Thyroid hormones reversibly inhibit metamorphic development in ophiuroid larvae

Area of Science:

• Endocrinology
• Marine Biology
• Developmental Biology

Background:

• Thyroid hormones (THs) are known to regulate metamorphosis in chordates.
• Evidence suggests THs also influence metamorphosis in invertebrates like echinoderms.
• Information on THs' role in ophiuroid (brittle star) metamorphic development is lacking.

Purpose of the Study:

• Investigate the role of thyroid hormones in the metamorphic development of the brittle star Ophiopholis aculeata.
• Determine the effects of THs and TH synthesis inhibition on brittle star metamorphosis and settlement.

Main Methods:

• Exposure of Ophiopholis aculeata larvae to thyroid hormones (T4) and thiourea (a TH synthesis inhibitor).
• Observation of developmental timing, metamorphosis, and settlement.
• Experimental manipulation of starvation conditions to assess its interaction with TH signaling.

Main Results:

• Thyroid hormones (T4) were found to reversibly inhibit metamorphic development and settlement in O. aculeata.
• Inhibition of TH synthesis using thiourea accelerated metamorphic development.
• Starvation accelerated juvenile morphogenesis and settlement, and also blocked the effect of thiourea, suggesting a link between food availability and TH function.

Conclusions:

• Thyroid hormone signaling plays a functional role in ophiuroid metamorphic development.
• THs may delay metamorphosis in O. aculeata, potentially in response to high food availability.
• These findings underscore the conserved and central role of endocrine signaling in regulating metamorphosis across diverse invertebrate taxa.