Who sells USDC?

Could you elaborate on who are the primary entities that sell USDC, a stablecoin designed to maintain a value equivalent to the US dollar? Are these sellers primarily centralized exchanges, decentralized finance (DeFi) platforms, or both? How do these sellers ensure that each USDC token is backed by a corresponding US dollar held in reserve, thus maintaining its stability and trustworthiness? Furthermore, are there any regulatory considerations or restrictions that govern the sale of USDC and the entities involved in its issuance and distribution?