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Y K Maruyama

Publications and source records attributed to Y K Maruyama.

5 recordsLinked to original sources
PubMed2000

A starfish homolog of mouse T-brain-1 is expressed in the archenteron of Asterina pectinifera embryos: possible involvement of two T-box genes in starfish gastrulation.

A cDNA clone for a starfish T-box gene (Ap-Tbr) was isolated and characterized. Molecular phylogenetic analysis showed that the Ap-Tbr gene was a member of the T-brain subfamily, which includes mouse T-brain-1 and Xenopus Eomesodermin. Ap-Tbr was expressed as early as in late blastulae, and the transcript was evident in a disc-like region at the vegetal end or the vegetal plate. In early gastrulae, the gene was expressed in the cells of the invaginated archenteron, from which the majority of mesodermal cells as well as some endodermal cells are derived. The Ap-Tbr expression disappeared by the end of gastrulation, and was not detected in early bipinnaria larvae. This expression pattern of Ap-Tbr suggests its role in an early step of archenteron invagination, associated with mesoderm and endoderm formation. Furthermore, double staining of late blastulae and early gastrulae with a probe specific for Ap-Tbr and one for ApBra (the starfish Brachyury gene) demonstrated that the regions of Ap-Tbr and ApBra expression at the vegetal/posterior end of the embryo did not overlap, the region with Ap-Tbr expression being encircled by a ring-shaped region of ApBra expression. A gap without expression of the two genes was located between them, and the gap was seen around the blastoporal lip in the early gastrula. These observations suggest implication of the two T-box genes, with different roles, in starfish gastrulation.

Amino Acid Sequence↗
PubMed1999

Dynamic patterns in the locomotion and feeding behaviors by the placozoan Trichoplax adhaerence.

The placozoan Trichoplax adhaerence is one of the most primitive multi-cellular organisms, and moves about accompanying perpetual changes in its shape. Changes in position, locomotion velocity and the outer shape of the organism were monitored quantitatively with use of a computer image analysis, and their dynamic patterns in free locomotion and upon feeding were analyzed in terms of non-linear dynamics. The organism changed its behavioral patterns discontinuously in response to various concentrations of yeast extracts (food). (1) At low concentrations, the organism moved fast with perpetual random changes in shape. Both locomotion velocity and shape changes exhibited 1/f fluctuations. (2) At high concentrations, the shape of the organism as well as the locomotion exhibited oscillations with periods of about 8 min. These limit cycle oscillations bifurcated into the period 2 at the highest concentration tested. The organism flattened more strongly and the locomotion was more reduced on the whole at higher concentrations. (3) At the intermediate concentrations, two patterns as monitored above appeared: one pattern continued for a while and switched to the other abruptly. (4) The average square displacement of the organism increased linearly with time in all cases, indicating that the locomotion is a Brownian movement. In this way, the feeding behaviors by the placozoan are organized as successive co-operative transitions among non-linear dynamic states.

Activity Cycles↗
PubMed1999

Pattern of Brachyury gene expression in starfish embryos resembles that of hemichordate embryos but not of sea urchin embryos.

Echinoderms, hemichordates and chordates are deuterostomes and share a number of developmental features. The Brachyury gene is responsible for formation of the notochord, the most defining feature of chordates, and thus may be a key to understanding the origin and evolution of the chordates. Previous studies have shown that the ascidian Brachyury (As-T and Ci-Bra) is expressed in the notochord and that a sea urchin Brachyury (HpTa) is expressed in the secondary mesenchyme founder cells. A recent study by [Tagawa et al. (1998)], however, revealed that a hemichordate Brachyury (PfBra) is expressed in a novel pattern in an archenteron invagination region and a stomodaeum invagination region in the gastrula. The present study demonstrated that the expression pattern of Brachyury (ApBra) of starfish embryos resembles that of PfBra in hemichordate embryos but not of HpTa in sea urchin embryos. Namely, ApBra is expressed in an archenteron invagination region and a stomodaeum invagination region.

Amino Acid Sequence↗
PubMed1991

Initiation of DNA replication cycle in fertilized eggs of the starfish, Asterina pectinifera.

Starfish oocytes or eggs were inseminated at various times between first prometaphase and pronuclear stage, and were subsequently labeled with the thymidine analogue 5-bromo-2'-deoxyuridine (BrdU) in order to detect the onset of DNA synthesis phase (S phase) during the first cell cycle using a monoclonal antibody against BrdU. The interval between fertilization and the first S phase was found to be constant (30-45 min, depending on batches) in eggs fertilized after formation of the first polar body. Eggs fertilized before first polar body formation, however, always entered the S phase 10-20 min after the second polar body formation. On the basis of these observations we conclude that (i) the chain of events triggered by fertilization, collectively called "postactivation process" for the first S phase, goes on in parallel with the process of maturation and (ii) only the final step of the postactivation process is arrested until the termination of meiosis. In eggs that had been fertilized before the first polar body formation, the female and male pronuclei exhibited uniformly distributed chromatin soon after the second polar body formation. In eggs that had been fertilized after the second polar body formation, however, the chromatin of the pronuclei remained fibrillar even during the S phase. Thus full decondensation of chromatin appears to depend on a certain advance in the postactivation process.

Animals↗