Thyroid hormone-induced cell death in sea urchin metamorphic development

Area of Science:

• Developmental Biology
• Endocrinology
• Marine Biology

Background:

• Thyroid hormones (THs) are crucial for regulating metabolism, homeostasis, and developmental transitions in various organisms.
• THs influence metamorphic processes in both vertebrates and invertebrates, including sea urchin larval development.
• Sea urchin larvae treated with thyroxine (T4) show accelerated juvenile structure formation and reduced larval arm length, but the underlying mechanisms are unclear.

Purpose of the Study:

• To investigate the role of programmed cell death (PCD) in thyroid hormone-induced larval arm reduction in sea urchin larvae.
• To determine the effects of different THs (T4, T3, rT3, Tetrac) on larval arm retraction and PCD.
• To compare the impact of TH treatment on PCD before and after the critical invagination stage of larval development.

Main Methods:

• Larval arm retraction was measured in response to various TH treatments in the sea urchin Strongylocentrotus purpuratus.
• Cell death was assessed using TUNEL, YO-PRO-1 staining, and caspase-3 activity assays.
• PCD levels were compared between pre-ingression and post-ingression larvae following TH exposure.

Main Results:

• T4 treatment induced the most significant reduction in larval arm length.
• A notable increase in PCD was observed in response to T4, T3, and Tetrac, but only in post-ingression larvae.
• No significant increase in PCD was detected in pre-ingression larvae treated with THs.

Conclusions:

• Thyroid hormones differentially regulate sea urchin larval development through PCD, particularly in post-ingression stages.
• PCD, in conjunction with cell proliferation, plays a significant role in mediating TH-induced developmental changes during sea urchin metamorphosis.
• These findings elucidate a key cellular mechanism by which THs control developmental transitions in marine invertebrates.