Left-right cortical interactions drive intracellular pattern formation in the ciliate Tetrahymena

Area of Science:

• Cell Biology
• Developmental Biology
• Genetics

Background:

• Cortical organelles in ciliates, including ciliary arrays, are precisely positioned along anterior-posterior and circumferential axes.
• Circumferential patterning, responsible for left-right asymmetry, is poorly understood.
• The model ciliate Tetrahymena typically forms a single oral apparatus.

Purpose of the Study:

• To investigate the mechanism of circumferential patterning and left-right asymmetry in ciliates.
• To identify genes involved in the positioning of cortical organelles.
• To understand the role of HPO1 in oral apparatus development.

Main Methods:

• Comparative next-generation sequencing to identify the HPO1 gene.
• Analysis of hpo1 mutant phenotypes, including multiple oral apparatus formation.
• Immunofluorescence to visualize Hpo1 protein localization and gradient formation.
• Genetic interaction studies with Bcd1.

Main Results:

• The hypoangular 1 (hpo1) gene encodes an ARMC9-like protein essential for circumferential patterning.
• Hpo1 forms a bilateral concentration gradient, with high levels on the right, excluding oral development from this side.
• Hpo1 interacts with Bcd1, a left-side enriched factor, and their combined loss is lethal and disrupts oral apparatus formation.
• Loss of Hpo1 leads to ectopic oral apparatus formation on the ventral surface.

Conclusions:

• Circumferential patterning in ciliates involves gradient-forming factors concentrated on either the right or left cortex.
• Interactions between cortical sides create boundary effects that position and shape developing organelles.
• HPO1 and Bcd1 play critical roles in establishing left-right asymmetry and proper organelle development in ciliates.