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Somitogenesis is a hallmark feature of all vertebrates and some invertebrate species that involves the periodic formation of block-like structures called somites. Somites are transient embryonic segments that eventually establish the entire vertebral column. A highly conserved molecular oscillator called the segmentation clock underlies this periodic event and the pace of this clock regulates the pace of somite formation. Although conserved signaling pathways govern the clock in most vertebrates, the mechanisms underlying the speciesspecific divergence in various clock characteristics remain elusive. For example, the segmentation clock in classical model species such as zebrafish, chick, and mouse embryos tick with a periodicity of ~30, ~90, and ~120 min respectively. This enables them to form the species-specific number of vertebrae during their overall timespan of somitogenesis. Here, we perform a systematic review of the species-specific features of the segmentation clock with a keen focus on mouse embryos. We perform this review using three different perspectives: Notchresponsive clock genes, ligand-receptor dynamics, and synchronization between neighboring oscillators. We further review reports that use non-classical model organisms and in vitro model systems that complement our current understanding of the segmentation clock. Our review highlights the importance of comparative developmental biology to further our understanding of this essential developmental process. [ABSTRACT FROM AUTHOR]

Membrane based separations offer an inexpensive and energy efficient pathway to purification. However, their use is often stifled during separation of organics due to low selectivity. This can be attributed to the inherent limitations of the synthesis methods employed, namely, interfacial polymerization and phase inversion. In this work, a new class of structure-by-design membranes are synthesized by surface modification of crosslinked polyimide using graft polymerization with a series of methacrylate monomers with differing chain lengths and chemistries. Graft polymerization of long chain monomers resulted in increased selectivity (α∼3.7 for 80-20 mol.% MeOH-toluene and α∼6 for 95-5 mol.% toluene-triisopropyl benzene (TIPB) for both test solutions) as a result of increased stiffness and order (using GIWAXS)). The observed selectivities renders these membranes competitive for organic solvent nanofiltration applications. In addition, pure solvent permeabilities were measured. The performance of these membranes was correlated with brush properties such as degree of grafting (using ATR-FTIR), surface polarity (contact angle measurements), stiffness (using QCM-D) and brush configuration in different solvent environments (using MD Simulations). MD simulations demonstrate that in mixtures containing hydrophobic species, polymers with longer hydrophobic side chains well more and form fuller matrices leading to increased solvent accessible surface area. GIWAXS results showed increased order with longer side chain length. These tunable membranes offer promise for organics separation. [Display omitted] • Tunable structure by design for polymer membranes. • Correlated brush length and brush chemistry with membrane selectivity. • Selectivity of 3.7 for methanol-toluene and ∼6 for toluene-TIPB mixtures. [ABSTRACT FROM AUTHOR]