Fgf19 is required for zebrafish lens and retina development

Fgf signaling plays crucial roles in morphogenesis. Fgf19 is required for zebrafish forebrain development. Here, we examined the roles of Fgf19 in the formation of the lens and retina in zebrafish. Knockdown of Fgf19 caused a size reduction of the lens and the retina, failure of closure of the choroids fissure, and a progressive expansion of the retinal tissue to the midline of the forebrain. Fgf19 expressed in the nasal retina and lens was involved in cell survival but not cell proliferation during embryonic lens and retina development. Fgf19 was essential for the differentiation of lens fiber cells in the lens but not for the neuronal differentiation and lamination in the retina. Loss of nasal fate in the retina caused by the knockdown of Fgf19, expansion of nasal fate in the retina caused by the overexpression of Fgf19 and eye transplantation indicated that Fgf19 in the retina was crucial for the nasal-temporal patterning of the retina that is critical for the guidance of retinal ganglion cell axons. Knockdown of Fgf19 also caused incorrect axon pathfinding. The present findings indicate that Fgf19 positively regulates the patterning and growth of the retina, and the differentiation and growth of the lens in zebrafish.     

spalt-induced specification of distinct dorsal and ventral domains is required for Drosophila tracheal patterning

Morphogenesis of the Drosophila tracheal system relies on different signalling pathways that have distinct roles in specifying both the migration of the tracheal cells and the particular morphological features of the primary branches. The current view is that the tracheal cells are initially specified as an equivalent group of cells whose diversification depends on signals from the surrounding cells. In this work, we show that the tracheal primordia are already specified as distinct dorsal and ventral cell populations. This subdivision depends on the activity of the spalt (sal) gene and occurs prior to the activity of the signalling pathways that dictate the development of the primary branches. Finally, we show that the specification of these two distinct cell populations, which are not defined by cell lineage, are critical for proper tracheal patterning. These results indicate that tracheal patterning depends not only on signalling from surrounding cells but also in the different response of the tracheal cells depending on their allocation to the dorsal or ventral domains.     

Dorsal–ventral patterning of the neural tube: A tale of three signals

Development of the vertebrate nervous system begins with the acquisition of neural identity from the midline dorsal‐ectodermal cells of the gastrulating embryos. The subsequent progressive specification of the neural plate along its anterior–posterior and dorsal–ventral (DV) axes allows the generation of the tremendous variety of neuronal and glial cells that compose the vertebrate central nervous system (CNS). Studies on the development of the spinal cord, the anatomically simplest part of the CNS, have generated most of our current knowledge on the signaling events and the genetic networks that orchestrate the DV patterning of the neural plate. In this review, we discuss the recent advances in our understanding of these events and highlight unresolved questions. We focused our attention on the activity and the integration of the three main instructive cues: Sonic hedgehog, the Wnts and the Bone Morphogenetic Proteins, giving particular attention to the less well understood dorsal signaling events. © 2012 Wiley Periodicals, Inc. Develop Neurobiol, 2012     

Coordinated regulation of the dorsal‐ventral and anterior‐posterior patterning of Xenopus embryos by the BTB/POZ zinc finger protein Zbtb14

During early vertebrate embryogenesis, bone morphogenetic proteins (BMPs) belonging to the transforming growth factor‐β (TGF‐β) family of growth factors play a central role in dorsal–ventral (DV) patterning of embryos, while other growth factors such as Wnt and fibroblast growth factor (FGF) family members regulate formation of the anterior–posterior (AP) axis. Although the establishment of body plan is thought to require coordinated formation of the DV and AP axes, the mechanistic details underlying this coordination are not well understood. Here, we show that a Xenopus homologue of zbtb14 plays an essential role in the regulation of both DV and AP patterning during early Xenopus development. We show that overexpression of Zbtb14 promotes neural induction and inhibits epidermal differentiation, thereby regulating DV patterning. In addition, Zbtb14 promotes the formation of posterior neural tissue and suppresses anterior neural development. Consistent with this, knock‐down experiments show that Zbtb14 is required for neural development, especially for the formation of posterior neural tissues. Mechanistically, Zbtb14 reduces the levels of phosphorylated Smad1/5/8 to suppress BMP signaling and induces an accumulation of β‐Catenin to promote Wnt signaling. Collectively, these results suggest that Zbtb14 plays a crucial role in the formation of DV and AP axes by regulating both the BMP and Wnt signaling pathways during early Xenopus embryogenesis.     

TGF-β type I receptor Alk5 regulates tooth initiation and mandible patterning in a type II receptor-independent manner

TGF-β superfamily members signal through a heteromeric receptor complex to regulate craniofacial development. TGF-β type II receptor appears to bind only TGF-β, whereas TGF-β type I receptor (ALK5) also binds to ligands in addition to TGF-β. Our previous work has shown that conditional inactivation of Tgfbr2 in the neural crest cells of mice leads to severe craniofacial bone defects. In this study, we examine and compare the defects of TGF-β type II receptor (Wnt1-Cre;Tgfbr2^fl/fl) and TGF-β type I receptor/Alk5 (Wnt1-Cre;Alk5^fl/fl) conditional knockout mice. Loss of Alk5 in the neural crest tissue resulted in phenotypes not seen in the Tgfbr2 mutant, including delayed tooth initiation and development, defects in early mandible patterning and altered expression of key patterning genes including Msx1, Bmp4, Bmp2, Pax9, Alx4, Lhx6/7 and Gsc. Alk5 controls the survival of CNC cells by regulating expression of Gsc and other genes in the proximal aboral region of the developing mandible. We conclude that ALK5 regulates tooth initiation and early mandible patterning through a pathway independent of Tgfbr2. There is an intrinsic requirement for Alk5 signal in regulating the fate of CNC cells during tooth and mandible development.     

Wnt signaling is required for antero-posterior patterning of the planarian brain

Wnt signaling functions in axis formation and morphogenesis in various animals and organs. Here we report that Wnt signaling is required for proper brain patterning during planarian brain regeneration. We showed here that one of the Wnt homologues in the planarian Dugesia japonica, DjwntA, was expressed in the posterior region of the brain. When DjwntA-knockdown planarians were produced by RNAi, they could regenerate their heads at the anterior ends of the fragments, but formed ectopic eyes with irregular posterior lateral branches and brain expansion. This suggests that the Wnt signal may be involved in antero-posterior (A-P) patterning of the planarian brain, as in vertebrates. We also investigated the relationship between the DjwntA and nou-darake/FGFR signal systems, as knockdown planarians of these genes showed similar phenotypes. Double-knockdown planarians of these genes did not show any synergistic effects, suggesting that the two signal systems function independently in the process of brain regeneration, which accords with the fact that nou-darake was expressed earlier than DjwntA during brain regeneration. These observations suggest that the nou-darake/FGFR signal may be involved in brain rudiment formation during the early stage of head regeneration, and subsequently the DjwntA signal may function in A-P patterning of the brain rudiment.     

Zic2 is required for neural crest formation and hindbrain patterning during mouse development

The Zic genes are the vertebrate homologues of the Drosophila pair rule gene odd-paired. It has been proposed that Zic genes play several roles during neural development including mediolateral segmentation of the neural plate, neural crest induction, and inhibition of neurogenesis. Initially during mouse neural development Zic2 is expressed throughout the neural plate while later on expression in the neurectoderm becomes restricted to the lateral region of the neural plate. A hypomorphic allele of Zic2 has demonstrated that in the mouse Zic2 is required for the timing of neurulation. We have isolated a new allele of Zic2 that behaves as a loss of function allele. Analysis of this mutant reveals two further functions for Zic2 during early neural development. Mutation of Zic2 results in a delay of neural crest production and a decrease in the number of neural crest cells that are produced. These defects are independent of mediolateral segmentation of the neurectoderm and of dorsal neurectoderm proliferation, both of which occur normally in the mutant embryos. Additionally Zic2 is required during hindbrain patterning for the normal development of rhombomeres 3 and 5. This work provides the first genetic evidence that the Zic genes are involved in neural crest production and the first demonstration that Zic2 functions during hindbrain patterning.     

Lipofection strategy for the study of Xenopus retinal development

The analysis of gene function during retinal development can be addressed by perturbing gene expression either by inhibition or by overexpression in desired regions and at defined stages of development. An in vivo lipofection strategy has been applied for stage-specific and region-specific expression of genes in Xenopus retina. Due to colipofection efficiency, this strategy enables us to study functional interaction of genes by lipofecting multiple expression constructs. This lipofection technique also allows us to transfect morpholino oligonucleotides into retinoblasts to block gene function. We present here various aspects of this technique, including recent improvements and modifications.     

Dissection of inhibitory Smad proteins: both N- and C-terminal domains are necessary for full activities of Xenopus Smad6 and Smad7

Smad6 and Smad7 comprise a subclass of vertebrate Smads that antagonize, rather than transduce, TGF-β family signaling. These Anti-Smads can block BMP signaling, as evidenced by their ability to induce a secondary dorsal axis when misexpressed ventrally in Xenopus embryos. Smad7 inhibits additional TGF-β related pathways, and causes spina bifida when misexpressed dorsally. We have performed structure-function analyses to identify domains of Anti-Smads that are responsible for their shared and unique activities. We find that the C-terminal domain of Smad7 displays strong axis inducing activity but cannot induce spina bifida. The isolated N-terminal domain of Smad7 is inactive but restores the ability of the C-terminus to cause spina bifida when the two are co-expressed. By contrast, the N- and C-terminal domains of Smad6 have weak axis inducing activity when expressed individually, but show full activity when co-expressed. Chimeric analysis demonstrates that the C-terminal domain of Smad7, but not Smad6, can induce spina bifida when fused to the N-terminal domain of either Smad6 or Smad7. Thus, although the C-terminal domain is the primary determinant of the intrinsic activity of Xenopus Anti-Smads, the N-terminal domain is essential for full activity, is interchangeable between Smad6 and 7, and can function in trans.     

The<Emphasis Type="Italic"> GAOLAOZHUANGREN2</Emphasis> gene is required for normal glucose response and development of<Emphasis Type="Italic"> Arabidopsis</Emphasis>

Recent studies of glucose (Glc) sensing and signaling have revealed that Glc acts as a critical signaling molecule in higher plants. Several Glc sensing-defective Arabidopsis mutants have been characterized in detail, and the corresponding genes encoding Glc-signaling proteins have been isolated. However, the full complexity of Glc signaling in higher plants is not yet fully understood. Here, we report the identification and characterization of a new Glc-insensitive mutant, gaolaozhuangren2 (glz2), which was isolated from transposon mutagenesis experiments in Arabidopsis. In addition to its insensitivity to Glc, the glz2 plant exhibits several developmental defects such as short stature with reduced apical dominance, short roots, small and dark-green leaves, late flowering and female sterility. Treatment with 4% Glc blocked expression of the OE33 gene in wild-type plants, whereas expression of this gene was unchanged in the glz2 mutant plants. Taken together, our results suggest that the GLZ2 gene is required for normal glucose response and development of Arabidopsis.Mingjie Chen and Xiaoxiang Xia contributed equally to this work.     

The <Emphasis Type="Italic">transformer2</Emphasis> gene in <Emphasis Type="Italic">Musca domestica</Emphasis> is required for selecting and maintaining the female pathway of development

We present the isolation and functional analysis of a transformer2 homologue Mdtra2 in the housefly Musca domestica. Compromising the activity of this gene by injecting dsRNA into embryos causes complete sex reversal of genotypically female individuals into fertile males, revealing an essential function of Mdtra2 in female development of the housefly. Mdtra2 is required for female-specific splicing of Musca doublesex (Mddsx) which structurally and functionally corresponds to Drosophila dsx, the bottom-most regulator in the sex-determining pathway. Since Mdtra2 is expressed in males and females, we propose that Mdtra2 serves as an essential co-factor of F, the key sex-determining switch upstream of Mddsx. We also provide evidence that Mdtra2 acts upstream as a positive regulator of F supporting genetic data which suggest that F relies on an autocatalytic activity to select and maintain the female path of development. We further show that repression of male courtship behavior by F requires Mdtra2. This function of F and Mdtra2 appears not to be mediated by Mddsx, suggesting that bifurcation of the pathway at this level is a conserved feature in the genetic architecture of Musca and Drosophila.Edited by D. Tautz