Loss of scleraxis leads to distinct reduction of mineralized intermuscular bone in zebrafish

Intermuscular bones(IBs)are ossified from tendons and only occur in lower teleosts.Positive association between the regulation of scleraxis gene(scx)and tendon development gave us reasons to speculate that the scx gene may play a potential role in regulating the development of IBs.A phylogenetic analysis conducted for this study revealed potential functional differentiation between two scx orthologues,scxa and scxb.The scxa^(-/-) and scxb^(-/-) zebrafish were generated through CRISPR-Cas9 technology to study the role of scx in the IB and rib development.The results showed a significant reduction of the number of IBs in adult scxa-1^(-/-) zebrafish,with almost 70%reduction(15-25 IBs)compared to the wild type scxa-1^(+/+)zebrafish(76-80 IBs).In the scxa-1^(+/+)adults,IBs were observed in both dorsal and tail segments;however,in scxa-1^(-/-)fish IBs were observed only in the tail segment(none in the dorsal segment).Although scxa-1^(-/-) zebrafish had rib defects,the mutants were viable and fertile as adult fish.The scxb^(-/-) zebrafish had the same number of IBs and same skeletal phenotype as the wild-type fish.This suggests that only scxa has a crucial role in the IB development,and confirms functional differentiation of scx orthologues.To further clarify the molecular mechanism by which scxa affects the IB development,we conducted comparative transcriptome analysis of dorsal tissue samples of scxa-1^(+/+)(with IBs)and scxa-1^(-/-) (without IBs),and further verified the expression of key genes via qPCR.This is the first study to identify a gene that controls the amount of IBs in fish,and it provides a new sight into the effects of scxa on the molecular mechanism of IB development in fish.

Enhanced weathering input from South Asia to the Indian Ocean since the late Eocene

nhanced silicate weathering induced by the uplift of the Himalayan-Tibetan Plateau(HTP)has been considered as the major cause of pCO_(2) decline and Cenozoic cooling.However,this hypothesis remains to be validated,largely due to the lack of a reliable reconstruction of the HTP weathering flux.Here,we present a 37-million-year record of the difference in the seawater radiogenic neodymium isotopic composition(△ε_(Nd))of Ocean Drilling Program(ODP)sites and Fe-Mn crusts between the northern and central Indian Ocean,which indicates the contribution of regional weathering input from the South Asian continent to the Indian Ocean.The results show a long-term increase in △ε_(Nd) and thus provide the first critical evidence of enhanced South Asian weathering input since the late Eocene.The evolution coincided well with major pulses of surface uplift in the HTP and global climatic transitions.Our foraminiferal eNd record suggests that tectonic uplift and silicate weathering in South Asia,especially in the Himalayas,might have played a significant role in the late Cenozoic cooling.

The genetic basis of the leafy seadragon's unique camouflage morphology and avenues for its efficient conservation derived from habitat modeling

The leafy seadragon certainly is among evolution’s most“beautiful and wonderful”species aptly named for its extraordinary camouflage mimicking its coastal seaweed habitat.However,limited information is known about the genetic basis of its phenotypes and conspicuous camouflage.Here,we revealed genomic signatures of rapid evolution and positive selection in core genes related to its camouflage,which allowed us to predict population dynamics for this species.Comparative genomic analysis revealed that seadragons have the smallest olfactory repertoires among all ray-finned fishes,suggesting adaptations to the highly specialized habitat.Other positively selected and rapidly evolving genes that serve in bone development and coloration are highly expressed in the leaf-like appendages,supporting a recent adaptive shift in camouflage appendage formation.Knock-out of bmp6 results in dysplastic intermuscular bones with a significantly reduced number in zebrafish,implying its important function in bone formation.Global climate change-induced loss of seagrass beds now severely threatens the continued existence of this enigmatic species.The leafy seadragon has a historically small population size likely due to its specific habitat requirements that further exacerbate its vulnerability to climate change.Therefore,taking climate change-induced range shifts into account while developing future protection strategies.

East Asian monsoon intensification promoted weathering of the magnesium-rich southern China upper crust and its global significance

The Oligocene-Miocene boundary Asian climatic reorganization linked to the northward migration of the East Asian monsoon into subtropical China is a potentially important but poorly constrained atmospheric CO_(2) consumption process.Here,we performed a first-order estimate of the CO_(2) consumption induced by silicate chemical weathering and organic carbon burial in subtropical China related to this climatic reorganization.Our results show that an increase in long-term CO_(2 )consumption by silicate weathering varies from 0.06×10^(12)to 0.87×10^(12)mol yr^(-1)depending on erosion flux reconstructions,with an~50%contribution of Mg-silicate weathering since the late Oligocene.The organic carbon burial flux is approximately 25%of the contemporary CO_(2) consumption by silicate weathering.The results highlight the significant role of weathering of the Mg-rich upper continental crust in East China,which would contribute to the rapid decline in atmospheric CO_(2) during the late Oligocene and the Neogene rise in the seawater Mg content.If this climatic reorganization was mainly induced by the Tibetan Plateau uplift,our study suggests that the growth of the Himalayan-Tibetan Plateau can lead to indirect modification of the global carbon and magnesium cycles by changing the regional hydrological cycle in areas of East Asia that are tectonically less active.

Evolution of Asian drying since 30 Ma revealed by clay minerals record in the West Pacific and its tectonic-climatic forcing

As the second largest dust source on the globe,the tectonic and climatic evolution of continental Asia has an important impact on regional and global climate change.The West Pacific is the main sediment sink for eolian dust transported eastward from the Asian interior.Clay minerals,as the major fine-grained weathering products of continental rocks,can be readily transported by wind or currents over long distances and thus have been widely used in the reconstruction of paleoclimate and weathering history.However,the overall evolutionary tendency and response mechanism of clay mineral records over large spatial and long timescales across Asia remain unclear.Here,two continuous and high-resolution clay mineral records since 30 Ma were reconstructed from sediments at Deep Sea Drilling Program(DSDP)Sites 292 and 296 in the Philippine Sea.Clay minerals and Sr-Nd isotope compositions were used to constrain provenance and reconstruct the drying history of the dust source region since the Oligocene.The results show that the clay-sized detrital sediments in the Philippine Sea are a mixture of Asian eolian dust and volcanic materials from the West Pacific arcs.Based on the clay mineral compositions and eolian flux,we reveal that the Asian interior has been continuously drying since the late Oligocene and that stepwise enhanced aridification occurred at approximately 20,14,7,and 3 Ma.Compared with other regions of the world,the relative contents of illite and chlorite increased more dramatically in Asia during the late Cenozoic,and the inconsistency became more obvious at approximately 20 Ma.Since 3 Ma,illite and chlorite have increased consistently across the globe.Combined with the Asian tectonic and climatic history,we suggest that the increase in illite and chlorite from Asia between 20 and 3 Ma was mainly in response to the uplift of the Himalayan-Tibetan Plateau,whereas after 3 Ma,it was primarily controlled by global cooling driven by the expansion of the Arctic ice sheet.