistem saraf pada hewan vertebrata yang tingkatannya lebih tinggi.
Salah satu contoh hewan invertebrata yang telah memiliki sistem saraf adalah planaria. Sistem saraf pada planaria disebut sistem saraf tangga tali yang tersusun atas sistem saraf pusat dan sistem saraf tepi.
Menurut Sinaga et al (2014) sistem saraf pusat planaria terdiri atas dua ganglion, yang terletak di daerah kepala. Dua ganglion pada daerah kepala ini disebut ganglion otak dan dua tali saraf longitudinal. Dari tiap ganglia terdapat seberkas saraf yang memanjang ke kaudal sepanjang bagian lateral tubuh. Tiap-tiap berkas saraf ini bercabang-cabang lagi menjadi cabang kecil yang menuju keseluruh bagian tubuh. Dua berkas saraf tadi satu sama lain dihubungkan oleh banyak cabang-cabang melintang mirip anak tangga. Sementara ganglion otak merupakan otak primitif yang berfungsi sebagai pusat koordinasi.

Axial patterning during planarian regeneration relies on a transcriptional circuit that confers distinct positional in-formation on the two ends of an amputated fragment. The earliest known elements of this system begin demarcating differencesbetween anterior and posterior wounds by 6 h post amputation. However, it is still unknown what upstream events break the axial symmetry, allowing a mutual repressor system to establish invariant, distinct biochemical states at the anterior and posterior ends. Here, we show that bioelectric signaling at 3 h is crucial for the formation of proper anterior-posterior polarity in planaria.Briefly manipulating the endogenous bioelectric state by depolarizing the injured tissue during the first 3 h of regeneration alters gene expression by 6 h post amputation and leads to a double-headed phenotype upon regeneration despite confirmed washout of ionophores from tissue. These data reveal a primary functional role for resting membrane potential taking place within the first3 h after injury and kick-starting the downstream pattern of events that elaborate anatomy over the following 10 days. We pro-pose a simple model of molecular-genetic mechanisms to explain how physiological events taking place immediately after injury regulate the spatial distribution of downstream gene expression and anatomy of regenerating planaria

Control of axial polarity during regeneration is a crucial open question. We developed a quantitative model of regenerating planaria, which elucidates self-assembly mechanisms of morphogen gradients required for robust body-plan control. The computational model has been developed to predict the fraction of heteromorphoses expected in a population of regenerating planaria fragments subjected to different treatments, and for fragments originating from different regions along the anterior-posterior and medio-lateral axis. This allows for a direct comparison between computational and experimental regeneration outcomes. Vector transport of morphogens was identified as a fundamental requirement to account for virtually scale-free self-assembly of the morphogen gradients observed in planarian homeo-stasis and regeneration. The model correctly describes altered body-plans following many known experimental manipulations, and accurately predicts outcomes of novel cutting scenarios , which we tested. We show that the vector transport field coincides with the alignment of nerve axons distributed throughout the planarian tissue, and demonstrate that the head-tail axis is controlled by the net polarity of neurons in a regenerating fragment. This model provides a comprehensive framework for mechanistically understanding fundamental aspects of body-plan regulation, and sheds new light on the role of the nervous system in directing growth and form. Author summary Understanding how large-scale anatomy emerges from the activity of cellular pathways is a key goal of evolutionary developmental biology. Elucidating the rules of body-wide mor-phogenesis is especially essential for transitioning molecular signaling data at the cellular level into advances in regenerative biomedicine. We constructed and analyzed a comprehensive , multiscale computational model to explain the determination of axial polarity during planarian regeneration. Uniquely, our model explains the various head-tail pat-terning outcomes of a wide range of molecular and physiological manipulations. Testing the novel predictions of this model revealed the nervous system as an instructive regulator of axial patterning. PLOS Computational Biology | https://doi.org/10.1371/journal.pcbi.

In the upper part of the northern flank of Mount Jaizkibel we find a cavity that develops under large blocks of sandstone of the Eocene age (Jaizkibel Formation), whose galleries are crossed by an underground stream. The cavity has several cave mouths and reaches 74 m of development. An interesting representation of aquatic fauna inhabits it, which includes chironomid larvae, Tricladida planarians, Niphargus troglobites amphipods, terrestrial isopods, Machiloidea tysanurans, Oxychillus snails and curious examples of irregular fungi of strange morphology. The work describes the cavity and its fauna.

Pollution is a major concern in urban areas. Due to its biological significance, genotoxicity should be a main focus for pollution biomonitoring, due mainly to the increasing complexity of the chemical environment in which organisms are exposed. Diluvio's Basin (Porto Alegre, RS, Brazil) is a heavily polluted urban ecosystem impacted by urban wastewater. Planarians are useful organism for evaluating environmental genotoxicity because of their high sensitivity, low cost, high proliferative rate and also because of their basal evolutionary position in relation to complex metazoans. Comet assay is a powerful and highly sensitive method of evaluating primary DNA lesions. Based on the unique features of planarians and the current environmental state of Diluvio's Basin, the aim of this work was to evaluate the genotoxic potential of this body of water using comet assay in planarians. Planarians were exposed to the water for 13 days in a laboratory and comet assay was performed in order to screen possible DNA damages. The results indicated an increasing gradient of damage towards basin's mouth. Such a gradient could be related to the gradual increase of pollutants among the different sample sites. Moreover, there seems to be a correlation between the urbanization gradient that exists within the watershed and the genotoxicity. Historical physical–chemical data was also gathered and examined for possible correlations with genotoxicity. Comet assay in planarians is a very promising test for environmental monitoring studies. Its application should be expanded.

Planarians possess remarkable stem cell populations that continuously support cellular turnover and are instrumental in the regeneration of tissues upon injury. Cellular turnover and tissue regeneration in planarians rely on the proper integration of local and systemic signals that regulate cell proliferation and cell death. Thus, understanding the signals controlling cellular proliferation and cell death in planarians could provide valuable insights for maintenance of adult body homeostasis and the biology of regeneration. Flow cytometry techniques have been utilized widely to identify, isolate, and characterize planarian stem cell populations. We developed alternative flow cytometry strategies that reduce the number of reagents and the time of sample preparation to analyze stem cells and cell death in planarians. The sensitivity of these methods is validated with functional studies using RNA interference and treatment with  γ irradiation or stressful conditions that are known to trigger cell death. Altogether, we provide a community resource intended to minimize adverse effects during ex vivo studies of stem cells and cell death in planarians.