Figure 8. Deep homology between HSN and mouse serotonergic raphe neurons.

(A) Micrograph of mouse embryonic day 11.5 hindbrain coronal section with DAPI staining. Square box indicates the region in A', B and C panels. VZ: ventricular zone, where progenitors are located. Scale bar: 100 μm. (B) BRN2 and 5HT co-staining. BRN2 is expressed in progenitors and differentiating serotonergic neurons. Arrowheads indicate double labeled cells. Scale bar: 20 μm. (C) SALL2 and 5HT co-staining. SALL2 is expressed in progenitors and differentiating serotonergic neurons. Arrowheads indicate double labeled cells. Scale bar: 20 μm. (D) Hierarchical clustering analysis of C. elegans neuron expression profiles with mouse serotonergic raphe neurons shows that HSN (in green) is closest to mouse serotonergic neurons (in blue). Other C. elegans serotonergic neuron classes (ADF and NSM in red) do not show a close relationship with mouse serotonergic raphe. R1D: Dorsal serotonergic neurons from rhombomere r1; R1M: Medial serotonergic neurons from rhombomere r1; R2: serotonergic neurons from rhombomere r2; R3: serotonergic neurons from rhombomere r3; R5: serotonergic neurons from rhombomere r5; R6: serotonergic neurons from rhombomere r6. See also Figure 8—figure supplement 1. (E) Micrographs showing tph-1::gfp expression in wild type animals, ast-1(ot417) mutants, and ast-1(ot417) mutants rescued with ast-1 cDNA or mouse Pet1 cDNA expressed under the bas-1 promoter whose expression in not affected in this mutant background. (F) Quantification of tph-1::gfp HSN expression rescue of different HSN TF collective mutants with worm and mouse ortholog cDNAs. n > 100 cells per condition. Fisher's exact test, *: p-value<0.05. ‘L’ indicates the transgenic line number.

Figure 8—figure supplement 1. HSN neuron is the C. elegans neuron molecularly closest to mouse raphe serotonergic neurons.

(A) pvclust was performed after removing 5HT pathway genes (cat-1, tph-1, bas-1 and cat-4) from the HSN to show that proximity between HSN and mouse raphe is not only due to 5HT pathway genes. (B) Clustering of worm neurons and mouse non-serotonergic control regions [cortical neurons from (Molyneaux et al., 2015) show that HSN expression data cluster with raphe transcriptome is specific as it does not occur with other mouse transcriptomic data. P1_cpn: Postnatal day 1 cortical projection neurons; P1_corticothal: Postnatal day 1 cortical thalamic neurons; P1_subcereb: Postnatal day 1 cortical subcerebral neurons. (C) 100 simulated 'HSN-like' neurons were obtained by assigning to each one the four 5HT pathway genes (cat-1, tph-1, bas-1 and cat-4) and 92 additional genes at random. None of these random profiles shows close proximity to the Raphe mouse neurons.