Ddc, also known as aromatic-l-amino-acid decarboxylase (AADC), is an enzyme that converts L-Dopa to dopamine [2]. Dopamine is a significant signaling molecule in the neuroendocrine system [3]. Ddc is involved in the dopamine-synthesizing pathway, and dopamine's functions are far-reaching in the nervous system, influencing processes like movement, mood, and reward-based learning. Genetic models can be valuable in studying Ddc to understand its precise role in these processes.

In Parkinson's disease (PD) research, although tyrosine hydroxylase (TH) expression is reduced in dopaminergic neurons in the substantia nigra pars compacta (SNpc), Ddc expression is relatively spared. Activation of DDC-positive neurons in the SNpc of an A53T-mutated alpha-synuclein overexpression model of PD, achieved through DDC-promoter-driven chemogenetic means, significantly alleviated parkinsonian motor symptoms and rescued nigrostriatal TH expression. This indicates that dormant dopaminergic neurons expressing Ddc could be a potential therapeutic target for PD [1]. Also, in crayfish (Procambarus clarkii), knockdown of Pc-ddc led to changes in the expression of genes related to the Toll (TLRs) signaling pathway and ROS-related antioxidant enzyme genes after bacterial challenge, suggesting that Ddc plays important mediating roles in the neuroendocrine immune (NEI) system of crayfish [3].

In conclusion, Ddc is crucial for dopamine synthesis, playing significant roles in the neuroendocrine system. In the context of PD, it offers a potential therapeutic target, as seen from the mouse model studies. In addition, its role in the innate immune reactions of crayfish shows its diverse functions across species. Research on Ddc using genetic models helps to understand its function in specific biological processes and disease conditions, providing insights for potential therapeutic strategies.