Characterization of the progression of cellular states during human embryogenesis can provide insights into the origin of pediatric diseases. We examined the transcriptional states of neural crest- and mesoderm-derived lineages differentiating into adrenal glands, kidneys, endothelium, and hematopoietic tissue between post-conception weeks 6 and 14 of human development. Our results reveal transitions connecting intermediate mesoderm and progenitors of organ primordia, the hematopoietic system, and endothelial subtypes. Unexpectedly, by using a combination of single cell transcriptomics and lineage tracing, we found that intra-adrenal sympathoblasts at that stage are directly derived from the nerve-associated Schwann cell precursors similarly to local chromaffin cells, whereas the majority of extra-adrenal sympathoblasts arise from the migratory neural crest. In humans, this process persists during several weeks of development within the large intra-adrenal ganglia-like structures, which may also serve as reservoirs of originating cells in neuroblastoma.

The second mission of the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment took place in August 1997. The experiment was flown aboard the ASTROnomical Shuttle PAllet Satellite (ASTRO‐SPAS) free‐flying platform launched by the NASA space shuttle. CRISTA analyzes the infrared radiation emitted by trace gases from the Earth limb in the altitude regime from the upper troposphere to the lower thermosphere. The main aim of CRISTA is to detect small‐scale dynamically induced structures in the distribution of trace constituents in the middle atmosphere. The instrument is therefore equipped with three telescopes that simultaneously collect the infrared radiation from three different air volumes. The high spatial density of the measurement grid obtained during the first CRISTA mission in November 1994, as well as the latitudinal coverage, was considerably improved by making use of newly developed satellite pointing and maneuvering capabilities. The altitude coverage was extended to include the upper troposphere where water vapor distributions are analyzed. Dynamically induced features are observed in practically all trace gases and at various spatial scales. The smallest scales that could be analyzed on the basis of the CRISTA data set are well below 100 km. Compared to the first mission, much more emphasis was laid on measurements in the upper mesosphere and lower thermosphere—this was possible because of higher radiometric sensitivities in some channels. Atomic oxygen, carbon dioxide, and ozone densities are derived in the upper mesosphere and lower thermosphere. The mission conditions allowed the study of polar stratospheric clouds (PSC) over the Antarctic and of polar mesospheric clouds (PMC) at high northern latitudes. For the first time, summer high latitude mesopause temperatures were retrieved from CO2 15‐μm spectra using a nonlocal thermodynamic equilibrium model. The derived temperatures compare well with a temperature climatology based on rocket soundings.

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[1] The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment measured the global distribution of CO 2 4.3 mm infrared emissions in the mesosphere and lower thermosphere during two Space Shuttle missions in November 1994 and August 1997. The daytime radiances have been inverted to CO 2 number densities in the 60-130 km range by using a nonlocal thermodynamic equilibrium model. A detailed sensitivity study of retrieved CO 2 number densities was carried out. The O( 1 D) excitation mechanism and model parameters constitute the most important uncertainties of retrieved CO 2 , typically 10-20%. The inaccuracy due to uncertainties in other atmospheric parameters is usually less than 10%. The CO 2 volume mixing ratio (VMR) deviates from being well mixed between 70 and 80 km, which is significantly lower than indicated by previous rocket-borne mass spectrometer data and model calculations but is in good agreement with the data obtained by other 4.3 mm emission and absorption experiments. The global distribution of CRISTA-2 CO 2 density shows significant longitudinal and latitudinal structures. The zonal mean CO 2 densities are increasing toward polar summer latitudes below 90 km and above 115 km. Between 90 and 115 km, the latitudinal gradient is reversed. At 100 km, the gradient is mostly pronounced, reaching up to 50% difference between low and high latitudes. These variations are compared with results obtained by the Thermosphere/Ionosphere/Mesosphere Electrodynamics General Circulation Model (TIME-GCM), showing very good agreement for the latitudinal distribution. Below 110 km, this variation is mostly due to the change in total density rather than to the CO 2 VMR.

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