Secretion by parafollicular cells beginning at birth: ultrastructural evidence from developing canine thyroid

Area of Science:

• Veterinary Histology
• Cell Biology
• Endocrinology

Background:

• Canine parafollicular cells, also known as C-cells, are crucial for thyroid hormone regulation.
• Understanding their developmental secretory activity is key to comprehending thyroid function in neonates.

Purpose of the Study:

• To investigate the ultrastructure of developing canine parafollicular cells.
• To test the hypothesis that parafollicular cell secretion is minimal before birth and highly active around birth.

Main Methods:

• Ultrastructural examination of developing canine parafollicular cells.
• Analysis of secretory granule accumulation and exocytosis events.
• Observation of intracisternal granule formation within the rough endoplasmic reticulum.

Main Results:

• Parafollicular cells accumulate secretory granules during fetal development.
• Evidence of exocytosis is scarce before birth but abundant at and after birth.
• Intracisternal granules appear in the rough endoplasmic reticulum preceding exocytosis.

Conclusions:

• Canine parafollicular cells become actively secretory around the time of birth.
• Secretory activity is significantly higher during the neonatal period compared to fetal or adult life.
• These findings highlight a critical developmental shift in parafollicular cell function linked to birth.