Temporally regulated cell migration is sensitive to variation in body size

ABSTRACTFew studies have measured the robustness to perturbations of the final position of a long-range migrating cell. In the nematodeCaenorhabditis elegans, the QR neuroblast migrates anteriorly, while undergoing three division rounds. We study the final position of two of its great-granddaughters, the end of migration of which was previously shown to depend on a timing mechanism. We find that the variance in their final position is similar to that of other long-range migrating neurons. As expected from the timing mechanism, the position of QR descendants depends on body size, which we varied by changing maternal age or using body size mutants. Using a mathematical model, we show that body size variation is partially compensated for. Applying environmental perturbations, we find that the variance in final position increased following starvation at hatching. The mean position is displaced upon a temperature shift. Finally, highly significant variation was found amongC. eleganswild isolates. Overall, this study reveals that the final position of these neurons is quite robust to stochastic variation, shows some sensitivity to body size and to external perturbations, and varies in the species.This article has an associated ‘The people behind the papers’ interview.

Timing in conversation is dynamically adjusted turn by turn: Evidence for lag-1 negatively autocorrelated turn taking times in telephone conversation

Conversational turn taking in humans has been deemed an exquisite feat of timing. Speakers tend to anticipate another speaker’s turn ending so as to rapidly initiate the next turn as a response. This rapid response often takes only around 200ms which is considerably less time than it would take to plan and initiate a next turn in response to a turn-final silence. The timing mechanism has been heavily debated, and revolves around questions such as who is doing the timing, and how to model such a timing mechanism. Here we replicate a basic phenomenon obtained in non-communicative timing research on human rhythmic tapping abilities. We show that turn transition times in phone conversations behave similarly as rhythmic tapping to a metronome. We show that there is serial dependence between turn transition times (TTT’s), such that TTT’s are lag-1 negatively autocorrelated, suggesting that there is a joint correction mechanism operating at the level of the dyad in TTT’s during telephone conversations. This finding, if replicated, has major implications for models describing turn taking, and confirms the joint anticipatory nature of human conversational dynamics. Future research is needed to see how pervasive serial dependencies in TTT’s are, such as for example in richer communicative face-to-face contexts where visual signals affect conversational timing.

Dynamics of Auxilin 1 and GAK in clathrin-mediated traffic

Clathrin-coated vesicles lose their clathrin lattice within seconds of pinching off, through the action of the Hsc70 “uncoating ATPase.” The J- and PTEN-like domain–containing proteins, auxilin 1 (Aux1) and auxilin 2 (GAK), recruit Hsc70. The PTEN-like domain has no phosphatase activity, but it can recognize phosphatidylinositol phosphate head groups. Aux1 and GAK appear on coated vesicles in successive transient bursts, immediately after dynamin-mediated membrane scission has released the vesicle from the plasma membrane. These bursts contain a very small number of auxilins, and even four to six molecules are sufficient to mediate uncoating. In contrast, we could not detect auxilins in abortive pits or at any time during coated pit assembly. We previously showed that clathrin-coated vesicles have a dynamic phosphoinositide landscape, and we have proposed that lipid head group recognition might determine the timing of Aux1 and GAK appearance. The differential recruitment of Aux1 and GAK correlates with temporal variations in phosphoinositide composition, consistent with a lipid-switch timing mechanism.

Some Questions and Answers About the Role of Hox Temporal Collinearity in Vertebrate Axial Patterning

The vertebrate anterior-posterior (A-P = craniocaudal) axis is evidently made by a timing mechanism. Evidence has accumulated that tentatively identifies the A-P timer as being or involving Hox temporal collinearity. Here, I focus on the two current competing models based on this premise. Common features and points of dissent are examined and a common model is distilled from what remains. This is an attempt to make sense of the literature.