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T Numakunai

Publications and source records attributed to T Numakunai.

15 recordsLinked to original sources
PubMed2000

Pigment cell-specific expression of the tyrosinase gene in ascidians has a different regulatory mechanism from vertebrates.

Tyrosinase is the key enzyme required for the synthesis of melanin pigments. Sequence comparison and functional analysis of the 5' upstream regions of vertebrate tyrosinase genes have revealed the importance of conserved E-box motifs in regulating their specific expression in pigment cells, optic cup-derived retinal pigment epithelium (RPE) and neural crest-derived melanocytes. In ascidians (more basal protochordates), two pigment cells that resemble vertebrate RPE cells are formed and specifically express the orthologous tyrosinase gene (HrTyr) in the cerebral vesicle located at the anterior end of the neural tube. To define regulatory sequences required for pigment cell-lineage-specific expression of HrTyr during embryogenesis, a series of mutations of the 5' upstream region of HrTyr were fused to the lacZ reporter gene and were microinjected into fertilized eggs. We found that the -152bp upstream of the translational start site is essential for expression in pigment cell precursors of tailbud-stage embryos. Further, additional positive and unique restriction elements were identified in the region up to -1.8kb. Surprisingly, in the -152bp minimal promoter or in other regions with regulatory activities, there are no E-box motifs or sequences correlating with other conserved elements regulating vertebrate tyrosinase promoters. The possibility that Pax proteins regulate HrTyr expression is also discussed.

Amino Acid Sequence↗
PubMed2000

Expression of the otx gene in the ciliary bands during sea cucumber embryogenesis.

The Otx gene encodes a homeodomain transcription factor that has a highly conserved role in brain formation of both flies and vertebrates. To deduce evolutionary relationship of the chordate central nervous system to the larval or adult nervous system of nonchordate deuterostomes, we characterized the expression of the Otx gene (Sj-Otx) throughout the entire embryonic and larval development of the sea cucumber Stichopus japonicus. Sj-Otx transcripts were detected in fertilized eggs and in the posterior part of the archenteron of gastrulae. However, the expression was downregulated as embryos developed into auricularia larvae. Sj-Otx was expressed again in the ciliary bands of late auricularia larvae, just before metamorphosis to doliolaria larvae. The expression domain corresponded to the domains moving to the mouth during metamorphosis and sinking into the buccal cavity, but not to the five transverse ciliary bands of the doliolaria. The expression gradually disappeared during further development and was not detected in juveniles. These results indicate that the gene responsible for chordate brain formation is expressed in the ciliary bands of auricularia larvae.

Amino Acid Sequence↗
PubMed1999

Structure and developmental expression of the ascidian TRP gene: insights into the evolution of pigment cell-specific gene expression.

The tyrosinase family in vertebrates consists of three related melanogenic enzymes: tyrosinase, tyrosinase-related protein-1 (TRP-1), and TRP-2. These proteins control melanin production in pigment cells and play a crucial role in determining vertebrate coloration. We have isolated a gene from the ascidian Halocynthia roretzi which encodes a tyrosinase-related protein (HrTRP) with 45-49% identity with vertebrate TRP-1 and TRP-2. The expression of the HrTRP gene in pigment lineage a8.25 cells starts at the early-mid gastrula stage, which coincides with the stage when these cells are determined as pigment precursor cells; therefore, it provides the earliest pigment lineage-specific marker, which enables us to trace the complete cell lineage leading to two pigment cells in the larval brain. In addition, the expression pattern of the HrTRP gene appears to share similar characteristics with the mouse TRP-2 gene although structurally the HrTRP gene is more closely related to mammalian TRP-1 genes. Based on these observations and on results from molecular phylogenetic and hybridization analyses, we suggest that triplication of the tyrosinase family occurred during the early radiation of chordates. Initially, duplication of an ancestral tyrosinase gene produced a single TRP gene before the urochordate and cephalochordate-vertebrate divergence, and a subsequent duplication of the ancestral TRP gene in the vertebrate lineage gave rise to two TRP genes before the emergence of teleost fishes. Evolution of the melanin synthetic pathway and possible phylogenetic relationships among chordate pigment cells that accommodate the metabolic process are discussed. Dev Dyn 1999;215:225-237.

Amino Acid Sequence↗
PubMed1997

Ascidian tyrosinase gene: its unique structure and expression in the developing brain.

Tadpole larvae of ascidians have two sensory pigment cells in the brain. One is the otolith cell that functions as a gravity receptor, the other pigment cell is part of a primitive photosensory structure termed the ocellus. These sensory cells, like vertebrate pigment cells, contain membrane-bounded melanin granules and are considered to reflect a crucial position in the evolutionary process of this cell type. To investigate the molecular changes accompanying the evolution of pigment cells, we have isolated from Halocynthia roretzi a gene encoding tyrosinase, a key enzyme in melanin biosynthesis. The cDNA has an open reading frame (ORF) of 596 amino acids, which is 36-39% identical in amino acid sequence to vertebrate tyrosinases. In addition, the sequence analysis of both cDNA and genomic clones reveals an unusual organization of the tyrosinase gene, an extraordinary 3' untranslated region of the transcripts with significant homology to the coding sequence, and a single short intron in the sequence encoding a cytoplasmic domain. Expression of the gene is detected first in two pigment precursor cells positioned in the neural plate of early neurulae, and later in two melanin-containing pigment cells within the brain of late tailbud embryos. Its expression pattern correlates well with the appearance of tyrosinase enzyme activity in the developing brain. These results provide the first description of pigment cell differentiation at the molecular level in the ascidian embryo, and also will contribute to a better understanding of the evolution of chordate pigment cells.

Amino Acid Sequence↗
PubMed1995

The structure of the Aplysia kurodai gene encoding ADP-ribosyl cyclase, a second-messenger enzyme.

The complete nucleotide (nt) sequences of the cDNA and gene encoding the marine mollusk Aplysia kurodai (Ak) ADP-ribosyl cyclase (ADRC) which synthesizes cyclic ADP-ribose (cADP-ribose), a second messenger for Ca2+ mobilization from endoplasmic reticulum, were determined. Ak ADRC consists of 258 amino acids (aa) (29 kDa). It shares 86% aa sequence homology with that from A. californica, and 31-32% homology with the human, rat and mouse cluster of differentiation 38 (CD38) that has both ADRC and cADP-ribose hydrolase activities. The Ak ADRC-encoding gene (ADRC) spans approx. 7 kb and contains eight exons and seven introns. The transcription start point (tsp) determined by primer extension analysis and S1 mapping is 28 bp downstream from the TATA box. This gene is expressed specifically in the ovotestis, although the mammalian CD38-encoding gene is expressed in many kinds of tissues and cells. The 5'-flanking region contains several consensus sequences responsible for the germ-cell-specific expression of the mouse zona pellucida 3 (ZP3) and Drosophila melanogaster chorion genes. The existence of the consensus sequences located at nt -1649, -1161, -234 and -90 may account for the ovotestis-specific expression of the Ak ADRC gene.

ADP-ribosyl Cyclase↗
PubMed1992

Accumulation of vanadium during embryogenesis in the vanadium-rich ascidian, Ascidia gemmata.

It is a remarkable and previously unrecognized fact that ascidians, which are known to contain high levels of vanadium in their blood cells, begin to accumulate vanadium during embryogenesis. This study revealed that the accumulation starts quite dramatically 2 wk after fertilization, and 2 mo later, the amount of vanadium in larvae is 600,000 times higher than that in the unfertilized egg. These results were obtained by neutron activation analysis, a highly sensitive method for determining levels of vanadium, in the Ascidia gemmata, the ascidian that contains the highest known levels of vanadium and accumulates vanadium at 150 mM in its blood cells, a concentration that corresponds to 4,000,000 times the concentration in seawater.

Animals↗
PubMed1982

Allogeneic cellular reactions between intra-specific types of a solitary ascidian, Halocynthia roretzi.

Coelomic cells from a solitary ascidian, Halocynthia roretzi, exibit a nonphagocytic cellular reaction against coelomocytes from different species and another individuals of the same species. The reaction was denoted contact reaction. While xenogeneic contact reactions were always observed, allogeneic reactions were observed in most but not all combinations of individuals. Three variant types of H. roretzi (Type A, B, C) inhabit the coast of northern Japan. They are reproductively isolated under natural conditions. Non-reactive combinations exist between the different types, in all possible combinations. The paterns and frequencies of reactivities between different variants are almost the same to those observed within a single type. The results of the alloreactivity suggest that the three types of H. roretzi became separate from each other very recently and still remain intra-specific variants.

Alleles↗