Morphological changes during the embryonic development of limbs of the green turtle,Chelonia mydas,were studied during the entire period of incubation,using transmission and scanning electron microscopy(TEM and SEM). ...Morphological changes during the embryonic development of limbs of the green turtle,Chelonia mydas,were studied during the entire period of incubation,using transmission and scanning electron microscopy(TEM and SEM). Limb buds were first observed at Stage 2. At that stage,the tip was covered with an apical ectodermal ridge(AER) which began to regress at Stage 6. Associated with AER was the presence of the mesenchymal cells which,consequently,differentiated into muscles,cartilage and bones. The gross features of the skeletal development appeared as a condensation of the cartilaginous structures in the proximal distal region of the limbs. The primordial digits were gradually enclosed by hard keratinized webbed skin. The increase in rate of ossification and skin pigmentation was correlated with the growth of the limbs. The development of the limbs was closely related to the transitional appearance of mucus secretion from the epidermis.展开更多
Limb loss shows recurrent phenotypic evolution across squamate lineages.Here,based on three de novo-assembled genomes of limbless lizards from different lineages,we showed that divergence of conserved non-coding eleme...Limb loss shows recurrent phenotypic evolution across squamate lineages.Here,based on three de novo-assembled genomes of limbless lizards from different lineages,we showed that divergence of conserved non-coding elements(CNEs)played an important role in limb development.These CNEs were associated with genes required for limb initiation and outgrowth,and with regulatory signals in the early stage of limb development.Importantly,we identified the extensive existence of insertions and deletions(In Dels)in the CNEs,with the numbers ranging from 111 to 756.Most of these CNEs with In Dels were lineagespecific in the limbless squamates.Nearby genes of these In Del CNEs were important to early limb formation,such as Tbx4,Fgf10,and Gli3.Based on functional experiments,we found that nucleotide mutations and In Dels both affected the regulatory function of the CNEs.Our study provides molecular evidence underlying limb loss in squamate reptiles from a developmental perspective and sheds light on the importance of regulatory element In Dels in phenotypic evolution.展开更多
Understanding limb development not only gives insights into the outgrowth and differentiation of the limb,but also has clinical relevance.Limb development begins with two paired limb buds(forelimb and hindlimb buds),w...Understanding limb development not only gives insights into the outgrowth and differentiation of the limb,but also has clinical relevance.Limb development begins with two paired limb buds(forelimb and hindlimb buds),which are initially undifferentiated mesenchymal cells tipped with a thickening of the ectoderm,termed the apical ectodermal ridge(AER).As a transitional embryonic structure,the AER undergoes four stages and contributes to multiple axes of limb development through the coordination of signalling centres,feedback loops,and other cell ac-tivities by secretory signalling and the activation of gene expression.Within the scope of proximodistal pattering,it is understood that while fibroblast growth factors(FGFs)function sequentially over time as primary components of the AER signalling process,there is still no consensus on models that would explain proximodistal patterning itself.In anteroposterior pattermning,the AER has a dual-direction regulation by which it promotes the sonic hedgehog(Shh)gene expression in the zone of polarizing activity(ZPA)for proliferation,and inhibits Shh expression in the anterior mesenchyme.In dorsoventral patterming,the AER activates Engrailed-1(En1)expression,and thus represses Wnt family member 7a(Wnt7a)expression in the ventral ectoderm by the expression of Fgfs,Sp6/8,and bone morpho-genetic protein(Bmp)genes.The AER also plays a vital role in shaping the individual digits,since levels of Fgf4/8 and Bmps expressed in the AER affect digit patterning by controlling apoptosis.In summary,the knowledge of crosstalk within AER among the three main axes is essential to understand limb growth and pattern fomation,as the development of its areas proceeds simultaneously.展开更多
文摘Morphological changes during the embryonic development of limbs of the green turtle,Chelonia mydas,were studied during the entire period of incubation,using transmission and scanning electron microscopy(TEM and SEM). Limb buds were first observed at Stage 2. At that stage,the tip was covered with an apical ectodermal ridge(AER) which began to regress at Stage 6. Associated with AER was the presence of the mesenchymal cells which,consequently,differentiated into muscles,cartilage and bones. The gross features of the skeletal development appeared as a condensation of the cartilaginous structures in the proximal distal region of the limbs. The primordial digits were gradually enclosed by hard keratinized webbed skin. The increase in rate of ossification and skin pigmentation was correlated with the growth of the limbs. The development of the limbs was closely related to the transitional appearance of mucus secretion from the epidermis.
基金the Strategic Priority Research Program of Chinese Academy of Sciences(XDB31000000)the National Natural Science Foundation of China(32220103004,32000296)+2 种基金the Second Tibetan Plateau Scientific Expedition and Research Program(2019QZKK0501)the International Partnership Program of Chinese Academy of Sciences(151751KYSB20190024)the Sichuan Science and Technology Program(2021JDJQ0002)。
文摘Limb loss shows recurrent phenotypic evolution across squamate lineages.Here,based on three de novo-assembled genomes of limbless lizards from different lineages,we showed that divergence of conserved non-coding elements(CNEs)played an important role in limb development.These CNEs were associated with genes required for limb initiation and outgrowth,and with regulatory signals in the early stage of limb development.Importantly,we identified the extensive existence of insertions and deletions(In Dels)in the CNEs,with the numbers ranging from 111 to 756.Most of these CNEs with In Dels were lineagespecific in the limbless squamates.Nearby genes of these In Del CNEs were important to early limb formation,such as Tbx4,Fgf10,and Gli3.Based on functional experiments,we found that nucleotide mutations and In Dels both affected the regulatory function of the CNEs.Our study provides molecular evidence underlying limb loss in squamate reptiles from a developmental perspective and sheds light on the importance of regulatory element In Dels in phenotypic evolution.
基金Key Research and Development Project of Shandong Province(No.2017G006043),China。
文摘Understanding limb development not only gives insights into the outgrowth and differentiation of the limb,but also has clinical relevance.Limb development begins with two paired limb buds(forelimb and hindlimb buds),which are initially undifferentiated mesenchymal cells tipped with a thickening of the ectoderm,termed the apical ectodermal ridge(AER).As a transitional embryonic structure,the AER undergoes four stages and contributes to multiple axes of limb development through the coordination of signalling centres,feedback loops,and other cell ac-tivities by secretory signalling and the activation of gene expression.Within the scope of proximodistal pattering,it is understood that while fibroblast growth factors(FGFs)function sequentially over time as primary components of the AER signalling process,there is still no consensus on models that would explain proximodistal patterning itself.In anteroposterior pattermning,the AER has a dual-direction regulation by which it promotes the sonic hedgehog(Shh)gene expression in the zone of polarizing activity(ZPA)for proliferation,and inhibits Shh expression in the anterior mesenchyme.In dorsoventral patterming,the AER activates Engrailed-1(En1)expression,and thus represses Wnt family member 7a(Wnt7a)expression in the ventral ectoderm by the expression of Fgfs,Sp6/8,and bone morpho-genetic protein(Bmp)genes.The AER also plays a vital role in shaping the individual digits,since levels of Fgf4/8 and Bmps expressed in the AER affect digit patterning by controlling apoptosis.In summary,the knowledge of crosstalk within AER among the three main axes is essential to understand limb growth and pattern fomation,as the development of its areas proceeds simultaneously.
