Genetic Mechanism That Defines the Characteristic Neurogenesis Patterns in the Neural Plate Using Hes/her Genes During Early Vertebrate Development.

In the early zebrafish neural plate, proneural cluster domains are defined by surrounding neural progenitor pools (NPPs), generating primary neurogenesis patterns. In each NPP, several Notch-independent Hes/her-type genes are expressed in distinct manners. Previous knockdown (KD) experiments induced ectopic neurogenesis in NPPs where only the targeted her genes were expressed, with other her genes absent, suggesting cooperative functions of Notch-independent her genes. In this study, to overcome the inherent limitations in KD approaches, we knocked out (KO) three her genes, her3, her5, and her11, using genome editing techniques. The resulting mutants exhibited ectopic neurogenesis patterns at the end of gastrulation, similar to those observed in KD experiments. KOs of her5 and her11 induced ectopic neurogenesis around the midbrain-hindbrain boundary, whereas her3 KO led to ectopic neurogenesis in rhombomere 1/2 and r4. In these cases, the expression of other Notch-independent her genes was not affected, except for her11, whose expression depended on her5. Analyses of compound mutants revealed that their phenotypes were essentially the sum of those of individual her mutants, indicating independent suppression of neurogenesis by Notch-independent her genes. In conclusion, different Notch-independent her genes collectively define the characteristic pattern of primary neurogenesis in the neural plate.