# Defective I1 dynein in Chlamydomonas axonemes is epistatic to the RII-binding domain function of radial spoke protein 3 (RSP3) in the regulation of ciliary motility

## TL;DR

This study shows that a mutation in I1 dynein overrides the effects of a RSP3 mutation in regulating ciliary movement in Chlamydomonas.

## Contribution

The paper demonstrates an epistatic relationship between I1 dynein and RSP3 in ciliary motility regulation.

## Key findings

- The ida1 mutation produces an ida1-like phenotype when combined with the 388 mutation.
- I1 dynein is downstream of RSP3's RII-binding domain in a signaling pathway.
- This supports a hierarchical signaling model for ciliary motility regulation.

## Abstract

In
Chlamydomonas
, the central pair (CP) and radial spoke (RS) complexes in the axoneme are key regulators of ciliary motility. Radial spoke protein 3 (RSP3) is an A-kinase anchoring protein (AKAP), and mutation of the RII-binding domain (
388
) results in specific ciliary motility defects. When combined with
ida1
, a mutant defective in the 1α-dynein heavy chain required for assembly of the I1 dynein complex, the phenotype of the resulting
388; ida1
double mutant is
ida1
-like, not
388
-like; thus,
ida1
is epistatic to
388
. These results support I1 dynein being downstream of the RSP3 RII-binding domain function in a signaling pathway that regulates
Chlamydomonas
ciliary motility.