Cabp4, also known as calcium-binding protein 4, is a neuronal Ca2+-binding protein expressed in the retina and cochlea. In the retina, it is crucial for the development and maintenance of the photoreceptor synapse, participating in signal transmission from rods and cones to second-order neurons. It interacts with proteins like Unc119 at the photoreceptor synapse, suggesting a role in neurotransmitter release and synapse maintenance. Protein phosphatase 2A dephosphorylates Cabp4 in the retina, regulating its function in fine-tuning presynaptic Ca2+ signals [2,3,4].

In mouse models, introducing a human CABP4 missense mutation (p.G155D) led to an imbalance in protein expression in brain regions and an increase in the frequency of micro-excitatory post-synaptic currents in cortical pyramidal cells, suggesting its role in seizure onset [1]. In double knockout mice (Cabp4(-/-)Gnat1(-/-)), cone synaptic function was severely disrupted, with reduced outer plexiform layer thickness and photoreceptor terminals [2].

In conclusion, Cabp4 is essential for photoreceptor synapse function in the retina and may be involved in epilepsy-related processes. Mouse models, especially knockout and mutant models, have been instrumental in revealing its functions in these specific biological and disease-related contexts, providing insights into the underlying mechanisms of retinal and epilepsy-related disorders.