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. 2024 Aug 15;15:7041. doi: 10.1038/s41467-024-50808-w

Fig. 1. Selective expansion of noni-sensing olfactory sensory neuron populations is a complex developmental trait.

Fig. 1

a Drosophilid phylogeny. Ma, million years ago. b Left top, drosophilid third antennal segment. Left bottom, antennal basiconic 3 (ab3) sensilla house neurons expressing Or22a (and Or22b in D. melanogaster and D. simulans; this paralog is lost in D. sechellia) (hereafter, “Or22a neuron”) and Or85c/b (hereafter, “Or85b neuron”). Right, antennal Or22a/(b) and Or85b expression in D. sechellia (Drosophila Species Stock Centre (DSSC) 14021-0248.07 (Dsec07)) and D. simulans (DSSC 14021-0251.004 (Dsim04)). Scale bar, 25 µm. In addition to ab3 sensilla (within the dashed line), Or85b is expressed in ~ 10 OSNs in ab6 sensilla (Supplementary Fig. 1b). c Sensilla numbers in D. melanogaster (Canton-S, CS), D. simulans (Dsim04) and D. sechellia (Dsec07) determined by RNA FISH using a diagnostic Or probe (grey background) for each sensillum class (ai: antennal intermediate, at: antennal trichoid, ac: antennal coeloconic, sac3: sacculus chamber 3). Ir neuron data are from21; Ir75d neurons common to ac1, ac2 and ac4 sensilla are not shown. For these and all other box plots, the centre line represent the median, the box bounds represent the first and third quartiles, and whiskers depict at maximum 1.5 × the interquartile range; individual data points are overlaid. Wilcoxon signed-rank test (two-sided) with comparison to D. melanogaster: ***P < 0.001; **P < 0.01; *P < 0.05; NS, not significant (P > 0.05). Sample sizes are indicated in the figure. d Reciprocal hemizygosity test in D. simulans/D. sechellia hybrids of contributions of Or22a/(b) and Or85c/b to species-specific OSN numbers, using RNA FISH to quantify numbers of Or22a/(b) and Or85b OSNs in the indicated genotypes (“Dsec +” = Dsec07, “Dsim +” = Dsim04, “Dsec -” = DsecOr22aRFP or DsecOr85bGFP, “Dsim -” = DsimOr22a/bRFP or DsimOr85bGFP). See Supplementary Fig. 1f for representative images. Wilcoxon signed-rank test (two-sided) with comparison to wild-type hybrids: ***P < 0.001; NS, P > 0.05. e Quantification of GFP-expressing neurons in antennae of DsecOr85bGFP, DsimOr85bGFP and F1 hybrid males and females, and in F2 progeny of backcrosses of F1 hybrid females to either parental strain. The black line indicates the mean cell number. f Logarithm of odds (LOD) score across all four chromosomes for loci impacting Or85b neuron numbers based on the phenotypic data in e. Solid and dashed horizontal lines mark P = 0.01 and 0.05, respectively. g Effect sizes for the significant QTL intervals on chromosomes 3 and X in the D. simulans backcross. A, D. simulans allele; B, D. sechellia allele. Horizontal lines indicate the mean ± SEM for the cell number count of each allelic combination. A candidate gene, lozenge—encoding a transcription factor involved in sensillar specification87—located directly below the X chromosome peak, did not influence species-specific OSN numbers (Supplementary Fig. 2e–i).