Journal
JOURNAL OF CELL SCIENCE
Volume 127, Issue 21, Pages 4714-4727Publisher
COMPANY BIOLOGISTS LTD
DOI: 10.1242/jcs.155275
Keywords
CEP290; Chlamydomonas; Cilia; Flagella; Nephrocystin-4; Transition zone
Categories
Funding
- National Institutes of Health [GM060992, GM030626]
- Robert W. Booth Endowment at UMMS
- National Institute of General Medical Sciences Institutional Development Award (IDeA) [P20 GM103449]
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The protein nephrocystin-4 (NPHP4) is widespread in ciliated organisms, and defects in NPHP4 cause nephronophthisis and blindness in humans. To learn more about the function of NPHP4, we have studied it in Chlamydomonas reinhardtii. NPHP4 is stably incorporated into the distal part of the flagellar transition zone, close to the membrane and distal to CEP290, another transition zone protein. Therefore, these two proteins, which are incorporated into the transition zone independently of each other, define different domains of the transition zone. An nphp4-null mutant forms flagella with nearly normal length, ultrastructure and intraflagellar transport. When fractions from isolated wild-type and nphp4 flagella were compared, few differences were observed between the axonemes, but the amounts of certain membrane proteins were greatly reduced in the mutant flagella, and cellular housekeeping proteins >50 kDa were no longer excluded from mutant flagella. Therefore, NPHP4 functions at the transition zone as an essential part of a barrier that regulates both membrane and soluble protein composition of flagella. The phenotypic consequences of NPHP4 mutations in humans likely follow from protein mislocalization due to defects in the transition zone barrier.
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