Who can issue an ETN?

Could you please elaborate on the entities that are capable of issuing an Exchange Traded Note (ETN)? Are there specific requirements or qualifications that these issuers must meet in order to offer ETNs to investors? Furthermore, how does the process of issuing an ETN differ from that of other financial instruments, and what role do regulators play in overseeing the issuance of ETNs? Additionally, are there any limitations or restrictions on who can invest in ETNs, and how do these factors influence the overall market for ETNs?