1,721,010 research outputs found
Epigenetics in tunicates.
No full textTunicates are marine animals close to vertebrates, and have the ability, unique among chordates, to form large colonies of clonal individuals. Among tunicates, the most frequently studied ascidians represent an ideal model for investigating aspects of epigenetics evidenced during the various phases of the life-cycle. Interestingly, the typical mosaic development of eggs and embryos of ascidians, considered as a classic example of autonomous genetic control of genes for specification of cell lineage, may now be interpreted in the light of cytoplasmic and extracellular influences on the regulation of gene activity. In addition, the capacity of several species to create similar individuals by means of two different developmental pathways - embryogenesis and blastogenesis - and the high regulative power shown by colonies in natural or experimental modifications of the environment, reveal the importance of the epigenetic phenomena (interactions) during the entire life cycle of these animals. Two species are of particular importance as models, the solitary Ciona intestinalis (whose genome has been recently sequenced) and the colonial Botryllus schlosseri. We report here examples of epigenetic phenomena in ascidians, to show that the various stages of the entire development of the phenotype are driven by a dynamic interplay of genome, cellular components and tissues, and their micro- and macro-environment
Application of a new bioindex based on hard substrate biocoenosis for the evaluation of the lagoon quality
No full textThis research was based on the study of the fouling in the Lagoon of Venice and its aim was to verify the reliability of an index of environmental quality applied to four stations of the Lagoon. Such index has been developed through
the collection of physico-chemical and biotic data and the study of their interrelation. From June 2007, panel systems, each one represented by a steel and a wood
panel (20 x 15 x 2.5 cm), were immersed in four different stations in order to collect data regarding a representative area of the Lagoon in a period – summer – which, although limited, corresponded to the maximum development and differentiation of the biocoenoses. Pictures of the panels, to control the ecological succession of the macrofouling community of hard substrates covering the panels, and values of physico-chemical parameters of the seawater, like temperature, pH and salinity were collected each month. Data were introduced in the bioindex to describe the status of health of the lagoon seawater in the four stations. The main work consisted in the biotic data
processing, through the analysis of the digital photos of the panels for the recognition of the species, their number and the covered area on the panels. The index of environmental quality under examination results useful for
evaluating the status of health of the lagoon seawater by means of a cheap and effective system. Results were compared with those previously obtained and have supplied confirmation of the utility of this bioindex, in spite of differences probably due more to little year's climatic change than significant variations in local parameters
Development of the motor nervous system in ascidians.
No full textThe motor nervous system of adult ascidians consists of neurons forming the cerebral ganglion fromwhich axons run out directly to the effectors, i.e., muscular and ciliary cells. In this study, we analyzed the development of the motor fibers, correlating this with organ differentiation during asexual reproduction in Botryllus schlosseri. We used a staining method for acetylcholinesterase, whose reaction product is visible with both light and electron microscopy and which labels entire nerves, including their thin terminals, making them identifiable between tissues. While the cerebral ganglion is forming, the axons elongate and follow stereotypical pathways to reach the smooth muscle cells of the body, the striated muscle of the heart, and the ciliated cells of the branchial stigmata and the gut. A strict temporal relation links the development
of the local neural network with its target organ, which is approached by nerves before the effector cells are fully differentiated. This process occurs for oral and cloacal siphons, branchial basket, gut, and heart. Axons grow through the extracellular matrix and arrive at their targets from different directions. In some cases, the blood sinuses constitute the favorite roads for growing axons, which seemto be guided by a mechanisminvolving contact guidance or stereotropism.
The pattern of innervation undergoes dynamic rearrangements and a marked process of elimination of axons, when the last stages of blastogenesis occur. The final pattern of motor innervation seems to be regulated by axon withdrawal, rather than apoptosis of motor neurons
Sexual reproduction in ascidians: comparative aspects of oviduct, ovulation and spawning
Full text linkIn the evolution of ascidians different reproductive strategies operated. One of the most important aspects was the passage from external to internaI fertilization and then from ovipaIity to ovovivipaIity and viviparity with consequent morpho-functional modifications to organs and gametes. This paper presents a short review on the ovary and oviduct, the plasticity of which had pIayed a cri tic role in permitting the evolutive changes of sexual
reproduction
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