Do thyroid hormones function in insects?

Area of Science:

• Insect endocrinology
• Molecular biology
• Comparative physiology

Background:

• Phenoxy-phenyl compounds and thyroxine mimic juvenile hormone III (JH III) in locust follicle cells.
• 3,3',5-triiodothyronine (T3) is as effective as JH III and shares its receptor and pathway.
• Other thyroxine derivatives show varying activities.

Purpose of the Study:

• To investigate the activity of different thyroxine derivatives on locust follicle cells.
• To elucidate the mechanism of T3 uptake and action.
• To explore the role of thyroid hormones in locust reproduction.

Main Methods:

• In vitro exposure of locust follicles to rhodamine-conjugated T3.
• Inhibition studies using cycloheximide, low temperature, JH I, and specific antiserum.
• Deiodinase inhibition assays with 6-n-propyl-2-thiouracil and aurothioglucose.
• Measurement of T3 and thyroxine immunoreactivity in locust hemolymph and food.

Main Results:

• T3 and T2 show significant activity, with T2 being more potent than JH III.
• T3 enters follicle cells via receptor-mediated endocytosis and is potentially converted to a more active form.
• T3 action is inhibited by deiodinase inhibitors and shows time-dependent activity, unlike T2.
• Thyroid hormones are present in locust hemolymph and food, with titers varying during the reproductive cycle.

Conclusions:

• Thyroid hormones, particularly T3, are actively taken up by locust follicle cells and influence their function.
• Thyroid hormones may act as signaling molecules in locust reproduction, potentially ingested and utilized by the insects.
• The findings suggest a novel role for thyroid hormones in insect endocrinology, distinct from their known roles in vertebrates.