Developing a sense of scents: plasticity in olfactory placode formation

Area of Science:

• Developmental biology
• Evolutionary biology
• Neuroscience

Background:

• Vertebrate sense organs primarily develop from sensory placodes, which are traditionally grouped by shared traits.
• This grouping often overlooks the unique developmental and evolutionary characteristics of individual placodes.

Purpose of the Study:

• To review olfactory placode development, including its origin, cell movements, derivatives, and developmental plasticity.
• To propose a revised terminology and conceptual model for anterior placodes by comparing olfactory, adenohypophyseal, and lens placodes.

Main Methods:

• Review of existing literature on sensory placode development.
• Comparative analysis of olfactory, adenohypophyseal, and lens placodes.
• Focus on gene expression, cell movements, and morphological changes.

Main Results:

• Olfactory placode development involves specific origins and cell movements, with notable developmental plasticity.
• Comparison suggests the peripheral olfactory sensory system should be termed neural ectoderm due to shared gene expression and differentiation with the olfactory bulb.
• A revised model groups anterior placodes with their central nervous system targets, highlighting shared patterning mechanisms.

Conclusions:

• Revision of terminology for anterior placodes is needed, recognizing their neural ectoderm nature and functional integration with the CNS.
• Understanding sensory systems requires analyzing them as functional units with their CNS targets, not in isolation.
• This integrated approach will advance our comprehension of sensory structure evolution.