Heterochronic transcription factor expression drives cone-dominant retina development in 13-lined ground squirrels

Area of Science:

• Developmental biology
• Evolutionary biology
• Neuroscience

Background:

• Mammalian retinas are typically rod-dominant, suited for low-light vision.
• Ground squirrels exhibit cone-dominant retinas, an adaptation for diurnal vision.
• The molecular basis for this retinal shift is poorly understood.

Purpose of the Study:

• To investigate the regulatory mechanisms behind cone-dominant retina development in the 13-lined ground squirrel (13LGS).
• To uncover the genetic and epigenetic factors driving the extended generation of cone photoreceptors.

Main Methods:

• Single-cell RNA sequencing (scRNA-Seq) to analyze gene expression.
• Assay for Transposase-Accessible Chromatin using sequencing (scATAC-Seq) to profile chromatin accessibility.
• Functional assays to test gene sufficiency in photoreceptor differentiation.

Main Results:

• Cone photoreceptors in 13LGS originate from both early and late-stage retinal progenitors.
• Key cone-promoting transcription factors (e.g., Onecut2, Pou2f1, Zic3) remain active in late progenitors.
• Cone differentiation factors (e.g., Thrb, Rxrg, Mef2c) are expressed precociously.
• Zic3 and Mef2c can promote cone and suppress rod fate via species-specific regulatory elements.

Conclusions:

• Developmental gene regulatory network modifications underlie cone-dominant retina formation.
• This adaptation involves a heterochronic shift in progenitor gene expression timing.
• Findings offer insights into sensory adaptation and potential cone regeneration strategies for vision disorders.