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Biomedical subjects

Koji Tamura

Publications and source records attributed to Koji Tamura.

8 recordsLinked to original sources
PubMed2003

Peptide synthesis with a template-like RNA guide and aminoacyl phosphate adaptors.

The genetic code is thought to have developed from an early system of RNA-dependent peptide synthesis. To investigate one kind of template-like peptide synthesis that might emerge from an RNA world, we constructed highly reactive aminoacyl phosphate oligonucleotides as adaptors that bound to RNA guide sequences. The reactive aminoacyl groups mimic a chemistry found in modern protein biosynthesis. Guide sequence interactions with adaptors were borrowed in part from universal contacts seen between tRNAs and rRNA. With these constructions, di- and tripeptides formed in a single guide sequence-dependent reaction. The order of amino acids was not random but directional in a way consistent with substrate reactivities. No ribosomes or ribozymes were required. Thus, aminoacyl phosphate adaptors and RNA guides could, in principle, have been intermediates in the transition from the RNA world to modern template-dependent protein synthesis.

Amino Acid Sequence↗
PubMed2003

tRNA structure goes from L to lambda.

In this issue of Cell, Ishitani et al. (2003) report, in a crystal, a new L-like structure of tRNA designated as lambda-form, where disruption of universal tertiary interactions is compensated by interactions with an enzyme that makes a base modification at the corner of the L.

Base Sequence↗
PubMed2003

Expression of rigf, a member of avian VEGF family, correlates with vascular patterning in the developing chick limb bud.

In a differential display screening for genes regulated by retinoic acid in the developing chick limb bud, we have isolated a novel gene, termed rigf, retinoic-acid induced growth factor, that encodes a protein belonging to the vascular endothelial growth factor (VEGF) family. Rigf transcripts were found in the posterior region of the limb bud in a region-specific manner as well as in other embryonic tissues and regions, including the notochord, head and trunk mesenchyme, retinal pigment epithelium, and branchial arches. Several manipulations revealed that retinoic acid and sonic hedgehog signaling pathways regulate rigf expression in the limb bud. VEGF family members, which promote the migration, differentiation and proliferation of endothelial cells in both blood and lymphatic vessels, are important factors for the formation of blood and lymphatic vasculatures during development. We demonstrated that the anterior border of the rigf expression domain in the limb bud corresponds with the position of the primary central artery (the subclavian artery in the forelimb), which is a main artery for supplying blood to the limb. These observations taken together with results from some experimental manipulations suggest that the limb tissue attracts blood vessels into the limb bud and that rigf is involved in the pattern formation of blood vessels in the limb.

Amino Acid Sequence↗
PubMed2002

Anteroposterior axis formation in Xenopus limb bud recombinants: a model of pattern formation during limb regeneration.

We previously showed that recombinant limb buds with dissociated and reaggregated mesenchyme develop more than 30 digits in Xenopus laevis, which exhibits different capacities for limb regeneration at different developmental stages (Yokoyama et al. [1998] Dev Biol 196:1-10). Cell-cell contact among anterior- and posterior-derived mesenchymal cells is required for anteroposterior (AP) axis formation of recombinant limbs in an intercalary manner. However, whether one-way induction from posterior cells to anterior cells as proposed by the polarizing zone model or interactions between anterior and posterior cells evoke the AP axis formation in recombinant limbs remains unclear. In this study, we found, by a combination of X-ray irradiation and a recombinant limb technique, that not one-way induction but interactions between anterior and posterior cells accompanied by cell contribution are indispensable for AP axis formation in recombinant limbs. Shh was expressed in posterior-derived not anterior-derived cells. We propose that the recombinant limb is an excellent model for examining the axis formation mechanism in regenerating limbs because, as in recombinant limbs, cell-cell contact among cells derived from different positions of an amputation plane occurs in the blastema of regenerating limbs.

Animals↗
PubMed2002

Use of an infrared sensor system to take long-term bedside measurements of rest-activity patterns in the elderly with dementia.

In order to study long-term rest-activity patterns of elderly residents in care facilities, an infrared sensor system was developed. This sensor system detects a resident's presence or absence from their bed and their activity with little inconvenience. Using this system, the rest-activity patterns of two elderly people with dementia was assessed over a period of 3 months. For both subjects, frequent activity peaks and absences from their beds were often observed during the night. Such a sensor system will be useful for evaluating the sleep-wake rhythms of people with sleep disorders.

Activity Cycles↗
PubMed2002

Specification and determination of limb identity: evidence for inhibitory regulation of Tbx gene expression.

Limb-type-specific expression of Tbx5/Tbx4 plays a key role in drawing distinction between a forelimb and a hindlimb. Here, we show insights into specification and determination during commitment of limb-type identity, in particular that median tissues regulate Tbx expressions. By using the RT-PCR technique on chick embryos, the onset of specific Tbx5/Tbx4 expression in the wing/leg region was estimated to be stage 13. Specification of the limb-type identity is thought to occur before stage 9, since all explants from stage 9 through 14 expressed the intrinsic Tbx gene autonomously in a simple culture medium. The results of transplantation experiments revealed that axial structures medial to the lateral plate mesoderm at the level of the wing region are capable of transforming leg identity to wing identity, suggesting that a factor(s) from the median tissues is involved in the limb-type determination. Nevertheless, the transplanted wing region was not converted to leg identity. The results of the transplantation experiments also suggested that wing-type identity is determined much earlier than is leg-type identity. Finally, we also found that inhibitory effects of median tissues mediate the specific expression of Tbx5/Tbx4 in the presumptive wing/leg region. We propose a model for limb-type identification in which inhibitory regulation is involved in restricting one Tbx gene expression by masking the other Tbx expression there.

Animals↗
PubMed2002

Cell adhesiveness and affinity for limb pattern formation.

Stage-dependent cell sorting in vitro is an intriguing property that mesenchymal cells of a chick limb bud have. We previously proposed that N-cadherin, a cell adhesion molecule, is involved in the sorting process and is likely to be a component of the mechanism of proximal-distal patterning in the developing limb (Yajima et al., (1999) Dev. Dynam. 216:274-284). Here, we present more direct evidence that N-cadherin is one of the molecules responsible for regulation of stage-dependent cell sorting in vitro. Our results suggest that N-cadherin, which accumulates in the distal region of the chick limb bud as limb development proceeds, is related to the positional identity that gives rise to the different shapes and numbers of cartilaginous elements along the proximal-distal axis. In this article we also give insights into positional identity which is mediated by Hoxgenes and cell surface property during limb development.

Animals↗