Molecular cloning of a zinc finger protein belonging to the GLI‐Krüppel family and its expression in the silk gland

We have isolated and characterized a zinc finger‐containing cDNA (ZSG‐1) from the middle silk gland of Bombyx mori. Sequence analysis indicates that the protein encoded by the ZSG‐1 transcript contains a domain of five fingers similar to the zinc finger repeats of the Xenopus transcription factor TFIIIA, the product of Drosophila segment polarity gene cubitus interruptus (ci) and the human zinc finger protein GLI, which has been found to be amplified in several human glioblastomas. The transcript expression pattern and protein distribution of ZSG‐1 during embryogenesis and silk gland development were analyzed by northern blot and immunohistochemistry. ZSG‐1 transcript was most strongly detected in the middle silk gland and weakly in the posterior silk gland at the fourth larval intermolt and molting stages. When the larvae entered the fifth intermolt, the expression of ZSG‐1 rapidly decreased by 2 days after the fourth ecdysis and maintained a low level thereafter in the middle silk gland, while the transcript in the posterior silk gland gradually became undetectable. The transcript was first detected at around stage 18 of early embryogenesis; it then increased to the maximum level by stage 27 and maintained a high level until hatching. Interestingly, the ZSG‐1 protein was most strongly distributed in the middle silk gland during embryonic silk gland development. The expression of ZSG‐1 in the silk glands suggests that this gene may play important roles in the development of silk gland.