An ascidian homolog of SEC61 is expressed predominantly in epidermal cells of the embryo.
In eukaryotic cells, SEC61 protein is essential for protein translocation across the endoplasmic reticulum membrane. Because of the ubiquitous nature of the protein, the expression of the corresponding gene(s) during embryogenesis has not received much attention. We found that an ascidian homolog of SEC61 is expressed predominantly in embryonic epidermal cells. A cDNA clone for Halocynthia roretzi SEC61 (HRSEC61) gene contains a single open reading frame that encodes a polypeptide of 475 amino acids. The degree of amino-acid identity was 87% between the ascidian and the dog and 55% between the ascidian and yeast. The HRSEC61 gene was transcribed maternally and zygotically. A low level of the corresponding mRNAs, about 2.3 kb in length, was found in eggs and early embryos. Zygotic mRNAs appeared after the gastrula stage, and the accumulation of the mRNAs was maximal at the neurula and tailbud stages. In situ hybridization of whole-mount specimens demonstrated that, although maternal mRNAs were distributed evenly in eggs and early embryos, the occurrence of zygotic mRNAs was predominant in differentiating epidermal cells. The predominant expression of HRSEC61 in embryonic epidermal cells was determined using cleavage-arrested embryos; those at the 16- or 32-cell stage expressed HRSEC61 in the presumptive epidermal cells of the animal hemisphere.
Ueki
T
T
Department of Zoology, Faculty of Science, Kyoto University, Japan.
Satoh
N
N
D000595:Amino Acid Sequence; D000818:Animals; D018076:DNA, Complementary; D004625:Embryo, Nonmammalian / Q000378:metabolism; D015870:Gene Expression; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics*; D008969:Molecular Sequence Data; D010802:Phylogeny; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D000069816:SEC Translocation Channels; D017386:Sequence Homology, Amino Acid; D014561:Urochordata / Q000196:embryology / Q000235:genetics*
D018076:DNA, Complementary; D008565:Membrane Proteins; D012333:RNA, Messenger; D000069816:SEC Translocation Channels