Spatially and temporally-restricted expression of two T-box genes during zebrafish embryogenesis

PLCε knockdown overcomes drug resistance to androgen receptor antagonist in castration-resistant prostate cancer by suppressing the wnt3a/β-catenin pathway

Most prostate cancers (Pcas) develop into castration-resistant prostate cancer (CRPC) after receiving androgen deprivation therapy (ADT). The expression levels of PLCε and wnt3a are increased in Pca and regulate androgen receptor (AR) activity. However, the biological function and mechanisms of PLCε and wnt3a in CRPC remain unknown. In this study, we found that the expression levels of PLCε, wnt3a, and AR were significantly increased in CRPC tissues as well as bicalutamide-resistant-LNCaP and enzalutamide-resistant-LNCaP cells. In addition, PLCε knockdown partly restored the sensitivity of drug-resistant cells to bicalutamide and enzalutamide by inhibiting the activity of the wnt3a/β-catenin/AR signaling axis. Interestingly, the resistance of LNCaP cells docetaxel is related to PLCε but not the wnt3a/β-catenin pathway. We also found that the combination of PLCε knockdown and enzalutamide treatment synergistically suppressed cell proliferation, tumor growth, and bone metastasis using in vitro and in vivo experiments. Our study revealed that PLCε is involved in the progression of drug-resistance in CRPC and could be a new target for the treatment of CRPC.

The origins, scaling and loss of tetrapod digits

Many of the great morphologists of the nineteenth century marvelled at similarities between the limbs of diverse species, and Charles Darwin noted these homologies as significant supporting evidence for descent with modification from a common ancestor. Sir Richard Owen also took great care to highlight each of the elements of the forelimb and hindlimb in a multitude of species with focused attention on the homology between the hoof of the horse and the middle digit of man. The ensuing decades brought about a convergence of palaeontology, experimental embryology and molecular biology to lend further support to the homologies of tetrapod limbs and their developmental origins. However, for all that we now understand about the conserved mechanisms of limb development and the development of gross morphological disturbances, little of what is presented in the experimental or medical literature reflects the remarkable diversity resulting from the 450 million year experiment of natural selection. An understanding of conserved and divergent limb morphologies in this new age of genomics and genome engineering promises to reveal more of the developmental potential residing in all limbs and to unravel the mechanisms of evolutionary variation in limb size and shape. In this review, we present the current state of our rapidly advancing understanding of the evolutionary origin of hands and feet and highlight what is known about the mechanisms that shape diverse limbs.This article is part of the themed issue 'Evo-devo in the genomics era, and the origins of morphological diversity'.

Evolution of the tbx6/16 subfamily genes in vertebrates: insights from zebrafish

In any comparative studies striving to understand the similarities and differences of the living organisms at the molecular genetic level, the crucial first step is to establish the homology (orthology and paralogy) of genes between different organisms. Determination of the homology of genes becomes complicated when the genes have undergone a rapid divergence in sequence or when the involved genes are members of a gene family that has experienced a differential gain or loss of its constituents in different taxonomic groups. Organisms with duplicated genomes such as teleost fishes might have been especially prone to these problems because the functional redundancies provided by the duplicate copies of genes would have allowed a rapid divergence or loss of genes during evolution. In this study, we will demonstrate that much of the ambiguities in the determination of the homology between fish and tetrapod genes resulting from the problems like these can be eliminated by complementing the sequence-based phylogenies with nonsequence information, such as the exon-intron structure of a gene or the composition of a gene's genomic neighbors. We will use the Tbx6/16 subfamily genes of zebrafish (tbx6, tbx16, tbx24, and mga genes), which have been well known for the ambiguity of their evolutionary relationships to the Tbx6/16 subfamily genes of tetrapods, as an illustrative example. We will show that, despite the similarity of sequence and expression to the tetrapod Tbx6 genes, zebrafish tbx6 gene is actually a novel T-box gene more closely related to the tetrapod Tbx16 genes, whereas the zebrafish tbx24 gene, hitherto considered to be a novel gene due to the high level of sequence divergence, is actually an ortholog of tetrapod Tbx6 genes. We will also show that, after their initial appearance by the multiplication of a common ancestral gene at the beginning of vertebrate evolution, the Tbx6/16 subfamily of vertebrate T-box genes might have experienced differential losses of member genes in different vertebrate groups and gradual pooling of member gene's functions in surviving members, which might have prevented the revelation of the true identity of member genes by way of the comparison of sequence and function.

Analysis of transcriptional codes for zebrafish dopaminergic neurons reveals essential functions of Arx and Isl1 in prethalamic dopaminergic neuron development

Distinct groups of dopaminergic neurons develop at defined anatomical sites in the brain to modulate function of a large diversity of local and far-ranging circuits. However, the molecular identity as judged from transcription factor expression has not been determined for all dopaminergic groups. Here, we analyze regional expression of transcription factors in the larval zebrafish brain to determine co-expression with the Tyrosine hydroxylase marker in dopaminergic neurons. We define sets of transcription factors that clearly identify each dopaminergic group. These data confirm postulated relations to dopaminergic groups defined for mammalian systems. We focus our functional analysis on prethalamic dopaminergic neurons, which co-express the transcription factors Arx and Isl1. Morpholino-based knockdown reveals that both Arx and Isl1 are strictly required for prethalamic dopaminergic neuron development and appear to act in parallel. We further show that Arx contributes to patterning in the prethalamic region, while Isl1 is required for differentiation of prethalamic dopaminergic neurons.

ViBE-Z: a framework for 3D virtual colocalization analysis in zebrafish larval brains

Precise three-dimensional (3D) mapping of a large number of gene expression patterns, neuronal types and connections to an anatomical reference helps us to understand the vertebrate brain and its development. We developed the Virtual Brain Explorer (ViBE-Z), a software that automatically maps gene expression data with cellular resolution to a 3D standard larval zebrafish (Danio rerio) brain. ViBE-Z enhances the data quality through fusion and attenuation correction of multiple confocal microscope stacks per specimen and uses a fluorescent stain of cell nuclei for image registration. It automatically detects 14 predefined anatomical landmarks for aligning new data with the reference brain. ViBE-Z performs colocalization analysis in expression databases for anatomical domains or subdomains defined by any specific pattern; here we demonstrate its utility for mapping neurons of the dopaminergic system. The ViBE-Z database, atlas and software are provided via a web interface.

Molecular cloning and expression analysis of T-bet in ginbuna crucian carp (Carassius auratus langsdorfii)

In the adaptive immune system of mammals, naive helper T (Th) cells differentiate into Th1 or Th2 cells. The T-box expressed in T cells (T-bet) is a member of a family of T-box transcription factors that regulates the expression of IFN-gamma and plays a crucial role in Th1 cell differentiation and cell-mediated immunity. We cloned and sequenced T-bet cDNA for the first time from non-mammalian species, ginbuna crucian carp. Ginbuna T-bet was composed of 608 predicted amino acids and showed 41.5% identity with human T-bet (Tbx21), and human and ginbuna T-bet share 77.3% identity in their T-box regions. Comparative genomic analysis showed conserved synteny in these regions between zebrafish, fugu, medaka and human T-bet. Phylogenetic analysis indicated that ginbuna T-bet is closely related to that of mouse and human. In unstimulated fish, ginbuna T-bet mRNA was strongly expressed in peripheral blood leukocytes (PBL), head kidney (HK) and spleen. RT-PCR analysis in kidney cells sorted by FACS revealed that T-bet was strongly expressed in surface-IgM-negative lymphocytes in comparison to IgM-positive lymphocytes. These results suggest that ginbuna T-bet is involved in the immune system, especially in T-cell function, and is an important tool to analyze teleost cell-mediated immunity.

A molecular analysis of neurogenic placode and cranial sensory ganglion development in the shark, Scyliorhinus canicula

In order to gain insight into the evolution of the genetic control of the development of cranial neurogenic placodes and cranial sensory ganglia in vertebrates, we cloned and analysed the spatiotemporal expression pattern of six transcription factor genes in a chondrichthyan, the shark Scyliorhinus canicula (lesser-spotted dogfish/catshark). As in other vertebrates, NeuroD is expressed in all cranial sensory ganglia. We show that Pax3 is expressed in the profundal placode and ganglion, strongly supporting homology between the separate profundal ganglion of elasmobranchs and basal actinopterygians and the ophthalmic trigeminal placode-derived neurons of the fused amniote trigeminal ganglion. We show that Pax2 is a conserved pan-gnathostome marker for epibranchial and otic placodes, and confirm that Phox2b is a conserved pan-gnathostome marker for epibranchial placode-derived neurons. We identify Eya4 as a novel marker for the lateral line system throughout its development, expressed in lateral line placodes, sensory ridges and migrating primordia, neuromasts and electroreceptors. We also identify Tbx3 as a specific marker for lateral line ganglia in shark embryos. We use the spatiotemporal expression pattern of these genes to characterise the development of neurogenic placodes and cranial sensory ganglia in the dogfish, with a focus on the epibranchial and lateral line placodes. Our findings demonstrate the evolutionary conservation across all gnathostomes of at least some of the transcription factor networks underlying neurogenic placode development.

The maternally expressed zebrafish T-box geneeomesoderminregulates organizer formation

Early embryonic development in many organisms relies upon maternal molecules deposited into the egg prior to fertilization. We have cloned and characterized a maternal T-box gene in the zebrafish, eomesodermin(eomes). During oogenesis, the eomes transcript becomes localized to the cortex of the oocyte. After fertilization during early cleavage stages, eomes is expressed in a vegetal to animal gradient in the embryo, whereas Eomesodermin protein (Eom) is distributed cytoplasmically throughout the blastoderm. Strikingly, following midblastula transition, nuclear-localized Eomesodermin is detected on the dorsal side of the embryo only. Overexpression of eomes results in Nodal-dependent and nieuwkoid/dharma (nwk/dhm) independent ectopic expression of the organizer markers goosecoid (gsc), chordin (chd) and floating head (flh) and in the formation of secondary axes. The same phenotypes are observed when a VP16-activator construct is injected into early embryos, indicating that eomes acts as a transcriptional activator. In addition, a dominant-negative construct and antisense morpholino oligonucleotides led to a reduction in gsc and flh expression. Together these data indicate that eomes plays a role in specifying the organizer.

Specification of the vertebrate eye by a network of eye field transcription factors

Several eye-field transcription factors (EFTFs) are expressed in the anterior region of the vertebrate neural plate and are essential for eye formation. The Xenopus EFTFs ET, Rx1, Pax6, Six3, Lhx2, tll and Optx2 are expressed in a dynamic, overlapping pattern in the presumptive eye field. Expression of an EFTF cocktail with Otx2 is sufficient to induce ectopic eyes outside the nervous system at high frequency. Using both cocktail subsets and functional (inductive) analysis of individual EFTFs, we have revealed a genetic network regulating vertebrate eye field specification. Our results support a model of progressive tissue specification in which neural induction then Otx2-driven neural patterning primes the anterior neural plate for eye field formation. Next, the EFTFs form a self-regulating feedback network that specifies the vertebrate eye field. We find striking similarities and differences to the network of homologous Drosophila genes that specify the eye imaginal disc, a finding that is consistent with the idea of a partial evolutionary conservation of eye formation.

T-brain homologue (HpTb) is involved in the archenteron induction signals of micromere descendant cells in the sea urchin embryo

Signals from micromere descendants play a crucial role in sea urchin development. In this study, we demonstrate that these micromere descendants express HpTb, a T-brain homolog of Hemicentrotus pulcherrimus. HpTb is expressed transiently from the hatched blastula stage through the mesenchyme blastula stage to the gastrula stage. By a combination of embryo microsurgery and antisense morpholino experiments, we show that HpTb is involved in the production of archenteron induction signals. However, HpTb is not involved in the production of signals responsible for the specification of secondary mesenchyme cells, the initial specification of primary mesenchyme cells, or the specification of endoderm.HpTb expression is controlled by nuclear localization ofβ-catenin, suggesting that HpTb is in a downstream component of the Wnt signaling cascade. We also propose the possibility that HpTbis involved in the cascade responsible for the production of signals required for the spicule formation as well as signals from the vegetal hemisphere required for the differentiation of aboral ectoderm.

Amphi-Eomes/Tbr1: an amphioxus cognate of vertebrate Eomesodermin and T-Brain1 genes whose expression reveals evolutionarily distinct domain in amphioxus development

A cDNA for a novel T-box containing gene was isolated from the amphioxus Branchiostoma belcheri. A molecular phylogenetic tree constructed from the deduced amino acid sequence of the isolated cDNA indicates that this gene belongs to the T-Brain subfamily. In situ hybridization reveals that the expression is first detected in the invaginating archenteron at the early gastrula stage and this expression is down-regulated at the neurula stage. In early larvae, the expression appears again and transcripts are detected exclusively in the pre-oral pit (wheel organ-Hatschek's pit of the adult). In contrast to the vertebrate counterparts, no transcripts are detected in the brain vesicle or nerve cord throughout the development. These results are interpreted to mean that a role of T-Brain products in vertebrate forebrain development was acquired after the amphioxus was split from the lineage leading to the vertebrates. On the other hand, comparison of the tissue-specific expression domain of T-Brain genes and other genes between amphioxus and vertebrates revealed that the pre-oral pit of amphioxus has several molecular features which are comparable to those of the vertebrate olfactory and hypophyseal placode.

Evolution of developmental functions by the Eomesodermin, T-brain-1, Tbx21 subfamily of T-box genes: insights from amphioxus

We have identified an amphioxus T-box gene that is orthologous to the Eomesodermin, T-brain-1, and Tbx21 genes of vertebrates, and we have characterized its expression pattern during embryonic and larval development. AmphiEomes/Tbr1/Tbx21 is maternally expressed in oocytes and cleavage stage embryos. After the onset of zygotic transcription at the blastula stage, it is expressed in invaginating mesendoderm cells during gastrulation, but it is downregulated in presumptive ectoderm and neurectoderm. Expression is seen in both axial and paraxial mesendoderm in neurulae and early larvae, but it is not detected in differentiated endoderm, somites, or notochord. Expression persists in mesendoderm cells of the tail bud in early larvae, but it disappears between 1 to 1.5 days post fertilization. Unlike orthologous genes in basal deuterostomes or vertebrates, no anterior neural expression domain is detected at any stage of development. Integrating phylogenetic and developmental data, we have reconstructed the evolutionary history of the Eomesodermin/Tbr1/Tbx21 subfamily of T-box genes from a single ancestral locus that originated very early in metazoan evolution, before the evolution of triploblasts from their diploblast ancestor.

Deuterostome brains: synopsis and commentary

The living deuterostomes comprise six monophyletic groups: (1) echinoderms + hemichordates, (2) tunicates, (3) cephalochordates, (4) myxinoids, (5) petromyzontoids, and (6) gnathostomes. The morphotype of the craniote (myxinoids + petromyzontoids + gnathostomes) central nervous system (CNS) comprises a fixed number of histogenetic units, formed by the intersection of transversely oriented neuromeres and longitudinally arranged zones. A well-developed built-in, natural coordinate system adds the third dimension to this morphotype. The classical subdivisions of the craniote CNS: prosencephalon (P), mesencephalon (M), rhombencephalon (R), and spinal cord (S) are each composed of a number of neuromeres. Chordates (larval tunicates + cephalochordates + craniotes) share a highly characteristic axial complex, encompassing a dorsal tubular CNS, a notochord and bilateral series of segmental muscles. In all chordates the CNS can be divided into a rostral (P-like + M-like), an intermediate (R-like) and a caudal (S-like) sector, and sets of homologous developmental genes play a role in this tripartitioning. There are no indications for the presence of olfactory or other telencephalic regions in the brain of non-craniote chordates. Convincing evidence that parts of the chordate CNS are homologous to parts of the larval or adult CNS of non-chordate deuterostomes (echinoderms + hemichordates) is lacking. The dorsal tubular CNS is most probably a chordate autapomorphy.

T-box genes in development: from hydra to humans

The T-box gene family was uncovered less than a decade ago but has been recognized as important in controlling many and varied aspects of development in metazoans from hydra to humans. Extensive screening and database searching has revealed several subfamilies of genes with orthologs in species as diverse as Caenorhabditis elegans and humans. The defining feature of the family is a conserved sequence coding for a DNA-binding motif known as the T-box, named after the first-discovered T-box gene, T or Brachyury. Although several T-box proteins have been shown to function as transcriptional regulators, to date only a handful of downstream target genes have been discovered. Similarly, little is known about regulation of the T-box genes themselves. Although not limited to the embryo, expression of T-box genes is characteristically seen in dynamic and highly specific patterns in many tissues and organs during embryogenesis and organogenesis. The essential role of several T-box genes has been demonstrated by the developmental phenotypes of mutant animals.

Overlapping expression of zebrafish T-brain-1 and eomesodermin during forebrain development

T-box transcription factors are important determinants of embryonic cell fate and behaviour. Two T-box genes are expressed in the developing telencephalon of several vertebrate species, including amphibia, birds and mammals. Here we report the cloning of zebrafish T-brain-1 (tbr1) and eomesodermin (eom). As a prelude to genetic studies of neuro-ectodermal fate determination we studied their expression pattern during embryogenesis and early larval development. Eom is expressed in the presumptive telencephalon from around the 4-5 somite stage in bilaterally symmetric groups of cells; the number of positive cells increases dramatically with time and encompasses the entire dorsal telencephalon by the 22 somite stage. Tbr1 is expressed from the 18 somite stage in a subset of eom-expressing cells. By 24 hpf eom and tbr1 are expressed in largely overlapping domains in the dorsal telencephalon, tbr1 is expressed in postmitotic cells whereas eomes is also expressed in proliferative ventricular zone cells. Both genes are also found in a small domain of the diencephalon bordering the telencephalon. A detailed analysis of the expression of tbr1 and eom in the brain of 4 day old larvae shows that the two T-box genes are differentially expressed in various cell populations of the developing brain.

Genetic and developmental bases of serial homology in vertebrate limb evolution

Two sets of paired appendages are a characteristic feature of the body plan of jawed vertebrates. While the fossil record provides a good morphological description of limb evolution, the molecular mechanisms involved in this process are only now beginning to be understood. It is likely that the genes essential for limb development in modern vertebrates were also important players during limb evolution. In recent years, genes from a number of gene families have been described that play important roles both in limb induction and in later patterning processes. These advances facilitate inquiries into several important aspects of limb evolution such as their origin, position along the body axis, number and identity. Integrating paleontological, developmental and genetic data, we propose models to explain the evolution of paired appendages in vertebrates. Whereas previous syntheses have tended to focus on the roles of genes from a single gene family, most notably Hox genes, we emphasize the importance of considering the interactions among multiple genes from different gene families for understanding the evolution of complex developmental systems. Our models, which underscore the roles of gene duplication and regulatory ‘tinkering’, provide a conceptual framework for elucidating the evolution of serially homologous structures in general, and thus contribute to the burgeoning field seeking to uncover the genetic and developmental bases of evolution.

T-Brain expression in the apical organ of hemichordate tornaria larvae suggests its evolutionary link to the vertebrate forebrain

T-box genes encode a novel family of sequence-specific activators that appear to play crucial roles in various processes of animal development. Although most of the T-box genes are involved in the mesoderm formation of chordate embryos, mammalian T-Brain is expressed in the developing central nervous system, and defines molecularly distinct domains within the cerebral cortex. Here we report the first invertebrate T-Brain homologue from the hemichordate acorn worm, Ptychodera flava, which we designate Pf-Tbrain. Developmental expression of Pf-Tbrain was examined by whole mount in situ hybridization to various stages of P. flava embryos. A weak, broad in situ hybridization signal of the Pf-Tbrain transcript is first detected during gastrulation in cells around the archenteron, but this signal disappears as gastrulation proceeds. At mid-gastrula an intense signal appears in several apical ectoderm cells of the gastrula. This signal becomes restricted to the apical region, where the eyespots or the light-sensory organ of the tornaria larva form. Expression of Pf-Tbrain in the apical sensory organ of the tornaria and vertebrate T-Brain in the forebrain suggests an evolutionary relationship between the non-chordate deuterostome larval apical sensory organ and the chordate forebrain.

A starfish homolog of mouse T-brain-1 is expressed in the archenteron of Asterina pectinifera embryos: possible involvement of two T-box genes in starfish gastrulation

A cDNA clone for a starfish T-box gene (Ap-Tbr) was isolated and characterized. Molecular phylogenetic analysis showed that the Ap-Tbr gene was a member of the T-brain subfamily, which includes mouse T-brain-1 and Xenopus Eomesodermin. Ap-Tbr was expressed as early as in late blastulae, and the transcript was evident in a disc-like region at the vegetal end or the vegetal plate. In early gastrulae, the gene was expressed in the cells of the invaginated archenteron, from which the majority of mesodermal cells as well as some endodermal cells are derived. The Ap-Tbr expression disappeared by the end of gastrulation, and was not detected in early bipinnaria larvae. This expression pattern of Ap-Tbr suggests its role in an early step of archenteron invagination, associated with mesoderm and endoderm formation. Furthermore, double staining of late blastulae and early gastrulae with a probe specific for Ap-Tbr and one for ApBra (the starfish Brachyury gene) demonstrated that the regions of Ap-Tbr and ApBra expression at the vegetal/posterior end of the embryo did not overlap, the region with Ap-Tbr expression being encircled by a ring-shaped region of ApBra expression. A gap without expression of the two genes was located between them, and the gap was seen around the blastoporal lip in the early gastrula. These observations suggest implication of the two T-box genes, with different roles, in starfish gastrulation.

Zebrafish tbx-c functions during formation of midline structures

Several genes containing the conserved T-box region in invertebrates and vertebrates have been reported recently. Here, we describe three novel members of the T-box gene family in zebrafish. One of these genes, tbx-c, is studied in detail. It is expressed in the axial mesoderm, notably, in the notochordal precursor cells immediately before formation of the notochord and in the chordoneural hinge of the tail bud, after the notochord is formed. In addition, its expression is detected in the ventral forebrain, sensory neurons, fin buds and excretory system. The expression pattern of tbx-c differs from that of the other two related genes, tbx-a and tbx-b. The developmental role of tbx-c has been analysed by overexpression of the full-length tbx-c mRNA and a truncated form of tbx-c mRNA, which encodes the dominant-negative Tbx-c. Overexpression of tbx-c causes expansion of the midline mesoderm and formation of ectopic midline structures at the expense of lateral mesodermal cells. In dominant-negative experiments, the midline mesoderm is reduced with the expansion of lateral mesoderm to the midline. These results suggest that tbx-c plays a role in formation of the midline mesoderm, particularly, the notochord. Moreover, modulation of tbx-c activity alters the development of primary motor neurons. Results of in vitro analysis in zebrafish animal caps suggest that tbx-c acts downstream of early mesodermal inducers (activin and ntl) and reveal an autoregulatory feedback loop between ntl and tbx-c. These data and analysis of midline (ntl−/− and flh−/−) and lateral mesoderm (spt−/−) mutants suggest that tbx-c may function during formation of the notochord.