,, 任彦栋, 邱强西北工业大学生态环境学院,西安 710072通讯作者: 邱强,博士,教授,研究方向：进化基因组学。E-mail:qiuqiang@lzu.edu.cn
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收稿日期:2021-02-4修回日期:2021-02-10网络出版日期:2021-04-16
Received:2021-02-4Revised:2021-02-10Online:2021-04-16
作者简介 About authors
王堃,博士,副教授,研究方向：脊椎动物演化。E-mail:
任彦栋,博士,博士后,研究方向：进化基因组学。E-mail:
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王堃, 任彦栋, 邱强. 脊椎动物从水生到陆生演化过程中的遗传创新. 遗传[J], 2021, 43(4): 291-294 doi:10.16288/j.yczz.21-063
泥盆纪时期(4亿年前)脊椎动物登陆事件是脊椎动物演化史上的一次巨大飞跃,需要脊椎动物在呼吸系统、运动系统和神经系统等诸多方面进行系统革新[1,2],从而适应从水生到陆生环境的改变。长期的古生物学和系统分类学研究显示,现存四足动物最近的鱼类近亲是肺鱼,而肉鳍鱼亚纲(包含空棘鱼、肺鱼和四足动物)与辐鳍鱼亚纲(常见的各种鱼)被统称为硬骨鱼纲。长期以来,肺鱼和早期辐鳍鱼类这些“活化石”鱼类基因组一直缺乏系统研究,特别是肺鱼拥有已知脊椎动物中最大的基因组(40 Gb以上),分析难度极大,因而硬骨鱼祖先到肉鳍鱼祖先再到陆生脊椎动物演化历程中的遗传创新机制这一重大科学问题始终没有得到很好解答。
2021年2月5日,Cell杂志在线发表了西北工业大学、中国科学院水生生物研究所、中国科学院昆明动物研究所、中国科学院北京基因组研究所、华大基因、丹麦哥本哈根大学、中国科学院古脊椎动物与古人类研究所、中国农业科学院农业基因组研究所、华南农业大学、武汉希望组生物技术公司等多个研究团队合作完成的两项脊椎动物演化的重大成果。通过对现生多个古代鱼类基因组的研究,以及进化生物学、鱼类学、古生物学、计算生物学和实验生物学等多学科交叉,分别从原始辐鳍鱼类和肺鱼两个不同的演化节点角度(图1),揭示了脊椎动物从水生到陆生转变的遗传创新基础[3,4],为理解脊椎动物的演化历史提供了新的遗传学证据。
1 原始辐鳍鱼类基因组的解析发现登陆的遗传基础已经在硬骨鱼类祖先出现
如何在缺少水体浮力的情况下支撑身体进行运动,以及如何呼吸空气中的氧,是脊椎动物从水生到陆生演化过程中需要克服的两个最重要障碍。原始辐鳍鱼类保留了一些克服从水到陆障碍有关的特征,如：拥有原始的用来呼吸空气的肺,可离水存活一段时间;拥有肌肉和内骨骼支撑的胸鳍柄,可以在水底爬行等。通过解析辐鳍鱼类基部的多鳍鱼(Polypterus senegalus)、匙吻鲟(Polyodon spathula)、弓鳍鱼(Amia calva)和鳄雀鳝(Atractosteus spatula)4个物种高质量的基因组,结合比较基因组分析和实验验证,从分子水平揭示了许多脊椎动物重要器官的同源关系,并首次提出与四足动物陆生适应相关器官和生理功能的遗传调控机制在其硬骨鱼祖先中已开始出现雏形,为后续肉鳍鱼登陆演化出四足动物这一飞跃提供了重要的遗传创新基础,包括：骨骼运动灵活性、空气呼吸功能以及心脏系统3个方面(图1)。图1
新窗口打开|下载原图ZIP|生成PPT图1脊椎动物水生-陆生转化过程中的基础与创新
Fig. 1The genetic foundation and innovation during the vertebrate water-to-land transition
原始辐鳍鱼类胸鳍的后基鳍骨与四足动物的“大臂”(肱骨)属于同源器官,但该器官在辐鳍鱼类中的真骨鱼这一支则特异性丢失[5,6,7,8]。该研究发现许多四足动物中调节四肢发育的增强子在原始辐鳍鱼类已经存在,其中一个极端保守的增强子甚至可以追溯到软骨鱼类,这一增强子可以调控下游与滑膜关节形成相关的Osr2基因的表达。通过再生实验以及原位表达分析,证实了该基因主要在后基鳍骨与鳍条的连接处表达,该区域对应了四足动物中的滑膜关节结构,揭示了滑膜关节雏形的遗传创新在硬骨鱼祖先中已经出现。
通过比较基因组分析发现,原始辐鳍鱼类的嗅觉感受器中,除了具有鱼类都拥有的检测水溶性分子的嗅觉受体之外,还具有能够检测空气分子的嗅觉受体,同时存在两种类型的嗅觉受体也暗示其具有潜在的空气呼吸能力。进一步的多器官表达谱和系统发育分析显示肺与鱼鳔的表达谱最为接近,部分在肺中特异性表达的基因在硬骨鱼的祖先中已经出现,暗示着“原肺”形成的分子基础早已存在。此外,原始辐鳍鱼类肺中高表达的基因显著集中在血管新生通路,可能与其肺或鱼鳔表面密布血管从而帮助氧气扩散及运输相关。以上结果表明,人们常见的真骨鱼的鱼鳔是由脊椎动物早期的肺演变而来,并且遗传基础早在硬骨鱼祖先阶段就已经产生。
空气呼吸能力的出现必然伴随着血液循环系统的提升,因而心脏和呼吸系统的协同演化对脊椎动物从水生到陆生的转变至关重要,从鱼类的一心房一心室到人类的两心房两心室,心脏的结构和功能也不断趋向完善和复杂。共线性分析发现,与心脏系统相关的基因在人类和多鳍鱼之间存在非常保守的共线性关系,表明这些基因具有保守的调控机制。该研究首次鉴定出一个Hand2基因的保守调控原件,在小鼠基因组中靶向删除该调控元件后,发现Hand2基因在在早期胚胎的右心室表达量降低,并导致心脏发育不全以及先天性死亡。
2 肺鱼基因组的解析揭示脊椎动物水生-陆生转变过程中的遗传创新
肺鱼是四足动物最近的现生姊妹群,是解析脊椎动物登陆过程不可或缺的桥梁。然而,肺鱼属物种基因组大小从40~100 Gb不等[9],是人类基因组大小的十数倍,对其超大基因组的解析成为巨大的挑战。该研究利用单分子测序技术,并开发了全新的组装算法,成功地解析了非洲肺鱼的基因组。该基因组组装大小为40.05 Gb,与预测大小相吻合,也是迄今已被解析的最大基因组。该基因组包含95.4%的脊椎动物完整基因,组装质量远超过2018年发表的美西螈(包含70%脊椎动物完整基因,32 Gb)[10]及2021年发表的澳洲肺鱼(包含67%脊椎动物完整基因,34 Gb)[11]基因组,标志着我国科研人员在解析超大复杂基因组方面已经达到国际顶尖水平。利用这一高质量基因组,研究人员揭示了肺鱼基因组增大之谜,并深入解析了脊椎动物在登陆过程中出现的新基因、新调控元件及其他遗传创新。这些遗传创新与脊椎动物水生-陆生转变过程中呼吸系统、四肢及运动系统、鳃弓演化和神经系统的演变密切相关(图1)。肺鱼基因组扩增主要是由于逆转录转座子在数亿年中持续插入造成的结果。这一持续性的基因组扩增使得肺鱼的内含子长度要远超其他物种。在肺鱼基因组中,基因长度超过1 Mb的有5000个,而在人类基因组中只有数十个。然而,这些超长基因的转录水平却并未受到很大影响,表明肺鱼具备对超长基因的高效转录机制。通过对数十个脊椎动物基因组的成分进行系统分析,发现与基因组大小呈显著正相关的不仅有逆转录转座子的数量,另外一类与抑制转座子直接相关的锌指蛋白也随着基因组的增大而普遍扩张,这类锌指蛋白还在肺鱼的生殖腺中高表达,可能在生殖系细胞中起到抑制转座子活性的作用。这可能是肺鱼基因组之所以能容忍数量庞大的逆转录转座子的因素之一,也是大基因组应对逆转录转座子的一种补偿机制。
四足动物的标志是五指的形成,这一表型也标志着脊椎动物真正走向陆地。此前的主流观点认为,Hoxa11和Hoxa13在四肢末端的互斥表达是五指形成的机制。当Hoxa11和Hoxa13在四肢末端共表达时,出现类似鱼鳍的表型;当Hoxa13在四肢末端抑制Hoxa11的表达时,则出现五指的表型,然而此前的研究始终未能发现这一调控背后所对应的遗传创新机制。在高质量肺鱼基因组基础上,该研究在Hoxa11上游200 bp左右发现了一个四足动物新起源的调控元件,可能与Hoxa13用以调控Hoxa11的时空表达密切相关。有趣的是,这一新起源的调控元件在蛇类和鸟类中发生了较大的变异,可能与其附肢的特化有关。该研究还发现了多个与手臂形成(桡骨出现和运动神经元能力增强)相关的遗传变异,包括影响四肢发育的角质鳍条蛋白编码基因在肺鱼(丢失一个拷贝)和四足动物(丢失全部拷贝)中渐进式丢失,控制后肢发育的Hox13b基因在四足动物中发生了特异性的大片段缺失,控制腰椎运动神经元发育的Hoxc10基因上游产生了四足类动物特异性的调控元件等。这些结果首次在全基因组水平揭示了脊椎动物获得陆地性附肢和运动能力的遗传创新机制。
液体(血液)与空气交界面对肺泡造成的表面张力是直接呼吸空气的陆生脊椎动物必须要面对的挑战,而肺表面活性剂基因的表达则是解决这一问题的关键。陆地脊椎动物中的肺表面活性剂基因包括SP-A、SP-B、SP-C和SP-D四种[12,13,14]。该研究发现这些基因经历了至少3步演化,从硬骨鱼祖先就开始出现的SP-B证明了硬骨鱼祖先就已经具备初步的空气呼吸能力;而从肉鳍鱼祖先出现的新基因SP-C,证明了肉鳍鱼祖先呼吸能力得到了进一步的增强;最终从四足动物祖先开始出现的新基因SP-A和SP-D,标志着陆生脊椎动物呼吸系统的完备。此外,Slc34a2基因在循环利用肺表面活性剂的磷脂质方面具有关键性作用,该基因在肺鱼和四足动物的肺中高表达,但在辐鳍鱼类的肺中低表达。此前研究表明,该基因在斑马鱼中主要在消化系统中表达,以提高磷元素的利用率[15,16]。因此,该基因可能是在肉鳍鱼祖先中被肺招募,使其呼吸功能得到了进一步增强。
在脊椎动物登陆过程中,大脑中最为显著的改变发生在负责情绪处理的杏仁核区域中[17]。从肺鱼和四足动物的共同祖先开始,杏仁核开始具备相对成熟的多分区结构[18,19]。该研究发现,在肺鱼和四足动物的祖先出现了两个新基因,Nps和Npsr,分别编码神经肽S及其受体。这两个新基因在杏仁核中表达,负责抗焦虑功能。此外,该研究还发现了多个与杏仁核有关的基因在肺鱼和四足动物祖先都出现了较大的氨基酸变异。这些结果提示肺鱼和四足动物在抗焦虑方面可能具有更强的能力,而这一能力的增强可能对陆地生活有益。
这两项创新性的研究成果,为人们更清晰描绘脊椎动物从水生到陆生的演化过程提供了新的遗传证据：(1)四足动物陆生性背后的遗传基础早在硬骨鱼共同祖先已经出现,对后续的跨越式演化提供了分子遗传基础,特别是调控空气呼吸功能、骨骼运动灵活性、以及心肺系统发育相关的古老基因和调控元件;(2)而肉鳍鱼的祖先则在空气呼吸、陆地运动和神经系统方面得到进一步的完善,为四足动物的最终登陆做好了前期准备。
参考文献 原文顺序
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Recent discoveries of previously unknown fossil forms have dramatically transformed understanding of many aspects of the fish-tetrapod transition. Newer paleobiological approaches have also contributed to changed views of which animals were involved and when, where, and how the transition occurred. This review summarizes major advances made and reevaluates alternative interpretations of important parts of the evidence. We begin with general issues and concepts, including limitations of the Paleozoic fossil record. We summarize important features of paleoclimates, paleoenvironments, paleobiogeography, and taphonomy. We then review the history of Devonian tetrapods and their closest stem group ancestors within the sarcopterygian fishes. It is now widely accepted that the first tetrapods arose from advanced tetrapodomorph stock (the elpistostegalids) in the Late Devonian, probably in Euramerica. However, truly terrestrial forms did not emerge until much later, in geographically far-flung regions, in the Lower Carboniferous. The complete transition occurred over about 25 million years; definitive emergences onto land took place during the most recent 5 million years. The sequence of character acquisition during the transition can be seen as a five-step process involving: (1) higher osteichthyan (tetrapodomorph) diversification in the Middle Devonian (beginning about 380 million years ago [mya]), (2) the emergence of
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Rich fossil evidence suggests that many traits and functions related to terrestrial evolution were present long before the ancestor of lobe- and ray-finned fishes. Here, we present genome sequences of the bichir, paddlefish, bowfin, and alligator gar, covering all major early divergent lineages of ray-finned fishes. Our analyses show that these species exhibit many mosaic genomic features of lobe- and ray-finned fishes. In particular, many regulatory elements for limb development are present in these fishes, supporting the hypothesis that the relevant ancestral regulation networks emerged before the origin of tetrapods. Transcriptome analyses confirm the homology between the lung and swim bladder and reveal the presence of functional lung-related genes in early ray-finned fishes. Furthermore, we functionally validate the essential role of a jawed vertebrate highly conserved element for cardiovascular development. Our results imply the ancestors of jawed vertebrates already had the potential gene networks for cardio-respiratory systems supporting air breathing.
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Lungfishes are the closest extant relatives of tetrapods and preserve ancestral traits linked with the water-to-land transition. However, their huge genome sizes have hindered understanding of this key transition in evolution. Here, we report a 40-Gb chromosome-level assembly of the African lungfish (Protopterus annectens) genome, which is the largest genome assembly ever reported and has a contig and chromosome N50 of 1.60 Mb and 2.81 Gb, respectively. The large size of the lungfish genome is due mainly to retrotransposons. Genes with ultra-long length show similar expression levels to other genes, indicating that lungfishes have evolved high transcription efficacy to keep gene expression balanced. Together with transcriptome and experimental data, we identified potential genes and regulatory elements related to such terrestrial adaptation traits as pulmonary surfactant, anxiolytic ability, pentadactyl limbs, and pharyngeal remodeling. Our results provide insights and key resources for understanding the evolutionary pathway leading from fishes to humans.
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The pectoral fins of Acipenseriformes possess endoskeletons with elements homologous to both the fin radials of teleosts and the limb bones of tetrapods. Here we present a study of pectoral fin development in the North American paddlefish, Polyodon spathula, and the white sturgeon, Acipenser transmontanus, which reveals that aspects of both teleost and tetrapod endoskeletal patterning mechanisms are present in Acipenseriformes. Those elements considered homologous to teleost radials, the propterygium and the mesopterygial radials, form via subdivision of an initially chondrogenic plate of mesenchymal cells called the endoskeletal disc. In Acipenseriformes, elements homologous to the sarcopterygian metapterygium develop separately from the endoskeletal disc as an outgrowth of the endoskeletal shoulder girdle that extends into the posterior margin of the finbud. As in tetrapods, the elongating metapterygium and the metapterygial radials form in a proximal to distal order as discrete condensations from initially nonchondrogenic mesenchyme. Patterns of variation seen in the Acipenseriform fin also correlate with putative homology: all variants from the
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Two major morphological changes occurred during the fin-to-limb transition: the appearance of the autopod, and the reduction of anterior skeletal elements. In the past decades, numerous approaches to the study of genetic developmental systems involved in patterning of fins/limbs among different taxa have provided clues to better understand the mechanism of the fin-to-limb transition. In this article, I discuss recent progress toward elucidating the evolutionary origin of the autopod and the mechanism through which the multiple-basal bones of ancestral fins were reduced into a single bone (humerus/femur). A particular focus of this article is the patterning mechanism of the tetrapod limb and chondrichthyan fin controlled by gene networks involving the 5'Hox genes, Gli3 and Shh. These recent data provide possible scenarios that could have led to the transformation of fins into limbs.
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A wrist joint and structures typical of the hand, such as digits, however, are absent in [Eustenopteron] (Andrews and Westoll, '68, p 240). Great changes must have been undergone during evolution of the ankle joint; the small number of large bones in the fin must somehow have developed into a large number of small bones, and it is very difficult to draw homologies in this region, or even be certain of what is being compared (Andrews and Westoll, '68, p 268). The tetrapod limb is one of the major morphological adaptations that facilitated the transition from an aquatic to a terrestrial lifestyle in vertebrate evolution. We review the paleontological evidence for the fin-limb transition and conclude that the innovation associated with evolution of the tetrapod limb is the zeugopodial-mesopodial transition, i.e., the evolution of the developmental mechanism that differentiates the distal parts of the limb (the autopodium, i.e., hand or foot) from the proximal parts. Based on a review of tetrapod limb and fish fin development, we propose a genetic hypothesis for the origin of the autopodium. In tetrapods the genes Hoxa-11 and Hoxa-13 have locally exclusive expression domains along the proximal-distal axis of the limb bud. The junction between the distal limit of Hoxa-11 expression and of the proximal limit of Hoxa-13 expression is involved in establishing the border between the zeugopodial and autopodial anlagen. In zebrafish, the expression domains of these genes are overlapping and there is no evidence for an autopodial equivalent in the fin skeleton. We propose that the evolution of the derived expression patterns of Hoxa-11 and Hoxa-13 may be causally involved in the origin of the tetrapod limb.
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How the hand and digits originated from fish fins during the Devonian fin-to-limb transition remains unsolved. Controversy in this conundrum stems from the scarcity of ontogenetic data from extant lobe-finned fishes. We report the patterning of an autopod-like domain by hoxa13 during fin development of the Australian lungfish, the most closely related extant fish relative of tetrapods. Differences from tetrapod limbs include the absence of digit-specific expansion of hoxd13 and hand2 and distal limitation of alx4 and pax9, which potentially evolved through an enhanced response to shh signaling in limbs. These developmental patterns indicate that the digit program originated in postaxial fin radials and later expanded anteriorly inside of a preexisting autopod-like domain during the evolution of limbs. Our findings provide a genetic framework for the transition of fins into limbs that supports the significance of classical models proposing a bending of the tetrapod metapterygial axis.
DOI:10.1093/molbev/mss159URL [本文引用: 1]
Haploid genomes greater than 25,000 Mb are rare, within the animals only the lungfish and some of the salamanders and crustaceans are known to have genomes this large. There is very little data on the structure of genomes this size. It is known, however, that for animal genomes up to 3,000 Mb, there is in general a good correlation between genome size and the percent of the genome composed of repetitive sequence and that this repetitive component is highly dynamic. In this study, we sampled the Australian lungfish genome using three mini-genomic libraries and found that with very little sequence, the results converged on an estimate of 40% of the genome being composed of recognizable transposable elements (TEs), chiefly from the CR1 and L2 long interspersed nuclear element clades. We further characterized the CR1 and L2 elements in the lungfish genome and show that although most CR1 elements probably represent recent amplifications, the L2 elements are more diverse and are more likely the result of a series of amplifications. We suggest that our sampling method has probably underestimated the recognizable TE content. However, on the basis of the most likely sources of error, we suggest that this very large genome is not largely composed of recently amplified, undetected TEs but may instead include a large component of older degenerate TEs. Based on these estimates, and on Thomson's (Thomson K. 1972. An attempt to reconstruct evolutionary changes in the cellular DNA content of lungfish. J Exp Zool. 180:363-372) inference that in the lineage leading to the extant Australian lungfish, there was massive increase in genome size between 350 and 200 mya, after which the size of the genome changed little, we speculate that the very large Australian lungfish genome may be the result of a massive amplification of TEs followed by a long period with a very low rate of sequence removal and some ongoing TE activity.
DOI:10.1038/nature25473URLPMID:29364871 [本文引用: 1]
The planarian Schmidtea mediterranea is an important model for stem cell research and regeneration, but adequate genome resources for this species have been lacking. Here we report a highly contiguous genome assembly of S. mediterranea, using long-read sequencing and a de novo assembler (MARVEL) enhanced for low-complexity reads. The S. mediterranea genome is highly polymorphic and repetitive, and harbours a novel class of giant retroelements. Furthermore, the genome assembly lacks a number of highly conserved genes, including critical components of the mitotic spindle assembly checkpoint, but planarians maintain checkpoint function. Our genome assembly provides a key model system resource that will be useful for studying regeneration and the evolutionary plasticity of core cell biological mechanisms.
DOI:10.1038/s41586-021-03198-8URLPMID:33461212 [本文引用: 1]
Lungfishes belong to lobe-fined fish (Sarcopterygii) that, in the Devonian period, 'conquered' the land and ultimately gave rise to all land vertebrates, including humans(1-3). Here we determine the chromosome-quality genome of the Australian lungfish (Neoceratodus forsteri), which is known to have the largest genome of any animal. The vast size of this genome, which is about 14x larger than that of humans, is attributable mostly to huge intergenic regions and introns with high repeat content (around 90%), the components of which resemble those of tetrapods (comprising mainly long interspersed nuclear elements) more than they do those of ray-finned fish. The lungfish genome continues to expand independently (its transposable elements are still active), through mechanisms different to those of the enormous genomes of salamanders. The 17 fully assembled lungfish macrochromosomes maintain synteny to other vertebrate chromosomes, and all microchromosomes maintain conserved ancient homology with the ancestral vertebrate karyotype. Our phylogenomic analyses confirm previous reports that lungfish occupy a key evolutionary position as the closest living relatives to tetrapods(4,5), underscoring the importance of lungfish for understanding innovations associated with terrestrialization. Lungfish preadaptations to living on land include the gain of limb-like expression in developmental genes such as hoxc13 and sall1 in their lobed fins. Increased rates of evolution and the duplication of genes associated with obligate air-breathing, such as lung surfactants and the expansion of odorant receptor gene families (which encode proteins involved in detecting airborne odours), contribute to the tetrapod-like biology of lungfishes. These findings advance our understanding of this major transition during vertebrate evolution.
DOI:10.1016/j.bpj.2009.08.045URLPMID:19917227 [本文引用: 1]
The presence of cholesterol is critical in defining a dynamic lateral structure in pulmonary surfactant membranes. However, an excess of cholesterol has been associated with impaired surface activity of surfactant. It has also been reported that surfactant protein SP-C interacts with cholesterol in lipid/protein interfacial films. In this study, we analyzed the effect of SP-C on the thermodynamic properties of phospholipid membranes containing cholesterol, and the ability of lipid/protein complexes containing cholesterol to form and respread interfacial films capable of producing very low surface tensions upon repetitive compression-expansion cycling. SP-C modulates the effect of cholesterol to reduce the enthalpy associated with the gel-to-liquid-crystalline melting transition in dipalmitoylphosphatidylcholine (DPPC) bilayers, as analyzed by differential scanning calorimetry. The presence of SP-C affects more subtly the effects of cholesterol on the thermotropic properties of ternary membranes, mimicking more closely the lipid composition of native surfactant, where SP-C facilitates the miscibility of the sterol. Incorporation of 1% or 2% SP-C (protein/phospholipid by weight) promotes almost instantaneous adsorption of suspensions of DPPC/palmitoyloleoylphospatidylcholine (POPC)/palmitoyloleoyl-phosphatidylglycerol (POPG) (50:25:15, w/w/w) into the air-liquid interface of a captive bubble, in both the absence and presence of cholesterol. However, cholesterol impairs the ability of SP-C-containing films to achieve very low surface tensions in bubbles subjected to compression-expansion cycling. Cholesterol also substantially impairs the ability of DPPC/POPC/POPG films containing 1% surfactant protein SP-B to mimic the interfacial behavior of native surfactant films, which are characterized by very low minimum surface tensions with only limited area change during compression and practically no compression-expansion hysteresis. However, the simultaneous presence of 2% SP-C practically restores the compression-expansion dynamics of cholesterol- and SP-B-containing films to the efficient behavior shown in the absence of cholesterol. This suggests that cooperation between the two proteins is required for lipid-protein films containing cholesterol to achieve optimal performance under physiologically relevant compression-expansion dynamics.
DOI:10.1016/j.bpj.2016.09.016URLPMID:27760357 [本文引用: 1]
To allow breathing and prevent alveolar collapse, lung surfactant (LS) develops a complex membranous system at the respiratory surface. LS is defined by a specific protein and lipid composition, including saturated and unsaturated phospholipid species and cholesterol. Surfactant protein C (SP-C) has been suggested to be an essential element for sustaining the presence of cholesterol in surfactant without functional impairment. In this work, we used a fluorescent sterol-partitioning assay to assess the effect of the surfactant proteins SP-B and SP-C on cholesterol distribution in membranes. Our results suggest that in the LS context, the combined action of SP-B and SP-C appears to facilitate cholesterol dynamics, whereas SP-C does not seem to establish a direct interaction with cholesterol that could increase the partition of free cholesterol into membranes. Interestingly, SP-C exhibits a membrane-fragmentation behavior, leading to the conversion of large unilamellar vesicles into highly curved vesicles approximately 25 nm in diameter. Sterol partition was observed to be sensitive to the bending of bilayers, indicating that the effect of SP-C to mobilize cholesterol could be indirectly associated with SP-C-mediated membrane remodeling. Our results suggest a potential role for SP-C in generating small surfactant structures that may participate in cholesterol mobilization and pulmonary surfactant homeostasis at the alveolar interfaces.
DOI:10.1016/s1095-6433(01)00308-7URLPMID:11369536 [本文引用: 1]
Pulmonary surfactant is a barrier material of the lungs and has a dual role: firstly, as a true surfactant, lowering the surface tension; and secondly, participating in innate immune defence of the lung and possibly other mucosal surfaces. Surfactant is composed of approximately 90% lipids and 10% proteins. There are four surfactant-specific proteins, designated surfactant protein A (SP-A), SP-B, SP-C and SP-D. Although the sequences and post-translational modifications of SP-B and SP-C are quite conserved between mammalian species, variations exist. The hydrophilic surfactant proteins SP-A and SP-D are members of a family of collagenous carbohydrate binding proteins, known as collectins, consisting of oligomers of trimeric subunits. In view of the different roles of surfactant proteins, studies determining the structure-function relationships of surfactant proteins across the animal kingdom will be very interesting. Such studies may reveal structural elements of the proteins required for surface film dynamics as well as those required for innate immune defence. Since SP-A and SP-D are also present in extrapulmonary tissues, the hydrophobic surfactant proteins SP-B and SP-C may be the most appropriate indicators for the evolutionary origin of surfactant. SP-B is essential for air-breathing in mammals and is therefore largely conserved. Yet, because of its unique structure and its localization in the lung but not in extrapulmonary tissues, SP-C may be the most important indicator for the evolutionary origin of surfactant.
DOI:10.1007/s10695-015-0116-zURLPMID:26298316 [本文引用: 1]
A sodium-dependent phosphate cotransporter gene, NaPi-IIb (slc34a2), was isolated from yellow catfish (Pelteobagrus fulvidraco) intestine through homology cloning and the rapid amplification of cDNA ends. The full-length cDNA of slc34a2 consisted of 2326 bp with an open reading frame encoding 621 amino acids, a 160-bp 5' untranslated region, and a 300-bp 3' untranslated region. The deduced amino acid sequence showed 79.0 and 70.9% sequence identity to Astyanax mexicanus and Pundamilia nyererei, respectively. The membrane-spanning domains based on the hydrophilic and hydrophobic properties of the deduced amino acids were predicted, and results showed that the putative protein had eight transmembrane domains, with the intracellular NH2 and COOH termini. Two functional regions including first intracellular loop and third extracellular loop as well as the six N-glycosylation sites in second extracellular loop were found. The slc34a2 mRNA in the tested tissues was examined through semiquantitative reverse transcription polymerase chain reaction and quantitative real-time PCR, with the highest level found in the anterior intestine, followed by the posterior and middle intestines. The slc34a2 mRNA expression in the whole intestine under different dietary phosphorus (P) treatments was detected using qPCR. The results showed that the slc34a2 expression levels in the low-P groups (0.33 and 0.56%) were significantly higher (p < 0.05) than levels in the sufficient-P (0.81%) and high-P (1.15, 1.31, and 1.57%) groups. High expression of slc34a2 mRNA in low-P groups stimulated P utilization efficiency, indicating the close relationship between genotype and phenotype in yellow catfish. In contrast with conventional strategies (formula and feeding strategies), this study provided another possible approach by using molecular techniques to increase the P utilization in yellow catfish.
DOI:10.1007/s10695-016-0282-7URLPMID:27620186 [本文引用: 1]
In this study, two isoforms slc34a2 genes (type IIb sodium-dependent phosphate cotransporter), slc34a2a2 and slc34a2b, were cloned from intestine and kidney of yellow catfish (Pelteobagrus fulvidraco), with rapid amplification of cDNA ends. The structure differences and the regulation effects of dietary VD3 under low phosphorus were compared among three isoforms of slc34a2 in yellow catfish. The predicted Slc34a2a2 and Slc34a2b proteins match 65 % and 53.8 % sequence identity, with Slc34a2a1, respectively. The membrane-spanning domains were different among these three isoforms. Intestinal Slc34a2a1 and Slc34a2a2 proteins had eight and eleven transmembrane domains, while renal Slc34a2b protein had nine. The tissue distribution study showed that same as slc34a2a1, slc34a2a2 mRNA was mainly distributed in intestine and slc34a2b mRNA in kidney. The effect of vitamin D3 (VD3) level on slc34a2 subfamily expression under low-phosphate conditions, induced by the addition of 0 (VD0), 324 (VD1), 1243 (VD2), 3621 (VD3), 8040 (VD4), or 22700 (VD5) IU VD3/kg feed, was assessed by qPCR. The dose-responsive expression of intestinal slc34a2a2 and high expression of intestinal slc34a2a2 in VD5 together with peak expression of kidney slc34a2b in VD3 coincided with the accumulation of body phosphate content. These data suggested that appropriate level of dietary VD3 up-regulated slc34a2a1, slc34a2a2, and slc34a2b mRNA levels, which increased phosphate retention. In conclusion, the current study provided another possible approach to improve dietary phosphate utilization by adding appropriate level of VD3 to a low-phosphate diet to regulate intestinal and renal slc34a2 gene expression and thus minimize the excretion of phosphorus in yellow catfish.
DOI:10.1159/000113276URLPMID:8564465 [本文引用: 1]
Recent studies of the limbic system of tetrapods have made data available that challenge some of the long-held tenets of forebrain evolution. Using the basic principle of parsimony--that the best hypotheses concerning homologies are those requiring the fewest number of evolutionary changes--we have reevaluated comparisons of tetrapod limbic systems. Given the current data, the following points appear to be justified: (1) the common ancestors of reptiles and mammals had a well-developed limbic system in which the basic subdivisions and connections of the amygdalar nuclei were established; (2) the ventral part of the lateral pallium in amphibians appears to be a single structure which corresponds to at least four areas in reptiles: centromedial DVR, ventral anterior amygdala, lateral amygdala, and part of the lateral cortex; (3) the medial pallium in amphibians appears to be homologous with the dorsal and medial cortices in reptiles and with the general and hippocampal cortices in mammals: (4) the cortical targets of the main olfactory bulb in reptiles and mammals appear to be homologous, and their common ancestor probably had a corresponding olfactory pallial field; (5) the targets of the accessory olfactory bulb in amphibians, reptiles, and mammals appear to be homologous, with the exception of nucleus sphericus in reptiles, which lacks an obvious homologue in non-reptiles.
DOI:10.1159/000204963URLPMID:19246896 [本文引用: 1]
Recent studies have greatly increased our knowledge of telencephalic organization in ray-finned fishes and terrestrial vertebrates, particularly amphibians. In contrast, little new information has been generated on telencephalic organization in lobe-finned fishes. The coelacanth, Latimeria, and three genera of lungfishes constitute the living lobe-finned fishes. Latimeria is extremely rare and critically endangered, so the living lungfishes, therefore, offer the only feasible source of new information on telencephalic organization in lobe-finned fishes. A re-examination of the cytoarchitectonics of the telencephalon in the Spotted African Lungfish has allowed the generation of a new model of telencephalic organization in lungfishes. To begin to test this model, examination was made of the telencephalic distribution of acetylcholinesterase, enkephalin, the neurotensin-related hexapeptide LANT6, nitric oxide synthase (nicotinamide adenine dinucleotide phosphate-diaphorase), substance P, and tyrosine hydroxylase. This distribution supports the new model and suggests that the medial pallial-subpallial border, the striatopallidal systems, and the amygdalar organization in this lungfish are more similar to these features in terrestrial vertebrates than was previously suspected.
DOI:10.1159/000229012URLPMID:19729895 [本文引用: 1]
The brains of lungfishes have received little attention in comparative neuroanatomy, in spite of the strategic position of these fishes in phylogeny, in that they are currently recognized as the closest living relatives of tetrapods. The neglect has probably been due to the difficulty of obtaining these unique animals, which comprise (along with the coelacanths) the only extant representatives of the lobe-finned fishes. Several previous studies have established the basic anatomy of the telencephalon in lungfishes, but many aspects of the intrinsic organization of the main telencephalic subregions have remained unclear. The immunohistochemical localization of diverse neurotransmitters, neuromodulators, and transcription factors expressed by genes involved in brain regionalization has served to clarify many aspects of the organization of the telencephalon in lungfishes. Here we describe the main immunohistochemical features of the telencephalon in two lungfish species, Protopterus dolloi and Neoceratodus forsteri. Our analysis highlights the common traits shared by lungfishes and tetrapods. These include four pallial regions, distinct striatal and pallidal components of the basal ganglia, specific regionalization of the septum, and the presence of three amygdaloid regions. In general, the use of immunohistochemistry in the study of the telencephalon of lungfishes reveals that this structure is notably more complex than previously thought and that it possesses all major subregions recognized in amphibians and amniotes.
