Src signaling in a low-complexity unicellular kinome.

Area of Science:

• Cell Biology
• Evolutionary Biology
• Biochemistry

Background:

• Creolimax fragrantissima belongs to the early-branching ichthyosporean lineage, a basal holozoan group.
• Its kinome is significantly reduced compared to metazoans, featuring only one non-receptor tyrosine kinase, CfrSrc.
• Unlike animal Src kinases, CfrSrc lacks a C-terminal inhibitory phosphorylation site due to the absence of Csk kinase.

Purpose of the Study:

• To investigate the regulatory mechanism of CfrSrc in Creolimax, given the absence of Csk.
• To identify potential phosphatases involved in the negative regulation of CfrSrc.
• To understand the adaptation of tyrosine kinase signaling in basal holozoans.

Main Methods:

• In vitro and in vivo assays were used to test the activity of CfrSrc and CfrPTP-3.
• Transcript levels of CfrSrc and several tyrosine-specific phosphatases (PTPs) were quantified across different life cycle stages.

Main Results:

• CfrPTP-3, a tyrosine-specific phosphatase, was identified as a suppressor of CfrSrc activity.
• Transcript levels of CfrPTP-3 and other PTPs are notably higher than CfrSrc in motile and sessile stages.
• This suggests a novel regulatory pathway for tyrosine kinase signaling in Creolimax.

Conclusions:

• Creolimax employs a tyrosine phosphatase (CfrPTP-3) to negatively regulate its sole tyrosine kinase (CfrSrc).
• This represents a potential co-option of a pre-existing PTP for Src regulation in a reduced kinome context.
• Creolimax serves as a valuable model for studying the evolution of tyrosine kinase signaling and its regulation.