From Del Rey:
Ponta is a Labrador retriever puppy, the Koizumi family’s pet. She’s full of energy and usually up to some kind of mischief. But when Grandpa Koizumi, an amateur inventor, creates the Guru Guru Bone, Ponta’s curiosity causes trouble. She nibbles the bone - and turns into a human girl! Now Ponta lives two lives: one canine and one human!
Winner of the Kodansha Manga Award for Shoujo 2000.