DNA Nanopore-Tethered Gold Needle Electrodes for Channel Current Recording.

Synthetic DNA nanopores are attracting attention as alternatives to conventional biological nanopores in nanopore sensors because of the high designability of their pore structures and functionability. However, the efficient insertion of DNA nanopores into a planar bilayer lipid membrane (pBLM) remains challenging. Although hydrophobic modifications such as the use of cholesterol are required to insert DNA nanopores into pBLMs, these modifications also induce negative effects, including the undesired aggregation of DNA structures. Herein, we describe an efficient method to insert DNA nanopores into pBLMs and measure the channel currents of DNA nanopores using a DNA nanopore-tethered gold electrode. When the pBLM is formed at the electrode tip by immersing the electrode into a layered bath solution comprising an oil/lipid mixture and an aqueous electrolyte, the electrode-tethered DNA nanopores are physically inserted into the pBLM. In this study, we designed a DNA nanopore structure that can be immobilized on the gold electrode based on a reported six-helix bundle DNA nanopore structure and prepared DNA nanopore-tethered gold electrodes. Thereafter, we demonstrated the channel current measurements of the electrode-tethered DNA nanopores, and a high insertion probability of the DNA nanopores was achieved. We believe that this efficient DNA nanopore insertion method can accelerate the application of DNA nanopores in stochastic nanopore sensors.

Spermatogenesis in bombyx mori. I. The canal system joining sister spermatocytes.

An electron microscopic investigation was made of the origin and morphology of the canal system that connects sister spermatocytes of larval Bombyx mori. Canal formation results from incomplete cleavages during the mitoses which immediately precede meiosis. We suggest the lip which surrounds each canal is derived from the contractile ring which is prevented from constricting completely by interaction with the midbody. Cells were found with as many as four canals which demonstrates that canal rims can persist through a number of mitotic cycles. Speculations are advanced as to the significance of these canals in restricting gonocytes from unlimited divisions.

Spermatogenesis in Bombyx mori. II. The ultrastructure of synapsed bivalents.

In Bombyx mori the male is the homogametic sex, crossing over occurs only in males, and chiasmata are observed in spermatocytes, but not in oocyte nuclei. If the assembly of synaptonemal complexes is an essential prerequisite for genetic crossing over and chiasmata formation, then the nuclei of Bombyx spermatocytes should contain synaptonemal complexes. Synaptonemal complexes were found in spermatocytes from young four instar larvae. The structure of meiotic bivalents is described using micrographs taken with 100 and 1000 KV electron microscopes. These data together with that from the literature are used to construct a three-dimensional model of the synaptonemal complex and to suggest its method of origin and its function during crossing over.