Monopolar protrusive activity: A new morphogenic cell behavior in the neural plate dependent on vertical interactions with the mesoderm in Xenopus

We compared the type and patterning of morphogenic cell behaviors driving c onvergent extension of the Xenopus neural plate in the presence and absence of persistent vertical signals from the mesoderm by videorecording explant s of deep neural tissue with involuted mesoderm attached and of deep neural tissue alone. In deep neural-over-mesoderm explants, neural plate cells ex press monopolar medially directed motility and notoplate cells express rand omly oriented motility, two new morphogenic cell behaviors. In contrast, in deep neural explants (without notoplate), all cells express bipolar mediol ateral cell motility. Deep neural-over-mesoderm and deep neural explants al so differ in degree of neighbor exchange during mediolateral cell intercala tion. In deep neural-over-mesoderm explants, cells intercalate conservative ly, whereas in deep neural explants cells intercalate more promiscuously. L ast, in both deep neural-over-mesoderm and deep neural explants, morphogeni c cell behaviors differentiate in an anterior-to-posterior and lateral-to-m edial progression. However, in deep neural-over-mesoderm explants, morphoge nic behaviors first differentiate in intervals along the anteroposterior ax is, whereas in deep neural explants, morphogenic behaviors differentiate co ntinuously from the anterior end of the tissue posteriorly. These results d escribe new morphogenic cell behaviors driving neural convergent extension and also define roles for signals from the mesoderm, up to and beyond late gastrulation, in patterning these cell behaviors. (C) 2000 Academic Press.