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Characterization of the Bombyx mori homolog of islet homeostasis protein (IHoP) cDNA: BmIHoP controls insulin secretion from the β-cells

Hyojung Shin, Kisang Kwon, Ji-Young Choi, O-Yu Kwon, Seung-Whan Kim

Islet homeostasis protein (IHoP) was firstly characterized as a novel protein that regulates glucagon synthesis in alpha-cells of pancreatic islet. Here, we report a cDNA designed BmIHoP encoding an IHop homolog cloned from the fat body of the silkworm, Bombyx mori, using conserved domain homology search method. The resultant BmIHoP translated into a protein that encodes 693 amino acids, with a theoretical isoelectric point of 5.15 and a molecular weight of 77.5 kDa. Homology analysis revealed that BmIHoP has higher similarity at the amino acid level with those of other species, 52% identity with H. sapiens, 52% with M. musculus, 51% with D. rerio, and 73% with D. melanogaster. The expression of BmIHoP was detected in all tissues tested with 4 fold higher expression in the midgut, Malpighian, ovary and testis, and stronger expression in the larval fat body at 5^th-3^rd instar. The overexpression of BmIHoP in the β-cells reduced insulin secretion, which is not associated with SOX17 regulation. To the best of our knowledge, this is the first report of B. mori IHoP cDNA, BmIHoP, and its associated role in controlling insulin secretion from the β-cells.