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Lycopodina hypogea is a carnivorous sponge that tolerates laboratory husbandry very well. During a digestion cycle, performed without any digestive cavity, this species undergoes spectacular morphological changes leading to a total regression of long filaments that ensure the capture of prey and their reformation at the end of the cycle. This phenomenon is a unique opportunity to analyze the molecular and cellular determinants that ensure digestion in the sister group of all other metazoans. Using differential transcriptomic analysis coupled with cell biology studies of proliferation, differentiation, and programmed cell deaths (i.e., autophagy and the destructive/constructive function of apoptosis), we demonstrate that the molecular and cellular actors that ensure digestive homeostasis in a sister group of all remaining animals are similar in variety and complexity to those controlling tissue homeostasis in higher vertebrates. During a digestion cycle, most of these actors are finely tuned in a coordinated manner. Our data benefits from complementary approaches coupling in silico and cell biology studies and demonstrate that the nutritive function is provided by the coordination of molecular network that impacts the cells turnover in the entire organism. [ABSTRACT FROM AUTHOR]

Sponges are an ancient basal life form, so understanding their evolution is key to understanding all metazoan evolution. Sponges have very unusual feeding mechanisms, with an intricate network of progressively optimized filtration units: from the simple choanocyte lining of a central cavity, or spongocoel, to more complex chambers and canals. Furthermore, in a single evolutionary event, a group of sponges transitioned to carnivory. This major evolutionary transition involved replacing the filter-feeding apparatus with mobile phagocytic cells that migrate collectively towards the trapped prey. Here, we focus on the diversity and evolution of sponge nutrition systems and the amazing adaptation to carnivory. [ABSTRACT FROM AUTHOR]