Ten Alarming Knowledge About Vasopressin Receptor
, 2003). To test the contribution of these domains to Hb9 function, we generated Hb9 transgenes in which either or both domains were deleted and compared their ability to rescue hb9 mutants relative to full-length Hb9 ( Figure?3). All transgenes are inserted in the same genomic location and are expressed at similar levels (data not shown). We found that whereas a full-length Hb9 transgene (Hb9 FL) fully rescues both muscle 6/7 innervation defects and robo2 expression Erlotinib purchase in hb9 mutants, the Eh domain deletion (Hb9��Eh) does not rescue motor axon pathfinding and only weakly rescues robo2 expression ( Figure?3). Conversely, the CtBP-interacting domain deletion (Hb9��CtBP) fully rescues both guidance and robo2 expression ( Figure?3). The double deletion (Hb9��Eh��CtBP) is not significantly different from Hb9��Eh in either assay ( Figure?3). GSK126 These results suggest that Hb9 indirectly activates robo2, perhaps by repressing a direct regulator of robo2, likely through a Groucho-dependent mechanism. The embryonic expression patterns of hb9 and the homeodomain transcription factor nkx6 largely overlap, and genetic analyses suggest that Hb9 and Nkx6 act in parallel to regulate motor axon guidance and multiple transcription factors ( Broihier et?al., 2004). We hypothesized that robo2 might be a shared Vasopressin Receptor downstream target of hb9 and nkx6. Indeed, nkx6 mutants have a significant decrease in robo2 expression in the RP motor neurons (81% robo2+ RP3 neurons in nkx6 heterozygotes versus 51.4% robo2+ RP3 neurons in nkx6 mutants; p?< 0.001, Student��s t test) ( Figures 4A and 4B). To determine if hb9 and nkx6 function in parallel to regulate robo2, we examined robo2 expression in hb9, nkx6 double mutants and observed a decrease relative to either single mutant (data not shown). However, we were not able to quantify robo2 expression in the double mutants because many cells are not labeled by hb9GAL4 or islet-tau-myc. Therefore, we looked for an alternative background to address whether nkx6 regulates robo2 in parallel with hb9. Removing one copy of nkx6 in hb9 mutants strongly enhances the motor axon phenotype (from 21.6% of hemisegments with 6/7 innervation defects in hb9/hb9 embryos to 45% in hb9, nkx6/hb9,+ embryos; p?< 0.001, Student��s t test) without producing the changes in markers observed in hb9, nkx6 double mutants ( Figures 4C and 4D). In this background, robo2 expression is significantly decreased relative to hb9 mutants (from 41% robo2+ RP3 neurons in hb9/hb9 embryos to 19% in hb9, nkx6/hb9,+ embryos; p?< 0.001, Student��s t test), suggesting that nkx6 promotes robo2 expression independently of hb9 ( Figure?4B).