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SILENCING OF RPATG8 IMPAIRS THE BIOGENESIS OF MATERNAL AUTOPHAGOSOMES IN VITELLOGENIC OOCYTES, BUT DOES NOT INTERRUPT FOLLICULAR ATRESIA IN THE INSECT VECTOR RHODNIUS PROLIXUS
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Abstract
Follicular atresia is the mechanism by which the oocyte contents are degraded during
oogenesis in response to stress conditions, allowing the energetic resources stored in the
developing oocytes to be reallocated to optimize female fitness. Autophagy is a conserved
intracellular degradation pathway where double-membrane vesicles are formed around target
organelles leading to their degradation after lysosome fusion. The autophagy-related
protein 8 (ATG8) is conjugated to the autophagic membrane and has a key role in the elongation
and closure of the autophagosome. Here we identified one single isoform of ATG8 in
the genome of the insect vector of Chagas Disease Rhodnius prolixus (RpATG8) and found
that it is highly expressed in the ovary during vitellogenesis. Accordingly, autophagosomes
were detected in the vitellogenic oocytes, as seen by immunoblotting and electron microscopy.
To test if autophagosomes were important for follicular atresia, we silenced RpATG8
and elicited atresia in vitellogenic females by Zymosan-A injections. We found that silenced
females were still able to trigger the same levels of follicle atresia, and that their atretic
oocytes presented a characteristic morphology, with accumulated brown aggregates.
Regardless of the difference in morphology, RpATG8-silenced atretic oocytes presented
the same levels of protein, TAG and PolyP, as detected in control atretic oocytes, as well as
the same levels of acidification of the yolk organelles. Because follicular atresia has the ultimate
goal of restoring female fitness, we tested if RpATG8-silenced atresia would result in
female physiology and behavior changes. Under insectarium conditions, we found that atresia-
induced control and RpATG8-silenced females present no changes in blood meal digestion,
survival, oviposition, TAG content in the fat body, haemolymph amino acid levels and
overall locomotor activity. Altogether, we found that autophagosomes are formed during
oogenesis and that the silencing of RpATG8 impairs autophagosome biogenesis in the oocytes. Nevertheless, regarding major macromolecule degradation and adaptations to the
fitness costs imposed by triggering an immune response, we found that autophagic organelles
are not essential for follicle atresia in R. prolixus.
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