Age, caste, and behavior determine the replicative activity of intestinal stem cells in honeybees (Apis mellifera L.)

Abstract

Abstract:Honeybees (Apis mellifera L.) display a pronounced natural aging plasticity. The differences in aging rates between the alternative phenotypes and behavioral classes could reflect differences in protection against damage or in the ability to repair vulnerable tissues. As in other animals, including humans, the gut is continually exposed to environmental insults and harbors a large population of replicating stem cells that maintain the intestinal epithelium. Through studies of the major internal organs using incorporation and immunodetection of the mitotic marker bromodeoxyuridine, the intestine was determined to be the main site of tissue renewal in adult honeybees. Proliferative activity of the intestinal stem cells was compared among queens, workers, and males of different ages. Simultaneous attempts to assess intestinal cell loss via apoptosis yielded inconclusive results. The relationship between intestinal cell proliferation and worker life-history was evaluated in greater depth by studying diutinus winter workers, reproductive workers, and by decoupling worker behavioral status from chronological age in a single-cohort colony. Intestinal cell proliferation was abundant in all groups and showed an agerelated decline in workers, queens, and males. At young ages, workers exhibited relatively more intestinal cell proliferation than did queens and queens more than drones, but the caste and sex differences decreased with age. Cell proliferation did not decrease beyond 6 weeks of age in older queens and in diutinus workers. Ovary activation did not correlate with the amount of intestinal stem cell proliferation in workers, although the queenless hive condition was associated with lower overall counts. In the single-cohort colony, nurse bees exhibited more cell proliferation than foragers, regardless of age. The overall results do not support our hypothesis that longer-lived phenotypes exhibit increased somatic repair in the form of higher replicative activity of intestinal stem cells. Instead, the observed proliferation patterns reflect differential demands for digestive activity in the different groups, which result in different requirements for replacement of lost intestinal cells. The maintenance of proliferative capacity for over 1 year suggests that queen intestinal stem cells have a relatively high replicative potential, but further studies are needed to relate honeybee lifespan differences to cellular aging.

Food manipulation in honeybees induces physiological responses at the individual and colony level

“…Nutritional stress may interact with pesticides or pathogens (Mayack and Naug 2009;Naug and Gibbs 2009). Specifically, nutritional stress could deplete ISC proliferative capacity by requiring more cell replacement (Ward et al 2008) and thus compromise the long-term turn-over of epithelial cells in the intestine. The turn-over of epithelial cells is important for maintaining a functional gut and preventing the spread of pathogens and toxins to other tissues.…”

“…At 8 and 36 days of age, 10 bees were randomly sampled from each cohort in the "low" and "high" treatment groups. These individuals were assayed for the quantity of cell proliferation in the central midgut with immuno-histological detection of the thymidineanalog 5′-bromo-2′-deoxyuridine (BrdU), which is incorporated into newly synthesized DNA, following (Ward et al 2008) with slight modifications.…”

“…Their active cell cycle may make the ISCs particularly sensitive physiological indicators for intestinal health (Davila et al 2004). In honeybees, their proliferative activity co-varies with the nutritive demands on the individual among age classes and castes (Ward et al 2008), but the ISCs have not yet been studied with regards to honeybee health. The only study that has specifically investigated the honeybee gut with respect to bee health focused on a global assessment of gene expression patterns (Johnson et al 2009a).…”

“…As a result of their continuous digestive activity and environmental insults, the cells of the gut epithelium need to be continuously replaced by intestinal stem cells (ISCs; Ohlstein and Spradling 2006). These ISCs are the only major population of replicative somatic cells in adult honeybees (Ward et al 2008). Their active cell cycle may make the ISCs particularly sensitive physiological indicators for intestinal health (Davila et al 2004).…”

“…Ribosomal RNA fragments were overrepresented in health-compromised samples (Johnson et al 2009a), which could be a sign of viral infection (Johnson et al 2009b) but also might indicate starvation (Zundel et al 2009). This project sought to extend our previous studies of the ISCs (Ward et al 2008) to the health-related context of nutrition by comparing the ISC replication pattern between three different diet treatments.…”