Structural characterization and distribution of zebrafish germ plasm during interphase and mitosis

In zebrafish, germ cells are responsible for transmitting the genetic information from one generation to the next. During the first cleavages of zebrafish embryonic development, a specialized part of the cytoplasm known as germ plasm, is responsible of committing four blastomeres to become the progenitors of all germ cells in the forming embryo. Much is known about how the germ plasm is spatially distributed in early stages of primordial germ cell development, a process described to be dependant on microtubules and actin. However, little is known about how the material is inherited after it reorganizes into a perinuclear location, or how is the symmetrical distribution regulated in order to ensure proper inheritance of the material by both daughter cells. It is also not clear whether there is a controlled mechanism that regulates the number of granules inherited by the daughter cells, or whether it is a random process. We describe the distribution of germ plasm material from 4hpf to 24hpf in zebrafish primordial germ cells using Vasa protein as marker. Vasa positive material appears to be conglomerate into 3 to 4 big spherical structures at 4hpf. While development progresses, these big structures become smaller perinuclear granules that reach a total number of approximately 30 at 24hpf. We investigated how this transformation occurs and how the minus-end microtubule dependent motor protein Dynein plays a role in this process. Additionally, we describe specific colocalization of microtubules and perinuclear granules during interphase and more interestingly, during all different stages of cell division. We show that distribution of granules follow what seems to be a regulated distribution: during cells division, daughter cells inherit an equal number of granules. We propose that due to the permanent colocalization of microtubular structures with germinal granules during interphase and cell division, a coordinated mechanism between these structures may ensure proper distribution of the material among daughter cells. Furthermore, we show that exposure to the microtubule-depolymerizing drug nocodazole leads to disassembly of the germ cell nuclear lamin matrix, chromatin condensation, and fusion of granules to a big conglomerate, revealing dependence of granular distribution on microtubules and proper nuclear structure.

On the correlation between electric polarizabilities and the ionization potential of atoms

It is found that the electric dipole polarizabilities of neutral atoms correlate very strongly with their first ionization potential within the groups of elements with the same angular momenta of the outermost electrons. As the latter values are known very accurately, this allows a very good (<30%) prediction of various atomic polarizabilities.

Electronic structure and properties of the group 4, 5 and 6 highest chlorides including elements 104, 105, and 106

Results of the Dirac-Slater discrete variational calculations for the group 4, 5, and 6 highest chlorides including elements 104, 105, and 106 have shown that the groups are not identical with respect to trends in the electronic structure and bonding. The charge density distribution data show that notwithstanding the basic increase in covalency within the groups this increase diminishes in going from group 4 to group 6. As a result, E106Cl_6 will be less stable toward thermal decomposition than WCl_6, which is confirmed by an estimated low E106-Cl bond energy. \delta H_form equal to -90.3 ± 6 kcal/rnol is obtained for E106Cl_6 in the gas phase, which is indicative of a very low stability of this compound. The stability of the maximum oxidation state is shown to decrease in the direction E104(+4) > E105(+5) > E106(+6).

Calculation of the hyperfine structure transition energy and lifetime in the one-electron Bi^82+ ion

We calculate the energy and lifetime of the ground state hyperfine structure transition in one-electron Bi^82+ . The influence of various distributions of the magnetic moment and the electric charge in the nucleus ^209_83 Bi on energy and lifetime is studied.

The electronic structure of anionic halide complexes of element 105 in aqueous solutions and their extraction by aliphatic amines

To study the complex formation of group 5 elements (Nb, Ta, Ha, and pseudoanalog Pa) in aqueous HCI solutions of medium and high concentrations the electronic structures of anionic complexes of these elements [MCl_6]^-, [MOCl_4]^-, [M(OH)-2 Cl_4]^-, and [MOCl_5]^2- have been calculated using the relativistic Dirac-Slater Discrete-Variational Method. The charge density distribution analysis has shown that tantalum occupies a specific position in the group and has the highest tendency to form the pure halide complex, [TaCl_6-. This fact along with a high covalency of this complex explains its good extractability into aliphatic amines. Niobium has equal trends to form pure halide [NbCl_6]^- and oxyhalide [NbOCl_5]^2- species at medium and high acid concentrations. Protactinium has a slight preference for the [PaOCl_5]^2- form or for the pure halide complexes with coordination number higher than 6 under these conditions. Element 105 at high HCl concentrations will have a preference to form oxyhalide anionic complex [HaOCl_5]^2- rather than [HaCl_6]^-. For the same sort of anionic oxychloride complexes an estimate has been done of their partition between the organic and aqueous phases in the extraction by aliphatic amines, which shows the following succession of the partition coefficients: P_Nb < P_Ha < P_Pa.