https://nova.newcastle.edu.au/vital/access/ /manager/Index en-au 5 https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:6863 Wed 11 Apr 2018 15:06:40 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:52566 Tue 17 Oct 2023 15:40:56 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:18116 2+-mediated activation of the anaphase-promoting complex/cyclosome (APC/C). Although the loss in activity of the M-phase kinase CDK1 is known to be an essential downstream event of this process, the contribution of phosphatases to arrest and meiotic resumption is less apparent, especially in mammals. Therefore, we explored the role of protein phosphatase 2A (PP2A) in mouse eggs using pharmacological inhibition and activation as well as a functionally dominant-negative catalytic PP2A subunit (dn-PP2Ac-L199P) coupled with live cell imaging. We observed that PP2A inhibition using okadaic acid induced events normally observed at fertilization: degradation of the APC/C substrates cyclin B1 and securin resulting from loss of the APC/C inhibitor Emi2. Although sister chromatids separated, chromatin remained condensed, and polar body extrusion was blocked as a result of a rapid spindle disruption, which could be ameliorated by non-degradable cyclin B1, suggesting that spindle integrity was affected by CDK1 loss. Similar cell cycle effects to okadaic acid were also observed using dominant-negative PP2Ac. Preincubation of eggs with the PP2A activator FTY720 could block many of the actions of okadaic acid, including Emi2, cyclin B1, and securin degradation and sister chromatid separation. Therefore, in conclusion, we used okadaic acid, dn-PP2Ac-L199P, and FTY720 on mouse eggs to demonstrate that PP2A is needed to for both continued metaphase arrest and successful exit from meiosis.]]> Sat 24 Mar 2018 08:04:35 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:6580 Sat 24 Mar 2018 07:49:18 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:6570 Sat 24 Mar 2018 07:49:16 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:6554 Sat 24 Mar 2018 07:48:22 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:27419 1 m, suggesting that deep nesting in V. panoptes may be an evolutionary response to egg desiccation during the long (approximately 8 months) dry season incubation period. Alternatively, lizards may avoid shallower nesting because even slight daily temperature fluctuations are detrimental to developing embryos; our data show that this species may have the most stable incubation environment of any reptile and possibly any ectotherm. Soil-filled burrows do not support the hypothesis generated for Daimonelix that the helix would provide more consistent temperature and humidity as a result of limited air circulation in dry palaeoclimates. We suggest that Daimonelix were used mainly for nesting or rearing young, because helical burrows of extant vertebrates are generally associated with a nest. The extraordinary nesting in this lizard reflects a system in which adaptive hypotheses for the function of fossil helical burrows can be readily tested.]]> Sat 24 Mar 2018 07:35:23 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:35384 Varanus panoptes and V. gouldii) have been discovered at depths of 2.3–3.0 m, suggesting that nesting at extreme depths in these species is an adaptive response to the lack of sufficient soil moisture at shallower depths. Herein, we examine this idea with V. panoptes, specifically predicting that deeper nests in a desert ecosystem compared with those in a savannah ecosystem are attributable to differences in the magnitude of rainfall. We excavated a communal nesting warren to a depth of 4 m and identified 11 fresh nests and 99 hatched nests. Mean nest depth in the present study was greater than that in savannah. However, nests were shallower than those of V. gouldii in the same general location, possibly because of local heterogeneity in soil moisture. Hatchlings excavated their own emergence burrows rather than following the burrows of their mothers, despite relatively great distances through resistant soils. Collectively, deep nesting creates energetic challenges for mothers and hatchlings, suggesting an adaptive function for the behavior.]]> Mon 22 Jul 2019 16:49:19 AEST ]]>