Two candidates, Smed-SOXB-1 and Smed-SOXB-2, homologs of mammalian members of this class, were identified in neoblasts The apparent lack of a Nanog homolog contrasts with extensive conservation of gene expression observed for its targets and indicates that in planaria, its role might be played by a different TF.Also, conserved expression of epigenetic regulators known to be required for maintaining pluripotency in ESCs (esBAF, MLL1, PRC2, and PAF1 complex) is critical for the maintenance of the neoblasts In planaria, Wnt signaling is associated with control of the regeneration and the specification of missing body part How do poles mediate tissue organization? In this chapter we describe general methods for keeping and maintaining Planarians, representative members of this phylum, exhibit an extraordinary ability to regenerate lost body parts, making this animal an attractive model for the study of stem cell biology (see Molecular mechanisms for pluripotency in neoblasts revealed similarity to those in mammalian ESCs. The platyhelminthes digestive system is not as complex as the other digestive system because of the makeup of the organism. Most flatworms are parasitic, including important parasites of humans. Digestive enzymes are secreted from the mouth to begin external digestion. Planarians are hermaphrodites, possessing testes, ovaries, and copulatory apparatus and have the capacity for sexual reproduction through cross-fertilization (Newmark and Sanchez Alvarado, 2002;Planarians are free-living invertebrates that employ motile cilia for locomotion. Figure 1: This planarian is a free-living flatworm that has an incomplete digestive system, an excretory system with a network of tubules throughout the body, and a nervous system made up of nerve cords running the length of the body with a concentration of nerves and photosensory and chemosensory cells at the anterior end. They have only one host during their life, typically of just one species. Certaines espèces sont capables de nager par ondulation. The gut may be a simple sac or highly branched. Furthermore, we elaborate on different imaging techniques used to analyze cilia physiology and structure, including live video microscopy, immunofluorescence analysis, and electron microscopy. Since they don’t have to contribute any energy or body volume to digestion, this leaves these animals more energy and body space to devote to reproduction.
All the larger forms are flat with ribbon-like or leaf-like shapes, since their lack of respiratory and circulatory systems means that they have to rely on (credit a: modification of work by Jan Derk; credit c: modification of work by “Sahaquiel9102″/Wikimedia Commons; credit d: modification of work by CDC)The monogeneans are external parasites mostly of fish with life cycles consisting of a free-swimming larva that attaches to a fish to begin transformation to the parasitic adult form. The remaining body of the tapeworm is made up of a long series of units called proglottids, each of which may contain an excretory system with flame cells, but will contain reproductive structures, both male and female. Turbellarians share some important characteristics with other Platyhelminthes. Turbellarians do not have a respiratory or circulatory system, they exchange gases by diffusion through all their cells. The system is responsible for regulation of dissolved salts and excretion of nitrogenous wastes. In some worms, their digestive system is reduced or completely absent, so food is absorbed through the cuticle. Most flatworms have an incomplete digestive system with an opening, the “mouth,” that is also used to expel digestive system wastes. In addition, the complete digestive system allows for an orderly progression of digestion of food matter and the specialization of different zones of the digestive tract.Describe a potential advantage and disadvantage of the cuticle of ecdysozoans.An advantage is that it is a tough covering that is protective against adverse environments, and predators and parasites. While a majority of these species live in marine environments, there are many others that can be found in freshwater environments as well as tropical terrestrial and moist temperate environments. Unlike in many other organisms, the intestinal luminal epithelium of flatworms consists entirely of developmentally static, postmitotic differentiated cells. They have a complete digestive system and a pseudocoelomic body cavity. Moreover, planarians are genetically amenable and defects that compromise the function and structure of the cilia are not detrimental for their overall health, making them an ideal system for cilia gene loss-of-function studies. They have a muscular mouth, called a pharynx, as well as a saclike digestive cavity. Unlike in many other organisms, the intestinal luminal epithelium of flatworms consists entirely of developmentally static, postmitotic differentiated cells. When the muscle tissue is eaten by the primary host, the cycle is completed. The planarian has very simple organ systems. The 17,000 described species have been identified from fossils (The Hexapoda have six legs (three pairs) as their name suggests. The mouth is located in the center of the underside of the body.