○Kazuhide Asakawa1,2,Gembu Abe1,Koichi Kawakami1,2
Genetic dissection of the hindbrain by the Gal4-UAS system in zebrafish
In vertebrates, the hindbrain plays critical roles in the generation of movements, such as locomotion and postural control.
To establish structure-function relationships in the hindbrain, we have been performing a screen for transgenic zebrafish line expressing Gal4FF, a variant of the yeast transcription factor Gal4,
in the hindbrain by the Tol2 transposon-mediated Gal4 trap approaches. From these screens, we have isolated a transgenic line (g35) that showed a predominant Gal4FF expression in the rhombomere (r, segmental unit of the hindbrain) 5 and r6.
To inactivate the Gal4FF-expressing hindbrain neurons in the g35 line, we crossed the g35 fish with the UAS:tetanus neurotoxin light chain (TeTxLC) fish, which carried the TeTxLC gene downstream of the UAS (the Gal4 target site).
When a tactile stimulus is given, zebrafish embryos escape away from the stimulus by swimming. In this behavior, the direction of the escape is largely determined by a bilateral sequence of two axial muscle contractions that occurs prior to swimming (i.e. initial contralateral turn and the following counter turn).
We found that g35;UAS:TeTxLC double transgenic embryos frequently showed the prolonged initial contralateral turns, and as a result, the direction of the escape became abnormal.
These observations indicate that r5 and/or r6 are involved in escape direction control in response to tactile stimulus and imply that the counter turn is directed by r5 and/or r6. Efforts to further dissect r5 and r6 with Gal4 trap approach and calcium imaging are in progress.