** Drug developer Dyne Therapeutics' DYN.O shares slide 14% to $19.09

** DYN late Monday kicked off public offering of $300 million worth of shares

** Stock closed up 9.5% on Monday after positive data for its muscle wasting drug

** Morgan Stanley, Jefferies, Stifel and Guggenheim Securities are joint book-running managers for offering

** Proceeds will be used to repay debt and advance the development of its pipeline, among other purposes

** DYN has 142.6 million outstanding shares as of September 30, according to its prospectus

** 13 of 16 brokerages rate the stock "buy" or higher and three "hold"; median PT $38 - data compiled by LSEG

** As of last close, DYN stock was down 5.8% YTD

(Reporting by Arasu Kannagi Basil in Bengaluru)

((ArasuKannagi.Basil@thomsonreuters.com))