A Zdhhc22-mCherry BAC transgenic mouse line reveals neuronal expression dynamics in the developing and adult CNS.

The DHHC palmitoyltransferase Zdhhc22 is known to play a role in neuronal differentiation, synaptic regulation, and brain development. While transcriptomic data hint at region-specific expression, its exact spatiotemporal and cell-type distribution in the mammalian brain is unclear. For this purpose, we generated a bacterial artificial chromosome (BAC) transgenic mouse line that expresses the mCherry fluorescent reporter driven by the Zdhhc22 promoter. We then analyzed Zdhhc22 expression from embryonic day 13.5 (E13.5) through adulthood. mCherry fluorescence was detected in many brain regions, including the cortex, thalamus, midbrain, piriform cortex, and brainstem. Interestingly, a dynamic developmental gene expression pattern was observed: Zdhhc22 expression was initially restricted to the cortical marginal zone between E13.5 and E15.5, it then expanded into deeper cortical layers by E17.5, and at postnatal day 0 (P0), it persisted in deep layers while also appearing in a new subset of cortical plate neurons. Through co-immunostaining, mCherry expression was found to be predominantly neuronal, showing strong co-localization with NeuN and minimal overlap with glial cells. In the cortex, Zdhhc22 expression showed no co-localization with CUX1 or CTIP2 but did partially overlap with FOG2, a marker for layer VI pyramidal neurons. A particularly striking finding was that nearly all marginal zone mCherry-positive cells co-expressed RELN, identifying them as Cajal-Retzius cells. This neuronal specificity was maintained in the adult brain. Our findings validate the Zdhhc22-mCherry BAC transgenic line as a faithful model of endogenous Zdhhc22 expression, providing invaluable insight into its cellular specificity and a powerful new tool for future research.