Fig 1: Regeneration of intra‐splenic transplanted thyroid tissue. A) PAS staining of a whole‐spleen section showing the regenerated thyroid tissue (ST) in the spleen 16 weeks post‐transplantation. The black dashed curves (‐ – ‐) outline the ST tissue. B) H&E staining analysis of the intra‐splenic regenerated thyroid tissue at weeks 2, 4, 8, 12, and 16. Upper panels show the thyroid tissue (ST) within the spleen, while lower panels provide detailed views of the regenerated thyroid follicles. The black dashed curves (‐ – ‐) outline the ST tissue. C) Weekly monitoring of the number of thyroid follicular epithelial cells in the intra‐splenic thyroid tissue for 16 consecutive weeks, with adult thyroid as control. The value for week 0 represents the calculated number of cells in the transplanted tissue blocks. n = 5 biological replicates. D) Weekly assessment of the number of thyroid follicles in the intrasplenic thyroid tissue for 16 weeks, with adult thyroid as control. The value for week 0 represents the calculated number of follicles in the transplanted tissue blocks. n = 3 biological replicates. E) Measurement of the volume of thyroid follicles, with adult thyroid as control. n = 40. F) Determination of the height of thyroid follicular epithelial cells, with adult thyroid as control. n = 50. G) Calculation of the thyroid follicular activation index, with adult thyroid as control. n = 50. H) Evaluation of proliferative activity through PCNA immunofluorescence staining (co‐staining with GFP to identify thyroid tissue in GFP‐transgenic mice). I) Comparison of IGF‐1 levels in spleen, muscle, and subcutis. n = 5 biological replicates. J) The proliferative activity of thyroid tissue blocks after co‐incubation with spleen homogenate (SH) was determined by EdU staining. K) Western blotting analysis of the Cyclin D1 expression in thyroid tissues after co‐incubation with spleen homogenate (SH), IGF‐1, and the inhibitor of the IGF‐1 receptor (picropodophyllin, AXL1717). L) Immunofluorescence staining of Cyclin D1 expression in the intra‐splenic regenerated thyroid tissue at weeks 2 and 16. Data presented as means ± SEM. Statistical analyses were performed using one‐way ANOVA followed by Tukey's multiple comparisons tests for (I). PAS, periodic acid‐Schiff; ST, intra‐splenic thyroid; SH, spleen homogenate; EdU, 5‐ethynyl‐2′‐deoxyuridine; ANOVA, analysis of variance.