Transcriptional remodeling of local thyroid hormone metabolism is associated with feather growth termination in chicken wing feathers.

Feather elongation is sustained by continuous cell proliferation within the feather follicle; however, the molecular mechanisms responsible for feather growth termination remain poorly understood. In this study, we investigated molecular changes associated with feather growth termination by comparing two chicken wing feather types with contrasting growth characteristics: primary wing feathers and primary coverts. Histological and bromodeoxyuridine incorporation analyses demonstrated that primary wing feathers remained in an active growth phase, whereas primary coverts exhibited pulp regression, reduced cell proliferation, and characteristics of growth termination. Gene expression analyses showed that primary coverts exhibited reduced expression of prolactin receptor (PRLR), type 2 iodothyronine deiodinase (DIO2), and insulin-like growth factor 2 (IGF2), together with marked induction of the thyroid hormone (TH)-inactivating enzyme type 3 iodothyronine deiodinase (DIO3). In contrast, primary wing feathers exhibited relatively higher expression of PRLR, DIO2, and IGF2 than primary coverts, while maintaining consistently low DIO3 expression. Reporter assays showed increased IGF2 promoter activity following triiodothyronine (T3) treatment in all three independent experiments, although the increase did not reach statistical significance. Thus, the reporter assay provides only tentative support for T3 responsiveness of the IGF2 promoter, consistent with our previous in vivo and primary-culture findings showing T3-dependent increases in IGF2 expression. These coordinated transcriptional changes are consistent with remodeling of local TH metabolism during the transition from active feather growth to growth termination. While local TH concentrations and direct deiodinase activities remain to be quantified, and the causal relationship between PRL/PRLR signaling and DIO3 induction remains unresolved, this study provides a molecular framework for understanding how local endocrine regulation translates systemic hormonal signals into feather type-specific growth responses during avian feather development.