Molecular pathways for learning in the single-cell Stentor coeruleus.

Area of Science:

• Cellular Biology
• Neuroscience
• Biochemistry

Background:

• The single-celled organism Stentor coeruleus displays habituation, a simple form of learning, by ceasing to contract in response to repeated mechanical stimuli.
• Understanding the molecular basis of this non-synaptic learning in Stentor can provide insights into fundamental memory mechanisms.

Purpose of the Study:

• To investigate the molecular underpinnings of memory formation and retention in Stentor coeruleus during habituation.
• To identify key proteins and signaling pathways involved in Stentor's learning process.

Main Methods:

• Treatment with protein synthesis inhibitors (cycloheximide, puromycin) to assess their effect on habituation.
• Proteomic and transcriptomic analyses to identify molecular changes during habituation and recovery.
• RNA interference (RNAi) to knock down specific genes, such as SteCoe_6763.
• Pharmacological manipulation using kinase/phosphatase inhibitors and extracellular calcium levels.

Main Results:

• Protein synthesis inhibitors accelerated habituation and prolonged memory in Stentor, unlike in metazoa.
• Proteomic and transcriptomic data implicated calcium signaling and protein phosphorylation in Stentor learning.
• Knocking down SteCoe_6763 accelerated habituation; increased extracellular calcium enhanced learning.
• Inhibitors of calcium/calmodulin-dependent kinase II (KN-93) impaired habituation, suggesting a role for this kinase.
• Habituation memory was heritable, persisting through cell division.

Conclusions:

• Cellular memory in Stentor involves modifications of mechanoreceptors via phosphorylation and calcium signaling.
• Response recovery requires new protein synthesis, while memory formation may involve post-translational modifications.
• Stentor's learning mechanisms offer a unique model for studying non-synaptic memory and its molecular basis.