Serine/threonine protein kinase that plays a role in a variety of different signaling pathways. Involved in early neuronal development; required for cell cycle exit and differentiation of primary neurons. May be required for the formation of dendritic spines and excitatory synapses (By similarity). Cooperates synergistically with mturn to promote primary neural differentiation within the neural plate. Involved in the cement gland formation. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Expressed from the egg to the tailbud stage embryo. Expressed at late gastrula/early neurula stages of development within the posterior neuroectoderm. Expressed in primary neurons as they differentiate in the neural plate at stage 14.5 in the area of the trigeminal placodes. Expressed in the cement gland at stage 17. Expressed during later phases in the notochord in tissues derived from dorsolateral cranial placodes. Up-regulated by the proneural transcription factors Neurog2, Neurod1 and Ebf3. Down-regulated by the Notch pathway. Morpholino knockdown of the protein causes inhibition of neuronal differentiation and an accumulation of neuronal progenitor cells in the anterior neural plate. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. STE20 subfamily.