DNA has received considerable attention as a promising building material owing to its ability to form predictable secondary structures through sequence-directed hybridization. [ 1 , 2 ] It has been shown that DNA can be precisely designed with specifi c sequences and self-assemble into two-or three-dimensional nanostructures, [3][4][5][6][7][8][9] fabricated to nanomachines or motors, [10][11][12][13] or used as a programmable template to direct the assembly of nanoparticles. [14][15][16][17] Recently, the concept of DNA assembly has been expanded to construct "DNA hydrogels", which are crosslinked networks swollen in an aqueous phase. [18][19][20][21][22][23][24][25][26][27][28][29][30][31] Though hydrogels have great potential in biological and medical applications, [32][33][34][35][36] such as drug and gene delivery, biosensing, and tissue engineering, studying the preparation of DNA hydrogels with designable properties is still in its early stages. In the past, several methods have been reported to prepare DNA hydrogels, for example, DNA directly extracted from the nucleus in nature, behaves like a long linear polymer and forms a hydrogel via physical entanglement or by chemical crosslinking of small molecules. [ 18 − 20] Similarly, DNA can be used as a negatively charged polymer and form a complex with cationic (poly)electrolytes through electrostatic interactions. [ 21 , 22 ] However, both methods treated DNA as a polymer and did not take advantage of the self-assembly of DNA into ordered structures, therefore, the resulting hydrogels lacked precise structural control and specifi c responses. Instead of using physical interactions, DNA can be covalently grafted onto synthetic polymers and serve as a cross-linker, the recognition of complementary DNA strands leads to crosslinking of polymer chains and causes hydrogel formation. [ 23 − 28] In general, the preparation of a DNA-polymer hybrid requires laborious modifi cation steps, and an easy and fast strategy to build tailored DNA hydrogels is desired. Luo and his coworkers have developed a new approach to construct pure DNA hydrogels: using well-designed DNA sequences, selfassembled DNA building blocks with more than two branches could be prepared and further enzymatic ligation between the building blocks led to DNA hydrogel formation. [ 29 ] These DNA hydrogels have been demonstrated for potential applications in controllable drug release [ 29 ] and cell-free protein-producing systems, [ 30 ] however, the enzymatic ligation is rather slow and the preparation is time-consuming. More recently, we have reported that pure DNA hydrogels could be made based on duplex formation and intermolecular i-motif structures. The DNA hydrogels showed a fast sol-gel transition upon changes in the pH, that is, within minutes, and released cargoes in a pH-controlled manner. [ 31 ] However, these DNA hydrogels were not stable under physiological conditions, which limited their in-vivo applications.Herein, we propose a new and general platform to create pure DNA hydrogels t...

Planar cell polarity (PCP) refers to coordinated polarization of cells within the plane of a cell sheet. A conserved signaling pathway is required for the establishment of PCP in epithelial tissues and for polarized cellular rearrangements known as convergent extension. During PCP signaling, core PCP proteins are sorted asymmetrically along the polarization axis; this sorting is thought to direct coordinated downstream morphogenetic changes across the entire tissue. Here, we show that a gene encoding a ciliary protein (a 'ciliary gene'), Ift88, also known as Polaris, is required for establishing epithelial PCP and for convergent extension of the cochlear duct of Mus musculus. We also show that the proper positioning of ciliary basal bodies and the formation of polarized cellular structures are disrupted in mice with mutant ciliary proteins ('ciliary mutants'), whereas core PCP proteins are partitioned normally along the polarization axis. Thus, our data uncover a distinct requirement for ciliary genes in basal body positioning and morphological polarization during PCP regulation.

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A rapidly formed supramolecular polypeptide-DNA hydrogel was prepared and used for in situ multilayer three-dimensional bioprinting for the first time. By alternative deposition of two complementary bio-inks, designed structures can be printed. Based on their healing properties and high mechanical strengths, the printed structures are geometrically uniform without boundaries and can keep their shapes up to the millimeter scale without collapse. 3D cell printing was demonstrated to fabricate live-cell-containing structures with normal cellular functions. Together with the unique properties of biocompatibility, permeability, and biodegradability, the hydrogel becomes an ideal biomaterial for 3D bioprinting to produce designable 3D constructs for applications in tissue engineering.