Abstract, Submarine hydrothermal vents are the only comtemporary geological environment which may be called truly primeval; they continue to be a major source of gases and dissolved elements to the modern ocean as they were to the Archean ocean. Then, as now, they encompassed a multiplicity of physical and chemical gradients as a direct result of interactions between extensive hydrothermal activity in the Earth's crust and the overlying oceanic and atmospheric environments. We have proposed that these gradients provided the necessary multiple pathways for the abiotic synthesis of chemical compounds, origin and evolution of "precetls' and 'precell' communities and, ultimately, the evolution of free-living organisms. This hypothesis is consistent with the tectonic, paleontological, and degassing history of the earth and with the use of thermal energy sources in the laboratory to synthesize amino acids and complex organic compounds. In this paper, we expand upon the geophysical, chemical, and possible microbiological analogies between contemporary and Archean hydrothermal systems and suggest several hypotheses, related to our model for the origin and evolution of life at Archean vents, which can be tested in present-day hydrothermal systems.
Lmx1b is a homeodomain transcription factor that regulates dorsal identity during limb development and Lmx1b knockout (KO) mice develop nearly symmetrical ventral‐ventral limbs with hypoplastic scapulae. Currently, downstream targets of Lmx1b within dorsal mesoderm that impart the limbs' unique dorsal asymmetry are unknown.
To identify genes targeted by Lmx1b, we compared gene arrays from Lmx1b KO and wild type (WT) mouse limbs during limb outgrowth and patterning, i.e., 11.5, 12.5, and 13.5 days post coitum (dpc). Real‐time PCR confirmed microarray results and whole mount in situ hybridization was used to localize and verify differential dorsal‐ventral expression.
Microarray analysis identified 23 targets differentially expressed in all three arrays. Real‐time PCR confirmed 17 up‐regulated and 2 down‐regulated targets. Whole mount in situ hybridization of WT 12.5 dpc embryos demonstrated a dorsal‐ventral asymmetric pattern for the validated targets, further categorized as skeletal, soft tissue or other. Skeletal targets, including Emx2, Matrilin1 and Matrilin4, demonstrated a loss of scapular expression in the Lmx1b KO mice. Soft tissue targets which demonstrated dorsal mesodermal staining in WT were drastically reduced in KO limbs. This study provides the most comprehensive characterization of skeletal and soft tissue genes regulated by Lmx1b during limb development to date. Our data also suggest targets which Lmx1b may augment to ensure proper scapular development. Further studies are warranted to determine the mechanism of Lmx1b target regulation during limb dorsalization. NIH HD39421
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