bluuebunny/crossref_metadata_2025 huggingface dataset:
Patterns of engrailed protein in early Drosophila embryos
Authors: Karr Timothy L. , Weir Michael P. , Ali Zehra , Kornberg Thomas
Published: April 2021

By the onset of gastrulation during nuclear cycle 14 of Drosophila embryogenesis, the engrailed gene is expressed in fourteen one-cell-wide stripes. Each stripe defines the anlagen of the posterior compartment of a metamerie segment. We report here several observations relating to the role and disposition of the engrailed protein during the embryonic stages that precede cellularization. We demonstrate that in embryos mutant for the engrailed gene, there were characteristic morphological abnormalities as early as the 6th cleavage cycle. In addition, the engrailed protein was detected in pre-cycle-9 embryos by Western blot analysis. When localization of engrailed protein begins during cycle 14, engrailed expression was first present in broad anterior and posterior regions before the fourteen-stripe pattern appeared.
Region-specific deposition of dermal proteins between dermis and epidermis during induction of chick feather and scale rudiments
Authors: Peterson Charlotte A. , Phillips William H. , Grainger Robert M.
Published: April 2021

To begin to study the role of particular proteins in inductive tissue interactions, we have used density labelling techniques to determine whether any dermal proteins are found between embryonic chick dermis and epidermis at a stage when the dermis plays an important inductive role in epidermal differentiation. Epidermis will form feathers or scales depending on whether it Interacts with dorsal or foot dermis, respectively, and the dermis can still influence epidermal differentiation when direct cell contact between the tissues ls blocked by a membrane filter during culturing (Peterson & Grainger, 1985). In transfilter experiments, we detect a subset of dermal proteins within the filter between the tissues. Several of these dermal proteins are deposited in a region-specific manner, that is, they are only found associated with filters from either dorsal or foot dermis.

We have previously shown that the expression of some of these proteins is specific to particular regions of dermis and is also associated with the inductive potential of the dermis (Peterson & Grainger, 1986). We detect only 17 dermal proteins which are transferred across the filter in these cultures and found in direct association with epidermis; of these 14 are common to both dorsal and foot dermis, and 3 are deposited in a region-specific manner. Our results lead us to hypothesize a significant function for certain dermal proteins in this Inductive interaction either as part of the extracellular matrix or in direct association with epidermis.
The early development of motor axon pathways in the locust embryo: the establishment of the segmental nerves in the thoracic ganglia
Authors: Whitington Paul M.
Published: April 2021

This study has identified the first five motor neurones to send axons out of the segmental nerves in the thoracic ganglia of the locust and has traced the pathways followed by these axons up to their divergence into the ganglionic nerve roots. These motor neurones send out axons in a stereotyped sequence over a short period, corresponding to 2% of embryonic development. Motor axons initially grow dorsally to contact the dorsal basal lamina and then posteriolaterally in a parallel array just beneath this membrane. At the edge of the CNS the axons diverge into either of two pathways: an anterior pathway, corresponding to nerve root 3 which is pioneered by the first motor axon to leave the CNS; and a posterior pathway, corresponding to nerve root 5, which is pioneered by the second motor axon. The first motor axon appears to grow circumferentially around the segmental border between the body wall and the base of the coxa, while the second is closely associated with the filopodia or axons of the afferent peripheral pioneer neurones. The later motor axons reliably follow the pathways pioneered by these first two axons. A small number of molecular markers would be sufficient to generate the observed patterns of axon growth by these early motor neurones and some of these same cues may be used to guide afferent axons into the CNS.
Preparation and characterization of cell-free protein synthesis systems from oocytes and eggs of Xenopus laevis
Authors: Patrick Tina D. , Lewer Clare E. , Pain Virginia M.
Published: April 2021

During the maturation of the oocytes of the frog Xenopus laevis, the rate of protein synthesis shows a twofold increase. Studies of the mechanisms involved in this stimulation have been seriously limited by the lack of an active cell-free translation system. We have now prepared such systems from oocytes, progesterone-matured oocytes and eggs of Xenopus laevis by induction of lysis by centrifugation of whole cells.

The extracts are highly active in incorporation of labelled amino acids and, in the progesterone-matured and egg extracts, a substantial proportion of this is due to reinitiation on endogenous mRNA, as shown by the use of inhibitors. The increased rate of protein synthesis previously observed in intact oocytes following progesterone-induced maturation is reflected in the relative activities of the extracts. The difference in activity is not due to the presence of a dominant inhibitor of translation in the extracts from unstimulated oocytes. Labelling studies with initiator tRNA ([35S]Met-tRNAf) indicate a higher concentration of 43S preinitiation complexes in the extracts from unstimulated oocytes, suggesting an impairment of initiation of translation at or after the mRNA-binding step. Extracts from both oocytes and progesterone-matured oocytes translated endogenous mRNAs to give products ranging over a wide spectrum of molecular weight. However, significant translation of exogenous (globin) mRNA required the presence of reticulocyte postribosomal supernatant, suggesting that one or more factors required for mRNA recruitment is limiting in these extracts.
Plasminogen activator expression in F9 teratocarcinoma embryoid bodies and their endoderm derivatives
Authors: Sabbag Kenneth R. , Casanova James E. , Grabel Laura B.
Published: April 2021

Plasminogen activators are believed to play an important role in tissue remodeling and cell migration. During mouse embryogenesis, visceral endoderm secretes urokinase-type plasminogen activator (uPA) whereas parietal endoderm secretes tissue-type plasminogen activator (tPA). Visceral endoderm from F9 embryoid bodies can transdifferentiate into parietal endoderm under the appropriate culture conditions. We have examined at the protein and mRNA levels the type of plasminogen activator expressed in whole embryoid bodies, visceral endoderm and its parietal endoderm derivatives. Our experiments show that the visceral endoderm on F9 embryoid bodies synthesizes and secretes substantial amounts of both tPA and uPA. In contrast, the parietal endoderm derived directly from the visceral endoderm secretes dramatically increased levels of tPA and decreases production of uPA to low or below detectable levels. These data support the finding that visceral endoderm can transdifferentiate to parietal endoderm. In addition, this transition provides an excellent model for studying the molecular basis of the coincident down- and upregulation of the two plasminogen activators as well as their potential function during embryogenesis.
Induction of functional cytodifferentiation in the epithelium of tissue recombinants : I. Homotypic seminal vesicle recombinants
Authors: Higgins Stephen J. , Young Peter , Brody Joel R. , Cunha Gerald R.
Published: April 2021

Functional cytodifferentiation of seminal vesicle epithelium was investigated in tissue recombinants. Neonatal rat and mouse seminal vesicles were separated into epithelium and mesenchyme using trypsin. Epithelium and mesenchyme were then recombined in vitro to form interspecific rat/mouse homotypic recombinants. Growth as renal grafts in adult male athymie mice resulted in seminal vesicle morphogenesis in 70 % of the recombinants (the remaining 30 % failed to grow). Functional cytodifferentiation was judged by the expression of the major androgen-dependent secretory proteins characteristic of the seminal vesicles of adult rats and mice. Antibodies specific for each of these proteins were used to screen tissue sections by immunocytochemistry and to probe protein extracts by immunoblotting techniques. The heterospecific recombinants synthesized the full range of seminal vesicle secretory proteins that typifies the species providing the epithelium of the recombinant, not the mesenchyme. There was little functional variation between individual recombinants. The time course of development corresponded to that of intact neonatal seminal vesicles grown under the same conditions. Morphogenesis and functional cytodifferentiation were not evident after one week, but were well advanced after two weeks. Seminal vesicle recombinants grown for three weeks were indistinguishable morphologically and functionally from normal adult seminal vesicles. In addition, the ability of adult seminal vesicle epithelium to be induced to proliferate was examined. In association with neonatal seminal vesicle mesenchyme, the epithelium of the adult seminal vesicle proliferated and retained its normal functional activity. Thus, seminal vesicle functional cytodifferentiation can be faithfully reproduced in homotypic tissue recombinants. The methods used in this study will be used to investigate seminal vesicle development in instructive inductions of heterotypic epithelia.
Change in motor neurone activity modifies the differentiation of a slow muscle in chick embryo
Authors: Fournier Le Ray C. , Renaud D. , Le Douarin G. H.
Published: April 2021

Slow-tonic anterior latissimus dorsi (ALD) muscle properties were studied following chronic spinal cord stimulation in chick embryo. Stimulation at a fast rhythm was applied from day 7, 8 or 10 of development until the end of embryonic life. When stimulation was applied from day 7 up to day 18 of development, ALD muscle exhibited at day 18 a large decrease in half time to peak of tetanic contraction, a large proportion of fast type II fibres and an increase in fast myosin light chain content as compared to control muscle. When stimulation started at day 8 of development, changes in properties of ALD muscle were reduced when compared to the previous experimental series. Indeed, no fast type II fibres were observed within the muscle, even when stimulation was prolongated until the 20th day of embryonic development. In addition, chronic stimulation at a fast rhythm initiated at day 10 of development did not modify ALD muscle differentiation. The present results indicate that a fast pattern of motor neurone activity can induce some slow-to-fast transformations of ALD muscle fibres. However, after the first week of embryonic life, ALD myotubes appeared refractory to these transformations. The possible mechanisms responsible for the transformation of slow myotubes and for their further loss of plasticity are discussed.
Systematic non-uniform distribution of parthenogenetic cells in adult mouse chimaeras
Authors: Nagy András , Sass Miklós , Markkula Merja
Published: April 2021

Even though pure parthenogenetic mouse embryos die shortly after implantation, their cells are capable of participating in normal development of chimaeras when aggregated with fertilized embryos. Here we present data on parthenogenetic contribution to the oocyte populations measured by progeny tests in female chimaeras, and on distribution of parthenogenetic cells among the different organs by GPI typing. Systematic uneven distribution was detected. The highest level of participation was registered in the tissues of permanent cells (e.g. up to 63 % in female germline). On the other hand, parthenogenetic cells were absent in several tissues that have extensive capacity for postnatal growth or selfrenewal. This finding suggests that uneven selective processes operate against parthenogenetic cells within certain differentiation pathways during fetal and postnatal life, as has already been observed in the development of extraembryonal membranes. It is likely that more than one mechanism is responsible for these selections. Parthenogenetic cells may start to differentiate in all cell lineages, but they are not able to react normally at certain points in the developmental pathway, for example to induction signals and, therefore, the cells fail to complete the normal processes of development, or to the proliferation requirement so that the fertilized counterpart gradually takes over the cell lineage. Paternally derived gene(s) might have a unique role in the development of tissues lacking parthenogenetic contribution.
Imaginal disc-autonomous expression of a defect in sensory bristle patterning caused by the lethal(3)ecdysoneless1 (l(3)ecd1) mutation of Drosophila melanogaster
Authors: Sliter Timothy J.
Published: April 2021

The temperature-sensitive mutation l(3)ecd1 of Dros­ophila melanogaster is known to autonomously impair the ability of the larval prothoracic gland to produce the steroid molting hormone ecdysone in response to stimu­lation by the tropic neuropeptide prothoracicotropic hormone. It is shown that autonomous expression of the l(3)ecct1 mutation in metamorphosing imaginal tissues disrupts the spatial pattern of sensory bristles. Transfer of homozygous mutant animals to the restrictive tem­perature at the time of pupariation resulted in the elimination of sensory microchaetae and macrochaetae. This effect was specific to the sensory bristles; nonsensory bristles were not eliminated, nor were other types of innervated cuticular sense organs. In the case of the dorsal thoracic macrochaetae, normal ecd gene function is required during an early period of bristle development (0—18 h after puparium formation at 20°C). It is during this period that important determinative events take place in developing imaginal tissues that are responsible for the establishment of bristle progenitor cells. It is proposed that the ecd gene product may be required for the response of certain classes of cells to specific, regulatory signals.
Cell proliferation and expression of cytokeratin filaments in F9 embryonal carcinoma cells
Authors: Kurki P. , Laasonen A. , Tan E. M. , Lehtonen E.
Published: April 2021

A double immunofluorescence method was developed for the monitoring of proliferation and differentiation of F9 embryonal carcinoma cells. Cytokeratin filament expression was used as a marker for differentiation, and proliferating cell nuclear antigen (PCNA)/cyclin or bromodeoxyuridine labeling were used as markers for proliferation. F9 cells had a high proliferation rate and were cytokeratin-filament-negative. Upon treatment with retinoic acid and dibutyryl cyclic AMP, cytokeratin-filament-positive cells with differentiated phenotype appeared. After 3 days, the extent of proliferation of cytokeratin-filament-positive cells was comparable to, but after 5 days significantly lower than, that of cytokeratin-filament-negative cells in the same culture. In differentiating F9 cells, cytokeratin filament expression is associated with, and even slightly precedes, the dramatic decrease in the rate of proliferation.
A premature acrosome reaction is programmed by mouse t haplotypes during sperm differentiation and could play a role in transmission ratio distortion
Authors: Brown Judith , Cebra-Thomas Judith A. , Bleil Jeffrey D. , Wassarman Paul M. , Silver Lee M.
Published: April 2021

Mouse t haplotypes are variant forms of chromosome 17 that can be transmitted at non-Mendelian ratios by heterozygous +/t males. The accumulated genetic data indicate that ’ +-sperm’ and ‘t-sperm’ are produced in equal numbers but that most ‘+-sperm’ are rendered dysfunctional, so that ‘t-sperm’ have a relative advan-tage at fertilization. To date, the basis for this t-induced sperm dysfunction has remained unknown. Here we demonstrate that a high proportion of sperm obtained from certain strains of +/t mice undergo a premature acrosome reaction under in vitro capacitation conditions.

The simplest interpretation of these data, in conjunction with previous results, is that developing ‘+-spermatids’ are preprogrammed by ‘i-spermatids’ to undergo this premature reaction. Since acrosome-reacted sperm are unable to participate in the process of fertilization, this defect could account for the extreme distortion of transmission ratio observed from mice heterozygous for a class of complete t haplotypes.
Mitotic domains reveal early commitment of cells in Drosophila embryos
Authors: Foe Victoria E.
Published: April 2021

In embryos of Drosophila melanogaster all the nuclei in the syncytial egg divide with global synchrony during the first 13 mitotic cycles. But with cellularization in the 14th cycle, global mitotic synchrony ceases. Starting about one hour into the 14th interphase, at least 25 ‘mitotic domains’, which are clusters of cells united by locally synchronous mitosis, partition the embryo blastoderm surface into a complex fine-scale pattern. These mitotic domains, which are constant from one embryo to the next, fire in the same temporal sequence in every embryo. Some domains consist of a single cell cluster straddling the ventral or dorsal midline. Most consist of two separate cell clusters that occupy mirror-image positions on the bilaterally symmetric embryo. Others comprise a series of members present not only as bilateral pairs but also as metameric repeats. Thus a domain can consist of either one, two, or many (if metamerically reiterated) clusters of contiguous cells. Within each cluster, mitosis starts in a single cell or in a small number of interior cells then spreads wave-like, in all directions, until it stops at the domain boundary. Each domain occupies a specific position along the anteroposterior axis - as determined by the expression pattern of the engrailed protein, and along the dorsoven-tral axis - as determined by cell count from the ventral midline.

The primordia of certain larval structures appear to consist solely of the cells of one specific mitotic domain. Moreover, cells in at least some mitotic domains share specific morphogenetic traits, distinct from those of cells in adjacent domains. These traits include cell shape, spindle orientation, and participation by all the cells of a domain in an invagination. The specialized behaviors of the various mitotic domains transform the monolayer cell sheet of the blastoderm into the multilayered gastrula. I conclude that the fine-scale partitioning of the newly cellularized embryo into mitotic domains is an early manifestation of the commitment of cells to specific developmental fates.
Control of peripheral glial cell proliferation: enteric neurons exert an inhibitory influence on Schwann cell and enteric glial cell DNA synthesis in culture
Authors: Eccleston P. A. , Bannerman P. G. C. , Pleasure D. E. , Winter J. , Mirsky R. , Jessen K. R.
Published: April 2021

Neuronal membranes from rat dorsal root ganglia provide a mitogenic signal to cultured Schwann cells and it has been suggested this is an important factor in regulating Schwann cell numbers during development. In this study, the influence of enteric neurons on the DNA synthesis of both Schwann cells and enteric glia has been investigated as well as the effect of axonal membrane fractions (axolemma) on enteric glia.

The proliferation rate of rat Schwann cells and enteric glia was assessed in culture using [3H]thymidine uptake and autoradiography in combination with immunolabelling to identify cell types. When purified rat Schwann cells were co-cultured with guinea pig enteric neurons, their DNA synthesis rate was reduced compared with control cultures of pure Schwann cells or Schwann cells not close to neurites or neuronal cell bodies. Nevertheless, in accordance with previous findings that sensory neurons stimulate Schwann cell division, these Schwann cells increased their DNA synthesis rate when in contact with neurites from purified guinea pig or adult rat dorsal root ganglion neurons and on exposure to bovine axolemmal fractions. The enteric neurons also suppressed the DNA synthesis of enteric glia in co-cultures of purified enteric neurons and enteric glia, while bovine axolemma stimulated their DNA synthesis.

These results indicate that a mitotic inhibitory signal is associated with enteric neurons and can exert its effect on both Schwann cells and enteric glia, and that enteric glia, like Schwann cells, are stimulated to divide by axolemmal fractions. It thus seems possible that during development glial cell numbers in the peripheral nervous system may be controlled by both positive and negative regulators of cell growth.
Epigenetic and genetic factors affect transgene methylation imprinting
Authors: Sapienza Carmen , Paquette Jean , Tran Thu Hang , Peterson Alan
Published: April 2021

In some lines of transgenic mice, the methylation of Mspl sites within or adjacent to the transgene locus is affected by the sex of the parent from which the transgene is inherited. These differences are consistent with a role for DNA methylation in genome imprinting. In a previous report, we noted that in one such line, all offspring of females exhibited hypermethylation of the transgene while only some offspring of males carried a hypometh-ylated transgene. In this report, we provide evidence that this phenomenon is controlled by at least two factors, one of which acts in cis and is dependent on the transgene locus, and one of which acts in trans and is supplied by the maternal genome. We also provide evidence that there are genetic differences between inbred mouse strains in the trans-acting factor.
Development and fertility of ovaries in the B6.YDOM sex-reversed female mouse
Authors: Taketo-Hosotani Teruko , Nishioka Yutaka , Nagamine Claude M. , Villalpando Irma , Merchant-Larios Horacio
Published: April 2021

When the Y chromosome of Mus musculus domesticas (YDOM) was introduced onto the C57BL/6 (B6) mouse background, half of the XY progeny (B6.YDOM) developed bilateral ovaries and female internal and external genitalia. We examined the fertility of the B6.YDOM sex-reversed female mouse. The chromosomal sex of the individual mouse was identified by dot hybridization with mouse Y chromosome-specific DNA probes. The results indicated that all XY females lacked regular estrous cyclicity although most were able to mate and ovulate after treatment with gonadotropins. When they had been ovariectomized and grafted with ovaries from the XX female litter mate, they initiated estrous cycli-city. Reciprocally, the XX female that had received XY ovarian grafts did not resume estrous cyclicity.

Development of the XY ovary was morphologically comparable to the XX ovary until 16 day of gestation (d.g.), when most germ cells had reached the zygotene or pachytene stage of meiotic prophase. However, by the day of delivery (19 or 20 d.g.), no oocyte remained in the medullary cords of the XY ovary. In the control XX ovary, the first generation of follicles developed in the medullary region, and 5Δ-3β-hydroxysteroid dehydrogenase (3β-HSDH) activity appeared first in the stromal cells around growing follicles by 10 days after birth. In contrast, in the XY ovary, follicles were not formed in the medullary region, and 3β-HSDH activity appeared in epithelial cells of the oocyte-free medullary cords. Primordial follicles in the cortex region continued development in both the XX and XY ovaries.

These results suggest that the XY female is infertile due to a defect inside the XY ovary. The prenatal loss of oocytes in the medullary cords may be a key event leading to abnormal endocrine function, and thereby, the absence of estrous cyclicity.
Autonomous expression of tissue-specific genes in dissociated sea urchin embryos
Authors: Stephens Laurie , Kitajima Takashi , Wilt Fred
Published: April 2021

The effects of disrupting cell interactions in early development were investigated by examining the accumulation of a primary mesenchyme specific transcript (SM50) and an aboral ectoderm-specific transcript (Spec 1) in cultures of sea urchin embryos that were dissociated at early stages and then cultured in CFSW. The expression of both SM50 and Spec 1 is temporally correct and remains restricted to the appropriate cell types, even if the embryo is dissociated as early as the 2-cell stage and maintained as a suspension of single cells. This result is consistent with the idea that the specificity of expression of these two genes, each characteristic of different lineages, is strongly regulated by information in the egg. Average SM50 expression is half that of intact embryos, but Spec 1 expression is very low, only 10–20 % of intact controls, suggesting some differences in the response of the two genes to lack of close cell interactions.
Retarded gastrulation and altered subsequent development of neural tissues in heparin-injected Xenopus embryos
Authors: Mitani Shohei
Published: April 2021

Gastrulation was examined in Xenopus embryos injected with various polysaccharides into the blastocoel cavity. The progression of gastrulation was assessed by observing pigmentation and yolk plug size in vegetative view embryos. In heparin-or dextran-sulphate-injected embryos, gastrulation was significantly retarded. This was further confirmed in tissue sections of embryos. In contrast, no such retardation was found in embryos injected with hyaluronic acid or chondroitin sulphate. A quantitative analysis showed that the extent of retardation in heparin-or dextran-sulphate-injected embryos was dose-dependent and that, after the initial retardation of up to 2–3 h, gastrulation progressed at a similar rate to controls.

At the time when untreated sibling embryos hatched, embryos injected with heparin or dextran sulphate showed abnormalities in their external appearance and swimming behavior in a dose-dependent manner. When these embryos were examined histologically or immuno-histochemically using tissue-specific monoclonal antibodies, it was found that central nervous system (CNS), especially the brain and eye structures, were most severely damaged. The extent of damage was again dosedependent. In contrast, neural-crest-derived melano-phores were abundant even in aneural larvae. No such change was found in embryos injected with hyaluronic acid or chondroitin sulphate.
Nucleotide sequence, chromosomal localization and developmental expression of the mouseint-1-related gene
Authors: McMahon Jill A. , McMahon Andrew P.
Published: April 2021

cDNA clones encoding the murine int-1 -related protein (m-irp) were isolated from an 8.5-day mouse embryo library, m-irp and its human counterpart, h-irp, share extensive nucleotide homology in coding (92 %) and 3’ untranslated (69 %) regions. At the amino acid level, m-irp and h-irp share 97 % of amino acids including all 24 cysteine residues, which are highly conserved among members of the int-1 family. However, in contrast to h-irp and int-1, the predicted m-irp protein sequence did not contain a signal peptide sequence. Analysis of polymerase chain reaction, amplified cDNA, and genomic sequences strongly suggests that a single-base substitution has created a new S’ splice site 17 bp 5’ of a highly conserved splice site. Splicing at this new site generates a mRNA-encoding an amino-terminal truncated protein. Splicing at the conserved splice site generates a mRNA species encoding a protein with a signal peptide sequence similar to h-irp. Close linkage between m-irp and the met oncogene maps m-irp sequences to proximal mouse chromosome 6. Adult and fetal expression of m-irp was examined by RNA blot analysis. Adult expression of m-irp is restricted to lungs and heart, and fetal expression, to placental tissue and to all stages of fetal development examined. In situ hybridization localized early fetal m-irp expression to the pericardium of the heart, to the umbilicus and associated allantoic mesoderm, and to the ventral lateral mesenchyme tissue surrounding the umbilical vein in the fetus. These results suggest a role for m-irp in the development of fetal allantoic communication.
Analysis of maternal effect mutant combinations elucidates regulation and function of the overlap of hunchback and Krüppel gene expression in the Drosophila blastoderm embryo
Authors: Gaul Ulrike , Jäckle Herbert
Published: April 2021

The metameric organisation of the Drosophila embryo is generated early during development, due to the action of maternal effect and zygotic segmentation and homeotic genes. The gap genes participate in the complex process of pattern formation by providing a link between the maternal and the zygotic gene activities. Under the, influence of maternal gene products they become expressed in distinct domains along the anteroposterior axis of the embryo; negative interactions between neighboring gap genes are thought to be involved in establishing the expression domains. The gap gene activities in turn are required for the correct patterning of the pairrule genes; little is known, however, about the underlying mechanisms.

We have monitored the distribution of gap and pairrule genes in wild-type embryos and in embryos in which the anteroposterior body pattern is greatly simplified due to combinations of maternal effect mutations (staufen exuperantia, rusa exuperantia, bicoid oskar, bicoid oskar torsolike, vasa torso exuperantia). We show that the domains of protein distribution of the gap genes hunchback and Krüppel overlap in wild-type embryos. Based on the analysis of the maternal mutant combinations, we suggest an explanation of how this overlap is generated. Furthermore, our data show that different constellations of gap gene activities provide different input for the pair-rule genes, and thus strongly suggest that the overlap of hunchback and Krüppel in wild-type is functional in the formation of the patterns of pair-rule genes.
Imaginal discs can be recovered from cultured embryos mutant for the segment-polarity genes engrailed, naked and patched but not from wingless
Authors: Simcox Amanda A. , Roberts Ian J. H. , Hersperger Evelyn , Gribbin M. Clare , Shearn Allen , Whittle J. Robert S.
Published: April 2021

Drosophila embryos homozygous for strong mutations in each of the segment-polarity genes wingless (wg), engrailed (en), naked (nkd) and patched (ptc) form a larval cuticle in which there is a deletion in every segment. The mutant embryos normally fail to hatch but by in vivo culture we were able to show which could produce adult structures. Cultured wg− embryos did not produce any adult structures. Cultured en− embryos produced eye-antennal derivatives and rarely produced partial thoracic structures. nkd− and ptc− embryos produced eye-antennal and thoracic derivatives. The nkd− and ptc− thoracic imaginal discs developed with an abnormal morphology and abnormal pattern of en-expression. Our findings are consistent with the idea that the thoracic imaginal discs derive from two adjacent groups of cells that express wg and en respectively in the embryo.
Retinoic acid induces a pattern of digits in anterior half wing buds that lack the zone of polarizing activity
Authors: Eichele Gregor
Published: April 2021

Wing buds whose posterior half is excised, develop into wings lacking distal structures. However, such experimentally generated preaxial half wing buds can be rescued by implanting a retinoic-acid-releasing bead at their anterior margin. The polarity of the pattern that originates from preaxial half wing buds is reversed. For example, instead of a 234 digit pattern typical for normal wings, the order of digits is 432. This result implies that retinoic acid has the capacity to reprogram anterior limb bud tissue, and that the resulting change in cell fate does not depend on the presence of posterior tissue regions such as the zone of polarizing activity (ZPA).
Expression of a Drosophila mRNA is under circadian clock control during pupation
Authors: Lorenz Lori J. , Hall Jeffrey C. , Rosbash Michael
Published: April 2021

Rhythmic eclosion of Drosophila adults requires per gene function. We have found that a previously identified 0.9 kb RNA transcribed from DNA adjacent to per becomes abundantly expressed during pupation, just prior to eclosion. The daily synchronized emergence of young adults, coupled with a subsequent rapid decay of the transcript, is responsible for what previously appeared to be cycling of the 0.9 kb RNA in adults. In situ hybridization analyses localize the 0.9 kb transcript to the epidermis of newly eclosed adults. Conceptual translation of genomic DNA and cDNA sequences predicts that the 0.9 kb transcript produces a 261 amino acid protein containing a putative signal sequence for membrane transport at its amino terminus. Pupae that reach the same stage of development at slightly different times of day show a subsequent synchronized rise in 0.9 kb RNA levels, indicating that the expression of this transcript is under circadian clock control.
Patterns of expression of a 15K β-D-galactoside-specific lectin during early development of the avian embryo
Authors: Levi Giovanni , Teichberg Vivian I.
Published: April 2021

We have determined, by immunohistochemical and biochemical techniques, the distribution of an endogenous β-D-galactoside-blnding lectin between the early primitive streak stage and the 5th day of embryonic development of the chick. The lectin, which was purified from the pectoral muscle of 16-day-old chick embryos, migrates on SDS–PAGE as a single polypeptide of relative molecular mass 15 × 103. Antibodies to this pure lectin interact with the 15K (K=103Mr) polypeptide as well as with a 6.5K polypeptide; this second component appears to be antigenically related to the 15K lectin, as antibodies affinity purified on the 15K band recognize both polypeptides.

In early stages of development, lectin immunoreactivity was present in most cells of the epiblast and hypoblast in the region of the primitive streak, while towards the edge of the area pellucida the epiblast was stained less intensely. During gastrulation, strong immunoreactivity was present also in migrating cells and in the mesoblast, while at the margin of the area pellucida the epiblast was negative.

Up to the 10-somite stage, lectin immunoreactivity was present in the somites, neural tube and presumptive cardiac region; the non-neural ectoderm and the extra-cellular matrix were not labeled; the predominant immunoreactive component at this stage of development was the 6.5K polypeptide. Later in development, the lectin immunoreactivity gradually disappeared from the dermamyotome and nervous system to reappear conspicuously as soon as a differentiated myotome could be detected. Immunoreactivity was very high in the myotome, skeletal and cardiac muscles and transient in smooth muscles. The only region of the nervous system that continued to express the lectin throughout development was the trigeminal (semilunar) ganglion; in all other regions of the nervous system, the lectin immuno-reactivity disappeared early in development to be re-expressed only much later. The lining epithelium of the digestive tract and other endodermal derivatives expressed the lectin transiently. In the extraembryonic membranes, immunoreactivity to the lectin was observed in the yolk sac and in both layers of the amnion.

The striking regulation of the expression of this endogenous lectin suggests that its functions are linked to cell proliferation and/or to the selective expression of a developmentally-timed cell phenotype.
Multiple steps in the localization of bicoid RNA to the anterior pole of the Drosophila oocyte
Authors: Johnston Daniel St. , Driever Wolfgang , Berleth Thomas , Richstein Sibyll , Nüsslein-Volhard Christiane
Published: April 2021

The anterior region of the Drosophila embryonic pattern is determined by a gradient of the bicoid (bed) protein. The correct formation of this gradient requires the localization of bed RNA to the anterior pole of the egg. Here we use a wholemount in situ technique to examine the process of bed RNA localization during oogenesis and embryogenesis. While bed protein becomes distributed in a gradient that extends throughout the anterior two thirds of the early embryo, bed RNA remains restricted to a much smaller region at the anterior pole. The difference between these distributions indicates that the shape of the protein gradient must depend to some extent on the posterior movement of the protein after it has been synthesized.

Four distinct phases of bed RNA localization can be distinguished during oogenesis. Between stages 6 and 9 of oogenesis, the RNA accumulates in a ring at the anterior end of the oocyte. During the second phase, in stage 9-10a follicles, the RNA also localizes to the apical regions of the nurse cells, demonstrating that the nurse cells possess an intrinsic polarity. As the nurse cells contract during stages 10b–ll, all of the bed RNA becomes localized to the cortex at the anterior end of the oocyte. During a final phase that must occur between stage 12 of oogenesis and egg deposition, the RNA becomes localized to a spherical region that occupies a slightly dorsal position at the anterior pole.

Mutations in the maternal-effect genes, exuperantia (exu) and swallow (sw), lead to an almost uniform distribution of bed RNA in the early embryo, while staufen (stau) mutations produce a gradient of RNA at the anterior pole, exu mutations disrupt the second stage of bcd RNA localization during oogenesis, su’w mutations disrupt the third, and stau mutations affect the fourth phase.
int-1 - a proto-oncogene involved in cell signalling
Authors: Mcmahon Andrew P. , Moon Randall T.
Published: April 2021

The int-1 gene was originally identified as a locus activated by mouse mammary tumor virus insertion. Cloning and sequencing of the mouse gene indicates that int-1 encodes a 41K, 370 amino acid, cysteine-rich protein with a potential hydrophobic signal peptide sequence. Expression studies clearly indicate that int-1 enters the secretory pathway and is probably secreted, although definitive evidence is lacking.

Drosophila int-1 encodes the wingless gene, wingless, a segment-polarity gene, is required for the establishment of normal pattern in each segment. Genetic studies indicate that the wingless protein is probably secreted since it is required for the maintenance of stable gene expression in neighboring cells.

int-1 is also expressed during early neural stages of frog and mouse development. In the mouse, where expression is well characterized, int-1 RNA is restricted to the dorsal midline of the neural tube. By analogy with Drosophila, int-1 may operate to specify position within this structure. To test this idea, we have interfered with normal int-1 expression by injection of int-1 RNA into frog embryos. This results in a striking and specific aberration, bifurcation of the anterior neural tube. Thus, it seems possible that in vertebrates int-1 is able to influence patterning events.
Temporal and spatial selection against parthenogenetic cells during development of fetal chimeras
Authors: Fundele Reinald H. , Norris Michael L. , Barton Sheila C. , Fehlau Monika , Howlett Sarah K. , Mills Walter E. , Surani M. Azim
Published: April 2021

The fate of parthenogenetic cells was investigated during development of fetal and early postnatal chimeras. On day 13 of embryonic development, considerable contribution of parthenogenetic cells was observed in all tissues of chimeric embryos, although selection against parthenogenetic cells seemed to start before day 13. Between days 13 and 15 of development, parthenogenetic cells came under severe selective pressure, which was most striking in tongue. The disappearance of parthenogenetic cells from tongue coincided with the beginning of myoblast fusion in this tissue. Severe selection against parthenogenetic cells was also observed in pancreas and liver, although in the latter, parthenogenetic cells were eliminated later than in skeletal muscle or pancreas. In other tissues, parthenogenetic cells may persist and participate to a considerable extent throughout the gestation period and beyond, although a significant decrease was observed in all tissues. Parthenogen-etic↔fertilized chimeras were significantly smaller than their non-chimeric littermates at all developmental stages. These results suggest that the absence of paternal chromosomes is largely incompatible with the maintenance of specific differentiated cell types. Furthermore, paternally derived genes seem to be involved in the regulation of proliferation of all cell types, as indicated by the drastic growth deceleration of parthenogen-etic↔fertilized chimeras and the overall decrease of parthenogenetic cells during fetal development. Chromosomal imprinting may have a role in maintaining a balance between cell growth and differentiation during embryonic development.

The major exception to the selective elimination of parthenogenetic cells appear to be the germ cells; viable offspring derived from parthenogenetic oocytes were detected, sometimes at a high frequency in litters of female parthenogenetic↔fertilized chimeras.
Melanization in albino mice transformed by introducing cloned mouse tyrosinase gene
Authors: Tanaka Satoshi , Yamamoto Hiroaki , Takeuchi Sakae , Takeuchi Takuji
Published: April 2021

We introduced a mouse tyrosinase minigene, mg-Tyrs-J, in which the authentic genomic 5′ non-coding flanking sequence was fused to a mouse tyrosinase cDNA, into fertilized eggs of albino mice.

Of the 25 animals that developed from the injected eggs, four mice exhibited pigmented hair and eyes. Histological analysis of the transgenic mice revealed that the melanogenesis was restricted to hair bulbs and eyes.

These results suggest that this minigene encodes active tyrosinase protein and that its 5′ flanking region contains the sequences regulating expression of mouse tyrosinase gene. This is the first report of a successful expression of tyrosinase gene and of pigment production in transgenic mice.
Mesoderm induction and the control of gastrulation in Xenopus laevis: the roles of fibronectin and integrins
Authors: Smith J. C. , Symes K. , Hynes R. O. , DeSimone D.
Published: April 2021

Exposure of isolated Xenopus animal pole ectoderm to the XTC mesoderm-inducing factor (XTC-MIF) causes the tissue to undergo gastrulation-like movements. In this paper, we take advantage of this observation to investigate the control of various aspects of gastrulation in Xenopus.

Blastomeres derived from induced animal pole regions are able, like marginal zone cells, but unlike control animal pole blastomeres, to spread and migrate on a fibronectin-coated surface. Dispersed animal pole cells are also able to respond to XTC-MIF in this way; this is one of the few mesoderm-specific responses to induction that has been observed in single cells.

The ability of induced animal pole cells to spread on fibronectin is abolished by the peptide GRGDSP. However, the elongation of intact explants is unaffected by this peptide. This may indicate that fibronectin-me-diated cell migration is not required for convergent extension.

We have investigated the molecular basis of XTC-MIF-induced gastrulation-like movements by measuring rates of synthesis of fibronectin and of the integrin fit chain in induced and control explants. No significant differences were observed, and this suggests that gastrulation is not initiated simply by control of synthesis of these molecules. In future work, we intend to investigate synthesis of other integrin subunits and to examine possible post-translational modifications to fibronectin and the integrins.
Effect of the X-linked gene Tabby (Ta) on eyelid opening and incisor eruption in neonatal mice is opposite to that of epidermal growth factor
Authors: Kapalanga Joachim , Blecher Stan R.
Published: April 2021

Studies on eyelid opening and incisor eruption in 216 neonatal Tabby (Ta)-bearlng mice and wildtype controls (35 Ta/Y, 62 +/Y, 30 Ta/Ta, 57 Ta/+ and 32 +/+) showed that in animals hemizygous and homozygous for Ta, the timing of eyelid opening and incisor eruption was significantly delayed (P<0.05). It was also observed that once open, the eyes of mutant pups do not remain open for long but soon close again for several days before reopening. An iterative eyes open-eyes closed process seems to continue beyond puberty. Studies In 25 epidermal growth factor (EGF)-treated mutants and 23 saline-treated controls showed that neonatal EGF injections (4μg g-1 body weight per day) reversed the delayed timing of eyelid opening and incisor eruption in hemizy gote and homozygote Tabby mice. However, both mutant and wildtype EGF-treated mice also showed the eyes open-eyes closed cycle, whereas untreated nonmutant mice did not. Because Tabby appears to be genetically homologous to the gene for human X-linked hypohidrotic ectodermal dysplasia, these results may have potential clinical significance. The eyes open-eyes closed cycle may involve cycling levels of EGF receptor; since the gene for this receptor shows homology with an oncogene, this system may be useful in studies on genetic control of oncogene function.
How embryos work: a comparative view of diverse modes of cell fate specification
Authors: Davidson Eric H.
Published: April 2021

Embryonic processes in the nematode C. elegans, the gastropod mollusc Ilyanassa, the dipteran Drosophila, the echinoid Strongylocentrotus purpuratus, the ascidian Ciona, the anuran Xenopus, the teleost Brachydanio and mouse are compared with respect to a series of parameters such as invariant or variable cleavage, the means by which the embryonic axes are set up, egg anisotropies and reliance on conditional or on autonomous specification processes. A molecular interpretation of these modes of specification of cell fate in the embryo is proposed, in terms of spatial modifications of gene regulatory factors. On this basis, classically defined phenomena such as regulative development and cytoplasmic localization can be interpreted at a mechanistic level, and the enormous differences between different forms of embryogenesis in the Animal Kingdom can be considered within a common mechanistic framework. Differential spatial expression of histospecific genes is considered in terms of the structure of the gene regulatory network that will be required in embryos that utilize cell–cell interaction, autonomous vs conditional specification and maternal spatial information to differing extents. It is concluded that the regulatory architectures according to which the programs of gene expression are organized are special to each form of development, and that common regulatory principles are to be found only at lower levels, such as those at which the control regions of histospecific structural genes operate.
Sialoconjugates and development of the tail bud
Authors: Griffith C. M. , Wiley M. J.
Published: April 2021

Using lectin histochemistry, we have previously shown that there are alterations in the distribution of glycoconjugates in the tail bud of chick embryos that parallel the developmental sequence of the caudal axis. If glycoconjugates or the cells bearing them play a role in caudal axial development, then, restriction of their availability by binding with lectins would be expected to produce abnormalities of caudal development. In the present study, we treated embryos at various stages of tail bud development by microinjection with a variety of lectins. Administration of WGA by sub-blastodermal injection resulted in high incidences of secondary neural tube and notochordal abnormalities in lectin-treated embryos. The incidence of malformations was dependent upon both the dose of WGA received and the stage of development at the time of treatment. Using an anti-WGA antibody, we have also shown binding of the lectin in regions where defects were found. The lectin WGA binds to the sialic acid residues of glycoconjugates and to yV-acetylglucosamine. Treatment of embryos with Limu-lus polyphemus lectin (LPL), which also binds to sialic acid, produced results similar to those of WGA. Treatments using lectins with other sugar-binding specificities, including succinylated WGA (with N-acetylglucosamine specificity only) produced defects that differed from those produced by WGA and LPL, and only with the administration of much higher doses. The results suggest that glycoconjugates in general and sialocopjugates in particular, or the cells carrying them, may have a role in caudal axial development.