Mechanistically, Pax8 expression was reduced upon METTL3 loss due to damaged m<sup>6</sup>A modification, which resulted in compromised thyroid epithelial cell polarization, differentiation and hormone synthesis.<h4>Conclusions</h4><i>Mettl3</i> functions as a key player of thyroid folliculogenesis and hormone secretion by coordinating thyrocyte polarization and differentiation progression, and its deficiency may lead to congenital hypothyroidism. The gene discussed is METTL3; the disease is congenital hypothyroidism.