MCS density is regulated by TRP channels in Drosophila photoreceptors. (A) Schematic showing the spatial orientation and dimensions of the location of TRP, TRPL, dEsyt and RDGB across the microvillar plasma membrane (rhabdomere) and the submicrovillar cisternae (SMC) (Left side) in a Drosophila photoreceptor cell (right side) (Image generated using Biorender, https://app.biorender.com/). (B) TEM images of a single ommatidium from wild type photoreceptors of flies reared in dark (i) day 1 and (iii) day 14, scale bar: 1 µm. (* - R7 photoreceptor). Magnified image showing a single photoreceptor from the same ommatidium on the left (ii) day1 and (iv) day 14. Scale bar: 200 nm. Arrow indicates the SMC forming an MCS with the microvillar PM. (C) TEM images of a single ommatidium from trpl³⁰²;trp³⁴³ photoreceptors of flies reared in dark (i) day 1 and (iii) day 14, scale bar: 1 µm. (* - R7 photoreceptor). Magnified image showing a single photoreceptor from the same ommatidium on the left (ii) day1 (iv) day 14. Scale bar: 500 nm. The arrow indicates the SMC forming an MCS with the microvillar PM. (D) Quantification of the number of MCS per photoreceptor of wild type day 1 v/s trpl³⁰²;trp³⁴³ day 1 old flies reared in dark; X-axis indicates the genotype and Y-axis indicates the number of MCS/photoreceptor. n = 30 photoreceptors from three separate flies (R1–R6) (N = 3; n = 30). (E) Quantification of the number of MCS per wild type photoreceptor of day 1 (D1) and day 14 (D14) old flies reared in the dark (from Fig. 1 B), X axis indicates the genotype and age of the fly. Y axis indicates the number of MCS/photoreceptor. n = 30 photoreceptors from three separate flies (R1–R6) (N = 3; n = 30). (F) Quantification of the number of MCS per trpl³⁰²;trp³⁴³ photoreceptor of day 1 (D1) and day 14 (D14) old flies reared in the dark (from Fig. 1 C), Y axis indicates the number of MCS/photoreceptor. n = 30 photoreceptors from three separate flies (R1–R6) (N = 3; n = 30). Violin plots with mean ± SD are shown. Statistical tests: (D–F) Student’s unpaired t test. ns - Not significant; ****P value <0.0001.