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Casein Kinases I of the Silkworm, Bombyx mori: Their Possible Roles in Circadian Timing and Developmental Determination

Hana Sehadova

Naoyuki Ichihara

Sachio Iwai

Division of Molecular Science, Graduate School of Science and Technology, Kobe University, Japan

Kazuei Mita

National Institute of Agrobiological Science, Japan

Makio Takeda

Division of Molecular Science, Graduate School of Science and Technology, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan; mtakeda{at}kobe-u.ac.jp

Doubletime (DBT), a homolog of casein kinase I[.epsilon] (CKI[.epsilon]), is an essential circadian clock component and developmental regulator in Drosophila melanogaster. The authors cloned a dbt homolog from the silkworm, Bombyx mori(Bmdbt), and examined its spatial and temporal expression in comparison to a CKI[.alpha] homolog (BmCKI[.alpha]). Four Bmdbt splice variants and 2 BmCKI[.alpha] splice variants were detected, and their expression patterns varied in different tissues. The level of Bmdbt transcript in the brain was constant under LD 12:12 while those of BmCKI[.alpha] transcripts fluctuated with a decrease at ZT12. In situ hybridization showed presumably identical distribution of dbt, CKI[.alpha], and per transcripts in the putative clock neurons of the head ganglia, as well as in the retina, where CKI-and PER-like immunoreactivities were colocalized, suggesting a possible involvement of both CKIs in the B. mori circadian system. Signals were detected at 4 Ia₁ neurons in each dorsolateral protocerebrum, 6 to 8 cells in the pars intercerebralis, about 6 cells in the suboesophageal ganglion, 2 neurons in the frontal ganglion, and most of the photoreceptors. All these cells contained dbt, CKI[.alpha], and per antisense transcripts. The Northern analysis of dbtand CKI[.alpha] transcripts at different developmental stages showed that both genes were expressed at relatively high levels during early embryogenesis and in the ovary. The levels of CKI[.alpha] transcripts were also high in the late larval stages until the mid-fifth instar and then suddenly disappeared before larval-pupal ecdysis. In contrast, the transcriptional activity of both genes was low in diapausing eggs.

Key Words: casein kinase • doubletime • PER • circadian rhythms • Bombyx mori • retina

Journal of Biological Rhythms, Vol. 21, No. 5, 335-349 (2006)
DOI: 10.1177/0748730406291734


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