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. 2021 Aug 5;11(1):15915.
doi: 10.1038/s41598-021-95309-8.

An apocrine mechanism delivers a fully immunocompetent exocrine secretion

Affiliations

An apocrine mechanism delivers a fully immunocompetent exocrine secretion

Denisa Beňová-Liszeková et al. Sci Rep. .

Abstract

Apocrine secretion is a recently discovered widespread non-canonical and non-vesicular secretory mechanism whose regulation and purpose is only partly defined. Here, we demonstrate that apocrine secretion in the prepupal salivary glands (SGs) of Drosophila provides the sole source of immune-competent and defense-response proteins to the exuvial fluid that lies between the metamorphosing pupae and its pupal case. Genetic ablation of its delivery from the prepupal SGs to the exuvial fluid decreases the survival of pupae to microbial challenges, and the isolated apocrine secretion has strong antimicrobial effects in "agar-plate" tests. Thus, apocrine secretion provides an essential first line of defense against exogenously born infection and represents a highly specialized cellular mechanism for delivering components of innate immunity at the interface between an organism and its external environment.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
(a) Laser confocal view of the prepupal SG from an 8–10 h old wild-type prepupa having an apocrine secretion in its lumen. Visualized are tumor suppressor protein p127l(2)gl (green), nuclear transcription factor BR–C (red), filamentous actin (dark blue), and DNA (light blue, Hoechst 33,258). The light yellow signal inside the lumen reflects the merging of the three proteinaceous signals. (b) Live imaging of late 3rd instar Sgs3-GFP larva. A strong GFP signal is found exclusively within the secretory granules inside the SGs. (c) When all of the Sgs-glue is not released from the SGs during pupariation, GFP signal is released into the SG lumen during apocrine secretion in the late prepupa at 8–10 h APF. (d) In the 12–13 h old prepupa (APF) the GFP signal becomes visible around the forming head capsula in the periexuvial space. (e) At the 5-h old pupa at 18 h APF, a more diffuse GFP signal is spread over almost the entire pupal body, concentrated inside the periexuvial space.
Figure 2
Figure 2
SG phenotype in eygC1/eygC53 mutants. (a) Longitudinal SEM view of the wild-type (Oregon R) SG at the end of the 3rd instar, with (b) detailed perpendicular view of its opening into the SG duct. (c) Laser confocal image of the anterior end of a wild-type 3rd larval instar SG showing a few columnar cells and the duct [tumor suppressor protein p127l(2)gl (green), nuclear transcription factor BR–C (red), and filamentous actin (blue)]. (d) SEM view of a eygC1/eygC53 mutant salivary gland, with (e) a detailed perpendicular view of the mutilated, closed anterior end of the gland lacking a duct. (f) Optical section of the anterior end of eygC1/eygC53 mutant 3rd larval instar SG showing that it is a closed sack having a few columnar cells and is missing a duct (channels as above).
Figure 3
Figure 3
Pupae unable to deliver an apocrine secretion or with impaired Dif or Rel signaling during the late-larval and prepupal period are more susceptible to microbial infection. Mutant eygC1/eygC53 pupae, who lack a SG duct to deliver the apocrine secretion, show reduced survival when challenged with Gram-negative (E. coli and P. aeruginosa) or Gram-positive (M. luteus and S. aureus) bacteria (a) or when challenged with yeasts or fungi (S. cerevisiae, C. albicans and B. bassiana) (b). Pupae with impaired Dif (Sgs4-Gal4 >  > UAS-DifRNAi) or Rel (Sgs4-Gal4 >  > UAS-DifRNAi) signaling show reduced survival when challenged with Gram-negative (E. coli and P. aeruginosa) or Gram-positive (M. luteus and S. aureus) bacteria (c). Pupae with compromised Rel expression are more sensitive to Gram-negative than Gram-positive bacteria, while those with compromised Dif expression are more sensitive to Gram-positive than Gram-negative bacteria. (d) Pupae with impaired Dif or Rel signaling have diminished survival when challenged with yeasts or fungi (S. cerevisiae, C. albicans and B. bassiana). Data shown are the means ± SEM of three independent experiments. Differences in survival were evaluated using the Mantel-Cox log-rank test: ns = not significant, *p < 0.05, **p < 0.001, ***p < 1 × 10–5, ****p < 1 × 10–10.
Figure 4
Figure 4
Germicidal properties of the proteinaceous apocrine secretion isolated from the lumen of late prepupal SGs. Apocrine secretion from the equivalent of 5, 20 or 100 wild-type SGs was applied in a 10 μl volume of sterile PBS onto 6-mm diameter Rotilabo filters placed on 10-cm LB-agar (a,b) or YPD-agar (c,d) plates previously spread with E. coli (a), S. aureus (b), S. cerevisiae (c), or C. albicans (d). Sectors 1, 2, and 3 had no filter, an untreated filter, or a filter with only PBS, respectively. Sectors 4, 5, and 6 had filters with the apocrine secretion from the equivalent of 5, 20, or 100 pairs of SGs, respectively. Greater amounts of the apocrine secretion were associated with increased growth inhibition for each microbe tested. Images show data from one representative experiment. The graph shows the mean diameter of growth inhibition, measured using Image J, observed in three replicate experiments (Error bars: 95% CI). There were statistically significant differences in the degree of growth inhibition of each microbe by different amounts of SG extract as determined by one-way ANOVA (E. coli:F(2,6) = 2788, p = 1.2e−09; S. aureus: F(2,6) = 192.8, p = 3.6e−06; S. cerevisiae: F(2,6) = 162.4, p = 6.0e−06; C. albicans: F(2,6) = 80.6, p = 4.6e−05). For each microbe, post-hoc TukeyHSD tests revealed significant differences (adjusted p < 0.05) in the mean growth inhibition by different amounts of SG extract in all pairwise comparisons. Differences in growth inhibition of Gram-negative (a) and Gram-positive (b) bacteria may partly reflect differences in culture density.

References

    1. Harder, J. J. Glandula nova lachrymalis una cum ductu excretorio in cervis et damis. Acta Eruditorum Lipsiae, 49–52 (1694).
    1. Purkinje JE. Beobachtungen der spiralen Schweisscanäle der menschlichen Epidermis. Amtl. Bericht über die Vers. deutcher Naturf. u Arzte zu Breslau. 1833;11:59.
    1. Schiefferdecker P. Die Hautdrüsen des Menschen und der Säugetiere, ihre biologische und rassenanatomische Bedeutung, sowie die Muscularis sexualis. Zoologica (Stuttgart) 1922;72:1–154.
    1. Farkaš R. Apocrine secretion: New insights into an old phenomenon. Biochim Biophys. Acta. 2015;1850:1740–1750. doi: 10.1016/j.bbagen.2015.05.003. - DOI - PubMed
    1. Fraenkel G, Brookes VJ. The process by which the puparia of many species of flies become fixed to a substrate. Biol. Bull. Mar. Lab. Woods Hole. 1953;105:442–449. doi: 10.2307/1538461. - DOI

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