Epigenetic rules for expression of cell adhesion molecules during morphogenesis.

Area of Science:

• Developmental Biology
• Cell Biology
• Molecular Biology

Background:

• Cell adhesion molecules (CAMs) are crucial for cell-to-cell connections and cell movement during embryonic development.
• CAMs regulate morphogenesis by linking epithelia and condensing mesenchyme.
• Ordered sequences of CAM expression are observed on cell surfaces during vertebrate development.

Purpose of the Study:

• To review evidence on the sequential expression of CAMs during embryonic induction.
• To elucidate the modulation rules governing CAM expression starting from early gastrulation.
• To explore the role of CAMs in establishing borders between cell collectives and regulating morphogenesis.

Main Methods:

• Review of existing evidence on CAM expression patterns during embryonic development.
• Analysis of CAM modulation rules in different embryonic tissues (mesenchyme and epithelia).
• Observation of CAM expression in the context of complex structure morphogenesis (e.g., feather, optic placode).

Main Results:

• Sequential CAM expression follows specific rules discernible from early gastrulation.
• Mesenchymal conversions utilize N-CAM with prevalence changes (N----0----N rule).
• Epithelia exhibit modulation between simultaneous N-CAM/L-CAM expression and single CAM expression (rule II).
• Proximity of cell collectives obeying different rules (I and II) at induction sites.
• Recursive application of CAM expression rules in complex structure formation.

Conclusions:

• Epigenetic rules governing CAM expression are conserved and precede the regulation of intracellular proteins.
• CAM expression is a fundamental mechanism for establishing tissue form through mechanochemical regulation.
• These rules are critical for regulating cell division, movement, and death during development.