Davis, P. J. | bioRxiv Science

bioRxiv2025

Prevalence and modulation of rat off-track head-scanning on linear tracks: possible implications for representational and dynamical properties of hippocampal place cells

(Re)mapping of different environments by hippocampal place cells is thought to reflect incidental learning. Rat "head scanning" is a spontaneous and presumed investigatory behavior that can trigger the onset of firing locations in place cells. This behavior was studied on (quasi-)circular tracks, and it was speculated that off-track head scans might have been overlooked or inadvertently discouraged in studies employing more common apparatus. To better understand the general prevalence and significance of off-track scanning, we investigated it in rats running laps on linear tracks in rooms featuring visual landmarks. Scanning spanned the length of the track, even in highly familiar conditions and in rats rewarded only at the two ends of the track. Thus, co-localized rewards are not necessary for the occurrence of this behavior. Scanning rate increased markedly in a novel room and then declined steeply during each daily session in this room over 3 days. Transient increases at the beginning of each daily session partially counteracted this decline, producing a "seesaw" profile that is reminiscent of previous observations on place cell plasticity. Therefore, the remapping that place cells are known to undergo in similar contextual changes could conceivably be facilitated by the putative surge of new place fields induced by increased scanning. Investigatory behaviors could thus be causally involved in the representational and dynamic properties of hippocampal representations. Addressing these possibilities offers insight into the incidental creation and update of a cognitive map. HIGHLIGHTSO_LIRat head scanning is known to trigger the onset of firing locations in place cells C_LIO_LIOff-track scanning occurs on linear tracks in familiar and novel conditions C_LIO_LICo-localized rewards are not necessary for scanning events C_LIO_LIResponse to a novel room resembles that seen in place cell dynamics C_LIO_LIRelationships between head scanning and place field formation could help uncover the incidental process of map making C_LI

neuroscience↗

bioRxiv2021

Kinetic pathway of ATP-induced DNA interactions of ParA2, a protein essential for segregation of Vibrio cholerae chromosome 2

Vibrio cholerae chromosome 2 (Chr2) requires its own ParABS system for segregation. Without it, V. cholerae becomes nonviable and loses pathogenicity. ParA2 of Chr2 is a Walker-type ATPase that is the main driver of Chr2 segregation. Most of our understanding of ParA function comes from studying plasmid partition systems. How ParA provides the motive force in segregation of chromosomes, which are much larger than plasmids, is less understood and different models have been proposed. Here we analyzed in vivo behavior and kinetic properties of ParA2 using cell imaging, biochemical and biophysical approaches. ParA2 formed an asymmetric gradient in the cell that localized dynamically in the cell cycle. We found that ParA2 dimers bind ATP and undergo a slow conformational change to an active DNA-binding state, similar to P1 ParA. The presence of DNA catalyzes ParA2 conformational change to allow cooperative binding of active ParA2 dimers to form higher-order oligomers on DNA. Nucleotide exchange rates were also slow, thus providing a control of ParA2 recruitment and dynamic localizations. Although highly conserved in biochemical properties, ParA2 showed faster overall ATP cycling and DNA-rebinding rates than plasmid ParAs, suggesting that this could be shared kinetic features among chromosomal ParAs to regulate the transport of a much larger DNA cargo.

biochemistry↗