16S rRNA probes hybridate on intracellular pigmented corpuscles in the midgut gland of the queen conch Lobatus gigas (Linnaeus, 1758)

DELLAGNOLA FEDERICO, CASTRO VAZQUEZ A, VEGA ISRAEL A

San Luis

Congreso; XXII Reunión de la Sociedad de Biología de Cuyo; 2014

Sociedad de Biología de Cuyo

The queen conch (Littorinimorpha, Strombidae) bears pigmented corpuscles in the midgut gland, which are morphologically similar to those borne by some Struthiolariidae (Littorinimorpha) and Ampullariidae (Architaenioglossa). We have revisited those previous morphological descriptions in which the attention was centered in some large oval bodies (~27 μm long) which are dark brown and have been considered morphs of an apicomplexan-like parasite. Also, in one of those descriptions, some round, Alcian Blue positive bodies have been mentioned as ?granules? of unknown function. In addition, this inclusions showed no in situ hybridization when exposed to a universal probe for eukaryotic 18S rRNA. We have described, in histological sections (stain with Nuclear Fast Red, Alcian Blue 8GX, eosin trichrome, from individuals collected in the Caribbean Sea, México) three types of corpuscles: (1) large, dark brown corpuscles, which are oval in shape; (2) smaller, round, light brown corpuscles; and (3) round, non-pigmented corpuscles of similar size, which show an Alcian Blue positive outer layer. Also, we exposed tissue sections for fluorescence in situ hybridization (FISH) probes that recognize generalized sequences of the 16S rRNA gene from Bacteria (EUB 338) and Cyanobacteria (CYA 361). Digestive gland sections exposed to either probes showed fluorescence on the large, oval pigmented corpuscles, but the label was much less intense on the small round ones when exposed to EUB338 or CYA361. A possible dietary origin of these corpuscles should be considered, because they may be digested remnants of cyanobacteria or chloroplast from the diet. However, an alternative hypothesis, similar to that proposed for species of Ampullariidae, is that they may be morphs of a prokaryotic endosymbiont.