NumbL is essential for Xenopus primary neurogenesis

Background: Members of the vertebrate Numb family of cell fate determinants serve multiple functions throughout early embryogenesis, including an essential role in the development of the nervous system. The Numb proteins interact with various partner proteins and correspondingly participate in multiple cellular activities, including inhibition of the Notch pathway. Results: Here, we describe the expression characteristics of Numb and Numblike (NumbL) during Xenopus development and characterize the function of NumbL during primary neurogenesis. NumbL, in contrast to Numb, is expressed in the territories of primary neurogenesis and is positively regulated by the Neurogenin family of proneural transcription factors. Knockdown of NumbL afforded a complete loss of primary neurons and did not lead to an increase in Notch signaling in the open neural plate. Furthermore, we provide evidence that interaction of NumbL with the AP-2 complex is required for NumbL function during primary neurogenesis. Conclusion: We demonstrate an essential role of NumbL during Xenopus primary neurogenesis and provide evidence for a Notch-independent function of NumbL in this context.