Fig. 3

gata1:GFP cells in the cerebellum are granule neurons. (A) Nucleotide and deduced amino acid sequence of isolated zebrafish gaba_ARα6-cDNA fragment. The characteristic subunit-specific Arginine-residue conserved throughout vertebrates is demarcated by a red box. (B) mRNA in situ hybridization to analyze gaba_ARα6-expression in zebrafish larvae at 7 dpf. In single optical sections recorded by confocal microscopy, 7 dpf larvae of the gata1:GFP strain display a close overlap of gaba_ARα6- and GFP-expression in the cerebellum [a-c, dorsolateral view to simultaneously show GFP-expressing cells in the dorsal (orange box) and the ventrolateral (blue box) cerebellum, respectively]. Magnifications of the developing dorsal cerebellum (d-f) and the ventrolateral cerebellum (g-i) demonstrate an almost complete overlap of gaba_ARα6- and GFP-expression. Few GFP-positive cells along the MHB (g, white arrowhead), which do not co-express gaba_ARα6-mRNA, may represent not yet terminally differentiated granule cells arriving after migration along the MHB. GFP-expression in zebrafish granule cells is also confined to parallel fibers (marked by white asterisk in panels b, c, e, f, h, i; see also Fig. 6), and thus, shows no co-localization with gaba_ARα6-mRNA expression. Abbr.: cb, cerebellum; MHB, midbrain-hindbrain boundary; rh, rhombencephalon.