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Vol. 16, Issue 3, 1355-1365, March 2005

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FLR-4, a Novel Serine/Threonine Protein Kinase, Regulates Defecation Rhythm in Caenorhabditis elegans

Masaya Take-uchi ^*  , Yuri Kobayashi ^*, Koutarou D. Kimura ^* , Takeshi Ishihara ^*  , and Isao Katsura ^* 

^* Structural Biology Center, National Institute of Genetics, The Graduate University for Advanced Studies, Mishima, Shizuoka-ken 411-8540, Japan; Department of Genetics, The Graduate University for Advanced Studies, Mishima, Shizuoka-ken 411-8540, Japan

Submitted April 1, 2004; Revised December 14, 2004; Accepted December 27, 2004
Monitoring Editor: Susan Strome

The defecation behavior of the nematode Caenorhabditis elegans is controlled by a 45-s ultradian rhythm. An essential component of the clock that regulates the rhythm is the inositol trisphosphate receptor in the intestine, but other components remain to be discovered. Here, we show that the flr-4 gene, whose mutants exhibit very short defecation cycle periods, encodes a novel serine/threonine protein kinase with a carboxyl terminal hydrophobic region. The expression of functional flr-4::GFP was detected in the intestine, part of pharyngeal muscles and a pair of neurons, but expression of flr-4 in the intestine was sufficient for the wild-type phenotype. Furthermore, laser killing of the flr-4–expressing neurons did not change the defecation phenotypes of wild-type and flr-4 mutant animals. Temperature-shift experiments with a temperature-sensitive flr-4 mutant suggested that FLR-4 acts in a cell-functional rather than developmental aspect in the regulation of defecation rhythms. The function of FLR-4 was impaired by missense mutations in the kinase domain and near the hydrophobic region, where the latter allele seemed to be a weak antimorph. Thus, a novel protein kinase with a unique structural feature acts in the intestine to increase the length of defecation cycle periods.

Present address: Special Researchers Program, Masai Initiative Research Unit, The Institute of Physical and Chemical Research (Riken), Hirosawa 2-1, Wako-shi, Saitama 351-0198, Japan.

Present address: Department of Biology, Faculty of Sciences, Kyushu University Graduate School, Hakozaki, Fukuoka 812-8581, Japan.

Address correspondence to: Isao Katsura (ikatsura{at}lab.nig.ac.jp).