bluuebunny/crossref_metadata_2025 huggingface dataset:
Fibroblast Growth Factor 10 (FGF10) and branching morphogenesis in the embryonic mouse lung
Authors: Bellusci Savério , Grindley Justin , Emoto Hisayo , Itoh Nobuyuki , Hogan Brigid L. M.
Published: April 2021

During mouse lung morphogenesis, the distal mesenchyme regulates the growth and branching of adjacent endoderm. We report here that fibroblast growth factor 10 (Fgf10) is expressed dynamically in the mesenchyme adjacent to the distal buds from the earliest stages of lung development. The temporal and spatial pattern of gene expression suggests that Fgf10 plays a role in directional outgrowth and possibly induction of epithelial buds, and that positive and negative regulators of Fgf10 are produced by the endoderm. In transgenic lungs overexpressing Shh in the endoderm, Fgf10 transcription is reduced, suggesting that high levels of SHH downregulate Fgf10.

Addition of FGF10 to embryonic day 11.5 lung tissue (endoderm plus mesenchyme) in Matrigel or collagen gel culture elicits a cyst-like expansion of the endoderm after 24 hours. In Matrigel, but not collagen, this is followed by extensive budding after 48-60 hours. This response involves an increase in the rate of endodermal cell proliferation. The activity of FGF1, FGF7 and FGF10 was also tested directly on isolated endoderm in Matrigel culture. Under these conditions, FGF1 elicits immediate endodermal budding, while FGF7 and FGF10 initially induce expansion of the endoderm. However, within 24 hours, samples treated with FGF10 give rise to multiple buds, while FGF7-treated endoderm never progresses to bud formation, at all concentrations of factor tested. Although exogenous FGF1, FGF7 and FGF10 have overlapping activities in vitro, their in vivo expression patterns are quite distinct in relation to early branching events. We conclude that, during early lung development, localized sources of FGF10 in the mesoderm regulate endoderm proliferation and bud outgrowth.
The Xenopus homeobox gene Twin mediates Wnt induction of Goosecoid in establishment of Spemann’s organizer
Authors: Laurent, Micheline N. , Blitz Ira L. , Hashimoto Chikara , Rothbacher Ute , Cho Ken W.-Y.
Published: April 2021

We describe the isolation of the Xenopus homeobox gene twin (Xtwn), which was identified in an expression cloning screen for molecules with dorsalizing activities. Injection of synthetic Xtwn mRNA restores a complete dorsal axis in embryos lacking dorsal structures and induces a complete secondary dorsal axis when ectopically expressed in normal embryos. The sequence homology, expression pattern and gain-of-function phenotype of Xtwn is most similar to the previously isolated Xenopus homeobox gene siamois (Xsia) suggesting that Xtwn and Xsia comprise a new subclass of homeobox genes important in dorsal axis specification. We find that Xtwn is able to activate the Spemann organizerspecific gene goosecoid (gsc) via direct binding to a region of the gsc promoter previously shown to mediate Wnt induction. Since Xtwn expression is strongly induced in ectodermal (animal cap) cells in response to overexpression of a dorsalizing Wnt molecule, we examined the possibility that Xtwn might be a direct target of a Wnt signal transduction cascade. First, we demonstrate that purified LEF1 protein can interact, in vitro, with consensus LEF1/TCF3-binding sites found within the Xtwn promoter. Second, these binding sites were shown to be required for Wnt-mediated induction of a Xtwn reporter gene containing these sites. As LEF1/TCF3 family transcription factors have previously been shown to directly mediate Wnt signaling, these results suggest that Xtwn induction by Wnt may be direct. Finally, in UV-hyperventralized embryos, expression of endogenous Xtwn is confined to the vegetal pole and a Xtwn reporter gene is hyperinduced vegetally in a LEF1/TCF3-binding-site-dependent manner. These results suggest that cortical rotation distributes Wnt-like dorsal determinants to the dorsal side of the embryo, including the dorsal marginal zone, and that these determinants may directly establish Spemann’s organizer in this region.
Analysis of the mechanism(s) of metaphase I arrest in strain LT mouse oocytes: participation of MOS
Authors: Hirao Yuji , Eppig John J.
Published: April 2021

Oocytes of almost all vertebrates become arrested at metaphase II to await fertilization. Arrest is achieved with the participation of a protein complex known as cytostatic factor (CSF) that stabilizes histone H1 kinase activity. MOS and mitogen-activated protein kinase (MAPK) are important components of CSF. Strain LT/Sv mice, and strains related to LT/Sv, produce a high percentage of atypical oocytes that are arrested at metaphase I when normal oocytes have progressed to metaphase II. The potential role of MOS in metaphase I arrest was investigated using strain LT/Sv and LT-related recombinant inbred strains, LTXBO and CX8-4. MOS and MAPK are produced and functional in maturing LT oocytes. Two experimental paradigms were used to reduce or delete MOS in LT oocytes and assess effects on metaphase I arrest. First, sense and antisense Mos oligonucleotides were microinjected into metaphase I-arrested oocytes. Antisense, but not sense, Mos oligonucleotides promoted the activation of metaphase I-arrested oocytes. Second, mice carrying a Mos null mutation were crossed with LT mice, the null mutation was backcrossed three times to LT mice, and Mos+’∼ N3 mice were intercrossed to produce Mos−/−, Mos+/− and Mos+/+ N3F1 mice. Oocytes of all three Mos genotypes of N3F1 mice sustained meiotic arrest for 17 hours indicating that metaphase I arrest is not initiated by a MOS-dependent mechanism. However, unlike Mos+/+ and Mos+/− CX8-4 N3F1 oocytes, metaphase I arrest of Mos−/− CX8-4 N3F1 oocytes was not sustained after 17 hours and became reversed gradually. These results, like the antisense Mos oligonucleotide microinjection experiments, suggest that MOS participates in sustaining metaphase I arrest in LT oocytes.
Cellular and axonal migrations are misguided along both body axes in the maternal-effect mau-2 mutants of Caenorhabditis elegans
Authors: Takagi Shin , Bénard Claire , Pak Julia , Livingstone David , Hekimi Siegfried
Published: April 2021

We have characterized the mau-2 mutants of Caenorhabditis elegans and found that migrating cells and axons are mispositioned along both the antero-posterior and dorso-ventral body axes. This is in contrast to previously characterized guidance mutations in Caenorhabditis and in Drosophila, which have been found to be axis-specific. Two observations suggest that mau-2 acts very early during development: most behavioral phenotypes of mau-2 can be rescued by a maternal effect, and variations in expressivity involve an entire body side at a time. The possibility that mau-2 is involved in the spatial organization of guidance cues encoded by other genes is discussed.
A single morphogenetic field gives rise to two retina primordia under the influence of the prechordal plate
Authors: Li Hua-shun , Tierney Christopher , Wen Leng , Wu Jane Y. , Rao Yi
Published: April 2021

Two bilaterally symmetric eyes arise from the anterior neural plate in vertebrate embryos. An interesting question is whether both eyes share a common developmental origin or they originate separately. We report here that the expression pattern of a new gene ET reveals that there is a single retina field which resolves into two separate primordia, a suggestion supported by the expression pattern of the Xenopus Pax-6 gene. Lineage tracing experiments demonstrate that retina field resolution is not due to migration of cells in the median region to the lateral parts of the field. Removal of the prechordal mesoderm led to formation of a single retina both in chick embryos and in Xenopus explants. Transplantation experiments in chick embryos indicate that the prechordal plate is able to suppress Pax-6 expression. Our results provide direct evidence for the existence of a single retina field, indicate that the retina field is resolved by suppression of retina formation in the median region of the field, and demonstrate that the prechordal plate plays a primary signaling role in retina field resolution.
klingon, a novel member of the Drosophila immunoglobulin superfamily, is required for the development of the R7 photoreceptor neuron
Authors: Butler Samantha J. , Ray Sandip , Hiromi Yasushi
Published: April 2021

klingon is a member of the Immunoglobulin superfamily and is expressed in a restricted pattern of neurons during embryonic neurogenesis and in the R7 photoreceptor precursor throughout its development. Starting from the H214 enhancer trap line, we identified a transcription unit, klingon, that encodes a putative protein of 528 amino acids and contains three C2-type Immunoglobulin-like domains followed by one fibronectin type III repeat. When Klingon is expressed in S2 tissue culture cells, it is associated with the cell membrane by a glycosyl-phosphatidylinositol linkage and can mediate homophilic adhesion. Genetic analysis has revealed that klingon is an essential gene that participates in the development of the R7 neuron. Ectopic expression of klingon in all neurons in a sevenless background can alter the position of the R8 rhabdomere.
Hox gene induction in the neural tube depends on three parameters: competence, signal supply and paralogue group
Authors: Grapin-Botton Anne , Bonnin Marie-Ange , Le Douarin Nicole M.
Published: April 2021

It has been previously shown that Hox gene expression in the rhombencephalon is controlled by environmental cues. Thus posterior transposition of anterior rhombomeres to the r7/8 level results in the activation of Hox genes of the four first paralog groups and in homeotic transformations of the neuroepithelial fate according to its position along the anteroposterior axis. We demonstrate here that although the anteroposterior levels of r2 to r6 express Hox genes they do not have inducing activity on more anterior territories. If transposed at the posterior rhombencephalon and trunk level, however, the same anterior regions are able to express Hox gene such as Hoxa-2, a-3 or b-4. We also provide evidence that these signals are transferred by two paths: one vertical, arising from the paraxial mesoderm, and one planar, travelling in the neural epithelium. The competence to express Hox genes extends up to the forebrain and midbrain but expression of Hox genes does not preclude Otx2 expression in these territories and results only in slight changes in their phenotypes. Similarly, rhombomeres transplanted to posterior truncal levels turned out to be able to express posterior genes of the first eight paralog groups to the exclusion of others located downstream in the Hox genes genomic clusters. This suggests that the neural tube is divided into large territories characterized by different Hox gene regulatory features.
The development of the posterior body in zebrafish
Authors: Kanki John P. , Ho Robert K.
Published: April 2021

In order to understand the developmental mechanisms of posterior body formation in the zebrafish, a fate map of the zebrafish tailbud was generated along with a detailed analysis of tailbud cell movements. The fate map of the zebrafish tailbud shows that it contains tissue-restricted domains and is not a homogeneous blastema. Furthermore, time-lapse analysis shows that some cell movements and behaviors in the tailbud are similar to those seen during gastrulation, while others are unique to the posterior body. The extension of axial mesoderm and the continuation of ingression throughout zebrafish tail development suggests the continuation of processes initiated during gastrulation. Unique properties of zebrafish posterior body development include the bilateral distribution of tailbud cell progeny and the exhibition of different forms of ingression within specific tailbud domains. The ingression of cells in the anterior tailbud only gives rise to paraxial mesoderm, at the exclusion of axial mesoderm. Cells of the posterior tailbud undergo subduction, a novel form of ingression resulting in the restriction of this tailbud domain to paraxial mesodermal fates. The intermixing of spinal cord and muscle precursor cells, as well as evidence for pluripotent cells within the tailbud, suggest that complex inductive mechanisms accompany these cell movements throughout tail elongation. Rates of cell proliferation in the tailbud were examined and found to be relatively low at the tip of the tail indicating that tail elongation is not due to growth at its posterior end. However, higher rates of cell proliferation in the dorsomedial region of the tail may contribute to the preferential posterior movement of cells in this tailbud region and to the general extension of the tail. Understanding the cellular movements, cell fates and gene expression patterns in the tailbud will help to determine the nature of this important aspect of vertebrate development.
nodal expression in the primitive endoderm is required for specification of the anterior axis during mouse gastrulation
Authors: Varlet Isabelle , Collignon Jérôme , Robertson Elizabeth J.
Published: April 2021

Mouse nodal, a member of the TGFβ family of secreted growth factors is essential for gastrulation. We recently generated a nodallacZ reporter allele by homologous recombination in ES cells. In the present study, β-galactosidase staining in the perigastrulation-stage embryo has demonstrated the site of highest nodal expression is localised to the prospective posterior region of the epiblast marking the site of primitive streak formation. We also documented transient nodal.lacZ expression in the visceral endoderm prior to and during early streak formation. A mosaic analysis using wild-type ES cells to rescuenodal-deficient embryos allowed us to document functionally distinct nodal activities in the embryonic ectodermal and primitive endo- dermal cell lineages. nodal signaling in the ectoderm is necessary for primitive streak formation as the gastrulation defect of nodal-deficient embryos can be rescued by the inclusion of small numbers of wild-type cells. In addition, we show that chimeric embryos composed of nodal- deficient primitive endoderm fail to develop rostral neural structures. Thus we conclude that the action of nodal, a TGF β-related growth factor expressed in the primitive endoderm, is critical for patterning of the anterior aspects of the A-P axis.
Two-step induction of chordotonal organ precursors in Drosophila embryogenesis
Authors: Okabe Masataka , Okano Hideyuki
Published: April 2021

The chordotonal (Ch) organ, an internal stretch receptor located in the subepidermal layer, is one of the major sensory organs in the peripheral nervous system of Drosophila melanogaster. Although the cell lineage of the Ch organ has been well characterized in many studies, the determination machinery of Ch organ precursor cells (COPs) remains largely unresolved. Here we report that the rhomboid (rho) gene and the activity of the Drosophila EGF receptor (DER) signaling pathway are necessary to induce specifically three of the eight COPs in an embryonic abdominal hemisegment. The cell-lineage analysis of COPs using the yeast flpase (flp/FRT) method indicated that each of the eight COPs originated from an individual undifferentiated ectodermal cell. The eight COPs in each abdominal hemisegment seemed to be determined by a two-phase induction: first, five COPs are determined by the action of the proneural gene atonal and neurogenic genes. Subsequently, these five COPs start to express therho gene, and rho activates the DER-signaling pathway in neighboring cells and induces argos expression. Three of these argos-expressing cells differentiate into the three remaining COPs and they prevent neighboring cells from becoming extra COPs.
Postmitotic cells fated to become rod photoreceptors can be respecified by CNTF treatment of the retina
Authors: Ezzeddine Z. Diala , Yang Xianjie , DeChiara Tom , Yancopoulos George , Cepko Constance L.
Published: April 2021

Lineage analyses of vertebrate retinae have led to the suggestions that cell fate decisions are made during or after the terminal cell division and that extrinsic factors can influence fate choices. The evidence for a role of extrinsic factors is strongest for development of rodent rod photoreceptors (‘rods’). In an effort to identify molecules that may regulate rod development, a number of known factors were assayed in vitro. Ciliary neurotrophic factor (CNTF) was found to have a range of effects on retinal cells. Addition of CNTF to postnatal rat retinal explants resulted in a dramatic reduction in the number of differentiating rods. Conversly, the number of cells expressing markers of bipolar cell differentiation was increased to a level not normally seen in vivo or in vitro. In addition, a small increase in the percentage of cells expressing either a marker of amacrine cells or a marker of Müller glia was noted.

It was determined that many of the cells that would normally differentiate into rods were the cells that differentiated as bipolar cells in the presence of CNTF. Prospective rod photoreceptors could make this change even when they were postmitotic, indicating that at least a subset of cells fated to be rods were not committed to this fate at the time they were born. These findings highlight the distinction between cell fate and commitment. Resistance to the effect of CNTF on rod differentiation occurred at about the time that a cell began to express opsin. The time of commitment to terminal rod differentiation may thus coincide with the initiation of opsin expression.

In agreement with the hypothesis that CNTF plays a role in rod differentiation in vivo, a greater percentage of cells were observed differentiating as rod photoreceptors in mouse retinal explants lacking a functional CNTF receptor, relative to wild-type littermates.
Specific residues in the Pbx homeodomain differentially modulate the DNA-binding activity of Hox and Engrailed proteins
Authors: Peltenburg Lucy T. C. , Murre Cornelis
Published: April 2021

Two classes of homeodomain proteins, Hox and Engrailed, have been shown to act in concert with the atypical homeodomain proteins Pbx and extradenticle. We now show that specific residues located within the Pbx homeodomain are essential for cooperative DNA binding with Hox and Engrailed gene products. Within the N-terminal region of the Pbx homeodomain, we have identified a residue that is required for cooperative DNA binding with three Hox gene products but not for cooperativity with Engrailed-2 (En-2). Furthermore, there are similarities between heterodimeric interactions involving the yeast mating type proteins MATa1 and MATα2 and those that allow the formation of Pbx/Hox and Pbx/En-2 heterodimers. Specifically, residues located in the a1 homeodomain that were previously shown to form a hydrophobic pocket allowing the α2 C-terminal tail to bind, are also required for Pbx/Hox and Pbx/En-2 cooperativity. Furthermore, we show that three residues located in the turn between helix 1 and helix 2, characteristic of many atypical homeodomain proteins, are required for cooperative DNA binding involving both Hox and En-2. Replacement of the three residues located in the turn between helix 1 and helix 2 of the Pbx homeodomain with those of the atypical homeodomain proteins controlling cell fate in the basidiomycete Ustilago maydis, bE5 and bE6, allows cooperative DNA binding with three Hox members but abolishes interactions with En-2. The data suggest that the molecular mechanism of homeodomain protein interactions that control cell fate in Saccharomyces cerevisiae and in the basidiomycetes may well be conserved in part in multicellular organisms.
Genetic analysis of the larval optic nerve projection in Drosophila
Authors: Schmucker Dietmar , Jäckle Herbert , Gaul Ulrike
Published: April 2021

The Drosophila larval optic nerve, called Bolwig’s nerve (BN), projects into the central brain along a simple invariant path. The growth of the BN proceeds in three phases, during which the nerve changes direction at two intermediate targets, P1 and P2. Here we show that the projection of the BN is amenable to genetic dissection. In a mutagenesis screen, we have isolated mutations in 13 genes that disrupt the BN projection in distinct phases of its development. The mutant phenotypes in combination with the expression patterns of corresponding candidate genes define cellular components necessary for directing the growth of the BN toward P2 and for redirecting its growth at P2, and reveal developmental strategies employed in the establishment of the BN projection.
Following cell fate in the living mouse embryo
Authors: Zernicka-Goetz M. , Pines J. , Hunter S. McLean , Dixon J. P. C. , Siemering K. R. , Haseloff J. , Evans M. J.
Published: April 2021

It has been difficult to follow many of the dramatic changes in cell fate and cell migration during mouse development. This is because there has been no enduring marker that would allow cells to be recognised in the living embryo. We believe that we have overcome this problem by developing a novel form of green fluorescent protein, named MmGFP, that proves to be easily visible and non toxic to mouse cells and does not perturb embryogenesis. We show that synthetic mRNA encoding MmGFP can be injected into blastomeres to follow the fate of their progeny during preimplantation development. We have made a stable embryonic stem cell line that expresses MmGFP and introduced these fluorescent cells into mouse embryos. For the first time, we have been able to follow the fate of embryonic stem cells in living embryos and to observe directly the contribution of these cells to distinct lineages of the postim-plantation embryo. This approach should lead to a more complete description of the dynamics of cell fate in the mouse.
XlPOU 2 is a potential regulator of Spemann’s Organizer
Authors: Witta Samir E. , Sato Sheryl M.
Published: April 2021

XlPOU 2, a member of the class III POU-domain family, is expressed initially at mid-blastula transition (MBT) and during gastrulation in the entire marginal zone mesoderm, including Spemann’s Organizer (the Organizer). To identify potential targets of XlPOU 2, the interaction of XlPOU 2 with other genes co-expressed in the Organizer was examined by microinjecting XlPOU 2’s mRNA into the lineage of cells that contributes to the Organizer, head mes-enchyme and prechordal plate. XlPOU 2 suppresses the expression of a number of dorsal mesoderm-specific genes, including gsc, Xlim-1, Xotx2, noggin and chordin, but not Xnot. As a consequence of the suppression of dorsal mesoderm gene expression, bone morphogenetic factor-4 (Bmp-4), a potent inducer of ventral mesoderm, is activated in the Organizer. Gsc is a potential target of XlPOU 2. XlPOU 2 is capable of binding a class III POU protein binding site (CATTAAT) that is located within the gsc promoter, in the activin-inducible (distal) element. Furthermore, XlPOU 2 suppresses the activation of the gsc promoter by activin signaling. At the neurula and tailbud stages, dorsoanterior structures are affected: embryos displayed micropthalmia and the loss of the first branchial arch, as detected by the expression of pax-6, Xotx2 and en-2. By examining events downstream from the Wnt and chordin pathways, we determined that XlPOU 2, when overexpressed, acts specifically in the Organizer, downstream from GSK-3β of the Wnt pathway and upstream from chordin. The interference in dorsalizing events caused by XlPOU 2 was rescued by chordin. Thus, in addition to its direct neuralizing ability, in a different context, XlPOU 2 has the potential to antagonize dorsalizing events in the Organizer.
The winged helix gene, Mf3, is required for normal development of the diencephalon and midbrain, postnatal growth and the milk-ejection reflex
Authors: Labosky Patricia A. , Winnier Glenn E. , Jetton Thomas L. , Hargett Linda , Ryan Aimee K. , Rosenfeld Michael G. , Parlow A. F. , Hogan Brigid L. M.
Published: April 2021

The mouse Mf3 gene, also known as Fkh5 and HFH-e5.1, encodes a winged helix/forkhead transcription factor. In the early embryo, transcripts for Mf3 are restricted to the presomitic mesoderm and anterior neurectoderm and mesoderm. By 9.5 days post coitum, expression in the nervous system is predominantly in the diencephalon, midbrain and neural tube. After midgestation, the highest level of mRNA is in the mammillary bodies, the posterior-most part of the hypothalamus. Mice homozygous for a deletion of the mf3 locus on a [129 × Black Swiss] background display variable phenotypes consistent with a requirement for the gene at several stages of embryonic and postnatal development. Approximately six percent of the mf3−/− embryos show an open neural tube in the diencephalon and midbrain region, and another five percent show a severe reduction of the posterior body axis; both these classes of affected embryos die in utero. Surviving homozygotes have an apparently normal phenotype at birth. Postnatally, however, mf3−/− pups are severely growth retarded and approximately one third die before weaning. This growth defect is not a direct result of lack of circulating growth hormone or thyrotropin. Mice that survive to weaning are healthy, but they show an abnormal clasping of the hindfeet when suspended by the tail. Although much smaller than normal, the mice are fertile. However, mf3−/− females cannot eject their milk supply to feed their pups. This nursing defect can be corrected with interperitoneal injections of oxytocin. These results provide evidence that Mf3 is required for normal hypothalamus development and suggest that Mf3 may play a role in postnatal growth and lactation.
Differential regulation of two sets of mesonephric tubules by WT-1
Authors: Sainio Kirsi , Hellstedt Paavo , Kreidberg Jordan A. , Saxén Lauri , Sariola Hannu
Published: April 2021

Mammalian renal development undergoes two transient stages, the pronephros and the mesonephros. While the regulation of metanephric differentiation has received considerable attention, very little is known about the mode of differentiation of the mesonephros and its regulation. We have followed mesonephric differentiation to unravel the developmental mechanisms and fates of mesonephric tubules by whole-mount immunohistology using anti-bodies to laminin, brush border epitopes, cytokeratin-8/18, p75 neurotrophin receptor and some other renal antigens as markers. In rat and mouse embryos, two distinct sets of tubules were observed throughout mesonephric development. Four to six pairs of cranial mesonephric tubules developed as outgrowths from the Wolffian duct. The majority of tubules were caudal tubules which never fused with the Wolffian and differentiated similarly to metanephric nephrons. The murine mesonephric tubules degenerate by apoptosis, except in males where the cranial tubules become the epididymal ducts. These developmental differences between the cranial and caudal sets of tubules suggested different regulatory systems for each. Targeted disruption of the Wilms’ tumour gene product, WT-1, results in renal aplasia, and a reduction in the number of mesonephric tubules (Kreidberg, J. A., Sariola, H., Loring, J., Maeda, M., Pelletier, J., Housman, D. and Jaenisch, R. (1993). Cell 74, 679-691). We therefore analysed more closely mesonephric differentiation in WT-1-deficient mice, and showed that they only develop the cranial mesonephric tubules but not the caudal ones. Thus, WT-1 appears to regulate only the development of the caudal mesonephric tubules that conceivably are formed from mesenchymal cells like the metanephric tubules. WT-1 therefore seems to be necessary for the mesenchyme to epithelium transitions at different stages of nephrogenesis.
who encodes a KH RNA binding protein that functions in muscle development
Authors: Baehrecke Eric H.
Published: April 2021

The Drosophila who (wings held-out) gene functions during the late stages of somatic muscle development when myotubes migrate and attach to specific epidermal sites. Animals lacking who function are capable of forming multinucleate myotubes, but these cells are restricted in migration. who mutants die at the end of embryogenesis with the posterior end of their cuticles arrested over the dorsal surface. Animals that possess weak who mutations either die as pupae, or survive as adults with defects in wing position. These phenotypes indicate that who also functions during metamorphosis, when muscles are reorganized to support adult structures and behavior. These embryonic and metamorphosis defects are similar to the phenotypes produced by previously identified genes that function in either muscle development or steroid signaling pathways. who transcription occurs in muscle and muscle attachment site cells during both embryogenesis and metamorphosis, and is inducible by the steroid ecdysone at the onset of metamorphosis. who encodes a protein that contains a KH RNA binding domain. Animals that possess a mutation in a conserved loop that links predicted α and β structures of this RNA binding motif lack who function. These results indicate that who plays an essential role in steroid regulation of muscle development.
A novel family of T-box genes in urodele amphibian limb development and regeneration: candidate genes involved in vertebrate forelimb/hindlimb patterning
Authors: Simon Hans-Georg , Kittappa Raja , Khan Paul A. , Tsilfidis Catherine , Liversage Richard A. , Oppenheimer Simone
Published: April 2021

In certain urodeles, a lost appendage, including hand and foot, can be completely replaced through epimorphic regeneration. The regeneration process involves cellular activities similar to those described for embryogenesis. Working on the assumption that the morphological pattern specific for a forelimb or a hindlimb is controlled by different gene activities in the two limbs, we employed a mRNA differential display screen for the detection of candidate limb identity genes. Using this approach, we have isolated a newt gene which in regenerating and developing limbs reveals properties expected of a gene having a role in controlling limb morphology: (1) it is exclusively expressed in the forelimbs, but not hindlimbs, (2) during embryonic development its expression is co-incident with forelimb bud formation, (3) it has an elevated message level throughout the undifferentiated limb bud and the blastema, respectively, and (4) it is expressed only in mesenchymal, but not in epidermal tissues. This novel newt gene shares a conserved DNA-binding domain, the T-box, with putative transcription factors including the Brachyury (T) gene product. In a following PCR-based screen, we used the evolutionarily conserved T-box motif and amplified a family of related genes in the newt; their different expression patterns in normal and regenerating forelimbs, hindlimbs and tail suggest, in general, an important role of T-domain proteins in vertebrate pattern formation.
Drosophila embryonic pattern repair: how embryos respond to bicoid dosage alteration
Authors: Namba Ruria , Pazdera Todd M. , Cerrone Richelle L. , Minden Jonathan S.
Published: April 2021

The product of the maternal effect gene, bicoid (bcd), is a transcription factor that acts in a concentration-dependent fashion to direct the establishment of anterior fates in the Drosophila melanogaster embryo. Embryos laid by mothers with fewer or greater than the normal two copies of bcd show initial alterations in the expression of the gap, seg-mentation and segment polarity genes, as well as changes in early morphological markers. In the absence of a fate map repair system, one would predict that these initial changes would result in drastic changes in the shape and size of larval and adult structures. However, these embryos develop into relatively normal larvae and adults. This indicates that there is plasticity in Drosophila embryonic development along the anterior-posterior axis. Embryos laid by mothers with six copies of bcd have reduced viability, indicating a threshold for repairing anterior-posterior mispatterning. We show that cell death plays a major role in correcting expanded regions of the fate map. There is a concomitant decrease of cell death in compressed regions of the fate map. We also show that compression of the fate map does not appear to be repaired by the induction of new cell divisions. In addition, some tissues are more sensitive to fate map compression than others.
The Drosophila gene fs(2)cup interacts with otu to define a cytoplasmic pathway required for the structure and function of germ-line chromosomes
Authors: Keyes Linda N. , Spradling Allan C.
Published: April 2021

The Drosophila ovarian tumor gene (otu) encodes cytoplas-mic proteins that are required in germ-line cells for cyst formation, nurse cell chromosome structure and egg maturation. We have analyzed a gene, fs(2)cup, that participates in many of the same processes and interacts with otu genetically. Both nurse cell and oocyte chromosomes require cup to attain a normal morphology. In addition, the gene is needed for the oocyte to grow normally by taking up materials transported from the nurse cells. The gene encodes a 1132-amino-acid protein containing a putative membrane-spanning domain. Cup protein (but not cup RNA) is trans-ported selectively into the oocyte in germarial cysts, like the p104 Otu protein. It is strongly associated with large structures in the cytoplasm and perinuclear region of nurse cells and, like Otu, moves to the periphery of these cells in stages 9-10. Moreover, cup mutations dominantly disrupt meiotic chromosome segregation. We propose that cup, otu and another interacting gene, fs(2)B, take part in a common cytoplasmic pathway with multiple functions during oogenesis.
The dorsoventral polarity of the presumptive limb is determined by signals produced by the somites and by the lateral somatopleure
Authors: Michaud, Jacques L. , Lapointe Françoise , Douarin Nicole M. Le
Published: April 2021

When it first appears at stage HH16, the wing bud is already polarized along the dorsoventral axis. To study the mechanisms leading to the establishment of its dorsoventral polarity, we decided to focus our attention on an earlier stage (HH13). Using the quail-chick chimera system, we first show that the presumptive wing mesoderm occupies the medial half of the somatopleure at the level of somites 15-20. The corresponding ectodermal area, however, will only give rise to the apical ectodermal ridge. The rest of the limb bud ectoderm originates from the ectoderm overlying the paraxial and the intermediate mesoderms for its dorsal aspect and the lateral somatopleural mesoderm for its ventral aspect. We next used five experimental paradigms to show that the dorsoventral polarity of the presumptive limb is determined by its environment. Thus, presumptive limb regions flanked on two sides by rows of somites give rise to bidorsal limb buds, indicating that the somites produce a dorsalizing factor. In addition, insertion of filters laterally to the presumptive limb region also results in bidorsal limb buds, suggesting that the lateral somato-pleure produces a ventralizing factor. We propose a model in which the polarizing activity of these two signals is mediated by the morphogenetic movements of the presumptive dorsal and ventral ectoderms, which carry the dorsoventral information over the limb bud mesenchyme.
buttonhead does not contribute to a combinatorial code proposed for Drosophila head development
Authors: Wimmer Ernst A. , Cohen Stephen M. , Jäckle Herbert , Desplan Claude
Published: April 2021

The Drosophila gap-like segmentation genes orthodenticle, empty spiracles and buttonhead (btd) are expressed and required in overlapping domains in the head region of the blastoderm stage embryo. Their expression domains correspond to two or three segment anlagen that fail to develop in each mutant. It has been proposed that these overlapping expression domains mediate head metamerization and could generate a combinatorial code to specify segment identity. To test this model, we developed a system for targeted gene expression in the early embryo, based on region specific promoters and the flp-out system. Misex-pression of btd in the anterior half of the blastoderm embryo directed by the hunchback proximal promoter rescues the btd mutant head phenotype to wild-type. This indicates that, while btd activity is required for the formation of specific head segments, its ectopic expression does not disturb head development. We conclude that the spatial limits of btd expression are not instructive for metamerization of the head region and that btd activity does not contribute to a combinatorial code for specification of segment identity.
Matrix metalloproteinases regulate morphogenesis, migration and remodeling of epithelium, tongue skeletal muscle and cartilage in the mandibular arch
Authors: Chin Jennie R. , Werb Zena
Published: April 2021

We have investigated the role of proteinases in the developmental program of bone, cartilage, tongue muscle and epithelial differentiation and remodeling in the mandibular arch during murine embryogenesis. Expression of matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) was tissue-specific with little or no expression in the epithelium of tooth buds, tongue or oral cavity. Gelatinase A mRNA transcripts were strongly expressed in the perichondrium of Meckel’s cartilage and mesenchymal areas of embryonic day 13-15 mandibles, whereas gelatinase B, collagenase-3, TIMP-1 and TIMP-2 mRNA were found primarily in the ossifying areas of the mandibles. The skeletal muscle of the tongue expressed stromelysin-3, TIMP-2 and TIMP-3 mRNA while stromelysin-3, TIMP-2 and gelatinase A were seen in the overlying connective tissue layer. Gelatinase A, gelatinase B, stromelysin-1, urokinase, TIMP-1 and TIMP-2 mRNA and protein activities were also detected in cultured mandibular explants. Culture of day 10 mandibular explants with a hydroxamic acid metalloproteinase inhibitor, but not with inhibitors of metalloendopeptidases (thiorphan and phosphoramidon), serine proteinases (aprotinin), cysteine proteinases (leupeptin) and urokinase (amiloride), altered mandibular morphogenesis dramatically. Development of the tongue (glossogenesis) and cartilage, but not bone or teeth was affected. Formation of the oral sulcus and fusion of the two epithelia of the medial sulcus were inhibited, and number and migration of myoblasts decreased. The resulting ‘tongue-tied phenotype’ indicates that MMPs are involved in epithelial morphogenesis and the migration of myoblasts to the region of the tongue. Development of the anterior segment of Meckel’s cartilage was also inhibited and proteoglycan content of the cartilage was reduced by inhibiting MMPs. Our data suggest that matrix metalloproteinases play a pivotal role in the morphogenesis of structures derived from epithelium (oral sulcus), cranial paraxial mesoderm (tongue) and cranial neural crest (Meckel’s cartilage).
Activation of dorsal development by contact between the cortical dorsal determinant and the equatorial core cytoplasm in eggs of Xenopus laevis
Authors: Kageura H.
Published: April 2021

In eggs of Xenopus laevis, dorsal development is activated on the future dorsal side by cortical rotation, after fertilization. The immediate effect of cortical rotation is probably the transport of a dorsal determinant from the vegetal pole to the equatorial region on the future dorsal side. However, the identity and action of the dorsal determinant remain problematic. In the present experiments, individual isolated cortices from various regions of the unfertilized eggs and embryos were implanted into one of several positions of a recipient 8-cell embryo. The incidence of secondary axes was used not only to locate the cortical dorsal determinant at different times but also to locate the region of the core competent to respond to the dorsal determinant. The dorsal axis-inducing activity of the cortex occurred around the vegetal pole of the unfertilized egg. During cortical rotation, it shifted from there to a wide dorsal region. This is apparently the first evidence for the presence of a dorsal determinant in the egg cortex. The competence of the core of the 8-cell embryo was distributed in the form of gradient with the highest responsiveness at the equator. These results suggest that, in the normal embryo, dorsal development is activated by contact between the cortical dorsal determinant and the equatorial core cytoplasm, brought together through cortical rotation.
Roles of Pax-6 in murine diencephalic development
Authors: Warren Natasha , Price David J.
Published: April 2021

Pax-6 is one of the earliest regulatory genes to be expressed in the diencephalon. We tested whether normal Pax-6 protein is required for early diencephalic development by examining morphology, precursor proliferation and patterns of regulatory gene expression in the embryonic diencephalon of Small-eye mice (Pax-6 mutants). In Smalleye mice, diencephalic morphology was abnormal at all the embryonic ages studied (days 10.5, 12.5 and 14.5). Regional differences in diencephalic cell density were lost, the diencephalon/mesencephalon boundary was unclear and the third ventricle was enlarged. We estimated diencephalic proliferative rates after labelling with bromodeoxyuridine and found that they were abnormally low in mutants aged embryonic day 10.5. In older mutants, the diencephalon contained fewer cells than normal.

In wild-type E14.5 diencephalon, Pax-6, Dlx-2 and Wnt- 3 are expressed in discrete regions along the rostrocaudal and dorsoventral axes. In situ hybridizations for these genes in E14.5 Small-eye mice revealed discrete zones of diencephalic expression that had similar relative positions to those in wild-type mice. Some differences of detail in their expression were seen: Pax-6 had an expanded rostral domain of expression and an abnormally indistinct caudal boundary; Dlx-2 had a diffuse, rather than a sharp, caudal boundary of expression; the normally high dorsal midline expression of Wnt-3 was lost. We conclude that normal expression of Pax-6 is required for the correct regulation of diencephalic precursor proliferation. Pax-6 may also control some aspects of diencephalic differentiation, but its mutation in Small-eye mice does not preclude the development of a degree of diencephalic regionalization resembling that in normal mice.
Location and growth of epaxial myotome precursor cells
Authors: Denetclaw Wilfred F. , Christ Bodo , Ordahl Charles P.
Published: April 2021

The skeletal muscle progenitor cells of the vertebrate body originate in the dermomyotome epithelium of the embryonic somites. To precisely locate myotome precursor cells, fluorescent vital dyes were iontophoretically injected at specific sites in the dermomyotome in ovo and the fates of dye-labeled cells monitored by confocal microscopy. Dyelabeled myotome myofibers were generated from cells injected along the entire medial boundary and the medial portion of the cranial boundary of the dermomyotome, regions in close proximity to the dorsal region of the neural tube where myogenic-inducing factors are thought to be produced. Other injected regions of the dermomyotome did not give rise to myotome fibers. Analysis of nascent myotome fibers showed that they elongate along the embryonic axis in cranial and caudal directions, or in both directions simultaneously, until they reach the margins of the dermomyotome. Finally, deposition of myotome fibers and expansion of the dermomyotome epithelium occurs in a lateral-to-medial direction. This new model for early myotome formation has implications for myogenic specification and for growth of the epaxial domain during early embryonic development.
Mash1 activates a cascade of bHLH regulators in olfactory neuron progenitors
Authors: Cau Elise , Gradwohl Gérard , Fode Carol , Guillemot François
Published: April 2021

The lineage of olfactory neurons has been relatively well characterized at the cellular level, but the genes that regulate the proliferation and differentiation of their progenitors are currently unknown. In this study, we report the isolation of a novel murine gene, Math4C/neurogenin1, which is distantly related to the Drosophila proneural gene atonal. We show that Math4C/neurogenin1 and the basic helix-loop-helix gene Mash1 are expressed in the olfactory epithelium by different dividing progenitor populations, while another basic helix-loop-helix gene, NeuroD, is expressed at the onset of neuronal differentiation. These expression patterns suggest that each gene marks a distinct stage of olfactory neuron progenitor development, in the following sequence: Mash1>Math4C/neurogenin1>NeuroD. We have previously reported that inactivation of Mash1 function leads to a severe reduction in the number of olfactory neurons. We show here that most cells in the olfactory epithelium of Mash1 mutant embryos fail to express Math4C/neurogenin1 or NeuroD. Strikingly, a subset of progenitor cells in a ventrocaudal domain of Mash1 mutant olfactory epithelium still express Math4C/neurogenin1 and NeuroD and differentiate into neurons. Cells in this domain also express Math4A/neurogenin2, another member of the Math4/neurogenin gene family, and not Mash1. Our results demonstrate that Mash1 is required at an early stage in the olfactory neuron lineage to initiate a differentiation program involving Math4C/neurogenin1 and NeuroD. Another gene activates a similar program in a separate population of olfactory neuron progenitors.
A new rhodopsin in R8 photoreceptors of Drosophila: evidence for coordinate expression with Rh3 in R7 cells
Authors: Papatsenko Dmitri , Sheng Guojun , Desplan Claude
Published: April 2021

The photoreceptor cells of the Drosophila compound eye are precisely organized in elementary units called ommatidia. The outer (R1-R6) and inner (R7, R8) photoreceptors represent two physiologically distinct systems with two different projection targets in the brain (for review see Hardie, 1985). All cells of the primary system, R1-R6, express the same rhodopsin and are functionally identical. In contrast, the R7 and R8 photoreceptors are different from each other. They occupy anatomically precise positions, with R7 on top of R8. In fact, there are several classes of R7/R8 pairs, which differ morphologically and functionally and are characterized by the expression of one of two R7-specific opsins, rh3 or rh4.

Here, we describe the identification of a new opsin gene,rhodopsin 5, expressed in one subclass of R8 cells. Interestingly, this subclass represents R8 cells that are directly underneath the R7 photoreceptors expressing rh3, but are never under those expressing rh4. These results confirm the existence of two subpopulations of R7 and R8 cells, which coordinate the expression of their respective rh genes. Thus, developmental signaling pathways between R7 and R8 lead to the exclusive expression of a single rhodopsin gene per cell and to the coordinate expression of another one in the neighboring cell. Consistent with this, rh5 expression in R8 disappears when R7 cells are absent (in sevenless mutant). We propose a model for the concerted evolution of opsin genes and the elaboration of the architecture of the retina.