(A) Dendrites of cultured hippocampal neurons (11DIV) expressing EGFP alone (mock) or EGFP and the indicated proteins. Branches of two neurons are shown. Neurl1-F: Neurons expressing Neurl1-F (Neurl1-Flag; Neurl1 overexpression). Neurl1Rm-F: mutant Neurl1-F. (B) Averaged density of dendritic protrusions + SEM [mock: 12 neurons, 2 branches/neuron (12×2×50μm); all the others: 8 neurons, 2 branches/neuron (8×2×50μm)]. The spine density of neurons overexpressing Neurl1, Neurl1+CPEB3, and CPEB3-UbKO were significantly increased compared to mock (CPEB3+Neurl1-F: p=0.041; all the others: p<0.0001). The difference between neurons overexpressing CPEB3 and neurons overexpressing CPEB3+Neurl1 was highly significant (p<0.0001). In the rest of the neurons, the density of protrusions was similar (p=0.6165), and significantly lower than mock (p<0.0003). See also Table S4 and Figure S7.