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Interactions between the neonate host and its gut microbiome are central to the development of a healthy immune system. However, the mechanisms by which animals alter early colonization of microbiota for their benefit remain unclear. Here, we investigated the role of early-life expression of the α2,6-sialyltransferase ST6GAL1 in microbiome phylogeny and mucosal immunity. Fecal, upper respiratory, and oral microbiomes of pups expressing or lacking St6gal1 were analyzed by 16S rRNA sequencing. At weaning, the fecal microbiome of St6gal1 -KO mice had reduced Clostridiodes, Coprobacillus, and Adlercreutzia , but increased Helicobacter and Bilophila. Pooled fecal microbiomes from syngeneic donors were transferred to antibiotic-treated wild-type mice, before analysis of recipient mucosal immune responses by flow cytometry, RT-qPCR, microscopy, and ELISA. Transfer of St6gal1- KO microbiome induced a mucosal Th17 response, with expression of T-bet and IL-17, and IL-22-dependent gut lengthening. Early life intestinal sialylation was characterized by RT-qPCR, immunoblot, microscopy, and sialyltransferase enzyme assays in genetic mouse models at rest or with glucocorticoid receptor modulators. St6gal1 expression was greatest in the duodenum, where it was mediated by the P1 promoter and efficiently inhibited by dexamethasone. Our data show that the inability to produce α2,6-sialyl ligands contributes to microbiome-dependent Th17 inflammation, highlighting a pathway by which the intestinal glycosylation regulates mucosal immunity. [ABSTRACT FROM AUTHOR]

The vertical distribution of zooplankton in the upper 700 m of the water column was investigated across the Almeria–Oran front (Alboran Sea) during winter 1997/98 (Almofront 2 cruise). Eight sites corresponding to three hydrodynamic structures (the Atlantic jet, an anticyclonic gyre and the surrounding Mediterranean waters) were explored, by day and at night, using multiple-net sampling. Results are presented for the major species of copepods (>500 μm), macroplankton and microplankton. Species inhabiting the surface layer or occupying it at night extended deeper in the gyre. On the other hand, mesopelagic species (e.g. Pleuromamma borealis, Pleuromamma abdominalis, Euphausia krohni and Cyclothone braueri) were found to live deeper, at least by day for the migrants, in the Mediterranean waters compared with the two other structures. These changes in preferential depths across the front are discussed in relation to environmental features, such as light level, abundance of food and mixed layer depth. This study also documented the vertical distribution of some overwintering copepod species (Calanus helgolandicus, Eucalanus hyalinus and Eucalanus monachus). [ABSTRACT FROM AUTHOR]