Segmentation of the central nervous system in leech

Area of Science:

• Developmental biology
• Neuroscience
• Cell biology

Background:

• The leech central nervous system (CNS) exhibits segmental iteration derived from embryonic lineages.
• Segmentation involves transverse fissures subdividing N lineage founder cells into ganglionic primordia.

Purpose of the Study:

• To investigate the relationship between N lineage cells and surrounding tissues during CNS segmentation.
• To determine the autonomous mechanisms driving fissure formation in the leech CNS.

Main Methods:

• Differential cell labeling using intracellular lineage tracers and antibodies.
• Cell ablation experiments to assess the necessity of external contacts.
• Biochemical arrest to observe cell behavior differences.

Main Results:

• Lateral ectodermal and muscle cell contacts are not required for initiating fissure formation.
• Ablation of nf primary blast cells can cause hemi-ganglia fusion; ns primary blast cell ablation leads to blast cell slippage.
• Distinct cell behaviors observed in biochemically arrested nf and ns primary blast cells suggest intrinsic differences.

Conclusions:

• Segmentation of the leech CNS appears to occur autonomously within the N lineage.
• Differences in cell adhesion and/or motility between alternating nf and ns primary blast cells are proposed as the basis for segmentation.
• These segmentation processes precede the expression of the leech engrailed-class gene.