ニサンカ タンソ コテイ ノ タメ ノ ヒカリ ユウキ ハンノウ システム ニ カンスル ケンキュウ

Planarians can propagate asexually by fission and successive regeneration. During head regeneration, they again form a new pair of eyes, and sometimes supernumerary eyes. The positions of normal and supernumerary eyes and their regeneration abilities are expected to be highly relevant to the question of where and how the field to regenerate eyes is determined. In this study, spontaneously generated supernumerary eyes were classified into various types. In all cases, they were formed in the anterior part of the head. Enucleation of a normal eye elicited regeneration of a new eye; however, enucleation of a supernumerary eye did not. The supernumerary eyes were morphologically and functionally indistinguishable from the normal eyes, revealed by the studies of immunohistology and photophobic response, respectively. From the obtained results, we proposed a model of the eye regeneration field that changes its distribution spatiotemporally during regeneration. Immunohistological studies also showed that the optic nerves from the normal and supernumerary eyes ran independently, which might have implication about the nature of guidance cues for the optic nerves

Dorsal and Ventral Positional Cues Required for the Onset of Planarian Regeneration May Reside in Differentiated Cells

AbstractWe previously showed by grafting experiments that the dorsoventral (DV) interaction evokes morphogenetic events similar to those that occur in regeneration. However, it is not yet understood whether the stem cells themselves or differentiated cells have the ability to induce regeneration. Here we demonstrated by a combination of X-ray irradiation and grafting experiments that the dorsal and ventral positional cues inducing morphogenetic events are retained in X-ray-irradiated tissues, suggesting that the differentiated cells may be responsible for the positional cues. We grafted a small piece of irradiated worm, in which the stem cells were certainly eliminated, to an intact one in DV-reversed orientation. We observed that projections were developed from the host–donor boundary, as in the previous experiments. Whole-mount in situ hybridization with several markers demonstrated that the projections had a newly established DV axis and also had anterior or posterior characteristics. Furthermore, chimeric analysis with a strain-specific marker showed that the projections consisted of nonirradiated cells and that IFb-expressing cells, which normally belonged to the ventral tissue, could be generated even from the stem cells located on the dorsal side. Taken together, the findings suggest that the stem cells may simply differentiate depending on the surroundings and that differentiated cells may present positional cues that induce morphogenesis

Germ plasm in Eleutherodactylus coqui, a direct developing frog with large eggs

<p>Abstract</p> <p>Background</p> <p>RNAs for embryo patterning and for germ cell specification are localized to the vegetal cortex of the oocyte of <it>Xenopus laevis</it>. In oocytes of the direct developing frog <it>Eleutherodactylus coqui</it>, orthologous RNAs for patterning are not localized, raising the question as to whether RNAs and other components of germ plasm are localized in this species.</p> <p>Methods</p> <p>To identify germ plasm, <it>E. coqui </it>embryos were stained with DiOC₆(3) or examined by <it>in situ </it>hybridization for <it>dazl </it>and <it>DEADSouth </it>RNAs. The cDNAs for the <it>E. coqui </it>orthologues were cloned by RT-PCR using degenerate primers. To examine activity of the <it>E. coqui </it>orthologues, RNAs, made from constructs of their 3'UTRs with <it>mCherry</it>, were injected into <it>X. laevis </it>embryos.</p> <p>Results</p> <p>Both DiOC₆(3) and <it>dazl </it>and <it>DEADSouth in situs </it>identified many small islands at the vegetal surface of cleaving <it>E. coqui </it>embryos, indicative of germ plasm. <it>Dazl </it>was also expressed in primordial germ cells in the genital ridge. The 3'UTRs of <it>E. coqui dazl </it>and <it>DEADSouth </it>directed primordial germ cell specific protein synthesis in <it>X. laevis</it>.</p> <p>Conclusions</p> <p><it>E. coqui </it>utilizes germ plasm with RNAs localized to the vegetal cortex to specify primordial germ cells. The large number of germ plasm islands suggests that an increase in the amount of germ plasm was important in the evolution of the large <it>E. coqui </it>egg.</p

DEADSouth protein localizes to germ plasm and is required for the development of primordial germ cells in Xenopus laevis

Summary DEADSouth mRNA is a component of germ plasm in Xenopus laevis and encodes a DDX25 DEAD-box RNA helicase. To determine the intracellular localization of DEADSouth protein, we injected mRNA encoding DEADSouth tagged with mCherry fluorescent protein into fertilized eggs from transgenic Xenopus expressing EGFP fused with a mitochondrial targeting signal. The DEADSouth-mCherry fusion protein was localized to the germ plasm, a mitochondria-rich region in primordial germ cells (PGCs). DEADSouth overexpression resulted in a reduction of PGC numbers after stage 20. Conversely, DEADSouth knockdown using an antisense locked nucleic acid gapmer inhibited movement of the germ plasm from the cortex to the perinuclear region, resulting in inhibition of PGC division at stage 12 and a decrease in PGC numbers at later stages. The knockdown phenotype was rescued by intact DEADSouth mRNA, but not mutant mRNA encoding inactive DEADSouth helicase. Surprisingly, it was also rescued by mouse vasa homolog and Xenopus vasa-like gene 1 mRNAs that encode DDX4 RNA helicases. The rescue was dependent on the 3′ untranslated region (3′UTR) of DEADSouth mRNA, which was used for PGC-specific expression. The 3′UTR contributed to localization of the injected mRNA to the germ plasm, resulting in effective localization of DEADSouth protein. These results demonstrate that localization of DEADSouth helicase to the germ plasm is required for proper PGC development in Xenopus laevis

Molecular cloning of bone morphogenetic protein (BMP) gene from the planarian Dugesia japonica

BMP (Bone Morphogenetic Protein) acts as a morphogen for dorso-ventral patterning and organogenesis in both vertebrate and invertebrate development. A cDNA encoding BMP (named Djbmp) has been cloned and sequenced from the planarian Dugesia japonica. The mature form of DjBMP which was deduced from the cDNA sequence was composed of 114 amino acid residues. The position of seven cysteine residues of the mature DjBMP was highly conserved among the TGF-beta superfamily. DjBMP had high similarity to human BMP-2A (50% amino acid identity), BMP-4 (49%) and Drosophila decapentaplegic protein (48%), indicating that DjBMP belongs to DVR (decapentaplegic-Vg1-related) group. The expression pattern in intact and regenerating planarians revealed by whole mount in situ hybridization suggested that the DjBMP plays a role not only in dorso-ventral but also in mid-lateral body patterning

Identification of two distinct muscles in the planarian Dugesia japonica by their expression of myosin heavy chain genes

Ultrastructural and physiological studies have shown that planarian muscles have some characteristics of smooth and some characteristics of striated muscles. To characterize planarian muscles, we isolated two myosin heavy chain genes (DjMHC-A and DjMHC-B) from a planarian, Dugesia japonica, by immunological screening, and analyzed their structures and spatial expression patterns. Structural analysis indicated that both MHC genes are striated-muscle-type myosin genes, although planarian muscles do not have any striation. In situ RNA hybridization showed that expression of the two myosin genes is spatially strictly segregated. DjMHC-A was expressed in pharynx muscles, pharynx cavity muscles, muscles surrounding the intestinal ducts, a subpopulation of body-wall muscles and several muscle cells in the mesenchymal region around the base of the pharynx. DjMHC-B was expressed in body-wall muscles (including circular, diagonal and longitudinal muscles), vertical muscles and horizontally oriented muscles. Double staining with DjMHC-A and -B probes clearly demonstrated that expression of the DjMHC-A and -B genes do not occur in the same cell. During regeneration, the number of cells positive for expression of each gene increased in the blastema region, suggesting that both types of muscle may be involved in blastema formation. DjMHC-B-positive cells disappeared from the body-wall muscle layer in the pharynx-cavity-forming region, whereas DjMHC-A-positive cells were markedly accumulated there, suggesting that the two types of muscle in the body wall layer may have distinct functions. These results indicate that planarians have at least two types of muscle that express striated-muscle-type MHC genes, but do not form striation