Fig. 1

CO₂ chemosensation controls the differentiation of crystal cells. Graphs indicate the number of crystal cells (CC) per lymph gland lobe. Bars in graphs: the median. n.s: not significant (p > 0.01). *p < 0.01; **p < 0.001; ***p < 0.0001. Scale Bar: 20μm. White dotted lines: lymph glands. Statistical results and genotypes are indicated in Supplementary Table 3. a A schematic representation of the primary lobe of the hematopoietic organ, the larval lymph gland. Undifferentiated blood progenitors reside in the inner core, termed the medullary zone (MZ), and give rise to mature blood cell lineages including crystal cells (CC, marked in yellow) that occupy a region termed the cortical zone (CZ). The posterior signaling center (PSC) secretes multiple factors to maintain the progenitors. Only the features relevant to this study are shown. b–l Loss of CO₂SN activity causes increased CC number. Wild-type third-instar larvae express fewer than 100-CCs per primary lymph gland lobe (CCs are marked in red, Lz) (b) Both homozygous (Gr63a¹/ Gr63a¹) (c) and heterozygous (Gr63a¹/+) mutants (d) of Gr63a, the gene encoding the chemoreceptor for CO₂ sensing, exhibit increased numbers of CCs. Quantitation of CC numbers shown in (e). Gr21a encodes the second subunit of the CO₂ chemoreceptor that functions with Gr63a. Knockdown of Gr21a function (Gr63a-gal4; UAS-Gr21a^RNAi) (f), or genetic ablation of the CO₂ receptor neuron by expression of pro-apoptotic genes, hid and rpr (Gr63a-gal4; UAS-hid,rpr) (g) or attenuation of synaptic transmission by expression of a temperature-sensitive form of the dynamin-like protein Shibire (Gr63a-gal4; UAS-Shi^ts1) (h), each causes a significant increase in the number of CCs. This phenotype is not observed in Gal4- or UAS-controls alone. Quantitation is shown in i. Absorption of ambient CO₂ in larval culture vial with the use of soda-lime, a mixture of bases that eliminates gaseous CO₂ (see Methods for detail), mimics the CO₂SN mutant phenotype (j). This phenotype is enhanced by a simultaneous knockdown of Gr21a in the CO₂SN (Gr63a-gal4; UAS-Gr21a^RNAi) (k). Quantitation shown in l. The blue shading in panels (l) represents soda-lime-induced low environmental CO₂ condition