A Dynamic Model for the Processive Motion of Dynein on Microtubules

We propose a dynamic mechanism for the processive motility of dynein on microtubules (MTs). The force generated for the motion of dynein is purely mechanical in origin. When a dynein monomer binds to a MT, the AAA ring of dynein might fit into one of the trenches on the outer surface of the MT, with the linker domain leaning on the ratchet-shaped protofilament. At room temperature, the dynein molecule exhibits random thermal motion on the outer surface of the MT. The collision between the asymmetric ratchet teeth and the linker exerts a reactive impulsive force on the dynein molecule. The probability of producing an impulse with a longitudinal component pointing to either end of the MT depends on the instantaneous motion of dynein, the shape of the linker, and the mass distribution of the dynein with/without a load. In the dynamic mechanism, dynein monomers can move independently and processively toward either end of the MT. Many observations of the motility of dynein can be reproduced in a simulation system.

Effect of Timing and Number of Intrauterine Insemination (IUI) on the Cycle Clinical Outcome

Objective To study the effect of timing and number of intrauterine insemination （IUI） per cycle on the outcome of artificial insemination by husband （AIH）. Methods A total of 195 infertile couples underwent 379 cycles of lUI with husband＇s sperm. They were divided into 4 groups according to the ovulation and the number of IUIs per cycle： single IUI was performed 24 h after hCG injection, including single IUI before ovulation （group A） and single IUI after ovulation （group B）; double IUI was performed 24 h and 48 h after hCG injection, including double IUI before and after ovulation （group C） and double IUI before ovulation （group D）. The relation-ship between IUI pregnancy rate and the factors like processed total motile sperm （PTMS）, timing and number of lUIs per cycle was analyzed. Results When PTMS〈5 × 10^6, only one case in group B got pregnant, while no pregnancy was observed in other groups. When PTMS ≥ 5 × 10^6, pregnancy rates in all group were improved significantly. The pregnancy rate in group B reached 32.22%, which was significantly higher than that in group A （14.12%）, group C （20.00%） and group D （17.39%）, respectively （P〈0.05）. Conclusion IUI treatment is recommended to be performed when PTMS ≥ 5 × 10^6. An ideal pregnancy rate can be achieved by single IUI which is performed 24 h after hCG injection, and double IUI performed without ovulation could not result in significant improvement of cycle pregnancy rate.