Methane and nitrous oxide in tidal estuaries

Estuaries contribute significantly (5-10 %) to the marine emission budget of methane and nitrous oxide. During the BIOGEST project we have measured the distribution of these two gases in the water column of nine tidal estuaries. In well-mixed estuaries, methane concentrations were high in the river end-member and initially decreased with increasing salinity, then increased at intermediate or high salinities before decreasing again going offshore. Tidal flats and creeks were identified as a methane sources to estuarine waters. Methane concentrations in river-dominated stratified estuaries were rather erratic. Nitrous oxide concentrations were always above atmospheric saturation levels and showed consistent and systematic relationships with distribution patterns of oxygen, ammonium, nitrite and nitrification activities. Nitrous oxide concentrations were very high in ammonium-rich and oxygen-depleted systems such as the Scheldt and Thames estuaries. Nitrous oxide concentrations were also high in the suboxic zone of fluidised mud systems of the Gironde estuary. If time permits, we will show laboratory results for nitrous oxide production in Scheldt water and we will speculate on the role of sediment versus water-column processes

A conserved regulatory program drives emergence of the lateral plate mesoderm

Cardiovascular cell lineages emerge with kidney, smooth muscle, and limb skeleton progenitors from the lateral plate mesoderm (LPM). How the LPM emerges during development and how it has evolved to form key lineages of the vertebrate body plan remain unknown. Here, we captured LPM formation by transgenic in toto imaging and lineage tracing using the first pan-LPM enhancer element from the zebrafish gene draculin (drl). drl LPM enhancer-based reporters are specifically active in LPM-corresponding territories of several chordate species, uncovering a universal LPM-specific gene program. Distinct from other mesoderm, we identified EomesA, FoxH1, and MixL1 with BMP/Nodal-controlled Smad activity as minimally required factors to drive drl-marked LPM formation. Altogether, our work provides a developmental and mechanistic framework for LPM emergence and the in vitro differentiation of cardiovascular cell types. Our findings suggest that the LPM may represent an ancient cell fate domain that predates ancestral vertebrates

Carbon sources of Antarctic nematodes as revealed by natural carbon isotope ratios and a pulse-chase experiment

δ13C of nematode communities in 27 sites was analyzed, spanning a large depth range (from 130 to 2,021 m) in five Antarctic regions, and compared to isotopic signatures of sediment organic matter. Sediment organic matter δ13C ranged from −24.4 to −21.9‰ without significant differences between regions, substrate types or depths. Nematode δ13C showed a larger range, from −34.6 to −19.3‰, and was more depleted than sediment organic matter typically by 1‰ and by up to 3‰ in silty substrata. These, and the isotopically heavy meiofauna at some stations, suggest substantial selectivity of some meiofauna for specific components of the sedimenting plankton. However, 13C-depletion in lipids and a potential contribution of chemoautotrophic carbon in the diet of the abundant genus Sabatieria may confound this interpretation. Carbon sources for Antarctic nematodes were also explored by means of an experiment in which the fate of a fresh pulse of labile carbon to the benthos was followed. This organic carbon was remineralized at a rate (11–20 mg C m−2 day−1) comparable to mineralization rates in continental slope sediments. There was no lag between sedimentation and mineralization; uptake by nematodes, however, did show such a lag. Nematodes contributed negligibly to benthic carbon mineralization

A conserved regulatory program drives emergence of the lateral plate mesoderm

Cardiovascular cell lineages emerge with kidney, smooth muscle, and limb skeleton progenitors from the lateral plate mesoderm (LPM). How the LPM emerges during development and how it has evolved to form key lineages of the vertebrate body plan remain unknown. Here, we captured LPM formation by transgenic in toto imaging and lineage tracing using the first pan-LPM enhancer element from the zebrafish gene draculin (drl). drl LPM enhancer-based reporters are specifically active in LPM-corresponding territories of several chordate species, uncovering a universal LPM-specific gene program. Distinct from other mesoderm, we identified EomesA, FoxH1, and MixL1 with BMP/Nodal-controlled Smad activity as minimally required factors to drive drl-marked LPM formation. Altogether, our work provides a developmental and mechanistic framework for LPM emergence and the in vitro differentiation of cardiovascular cell types. Our findings suggest that the LPM may represent an ancient cell fate domain that predates ancestral vertebrates

A conserved regulatory program initiates lateral plate mesoderm emergence across chordates

Cardiovascular lineages develop together with kidney, smooth muscle, and limb connective tissue progenitors from the lateral plate mesoderm (LPM). How the LPM initially emerges and how its downstream fates are molecularly interconnected remain unknown. Here, we isolate a pan-LPM enhancer in the zebrafish-specific draculin (drl) gene that provides specific LPM reporter activity from early gastrulation. In toto live imaging and lineage tracing of drl-based reporters captures the dynamic LPM emergence as lineage-restricted mesendoderm field. The drl pan-LPM enhancer responds to the transcription factors EomesoderminA, FoxH1, and MixL1 that combined with Smad activity drive LPM emergence. We uncover specific activity of zebrafish-derived drl reporters in LPM-corresponding territories of several chordates including chicken, axolotl, lamprey, Ciona, and amphioxus, revealing a universal upstream LPM program. Altogether, our work provides a mechanistic framework for LPM emergence as defined progenitor field, possibly representing an ancient mesodermal cell state that predates the primordial vertebrate embryo