Programmed cell death in the larval salivary glands of Apis mellifera (Hymenoptera, Apidae)

Abstract

The morphological and histochemical features of degeneration in honeybee (Apis mellifera) salivary glands were investigated in 5th instar larvae and in the pre-pupal period. The distribution and activity patterns of acid phosphatase enzyme were also analysed. As a routine,the larval salivary glands were fixed and processed for light microscopy and transmission electron microscopy.Tissue sections were subsequently stained with haematoxylin -eosin,bromophenol blue,silver,or a variant of the critical electrolyte concentration (CEC) method.Ultrathin sections were contrasted with uranyl acetate and lead citrate.Glands were processed for the histochemical and cytochemical localization of acid phosphatase,as well as biochemical assay to detect its activity pattern. Acid phosphatase activity was histochemically detected in all the salivary glands analysed.The cytochemical results showed acid phosphatase in vesicles, Golgi apparatus and lysosomes during the secretory phase and,additionally, in autophagic structures and luminal secretion during the degenerative phase. These findings were in agreement with the biochemical assay. At the end of the 5th instar, the glandular cells had a vacuolated cytoplasm and pyknotic nuclei, and epithelial cells were shed into the glandular lumen.The transition phase from the 5th instar to the pre-pupal period was characterized by intense vacuolation of the basal cytoplasm and release of parts of the cytoplasm into the lumen by apical blebbing; these blebs contained cytoplasmic RNA, rough endoplasmic reticule and, occasionally, nuclear material. In the pre-pupal phase, the glandular epithelium showed progressive degeneration so that at the end of this phase only nuclei and remnants of the cytoplasm were observed.The nuclei were pyknotic,with peripheral chromatin and blebs. The gland remained in the haemolymph and was recycled during metamorphosis. The programmed cell death in this gland represented a morphological form intermediate between apoptosis and autophagy.

Autophagy precedes apoptosis during the remodeling of silkworm larval midgut

“…In Lepidoptera, apoptosis has been suggested to be involved in cell death of various larval organs during metamorphosis [12][13][14][15][16][17][18][19], but solid experimental evidence for the intervention of autophagy is lacking; furthermore, the relationship between these two processes in insect tissues and organs undergoing cell death is still cryptic [15,18,[20][21][22][23][24]. For these reasons, the current literature is basically fragmentary and confusing.…”

Toxicological and Histopathological Effects of Boric Acid on <I>Atta sexdens rubropilosa</I> (Hymenoptera: Formicidae) Workers

“…At the concentration of 0.2%, these structures were clearly visible only after 168 h of treatment. Autophagic vacuoles usually appear in the midgut of older bees (Mello et al 1971) and in insect tissues undergoing metamorphosis (Beaulaton and Lockshin 1982, Lockshin and Zakeri 1994, Silva-Zacarin 2007, Silva-Zacarin et al 2007b. Autophagic vacuoles are indicative of programmed cell death by autophagy.…”

Morphological alterations induced by boric acid and fipronil in the midgut of worker honeybee (Apis mellifera L.) larvae

“…In the midgut cells of the larvae treated with fipronil, the picnotic nuclei observed are often described in organs undergoing degeneration in Hymenoptera (Gregorc and Bowen 1996;CruzLandim and Cavalcante 2003;Silva-Zacarin et al 2007). Highly picnotic nuclei indicate low transcriptional activity due to chromatinic compacting, suggesting that the cells are in an advanced cell death process (Häcker 2000;Silva-Zacarin et al 2008).…”