bluuebunny/crossref_metadata_2025 huggingface dataset:
Biphasic activation of the BMP pathway patterns the Drosophila embryonic dorsal region
Authors: Dorfman Ruslan , Shilo Ben-Zion
Published: April 2021

The BMP pathway patterns the dorsal region of the Drosophila embryo. Using an antibody recognizing phosphorylated Mad (pMad), we followed signaling directly. In wild-type embryos, a biphasic activation pattern is observed. At the cellular blastoderm stage high pMad levels are detected only in the dorsal-most cell rows that give rise to amnioserosa. This accumulation of pMad requires the ligand Screw (Scw), the Short gastrulation (Sog) protein, and cleavage of their complex by Tolloid (Tld). When the inhibitory activity of Sog is removed, Mad phosphorylation is expanded. In spite of the uniform expression of Scw, pMad expansion is restricted to the dorsal domain of the embryo where Dpp is expressed. This demonstrates that Mad phosphorylation requires simultaneous activation by Scw and Dpp. Indeed, the early pMad pattern is abolished when either the Scw receptor Saxophone (Sax), the Dpp receptor Thickveins (Tkv), or Dpp are removed. After germ band extension, a uniform accumulation of pMad is observed in the entire dorsal domain of the embryo, with a sharp border at the junction with the neuroectoderm. From this stage onward, activation by Scw is no longer required, and Dpp suffices to induce high levels of pMad. In these subsequent phases pMad accumulates normally in the presence of ectopic Sog, in contrast to the early phase, indicating that Sog is only capable of blocking activation by Scw and not by Dpp.
Local nonpermissive and oriented permissive cues guide vestibular axons to the cerebellum
Authors: Tashiro Yasura , Miyahara Mikiko , Shirasaki Ryuichi , Okabe Masaru , Heizmann Claus W. , Murakami Fujio
Published: April 2021

Information that originates from peripheral sensory organs is conveyed by axons of cephalic sensory cranial ganglia connecting the sensory organs to appropriate central targets in the brain. Thus, the establishment of correct axonal projections by sensory afferents is one of the most important issues in neural development. Previously, we examined the development of the vestibular nerve that originates from the VIIIth ganglion using a flat whole-mount preparation of the rat hindbrain and developed an in vitro, culture preparation that can recapitulate vestibular nerve development (Tashiro, Y., Endo, T., Shirasaki, R., Miyahara, M., Heizmann, C. W. and Murakami, F. (2000) J. Comp. Neurol. 417, 491-500). Both in vivo and in vitro, the ascending branch of the VIIIth ganglion projecting to the cerebellum reaches the base of the cerebellar primordium and starts to splay out towards the rhombic lip, apparently avoiding the ventral metencephalon. We now examine the nature of cues that guide vestibulocerebellar axons by applying various manipulations to the flat whole-mount in vitro preparation. Our observations suggest that local nonpermissive cues and oriented cues play a pivotal role in the guidance of vestibular axons to their central target.
TGFβ2, LIF and FGF2 cooperate to induce nephrogenesis
Authors: Plisov Sergei Y. , Yoshino Kiyoshi , Dove Lee F. , Higinbotham Kathleen G. , Rubin Jeffrey S. , Perantoni Alan O.
Published: April 2021

The metanephric kidney develops from interactions between the epithelial ureteric bud and adjacent metanephric mesenchyme, which is induced by the bud to form the epithelia of the nephron. We have found that leukemia inhibitory factor (LIF) and transforming growth factor β 2 (TGFβ 2) are secreted by inductive rat bud cells and cooperate to enhance and accelerate renal tubule formation in uninduced rat metanephric mesenchymal explants. LIF alone or TGFβ 2 with fibroblast growth factor 2 induced numerous tubules in isolated mesenchymes over an 8 day period, while (in combination) all three caused abundant tubule formation in 72 hours. Furthermore, neutralization of Wnt ligands with antagonist-secreted Frizzled-related protein 1 abrogated these responses and combinatorial cytokine/growth factor stimulation of explants augmented nuclear activation of Tcf1/Lef1, suggesting that LIF and TGFβ 2/FGF2 cooperate to regulate nephrogenesis through a common Wnt-dependent mechanism.
A single histone H1 isoform (H1.1) is essential for chromatin silencing and germline development in Caenorhabditis elegans
Authors: Jedrusik Monika A. , Schulze Ekkehard
Published: April 2021

In remarkable contrast to somatic cells, the germline of the nematode Caenorhabditis elegans efficiently silences transgenic DNA. The molecular mechanisms responsible for this have been shown to implicate chromatin proteins encoded by the mes genes (Kelly, W. G. and Fire, A. (1998) Development 125, 2451-2456), of which two are the C. elegans homologs of Polycomb Group gene transcriptional repressors. We have analyzed the contribution of the histone H1 gene family to this specific aspect of germ cells in C. elegans. We show with isotype-specific double stranded RNA-mediated interference (RNAi) that a single member of this gene family (H1.1) is essential for the repression of a silenced reporter-transgene in the germline of hermaphrodites and males, whereas no change is found in the somatic expression of this reporter. Additionally, RNA-mediated interference with H1.1 gene expression can cause a phenotype with severe affection of germline proliferation and differentiation in the hermaphrodite, and even sterility (5%-11% penetrance). These and further features observed in histone H1.1 RNAi experiments are also characteristic of the mes phenotype (Garvin, C., Holdeman, R. and Strome, S. (1998) Genetics 148, 167-185), which is believed to result from the desilencing of genes required for somatic differentiation in the germline. Our observations therefore support this interpretation of the mes phenotype and they identify a single histone H1 isoform (H1.1) as a new component specifically involved in chromatin silencing in the germline of C. elegans.
Defective zonae pellucidae in Zp2-null mice disrupt folliculogenesis, fertility and development
Authors: Rankin Tracy L. , O’Brien Marilyn , Lee Eric , Wigglesworth Karen , Eppig John , Dean Jurrien
Published: April 2021

All vertebrate eggs are surrounded by an extracellular matrix. This matrix is known as the zona pellucida in mammals and is critically important for the survival of growing oocytes, successful fertilization and the passage of early embryos through the oviduct. The mouse zona pellucida is composed of three glycoproteins (ZP1, ZP2 and ZP3), each encoded by a single copy gene. Using targeted mutagenesis in embryonic stem cells, Zp2-null mouse lines have been established. ZP1 and ZP3 proteins continue to be synthesized and form a thin zona matrix in early follicles that is not sustained in pre-ovulatory follicles. The abnormal zona matrix does not affect initial folliculogenesis, but there is a significant decrease in the number of antral stage follicles in ovaries isolated from mice lacking a zona pellucida. Few eggs are detected in the oviduct after stimulation with gonadotropins, and no two-cell embryos are recovered after mating Zp2-null females with normal male mice. The structural defect is more severe than that observed in Zp1-null mice, which have decreased fecundity, but not quite as severe as that observed in Zp3-null mice, which never form a visible zona pellucida and are sterile. Although zona-free oocytes matured and fertilized in vitro can progress to the blastocyst stage, the developmental potential of blastocysts derived from either Zp2- or Zp3-null eggs appears compromised and, after transfer to foster mothers, live births have not been observed. Thus, in addition to its role in fertilization and protection of early embryos, these data are consistent with the zona pellucida maintaining interactions between granulosa cells and oocytes during folliculogenesis that are critical to maximize developmental competence of oocytes.
mKlf7, a potential transcriptional regulator of TrkA nerve growth factor receptor expression in sensory and sympathetic neurons
Authors: Lei Lei , Ma Long , Nef Serge , Thai To , Parada Luis F.
Published: April 2021

Development of the nervous system relies on stringent regulation of genes that are crucial to this process. TrkA, the receptor for nerve growth factor (NGF), is tightly regulated during embryonic development and is essential for the survival and differentiation of neural crest-derived sensory and sympathetic neurons. We have previously identified a mouse TrkA enhancer and have characterized several cis regulatory elements that are important for appropriate TrkA expression in vivo. We now report the cloning of a novel gene encoding a Kruppel-like factor from a mouse dorsal root ganglion expression library. This Kruppel-like factor, named mKlf7, binds specifically to an Ikaros core binding element that is crucial for in vivo TrkA enhancer function. Using in situ hybridization, we demonstrate that mKlf7 is coexpressed with TrkA in sensory and sympathetic neurons during embryogenesis and in adulthood. These data are consistent with the idea that mKlf7 may directly regulate TrkA gene expression in the peripheral nervous system.
Orc mutants arrest in metaphase with abnormally condensed chromosomes
Authors: Pflumm Michelle F. , Botchan Michael R.
Published: April 2021

The origin recognition complex (ORC) is a six subunit complex required for eukaryotic DNA replication initiation and for silencing of the heterochromatic mating type loci in Saccharomyces cerevisiae. Our discovery of the Drosophila ORC complex concentrated in the centric heterochromatin of mitotic cells in the early embryo and its interactions with heterochromatin protein 1 (HP-1) lead us to speculate that ORC may play some general role in chromosomal folding. To explore the role of ORC in chromosomal condensation, we have identified a mutant of subunit 5 of the Drosophila melanogaster origin recognition complex (Orc5) and have characterized the phenotypes of both the Orc5 and the previously identified Orc2 mutant, k43. Both Orc mutants died at late larval stages and surprisingly, despite a reduced number of S-phase cells, an increased fraction of cells were also detected in mitosis. For this latter population of cells, Orc mutants arrest in a defective metaphase with shorter and thicker chromosomes that fail to align at the metaphase plate within a poorly assembled mitotic spindle. In addition, sister chromatid cohesion was frequently lost. PCNA and MCM4 mutants had similar phenotypes to Orc mutants. We propose that DNA replication defects trigger the mitotic arrest, due to the fact that frequent fragmentation was observed. Thus, cells have a mitotic checkpoint that senses chromosome integrity. These studies also suggest that the density of functional replication origins and completion of S phase are requirements for proper chromosomal condensation.
Germ cell expression of the transcriptional co-repressor TIF1β is required for the maintenance of spermatogenesis in the mouse
Authors: Weber Philipp , Cammas Florence , Gerard Christelle , Metzger Daniel , Chambon Pierre , Losson Régine , Mark Manuel
Published: April 2021

The gene for transcriptional intermediary factor 1β (TIF1β) encodes a transcriptional co-repressor known to play essential roles in chromatin remodeling as well as in early embryonic development. During spermatogenesis, TIF1β is preferentially associated with heterochromatin structures of Sertoli cells and round spermatids, as well as with meiotic chromosomes. Its expression is tightly regulated within spermatocyte and spermatid populations, and it is undetectable in spermatogonia. Spatiotemporally controlled ablation of TIF1β by using a germ cell lineage-specific CreERT/loxP system leads to testicular degeneration. This degeneration is not due to impairment of chromatin remodeling processes during meiosis and spermiogenesis, as TIF1β-deficient spermatocytes are able to complete their differentiation into spermatozoa. It rather occurs as a consequence of shedding of immature germ cells (spermatocytes and spermatids), and disappearance of stem spermatogonia. These results indicate that TIF1β has important functions in the homeostasis of the seminiferous epithelium, and probably plays a crucial role in the network of paracrine interactions between germ cell subpopulations and/or Sertoli cells.
Hairy/E(spl)-related(Her) genes are central components of the segmentation oscillator and display redundancy with the Delta/Notch signaling pathway in the formation of anterior segmental boundaries in the zebrafish
Authors: Oates Andrew C. , Ho Robert K.
Published: April 2021

We have examined the expression of a Hairy/E(spl)-related (Her) gene, her7, in the zebrafish and show that its expression in the PSM cycles similarly to her1 and deltaC. A decrease in her7 function generated by antisense oligonucleotides disrupts somite formation in the posterior trunk and tail, and disrupts the dynamic expression domains of her1 and deltaC, suggesting that her7 plays a role in coordinating the oscillations of neighboring cells in the presomitic mesoderm. This phenotype is reminiscent of zebrafish segmentation mutants with lesions in genes of the Delta/Notch signaling pathway, which also show a disruption of cyclic her7 expression. The interaction of HER genes with the Delta/Notch signaling system was investigated by introducing a loss of her7 function into mutant backgrounds. This leads to segmental defects more anterior than in either condition alone. Combining a decrease of her7 function with reduction of her1 function results in an enhanced phenotype that affects all the anterior segments, indicating that Her functions in the anterior segments are also partially redundant. In these animals, gene expression does not cycle at any time, suggesting that a complete loss of oscillator function had been achieved. Consistent with this, combining a reduction of her7 and her1 function with a Delta/Notch mutant genotype does not worsen the phenotype further. Thus, our results identify members of the Her family of transcription factors that together behave as a central component of the oscillator, and not as an output. This indicates, therefore, that the function of the segmentation oscillator is restricted to the positioning of segmental boundaries. Furthermore, our data suggest that redundancy between Her genes and genes of the Delta/Notch pathway is in part responsible for the robust formation of anterior somites in vertebrates.
Eya1is required for the morphogenesis of mammalian thymus, parathyroid and thyroid
Authors: Xu Pin-Xian , Zheng Weiming , Laclef Christine , Maire Pascal , Maas Richard L. , Peters Heiko , Xu Xin
Published: April 2021

Eyes absent (Eya) genes regulate organogenesis in both vertebrates and invertebrates. Mutations in human EYA1 cause congenital Branchio-Oto-Renal (BOR) syndrome, while targeted inactivation of murine Eya1 impairs early developmental processes in multiple organs, including ear, kidney and skeletal system. We have now examined the role of Eya1 during the morphogenesis of organs derived from the pharyngeal region, including thymus, parathyroid and thyroid. The thymus and parathyroid are derived from 3rd pharyngeal pouches and their development is initiated via inductive interactions between neural crest-derived arch mesenchyme, pouch endoderm, and possibly the surface ectoderm of 3rd pharyngeal clefts. Eya1 is expressed in all three cell types during thymus and parathyroid development from E9.5 and the organ primordia for both of these structures failed to form in Eya1–/– embryos. These results indicate that Eya1 is required for the initiation of thymus and parathyroid gland formation. Eya1 is also expressed in the 4th pharyngeal region and ultimobranchial bodies. Eya1–/– mice show thyroid hypoplasia, with severe reduction in the number of parafollicular cells and the size of the thyroid lobes and lack of fusion between the ultimobranchial bodies and the thyroid lobe. These data indicate that Eya1 also regulates mature thyroid gland formation. Furthermore, we show that Six1 expression is markedly reduced in the arch mesenchyme, pouch endoderm and surface ectoderm in the pharyngeal region of Eya1–/– embryos, indicating that Six1 expression in those structures is Eya1 dependent. In addition, we show that in Eya1–/– embryos, the expression of Gcm2 in the 3rd pouch endoderm is undetectable at E10.5, however, the expression of Hox and Pax genes in the pouch endoderm is preserved at E9.5-10.5. Finally, we found that the surface ectoderm of the 3rd and 4th pharyngeal region show increased cell death at E10.5 in Eya1–/– embryos. Our results indicate that Eya1 controls critical early inductive events involved in the morphogenesis of thymus, parathyroid and thyroid.
Effects of heterodimerization and proteolytic processing on Derrière and Nodal activity: implications for mesoderm induction inXenopus
Authors: Eimon Peter M. , Harland Richard M.
Published: April 2021

Derrière is a recently discovered member of the TGFβ superfamily that can induce mesoderm in explant assays and is expressed at the right time and location to mediate mesoderm induction in response to VegT during Xenopus embryogenesis. We show that the ability of Derrière to induce dorsal or ventral mesoderm depends strictly on the location of expression and that a dominant-negative Derrière cleavage mutant completely blocks all mesoderm formation when ectopically expressed. This differs from the activity of similar Xnr2 cleavage mutant constructs, which are secreted and retain signaling activity. Additional analysis of mesoderm induction by Derrière and members of the Nodal family indicates that these molecules are involved in a mutual positive-feedback loop and antagonism of either one of the signals can reduce the other. Interaction between Derrière and members of the Nodal family is also shown to occur through the formation of heterodimeric ligands. Using an oocyte expression system we show direct interaction between the mature Derrière ligand and members of both the Nodal and BMP families. Taken together, these findings indicate that Derrière and Nodal proteins probably work cooperatively to induce mesoderm throughout the marginal zone during early Xenopus development.
The role of bone morphogenetic proteins in the differentiation of the ventral optic cup
Authors: Adler Ruben , Belecky-Adams Teri L.
Published: April 2021

The ventral region of the chick embryo optic cup undergoes a complex process of differentiation leading to the formation of four different structures: the neural retina, the retinal pigment epithelium (RPE), the optic disk/optic stalk, and the pecten oculi. Signaling molecules such as retinoic acid and sonic hedgehog have been implicated in the regulation of these phenomena. We have now investigated whether the bone morphogenetic proteins (BMPs) also regulate ventral optic cup development. Loss-of-function experiments were carried out in chick embryos in ovo, by intraocular overexpression of noggin, a protein that binds several BMPs and prevents their interactions with their cognate cell surface receptors. At optic vesicle stages of development, this treatment resulted in microphthalmia with concomitant disruption of the developing neural retina, RPE and lens. At optic cup stages, however, noggin overexpression caused colobomas, pecten agenesis, replacement of the ventral RPE by neuroepithelium-like tissue, and ectopic expression of optic stalk markers in the region of the ventral retina and RPE. This was frequently accompanied by abnormal growth of ganglion cell axons, which failed to enter the optic nerve. The data suggest that endogenous BMPs have significant effects on the development of ventral optic cup structures.
The zebrafish T-box genesno tailandspadetailare required for development of trunk and tail mesoderm and medial floor plate
Authors: Amacher Sharon L. , Draper Bruce W. , Summers Brian R. , Kimmel Charles B.
Published: April 2021

T-box genes encode transcriptional regulators that control many aspects of embryonic development. Here, we demonstrate that the mesodermally expressed zebrafish spadetail (spt)/VegT and no tail (ntl)/Brachyury T-box genes are semi-redundantly and cell-autonomously required for formation of all trunk and tail mesoderm. Despite the lack of posterior mesoderm in spt–;ntl– embryos, dorsal-ventral neural tube patterning is relatively normal, with the notable exception that posterior medial floor plate is completely absent. This contrasts sharply with observations in single mutants, as mutations singly in ntl or spt enhance posterior medial floor plate development. We find that ntl function is required to repress medial floor plate and promote notochord fate in cells of the wild-type notochord domain and that spt and ntl together are required non cell-autonomously for medial floor plate formation, suggesting that an inducing signal present in wild-type mesoderm is lacking in spt–;ntl– embryos.
Identification and analysis ofDYAD: a gene required for meiotic chromosome organisation and female meiotic progression inArabidopsis
Authors: Agashe Bhavna , Prasad Chellapilla Krishna , Siddiqi Imran
Published: April 2021

The dyad mutant of Arabidopsis was previously identified as being defective in female meiosis. We report here the analysis of the DYAD gene. In ovules and anthers DYAD RNA is detected specifically in female and male meiocytes respectively, in premeiotic interphase/meiotic prophase. Analysis of chromosome spreads in female meiocytes showed that in the mutant, chromosomes did not undergo synapsis and formed ten univalents instead of five bivalents. Unlike mutations in AtDMC1 and AtSPO11 which also affect bivalent formation as the univalent chromosomes segregate randomly, the dyad univalents formed an ordered metaphase plate and underwent an equational division. This suggests a requirement for DYAD for chromosome synapsis and centromere configuration in female meiosis. The dyad mutant showed increased and persistent expression of a meiosis-specific marker, pAtDMC1::GUS during female meiosis, indicative of defective meiotic progression. The sequence of the putative protein encoded by DYAD did not reveal strong similarity to other proteins. DYAD is therefore likely to encode a novel protein required for meiotic chromosome organisation and female meiotic progression.
Distinct requirements for extra-embryonic and embryonic bone morphogenetic protein 4 in the formation of the node and primitive streak and coordination of left-right asymmetry in the mouse
Authors: Fujiwara Takeshi , Dehart Deborah B. , Sulik Kathleen K. , Hogan Brigid L. M.
Published: April 2021

In the mouse and chick embryo, the node plays a central role in generating left-right (LR) positional information. Using several different strategies, we provide evidence in the mouse that bone morphogenetic protein 4 (Bmp4) is required independently in two different sites for node morphogenesis and for LR patterning. Bmp4 expression in the trophoblast-derived extra-embryonic ectoderm is essential for the normal formation of the node and primitive streak. However, tetraploid chimera analysis demonstrates that Bmp4 made in epiblast-derived tissues is required for robust LR patterning, even when normal node morphology is restored. In the absence of embryonic Bmp4, the expression of left-side determinants such as Nodal and Lefty2 is absent in the left lateral plate mesoderm (LPM). Noggin-mediated inhibition of Bmp activity in cultured wild-type embryos results in suppression of Nodal expression in the LPM. Thus, unlike previous models proposed in the chick embryo in which Bmp4 suppresses left-sided gene expression, our results suggest that Bmp acts as a positive facilitator of the left-sided molecular cascade and is required for Nodal induction and maintenance in the left LPM.
Teneurin 2 is expressed by the neurons of the thalamofugal visual system in situ and promotes homophilic cell-cell adhesion in vitro
Authors: Rubin Beatrix P. , Tucker Richard P. , Brown-Luedi Marianne , Martin Doris , Chiquet-Ehrismann Ruth
Published: April 2021

The transmembrane glycoprotein teneurin 2 is expressed by neurons in the developing avian thalamofugal visual system at periods that correspond with target recognition and synaptogenesis. Partial and full-length teneurin 2 constructs were expressed in cell lines in vitro. Expression of the cytoplasmic domain is required for the induction of filopodia, the transport of teneurin 2 into neurites and the co-localization of teneurin 2 with the cortical actin cytoskeleton. In addition, expression of the extracellular domain of teneurin 2 by HT1080 cells induced cell aggregation, and the extracellular domain of teneurin 2 became concentrated at sites of cell-cell contact in neuroblastoma cells. These observations indicate that the homophilic binding of teneurin 2 may play a role in the development of specific neuronal circuits in the developing visual system.
Mezzo, apaired-likehomeobox protein is an immediate target of Nodal signalling and regulates endoderm specification in zebrafish
Authors: Poulain Morgane , Lepage Thierry
Published: April 2021

Endoderm specification in zebrafish is mediated by the zygotic transcription factors Bon/Mixer, Faust/Gata5, Casanova and Sox17, whose expression is induced by Nodal signalling. Bon/Mixer and Gata5 require Casanova in order to promote endoderm formation and all three factors act upstream of sox17, but it is not clear whether Casanova acts downstream of or in parallel to Bon/Mixer and Gata5. An additional factor induced at the margin of the blastoderm by Nodal signalling is thought to be required to induce casanova expression. We show that Mezzo, a novelpaired-like homeobox protein, may be this missing transcription factor. The homeobox of Mezzo is mostly related to the homeodomain of the Mix-like and Mixer homeoproteins, but Mezzo is distinct from Bon/Mixer, the product of the bonnie and clyde gene. Like bon/mixer, mezzois expressed transiently in mesendoderm precursors. By analysing the expression of mezzo in various mutants of Nodal signalling, we show that its expression strictly depends on a functional Nodal signalling pathway. By expressing a constitutively active Nodal receptor in the presence of translation inhibitors, we further demonstrate that mezzo, bonnie and clyde, and casanova are all immediate early targets of Nodal signalling, while sox17 requires post-MBT protein synthesis in order to be induced. Overexpression of mezzo mRNA can induce ectopic expression of casanova and sox17 and can also turn on the pan mesodermal marker gene ntl. We show that the function ofmezzo is redundant with that of bonnie and clyde and thatmezzo RNA can partially rescue bonnie and clyde mutants. Injection of antisense Morpholino oligonucleotides targeted againstmezzo into bonnie and clyde mutant embryos abolishes allsox17 expression and aggravates their mutant phenotype. These results highlight the complexity of the transcriptional network operating during endoderm formation. They place mezzo as a new transcription factor with unique properties acting in parallel with bonnie and clyde,faust and casanova in the Nodal signalling pathway that controls specification of mesoderm and endoderm in zebrafish.
Genetic and molecular characterization of a noveliab-8regulatory domain in theAbdominal-Bgene ofDrosophila melanogaster
Authors: Estrada Beatriz , Casares Fernando , Busturia Ana , Sánchez-Herrero Ernesto
Published: April 2021

Homeotic (or Hox) genes are key determinants in specifying the anteroposterior axis of most animals. The temporal and spatial expression of these genes requires the presence of large and complex cis-regulatory regions. The Abdominal-B Hox gene of the bithorax complex ofDrosophila is regulated by several infraabdominal domains,which determine Abdominal-B expression in abdominal segments A5 to A9(parasegments 10 to 14). Some of the infraabdominal domains have been characterized, including an infraabdominal-8 domain, which has been located 3′ to the Abdominal-B transcription unit. We have analyzed the expression and mutant phenotype of a P-lacZ element inserted close to the Abdominal-B m origin of transcription and of derivatives of this transposon. Some of these derivatives represent a particular class of mutations in the bithorax complex, because they transform the eighth and ninth abdominal segments without affecting more anterior metameres. The analysis of these mutations and of transformants carrying sequences upstream the Abdominal-B m transcription unit has allowed us to define a new infraabdominal-8 regulatory region, located 5′ to the Abdominal-B transcription unit, and has helped to characterize better the complex regulation of the Abdominal-Bgene.
Zeste maintains repression ofUbxtransgenes: support for a new model of Polycomb repression
Authors: Hur Man-Wook , Laney Jeffrey D. , Jeon Sang-Hack , Ali Janann , Biggin Mark D.
Published: April 2021

During late embryogenesis, the expression domains of homeotic genes are maintained by two groups of ubiquitously expressed regulators: the Polycomb repressors and the Trithorax activators. It is not known how the activities of the two maintenance systems are initially targeted to the correct genes. Zeste and GAGA are sequence-specific DNA-binding proteins previously shown to be Trithorax group activators of the homeotic gene Ultrabithorax (Ubx). We demonstrate that Zeste and GAGA DNA-binding sites at the proximal promoter are also required to maintain, but not to initiate, repression of Ubx. Furthermore, the repression mediated by Zeste DNA-binding site is abolished in zeste null embryos. These data imply that Zeste and probably GAGA mediate Polycomb repression. We present a model in which the dual transcriptional activities of Zeste and GAGA are an essential component of the mechanism that chooses which maintenance system is to be targeted to a given promoter.
Cell turnover in the spinal ganglia ofXenopus laevistadpoles
Authors: Prestige M. C.
Published: April 2021

HUGHES (1961) has drawn up a balance-sheet of the lumbar ventral horn cells during the development of Xenopus, based both on counts of numbers of ventral horn cells throughout differentiation and of the number of degenerating cells among them at each stage. In this way, he showed that the total number of ventral horn cells is reduced from between 3000 and 4000 at differentiation to 1200 at the end of metamorphosis; that the most rapid period of decline in cell numbers is accompanied by a peak in the time graph of the number of degenerations; and concluded that for every neurone which finally differentiates, some eight or nine neuroblasts undergo degeneration. This is an example of histogenetic degeneration (Glücksmann, 1951), that is, cell death relating to the differentiation of functioning organs.
Studies on the growth of 5-day-old rabbit blastocysts in vitro
Authors: Daniel Joseph C.
Published: April 2021

The optimal concentrations of a variety of components for promoting growth of 5-day-old rabbit blastocysts in vitro were determined. Growth, under different modifications of the basic medium (F10 plus 15 per cent, maternal rabbit serum) was expressed as the tangent of the growth curve plotted after 4 hr. and 24 hr. of incubation, where the average normal in vivo tangent is equal to 1. Improved growth was observed with limited increase in the concentrations of glycine, alanine, glutamic acid, threonine, serine and pyruvate, with the addition of lactate and a reduction in concentration of glucose. Addition of glycogen made a slight improvement in growth but linoleic acid suppressed growth. The effective concentrations of pyruvate and serine appear to be mutually interdependent. From the optima so revealed, the F10 medium was modified. This modified F10 medium alone supports good growth of 5-day-old blastocysts but when serum is added to 5 per cent., growth is within the range of that occurring in vivo.
A quantitative study of the development of the nerves in the hind-limb ofEleutherodactylus martinicensis
Authors: Hughes Arthur
Published: April 2021

The numbers of fibres within the peripheral nerves to the hind-limb of Eleutherodactylus martinicensis have been studied during development. The results have been collated with observations on the development of movement in the living embryo. By the time that the first movements of the limb occur, most of its nerves are recognizable, though the muscles themselves are still in an early stage of differentiation. The numbers of fibres in these nerves is then not greatly different from those which are found at the end of development. As the limb movements increase in scope, the numbers of fibres within the larger nerves increase to a maximum. In the last 2 days of development, when the tail of the embryo is being resorbed, a drastic loss of fibres occurs in the larger nerves, both muscular and cutaneous. This is accompanied by an increase in diameter in some of the remaining fibres. The larger muscles of the thigh decrease in volume towards the end of development, at approximately the same time as the number of fibres in the nerves by which they are supplied is reduced. A hypothesis is suggested of the origin of specific relationships between nerve fibre and end organ by selection.
Development of kidney-specific antigens: an immunohistological study
Authors: Okada T. S.
Published: April 2021

Highly ‘kidney-specific’ antiserum-globulins prepared against a particular sub-fraction isolated from the microsomal fraction of adult chicken kidney were conjugated with fluorescein and used as a staining reagent to study the development of mesonephros in the chick embryos. Mesonephric cords from the midabdominal region at different developmental stages from stage 16 to stage 31 were studied in (a) paraffin sections, and (b) smeared preparations of the dissociated cells. In the differentiated mesonephros at stages 27−30 specific fluorescence of antibody staining appeared in the cells of proximal secretory tubules. First intense fluorescence in the development occurred, coinciding with the first histological organization of epithelium at stage 20−21. Weak specific fluorescence was also detected in the cells of the condensed nephrogenic mesenchyme. Throughout the development of the tubular epithelium fluorescence appeared in a particular locus of the cells, i.e. only the apical part. In the earlier stages perhaps prior to epithelial formation, a fluorescent dot was sometimes detected apparently inside the nucleus. Diffuse reaction over the cytoplasm has never been observed. The proportion of the fluorescent positive cells in the whole cell population of the mesonephric cords steeply increased from stage 21 (9 per cent.) to stage 27 (45 per cent.). By combining the antibody staining technique with autoradiography, it was revealed that the percentage of the cells incorporating 3H-thymidine in the fluorescent positive cells was about twice as high as that in the negative cells at stages 22 and 25. At the final stage of the development (stage 28) there was little difference in the percentage of the isotopically labelled cells between positive and negative cells. The present results indicate that the antibody staining technique can be a potent tool to study acquisition of tissue-specificity in nephrogenesis. It is suggested that the initial synthesis of the molecules with immunological kidney specificity occurs in the nuclei in the early stages of development; in the next step when the proliferation rate of the cells with such molecules becomes particularly high, the synthesis may occur only in the apical part of the cells.
The effects of D- and L-threo-chloramphenicol on the early development of the chick embryo
Authors: Billett F. S. , Collini Rosalba , Hamilton Louie
Published: April 2021

In the presence of 200-300 μg./ml. of D-threo-chloramphenicol, chick embryos explanted at the full streak to head-fold stage develop abnormally. In the presence of the same and higher concentrations (600 μg./ml.) of the L-isomer, development is almost normal. The most obvious features of the response to D-threo-chloramphenicol are a failure of the neural tube to close and an inhibition of haemoglobin formation. In order to inhibit haemoglobin formation in the area vasculosa, it is necessary to treat the embryos several hours before the haemoglobin would appear. The abnormalities are accompanied by a reduction in the area of the blastoderm and of the area vasculosa. A high concentration of the L-threo compound, although it does not produce the embryonic abnormalities, does reduce the size of the blastoderm. The failure of the L-isomer to give rise to the abnormalities caused by the D-isomer suggests that the teratological response is due to an inhibition of protein synthesis caused primarily by an interference with the function of messenger RNA.
Morphological and functional development of the ovary of the mouse II. The development of the ovary in transplantation conditions in adult spayed hosts
Authors: Ben-Or Sarah
Published: April 2021

Grafts of ovarian tissue transplanted into adult spayed hosts ‘take’ well and remain functional for relatively long periods, even in homologous systems (Parkes, 1956; Harris & Eakin, 1949). Under the influence of the high endogenous gonadotrophic potential of the host, grafts of very young ovaries continue to develop and reach maturity even earlier than they would in their normal surroundings (Goodman, 1934; Dunham, Watts & Adair, 1941).
The utilization of yolk platelets by tissues ofXenopusembryos studied by a safranin staining method
Authors: Selman G. G. , Pawsey G. J.
Published: April 2021

The amphibian yolk platelet is a particular kind of food-reserve granule which may be easily recognized by microscopy and which is abundant in the cytoplasm of amphibian eggs and embryos. Wallace & Karasaki (1963) developed a method by which intact yolk platelets were isolated from eggs of Rana pipiens and were shown by electron microscopy to be practically free from other materials. Chemical analysis of such yolk platelets by Wallace (1963a, b) showed that the crystalline main body is made up of two components, a phosphoprotein of similar amino-acid composition to avian phosvitin and a lipoprotein similar to avian a-lipovitellin, the molecular proportions being 2 to 1 respectively. Surrounding this crystalline main body of the yolk platelet there is a granular peripheral zone which has been reported to contain both protein resembling histone (Horn, 1962) and polysaccharide (Ohno, Karasaki & Takata, 1964). Histochemical work by Ohno, Karasaki & Takata (1964) showed there was no nucleic acid detectable in yolk platelets, and although nucleic acids have often been reported present in isolated yolk fractions subjected to biochemical analysis, it seems probable in view of the experience of Wallace (1963a) that such reports were due to contamination either by follicle cells or cytoplasm. The ultrastructure of the amphibian yolk platelet has been described by Karasaki (1962, 1963a), Ward (1962) and Lanzavecchia (1965). Wallace (1963Ô) proposed a molecular structure for the main body component of a yolk platelet which appears to fit all known data from previous biochemical, biophysical and electron-optical analyses.
The oocyte of the domestic chicken shortly after hatching, studied by electron microscopy
Authors: Greenfield M. L.
Published: April 2021

Oocytes taken from chickens from 1 day to 11 weeks after hatching have been examined by electron microscopy. Early extra-follicular oocytes have chromosome filaments in the nucleus at the prophase of meiosis. The fine structure of these filaments is described and is found to vary according to the size and age of the oocyte. The Balbiani body present in oocytes of about 8-20 μ in diameter has been shown to consist of paired centrioles surrounded by Golgi vesicles and an outer border of mitochondria. Golgi vesicles and mitochondria were dispersed in larger oocytes, and in those larger than about 80 μ the mitochondria formed a cortical layer. In oocytes with a diameter greater than about 100 μ macrobodies (clusters of lining bodies) were mainly confined to the periphery of the oocyte, whereas in others they were present, together with lipid drops, mainly in the interior. Folding of the oocyte membrane was observed in many oocytes measuring about 100 μ in diameter, but was much more pronounced in oocytes above 250 μ. In these oocytes cortical vesicles in close proximity to the crypts of the folds appear to have been formed by pinocytosis. In the follicle cells of oocytes 250 in diameter and over, large masses of glycogen granules occur in the cytoplasm near the oocyte membrane.
Oogenesis in adult prosimians
Authors: Ioannou J. M.
Published: April 2021

It has been claimed that new germ cells are formed after maturity in certain female prosimians. A histological study was made of the ovaries of adults of four of these species (Galago crassicaudatus, G. demidoffi, Perodicticus potto and Loris tardigradus lydekkerianus), and of juvenile specimens of Loris. In addition, two adult female G. demidoffi were injected with 3H-thymidine and their ovaries subjected to autoradiographic examination. Mitotically active oogonia and/or oocytes in the early stages of meiotic prophase were present in all the adult prosimians examined; in G. demidoffi some of these cells incorporated 3H-thymidine, suggesting that DNA synthesis was in progress. These observations indicate that active oogenesis was taking place. There is no reason to believe, however, that new germ cells are formed other than by division of pre-existing oogonia.
The morphology and development ofDrosophilaeye
Authors: Hanly E. W. , Fuller C. William , Stanley M. S. Millam
Published: April 2021

The development of pigment in the eye of Drosophila melanogaster and other insects has been the subject of many studies and much controversy. It has been established that the red color of eyes of wild-type D. melanogaster is due to the presence of two classes of pigments, ommochromes and pteridines (Ziegler, 1961). The relationships among the various members of each class are still obscure; the biosynthetic pathways are yet to be elucidated. No specific enzyme involved in the synthesis of any member of either group has been isolated or characterized. It has been suggested, however (Hadorn, 1955), that these metabolic pathways may involve several organs, including the eye, but that the final deposition and conversion occur only in the eye. The recent development of a satisfactory technique for the culture of Drosophila organs (Schneider, 1964) has made possible the study of pigment development in the isolated eye and in eyes associated with selected organs. Thus it is possible to test the hypothesis that organs interact in the formation of eye pigments.
The neural crest and the acoustic ganglion
Authors: Deol M. S.
Published: April 2021

There is no agreement about the origin of the acoustic ganglion. Some investigators maintain that it originates in the neural crest, and others that it arises from the otic placode. It was thought that mutant genes might help in resolving the doubt. The gene piebald-lethal (s1) affecting pigmentation in the mouse was selected for this purpose. There was strong evidence that the piebald locus influenced the development of the neural crest before its differentiation into melanoblasts and ganglionic primordia. Histological examination revealed striking abnormalities in the inner ear of all piebald-lethal mice. The neural epithelium was invariably affected. In view of the known action of the piebald locus on the neural crest and the intimate developmental relationship between the acoustic ganglion and the neural epithelium, the most plausible explanation of these abnormalities is that the neural crest contributes to the formation of the acoustic ganglion in the mouse. This conclusion is supported by studies on two other mutants (white and pallid) in which defects of pigmentation and the inner ear occur together. The presence of similar abnormalities, either observed or deduced from deafness, in the inner ear of white cats and piebald dogs suggests that the acoustic ganglion in these animals has a similar origin.
Strontium-90 and intrauterine development in the rat
Authors: Hopkins B. J. , Casarett G. W. , Tuttle L. W. , Baxter R. C.
Published: April 2021

Single doses of strontium-90 (191 μc or 382 μc) were injected intravenously to pregnant rats on the 2nd or 10th day post-conception and the developing offspring were observed for deleterious effects on the 20th day post-conception. Injection of either dose on the 2nd day post-conception caused a significant increase in intrauterine mortality and fetal growth retardation (stunting), but a significant increase in morphological defects other than stunting was not observed. Injection on the 10th day post-conception caused little or no increase in mortality or growth retardation following a dose of 191 μc, and only slight increases after doses of 382 μc. However, gross morphological defects of various types were observed at both dose levels, but fewer varieties of defect at the lower dose. The most common defects were, in decreasing order of frequency, taillessness, retarded growth, reduced eye volume, skeletal defects, and interscapular depression. The radiation dose rate to both the uterus and the embryo was high soon after injection, then declined to low levels. A second peak in dose rate to the embryo occurred during late fetal life while that to the uterus remained low. The deleterious effects observed appeared to be dependent upon the total dose of 90Sr to the dam and the gestation age at time of injection.
Ultrastructure of adrenal medulla of the prenatal rat
Authors: Ratzenhofer Max , Müller Otfried
Published: April 2021

The ultrastructure of the adrenal medulla in adult laboratory animals has been described in a number of reports (Lever, 1955; Sjôstrand & Wetzstein, 1956; Wetzstein, 1957; de Robertis & vaz Ferreira, 1957; Erânkô & Hânninen, 1960; Yates, 1963, 1964a, b, c;Coupland, 1965a, b; Elfvin, 1965a, b). Since the introduction of the glutaraldehyde fixation technique, it has been possible to distinguish clearly between cells storing adrenalin and those storing noradrenalin by the different densities of their granules (Coupland, Pyper & Hopwood, 1964; Coupland, 1965 a; Elfvin, 1965 a). In order to study the histophysiology of the secretory process of catecholamines, suprarenal glands have been investigated under normal conditions and under the influence of mechanical, physical and chemical-pharmacological agents (the above references and Graf, 1966). The purpose of the present investigation was to study the structure of adrenal medulla of the rat during the prenatal period and to relate the findings to the process of secretion in the medullary cells.
Regeneration and growth control inNereis
Authors: Golding D. W.
Published: April 2021

Caudal regeneration in Nereis diversicolor is that rapid proliferation of segments which occurs after loss of part of the posterior of the body and the reformation of the pygidium. The rate of segment proliferation is highest during the production of the first new segments. Thereafter, the rate declines rapidly with each passing week, though if the regenerated segments are amputated, rapid proliferation is again resumed (Golding, 1967). Two explanations of these results are possible. First, the declining rate of segment proliferation during regeneration may be the result of a declining concentration of hormone in the body fluids. There may be a feed-back from the regenerating tail to the ganglion. As segments are proliferated, the secretory activity of the ganglion is suppressed. Secondly, the level of hormone in the body fluids may remain constant, the proliferating region of the pygidium becoming progressively more insensitive as regeneration proceeds.