ABSTRACTIn horizontally transmitted symbioses, structural, biochemical, and molecular features both facilitate host colonization by specific symbionts and mediate their persistent carriage. In the association between the squidEuprymna scolopesand its luminous bacterial partnerVibrio fischeri, the symbionts interact with two epithelial fields; they interact (i) transiently with the superficial ciliated field that potentiates colonization and regresses within days of colonization and (ii) persistently with the cells that line the internal crypts, whose ultrastructure changes in response to the symbionts. Development of the association creates conditions that promote the symbiotic partner over the lifetime of the host. To determine whether light organ maturation requires continuous interactions withV. fischerior only the signaling that occurs during its initiation, we compared 4-week-old squid that were uncolonized with those colonized either persistently by wild-typeV. fischerior transiently by aV. fischerimutant that triggers early events in morphogenesis but does not persist. Microscopic analysis of the light organs showed that, while morphogenesis of the superficial ciliated field is greatly accelerated byV. fischericolonization, its eventual outcome is largely independent of colonization state. In contrast, the symbiont-induced changes in crypt cell shape require persistent host-symbiont interaction, reflected in the similarity between uncolonized and transiently colonized animals. Transcriptomic analyses reflected the microscopy results; host gene expression at 4 weeks was due primarily to the persistent interactions of host and symbiont cells. Further, the transcriptomic signature of specific pathways reflected the daily rhythm of symbiont release and regrowth and required the presence of the symbionts.IMPORTANCEA long-term relationship between symbiotic partners is often characterized by development and maturation of host structures that harbor the symbiont cells over the host’s lifetime. To understand the mechanisms involved in symbiosis maintenance more fully, we studied the mature bobtail squid, whose light-emitting organ, under experimental conditions, can be transiently or persistently colonized byVibrio fischerior remain uncolonized. Superficial anatomical changes in the organ were largely independent of symbiosis. However, both the microanatomy of cells with which symbionts interact and the patterns of gene expression in the mature animal were due principally to the persistent interactions of host and symbiont cells rather than to a response to early colonization events. Further, the characteristic pronounced daily rhythm on the host transcriptome required persistentV. fischericolonization of the organ. This experimental study provides a window into how persistent symbiotic colonization influences the form and function of host animal tissues.
An ultradian feeding schedule in rats affects metabolic gene expression in liver, brown adipose tissue and skeletal muscle with only mild effects on circadian clocks
