Genetic dissection of the hindbrain by the Gal4-UAS system in zebrafish

â—‹Kazuhide Asakawa1, Gembu Abe2, Koichi Kawakami1,2

1)Dept. of Developmental Genet., Natl. Inst. of Genet., Mishima / Shizuoka, Japan 2)SOKENDAI, Mishima, Japan

The hindbrain plays critical roles in the generation of movements. To establish structure-function relationships in the hindbrain, we have been performing a Gal4 trap screening in zebrafish and collecting transgenic lines expressing Gal4FF, a variant of the yeast transcription factor Gal4, in specific cell-types or domains of the hindbrain. Among these, we identified a line that carried the Gal4FF trap construct in the mafb gene, which encodes a transcription factor for hindbrain patterning, and expressed Gal4FF predominantly in the rhombomere (r) 5 and r6, as well as in a group of cells in r4. To disclose the roles of mafb-positive neurons in movement control, we crossed the mafb-Gal4FF fish with the UAS:tetanus neurotoxin light chain (TeTxLC) fish, which carried the TeTxLC gene downstream of the UAS (the Gal4 target site), and investigated the behavior of the offspring. In zebrafish embryos, the escape direction in response to a tactile stimulus is largely determined by a bilateral sequence of two axial muscle contractions that occurs prior to swimming (i.e. initial contralateral turn and the counter turn). We found that the mafb-Gal4FF;UAS:TeTxLC double transgenic embryo showed the initial contralateral turn with a longer duration and, in some cases, failed to perform the counter turn, resulting in an abnormal escape direction. Based on these observations, we propose that the mafb-positive neurons control the escape direction by regulating the counter turn. Efforts to further dissect mafb-positive neurons are currently in progress.