Consider Pure Mapping Class Group of the sphere $\mathbb{S}^2$ with finitely many marked points $P$, i.e. $$ \mathrm{PMCG}(\mathbb{S}^2, P) = \{\varphi \in \mathrm{Homeo}^+(\mathbb{S}^2) : \varphi|_{P} = \mathrm{id}\}/\sim, $$ where $\mathrm{Homeo}^+(\mathbb{S}^2)$ is a group of all orientation-preserving homeomorphisms on $\mathbb{S}^2$ and $\sim$ is isotopy realtive $P$.
My question is about Dehn twists generating this group. It seems that it should be finitely generated by Dehn twists, as it usually happens, but I don't have neither proof nor reference...
Also, if it is true, is there any particular set of closed simple curves such that Dehn twists about them generate $\mathrm{PMCG}(\mathbb{S}^2, P)$, like, for example, Lickorish curves provide generating set for $\mathrm{MCG}(S_g)$?
I can imagine, for example, that one can take a tree on $\mathbb{S^2}$ with vertex set $P$, take curves closely around each edge, and this construction will provide desirable set of curves...