Multiple roles for Hedgehog signaling in zebrafish pituitary development

Area of Science:

• Developmental biology
• Endocrinology
• Molecular signaling

Background:

• The adenohypophysis (anterior pituitary) develops from anterior neural plate cells via inductive signaling.
• Current models propose oral ectoderm-derived Shh patterns the pituitary after placode induction.

Purpose of the Study:

• To investigate the precise timing and source of Hedgehog (Hh) signaling during pituitary development.
• To elucidate the role of Hh signaling in adenohypophysis induction and patterning.

Main Methods:

• Pharmacological inhibition of Hh signaling using cyclopamine.
• Analysis of zebrafish Hh pathway mutants (smu/smo, yot/gli2, dtr/gli1).
• Gene expression analysis (ptc1, nk2.2, lim3, Prolactin, Somatolactin).

Main Results:

• Hh signaling is required between 10-15 hours of development for zebrafish adenohypophysis induction, originating from neural ectoderm.
• Blocking Hh signaling later (15-20 hours) disrupts patterning genes and hormone expression.
• Overexpression of Shh leads to expanded adenohypophysis and increased hormone-secreting cells.
• Mutations in Hh pathway genes cause a spectrum of pituitary defects, from complete loss to subtle patterning issues.

Conclusions:

• Hh signaling from neural ectoderm is essential for both the induction and functional patterning of the vertebrate pituitary gland.
• These findings reveal multiple roles for Hh signaling in pituitary formation.
• Defects observed in zebrafish mutants may correlate with human congenital disorders involving Hh signaling.