Month: September 2022

DOWNSTREAM EFFECTS. "The asymmetrically localized Par proteins in turn shape the distributions of cytoplasmic factors that specify different developmental potentials. They also shape the distributions of cortical factors that position the mitotic spindle, and thus the first cleavage furrow, to segregate correctly developmental potentials to unequally sized daughters." https://lnkd.in/dAxynvD View in LinkedIn

CUE IDENTITIES. "The identity of the cue(s) that trigger polarization, and whether this cue involves microtubules, has been an ongoing controversy." https://lnkd.in/dAxynvD View in LinkedIn

CUES AND NO CUES. "Some symmetry-breaking systems require a polarizing cue. Others can spontaneously break symmetry in the absence of any cues, often by amplifying local stochastic fluctuations in the concentrations of participating molecules. In these cases, polarizing cues “choose” the axis of symmetry breaking." https://lnkd.in/dAxynvD View in LinkedIn

CUE THRESHOLD. "There is a threshold level of inhibition that the cue must exceed to trigger symmetry breaking. This could either be a threshold in the inhibition domain size, the duration of inhibition, or both." https://lnkd.in/dAxynvD View in LinkedIn

CUE CANDIDATES. "These observations suggest the attractive possibility that the threshold for triggering a self-amplifying asymmetry is associated with the formation kinetics of local Rho-depleted and/or Par-2-rich/myosin inhibitory domains. Simple mathematical analyses show that such feedback loops could endow the cortex with a threshold response." https://lnkd.in/dAxynvD View in LinkedIn

BYZANTINE REGULATION. "Upstream cue(s) aside, the regulation of POP-1 asymmetry and binary specification in C. elegans seems byzantine. Indeed, nematodes are the only animal phylum with multiple β-catenin genes, and the nematode β-catenins are extremely diverged in amino acid sequence; most animal genomes encode a single β-catenin, although vertebrates encode one additional β-catenin homolog called plakoglobin." https://lnkd.in/dAxynvD View in LinkedIn

FURTHER COMPLEXIFICATION. "Adding another input to an already complex process, a nuclear hormone receptor was recently shown to influence binary specification." https://lnkd.in/dAxynvD View in LinkedIn

WHY SO OVER-COMPLEX? "Thus multiple inputs can influence binary specification. The evolutionary advantage of this complicated regulatory process is not obvious: Why establish a single regulatory module, with multiple upstream inputs and a presumably extensive promoter response network, to influence nearly every cell fate decision made during development?" https://lnkd.in/dAxynvD View in LinkedIn

ANALOGOUS SYSTEM. "The answer to this evolutionary puzzle may reside within the recent discovery of a remarkably similar β-catenin mediated binary specification mechanism in another animal phylum. During the asymmetric, spirally patterned embryonic cell divisions of the polychaete annelid Platynereis dumerilii, a well conserved β-catenin accumulates to high levels in all vegetal pole daughter nuclei, and to low levels in all animal pole daughter nuclei." https://lnkd.in/dAxynvD View in LinkedIn

CONVERGENCE EXPLANATION. "Given the discovery of β-catenin-mediated binary specification systems in two distantly related animal phyla, one wonders whether binary specification might have an ancient evolutionary origin, or instead be an example of evolutionary convergence. A new report favors the latter possibility." https://lnkd.in/dAxynvD View in LinkedIn