Yes it's "just releasing some chemicals", vast and complex regulatory networks of chemicals. They then did RNAseq experiments (measures which genes are transcr

Yes it's "just releasing some chemicals", vast and complex regulatory networks of chemicals. They then did RNAseq experiments (measures which genes are transcribed [are active]) in the two legs separately and looked for statistically significant differences (which genes are active in the injected leg but not the other one?) and found: "enrichment of several pathways related to stress and immune responses in the left cartilage.In particular, we found several stress-related transcripts that shared a similar left–right pattern of expression within each embryo"