Provenance and tectonic setting transition as recorded in the Neoproterozoic strata, western Jiangnan Orogen:Implications for South China within Rodinia

The Neoproterozoic Tonian strata (ca.870-725 Ma) in the western Jiangnan Orogen archive the records of sedimentary provenance and tectonic setting which can be used to understand the geological evolution of the South China Continent.These strata are separated into the basement and cover sequences by a regional angular unconformity.The basement sequence can be subdivided into the lower and the upper parts by the widespread interbedded ca.840 Ma basalt with pillow structure.In the present work,234 concordant detrital zircon analyses are obtained from three Tonian sandstone samples in the Fanjingshan district,Guizhou Province.Combined with previous results,a total of 1736 analyses of detrital zircon U-Pb ages derived from 12 formations of Tonian strata in the western Jiangnan Orogen are used to decipher the integrated sedimentary and tectonic histories.The zircons from the lowermost part of the basement sequence (the Yujiagou Formation) show oval morphology and display two Paleoproterozoic age peaks at 2325 Ma and 1845 Ma which are similar with the detrital zircon age peaks from the Late Paleoproterozoic to Early Mesoproterozoic Dongchuan/Dahongshan/Hekou groups,suggesting a passive margin basin in which the sediments were mainly sourced from the southwestern Yangtze Block.However,the zircon age population of the lower part of the basement sequence (the Xiaojiahe,Huixiangping formations and their equivalents) indicates the sedimentary derivation from bidirectional sources (the ca.870 Ma arc materials in the south and the old detritus from the southwestern Yangtze Block) which is consistent with a back arc setting for the deposition of the sediments.Zircons from the upper part of the basement sequence (the Duyantang Formation and its equivalent) show euhedral and subangular morphology and display a unimodal age peak at ca.835 Ma.This sequence was possibly deposited in a convergent setting and the detritus were came from the locally distributed syn-collisional igneous rocks.The lower part of the cover sequence (the Xinzhai and Wuye formations and their equivalents) shows a distinct zircon age peak at 815-809 Ma and two subordinate peaks at 2485 Ma and 2018 Ma,suggesting that the basin had gradually transformed into a continental rift basin and received the detritus from the ca.815 Ma post-collisional magmatic rocks as well as from different Paleoproterozoic source rocks in the northern Yangtze Block.We propose a tectonic evolution model that envisages eruption of ca.840 Ma basalt in a back arc basin that existed during ca.870-835 Ma,an angular unconformity was formed during amalgamation of the Yangtze Block and the Cathaysia Block at ca.835-820 Ma and the rifting of the South China Continent was initiated at ca.800 Ma.Our study concludes that the South China Continent was formed on the periphery of the Rodinia supercontinent.

FGF8 signaling sustains progenitor status and multipotency of cranial neural crest-derived mesenchymal cells in vivo and in vitro

The cranial neural crest(CNC)cells play a vital role in craniofacial development and regeneration.They are multi-potent progenitors,being able to differentiate into various types of tissues.Both pre-migratory and post-migratory CNC cells are plastic,taking on diverse fates by responding to different inductive signals.However,what sustains the multipotency ofCNCcells andderivatives remains largely unknown.In this study,we present evidence that FGF8 signaling is able to sustain progenitor status and multipotency of CNC-derived mesenchymal cells both in vivo and in vitro.We show that augmented FGF8 signaling in pre-migratory CNC cells prevents cell differentiation and organogenesis in the craniofacial region by maintaining their progenitor status.CNC-derived mesenchymal cells with Fgf8 overexpression or control cells in the presence of exogenous FGF8 exhibit prolonged survival,proliferation,and multi-potent differentiation capability in cell cultures.Remarkably,exogenous FGF8 also sustains the capability of CNC-derived mesenchymal cells to participate in organogenesis such as odontogenesis.Furthermore,FGF8-mediated signaling strongly promotes adipogenesis but inhibits osteogenesis of CNC-derived mesenchymal cells in vitro.Our results reveal a specific role for FGF8 in the maintenance of progenitor status and in fate determination of CNC cells,implicating a potential application in expansion and fate manipulation of CNC-derived cells in stem cell-based craniofacial regeneration.

The kinetics of force-dependent hybridization and strand-peeling of short DNA fragments

Deoxyribonucleic acid(DNA) carries the genetic information in all living organisms. It consists of two interwound single-stranded(ss) strands, forming a double-stranded(ds) DNA with a right-handed double-helical conformation. The two strands are held together by highly specific basepairing interactions and are further stabilized by stacking between adjacent basepairs. A transition from a dsDNA to two separated ssDNA is called melting and the reverse transition is called hybridization. Applying a tensile force to a dsDNA can result in a particular type of DNA melting, during which one ssDNA strand is peeled away from the other. In this work, we studied the kinetics of strand-peeling and hybridization of short DNA under tensile forces. Our results show that the force-dependent strand-peeling and hybridization can be described with a simple two-state model. Importantly, detailed analysis of the force-dependent transition rates revealed that the transition state consists of several basepairs dsDNA.

Phosphorylation of ATF2 promotes odontoblastic differentiation via intrinsic HAT activity

Mouse dental papilla cells(mDPCs)are cranial neural crest-derived dental mesenchymal cells that give rise to dentin-secreting odontoblasts after the bell stage during odontogenesis.The odontoblastic differentiation of mDPCs is spatiotemporally regulated by transcription factors(TFs).Our previous work reveals that chromatin accessibility was correlated with the occupation of the basic leucine zipper TF family during odontoblastic differentiation.However,the detailed mechanism by which TFs regulate the initiation of odontoblastic differentiation remains elusive.Here,we report that phosphorylation of ATF2(p-ATF2)is particularly increased during odontoblastic differentiation in vivo and in vitro.ATAC-seq and p-ATF2 CUT&Tag experiments further demonstrate a high correlation between p-ATF2 localization and increased chromatin accessibility of regions near mineralization-related genes.Knockdown of Atf2 inhibits the odontoblastic differentiation of mDPCs,while overexpression of p-ATF2 promotes odontoblastic differentiation.ATAC-seq after overexpression of p-ATF2 reveals that p-ATF2 increases the chromatin accessibility of regions adjacent to genes associated with matrix mineralization.Furthermore,we find that p-ATF2 physically interacts with and promotes H2BK12 acetylation.Taken together,our findings reveal a mechanism that p-ATF2 promotes odontoblastic differentiation at initiation via remodeling chromatin accessibility and emphasize the role of the phosphoswitch model of TFs in cell fate transitions.