Abstract
Thyroid hormones (THs) are important metabolic, growth, and differentiation regulators. As amphipathic ligands, TH access to target cells is limited by specific transporters. MCT8 is a high-affinity, bidirectional transporter of thyroid hormone. However, the role of Mct8 during adrenal development is not well understood. The adrenal cortex is a hormone-sensitive organ that experiences dramatic postnatal remodeling in rodents, with the transient X-zone regressing in males and persisting in females. This study aimed to characterize the spatial and temporal expression of Mct8 in development and determine whether post-weaning exogenous T3 alters this expression. Male and female wild-type (WT) and Mct8 knockout (Mct8KO) adrenal glands were harvested at postnatal days (P) 7, 14, 21, and 35. Mct8 mRNA abundance was determined by qRT-PCR. Hematoxylin staining was used to visualize adrenal morphology. Spatial localization of Mct8 expression was confirmed using the LacZ reporter of the Mct8 locus. Additional male and female mice were treated with T3 from P21-P35 to determine the effect of excess thyroid hormone on adrenal structure and Mct8 levels. The adrenal expression of Mct8 followed a biphasic developmental trajectory, with an initial peak in expression at P7, a gradual decrease in expression through P21, and a second, less substantial increase by P35. LacZ analysis revealed Mct8 promoter activity was spatially restricted to the inner cortex and medulla, and this persisted in females but was lost in males after X-zone regression. The persistence of the X-zone in T3-treated mice, regardless of genotype, further supports the idea that thyroid hormone signaling can influence adrenal structure through both Mct8-dependent and independent pathways, potentially involving efflux mechanisms. However, additional functional studies are needed to confirm these mechanisms.
Advisor
David Sharlin
Committee Member
Allison Land
Committee Member
Keenan Hartert
Date of Degree
2025
Language
english
Document Type
Thesis
Degree
Master of Science (MS)
Program of Study
Biology
Department
Biological Sciences
College
Science, Engineering and Technology
Recommended Citation
Youngberg, K. K. (2025). Developmental expression of thyroid hormone transporter Mct8 in the murine adrenal gland [Master’s thesis, Minnesota State University, Mankato]. Cornerstone: A Collection of Scholarly and Creative Works for Minnesota State University, Mankato. https://cornerstone.lib.mnsu.edu/etds/1566/
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Included in
Endocrine System Commons, Hormones, Hormone Substitutes, and Hormone Antagonists Commons
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