Figure 4

Unlike lamprey tarl, zebrafish tarl is not expressed in the nose. (A) Lamprey (Lampetra fluviatilis) tarl7a probe was used to perform chromogenic in situ hybridization of horizontal cryostat sections of olfactory epithelia. Scale bars: left panel 200 μm, middle panel 50 μm and right panels 10 μm. Note expression in sparse cells within the olfactory lamellae, characteristic for olfactory receptors. (B) Middle column, top panel, RT-PCR for Dr-tarl1 with primer pair 1 (see Materials and Methods) shows extremely faint signal in the OE, a strong signal in the brain (Br) and moderate expression in the trunk (Tr). Dr-tarl1 primer pair 2 gave same results (data not shown); M, marker, numbers refer to bp. Middle panel, beta-actin was used as control, and shows equal loading in all tissues as well as absence of genomic DNA in the cDNA preparation (gen, genomic DNA). Both in situ hybridization of horizontal cryostat sections of olfactory epithelia (left panel, scale bar 50 μm) and whole mount in situ hybridization of 5 dpf zebrafish larvae (top right panel, dorsal view; bottom panel, frontal view) show absence of tarl1 expression in the nose. In situ hybridization results shown are for probe 1 corresponding to primer pair 1 (see Materials and Methods). All but one panel have been modified from the PhD thesis of one author⁴³. Bottom row, as a positive control, S100z expression is shown in the adult nose (left and middle panel, scale bars 100 and 20 μm, respectively) and in 5 dpf larvae, same orientation as for tarl1 expression. The nose (black arrows) is visible as two anterior bluish spots (top panel, dorsal view) and medially adjacent to the eyes (bottom panel, frontal view).