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Chlamydomonas protein kinase MAK phosphorylates FAP256/CEP104 and regulates axonemal microtubule assembly

Yi Zhang1, Xinjia Yang1, Junmin Pan1,2

  • 1MOE Key Laboratory of Protein Sciences, State Key Laboratory of Complex, Severe, and Rare Diseases, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China.

Proceedings of the National Academy of Sciences of the United States of America
|November 13, 2025
PubMed

Insights

Chlamydomonas MAK (CrMAK) regulates ciliary microtubule assembly by phosphorylating FAP256/CEP104. This kinase activity is crucial for forming cilia, as its loss results in aciliated cells, revealing a key mechanism in axonemal microtubule organization.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Organelle Biology

Background:

  • Cilia are essential organelles with axonemal microtubules, assembled via intraflagellar transport and diffusion.
  • The precise regulation and control mechanisms governing axonemal microtubule assembly remain largely unclear.
  • Understanding these processes is vital for comprehending ciliary function and associated diseases.

Purpose of the Study:

  • To elucidate the regulatory mechanism controlling axonemal microtubule assembly in Chlamydomonas.
  • To identify key proteins involved in the spatial and temporal regulation of ciliary growth.
  • To investigate the role of Chlamydomonas MAK (CrMAK) in cilia formation.

Main Methods:

  • Biochemical assays to determine CrMAK kinase activity and substrate interaction.
  • Immunofluorescence microscopy to localize CrMAK and FAP256/CEP104 within cilia.
  • Genetic analysis of CrMAK loss-of-function mutants to assess ciliary assembly defects.

Main Results:

  • CrMAK, a homolog of mammalian ICK/MAK, regulates axonemal microtubule assembly through phosphorylation of FAP256/CEP104.
  • CrMAK localizes to the axoneme and is enriched at the ciliary tip during active assembly, acting downstream of a length-regulatory complex.
  • Loss of CrMAK or its kinase activity leads to complete loss of cilia (aciliated cells), and dephosphorylation of FAP256/CEP104 impairs ciliary assembly.

Conclusions:

  • CrMAK is a critical kinase that governs axonemal microtubule assembly by phosphorylating FAP256/CEP104.
  • This phosphorylation event is essential for proper ciliary structure and function.
  • The study reveals a novel molecular pathway controlling the formation of axonemal microtubules, crucial for ciliary biogenesis.
Keywords:
CEP104/FAP256MAK/ICKRCKsaxonemal microtubulesciliogenesis

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