bluuebunny/crossref_metadata_2025 huggingface dataset:
The dorsoventral axis is specified prior to first cleavage in the direct developing sea urchin Heliocidaris erythrogramma
Authors: Henry Jonathan J. , Wray Gregory A. , Raff Rudolf A.
Published: April 2021

Previous fate mapping studies as well as the culture of isolated blastomeres have revealed that the dorsoventral axis is specified as early as the 2-cell stage in the embryos of the direct developing echinoid, Heliocidaris erythrogramma. Normally, the first cleavage plane includes the animal-vegetal axis and bisects the embryo between future dorsal and ventral halves. Experiments were performed to establish whether the dorsoventral axis is set up prior to the first cleavage division in H. erythrogramma. Eggs were elongated and fertilized in silicone tubes of a small diameter in order to orient the cleavage spindle and thus the first plane of cell division. Following first cleavage, one of the two resulting blastomeres was then microinjected with a fluorescent cell lineage tracer dye. Fate maps were made after culturing these embryos to larval stages. The results indicate that the first cleavage division can be made to occur at virtually any angle relative to the animal-vegetal and dorsoventral axes. Therefore, the dorsoventral axis is specified prior to first cleavage. We argue that this axis resides in the unfertilized oocyte rather than being set up as a consequence of fertilization.
Isolation of an abdominal-A gene from the locust Schistocerca gregaria and its expression during early embryogenesis
Authors: Tear Guy , Akam Michael , Martinez-Arias Alfonso
Published: April 2021

Using sequence homology to Drosophila homeobox-containing genes, we have cloned a homologue of abdominal-A from the locust Schistocerca gregaria. The Schistocerca clone encodes a stretch of 78 amino acids including the homeodomain and its flanking regions identical to the corresponding region of abdominal-A.

We have shown by in situ hybridization that this gene is transcribed and have used an antibody raised against its protein product to examine the expression of abdominal-A during early Schistocerca embryogenesis. Schistocerca is a short germ insect. Although the segmented body plan is very similar to that of Drosophila, the segments are generated sequentially by a process of growth, not simultaneously by subdivision of a syncytial blastoderm. In both organisms, abdominal-A is expressed throughout the abdomen from a sharp anterior boundary located within the first abdominal segment (Al). The initial activation of the genes in the two species differs. Schistocerca initiates expression in a small group of cells in the anterior of A2, shortly after this segment is defined by the appearance of engrailed protein. This contrasts with the appearance of abdominal-A expression in Drosophila, which appears simultaneously throughout the entire abdomen.
Two distinct mechanisms localise cyclin B transcripts in syncytial Drosophila embryos
Authors: Raff Jordan W. , Whitfield William G. F. , Glover David M.
Published: April 2021

We demonstrate that two independent mechanisms act on maternally derived cyclin B transcripts to concentrate the transcripts at the posterior pole of the Drosophila oocyte and at the cortex of the syncytial embryo. The cortical accumulation occurs because the cyclin B transcript is concentrated around nuclei and comigrates with them to the cortex. The perinuclear localisation of the transcript is blocked by inhibitors of microtubule polymerisation and the transcript colocalises with microtubular structures during the cell cycle, suggesting that the transcript is associated either directly or indirectly with microtubules. Neither microtubules nor actin filaments are required to maintain the posterior concentration of cyclin B transcripts. Instead, this seems to depend on the association of the transcripts with a component of the posterior cytoplasm. The distribution pattern of the transcript at the posterior pole throughout embryogenesis and in a variety of mutant embryos suggests that this component is associated with polar granules.
Expression in non-lens tissues of an enzyme activity related to the ‘lensspecific’ protein, δ crystallin
Authors: Pomerai D. I. De , Ip W. K. , Laughlin M. Mc , Perry K. C.
Published: April 2021

When chick embryo neural retina (NR) cells are cultured for long periods in vitro, they undergo extensive trans differentiation into lens and express the lens protein, δcrystallin. We now demonstrate that this process is accompanied by a change in the chromatin conformation of the δ-gene locus from DNAasel-resistant to DNAasel-sensitive in the nuclei of most cells. Transcripts hybridising to a δprobe are also much more prevalent among the in vitro transcription products from lens or transdifferentiated NR culture nuclei, as compared to nuclei from fresh NR tissue. Published evidence indicates that the chick δ1 crystallin gene encodes the major structural protein of embryonic lens fibres, whereas the closely related δ2 gene may encode the urea-cycle enzyme argininosuccinate lyase (ASL). Our present data lends further support to this view. Both immunodetectable δ-related protein(s) and ASL activity are present in fresh embryonic NR tissue, as well as in mouse and Rana liver, and in Rana lens. Our polyclonal anti-δ antibody also cross-reacts with a major constituent of commercial bovine ASL, of the same molecular size as chick δcrystallin. Immunoselection studies suggest that the ASL activity in chick embryonic NR is conferred mainly by the δ-related protein band. So-called ‘ectopic’ expression of δ crystallin in embryonic NR (and other tissues) may thus involve the δ2/ASL gene, and could reflect some metabolic requirement for ASL activity.
In situ localization of storage protein mRNAs in developing meristems of Brassica napus embryos
Authors: Fernandez Donna E. , Turner F. Rudolf , Crouch Martha L.
Published: April 2021

Probes derived from cDNA clones of napin and cruciferin, the major storage proteins of Brassica napus, and in situ hybridization techniques were used to examine changes in the spatial and temporal distribution of storage protein messages during the course of embryogeny, with a special emphasis on the developing apical meristems. Napin mRNAs begin to accumulate in the cortex of the axis during late heart stage, in the outer faces of the cotyledons during torpedo stage and in the inner faces of the cotyledons during cotyledon stage. Cruciferin mRNAs accumulate in a similar pattern but approximately 5 days later. Cells in the apical regions where root and shoot meristems develop do not accumulate storage protein messages during early stages of embryogeny. In the upper axis, the boundary between these apical cells and immediately adjacent cells that accumulate napin and cruciferin mRNAs is particularly distinct. Our analysis indicates that this boundary is not related to differences in tissue or cell type, but appears instead to be coincident with the site of a particular set of early cell divisions. A major change in the mRNA accumulation patterns occurs halfway through embryogeny, as the embryos enter maturation stage and start drying down. Final maturation of the shoot apical meristem is associated with the development of leaf primordia and the accumulation of napin mRNAs in the meristem, associated leaf primordia and vascular tissue. Cruciferin mRNAs accumulate only in certain zones of the shoot apical meristem and on the flanks of leaf primordia. Neither type of mRNA accumulates in the root apical meristem at any stage.
Development of the Xenopus laevis hatching gland and its relationship to surface ectoderm patterning
Authors: Drysdale Thomas A. , Elinson Richard P.
Published: April 2021

An antibody that recognizes tyrosine hydroxylase can be used as a marker for hatching gland cells in Xenopus embryos. Using this marker, we have shown that hatching gland cells are induced at the end of gastrulation and that presumptive hatching gland cells are localized to the anterior neural folds in Xenopus. The movements of neurulation bring the hatching gland cells together to form a characteristic Y pattern on the dorsoanterior surface of the head. The Y pattern delineates several zones of surface ectoderm which can be visualized by the presence or absence of ciliated cells. As development proceeds the hatching gland pattern is altered, demonstrating the active changes involved in forming the face. Lithium, UV irradiation and retinoic acid can be used to alter the hatching gland pattern in specific ways which help to understand the underlying mechanisms of ectodermal patterning.
Identification and expression of a regeneration-specific homeobox gene in the newt limb blastema
Authors: Brown Robin , Brockes Jeremy P.
Published: April 2021

Adult urodele amphibians are able to regenerate their limbs through the formation of a blastema, a growth zone of undifferentiated mesenchymal cells that arises locally at the plane of amputation. In an effort to define genes involved in pattern formation by the blastema, we isolated from a newt forelimb blastema library cDNA clones that identify a homeobox gene termed NvHbox 2. The amino acid sequence of the homeodomain is identical to that of the recently identified human H0X-4f gene (Acampora et al. 1989) and of the mouse Hox-5.5 (Dolle et al. 1989). NvHbox 2 is expressed in the limb blastema as a transcript of 3.4 kb that is not detectable in the normal limb. Analysis by RNAase protection demonstrates expression in limb and tail blastemas, but not in any of the adult tissues or organs tested. In the limb blastema NvHbox 2 was expressed in mesenchymal but not epithelial tissue. When matched and normalised samples of RNA from proximal (mid-humerus) and distal forelimb (mid-radius) blastemas were compared, the level of expression of NvHbox 2 was found to be 3- to 5-fold higher proximally. At two time points after injection of a proximalising dose of retinoic acid, the level of expression in a distal blastema was not increased in comparison to controls.
Isolation and characterisation of a testis-expressed developmentally regulated gene from the distal inversion of the mouse t-complex
Authors: Mazarakis Nicholas D. , Nelki Daniel , Lyon Mary F. , Ruddy S. , Evans E. P. , Freemont Paul , Dudley Keith
Published: April 2021

We differentially screened a pool of mouse testis clones in order to identify genes important in germ cell development. One of the isolated clones was found to be expressed only in the male germ line where it is first detected at around the pachytene spermatocyte stage. This gene maps to a subregion of the t-complex in the distal inversion near, but not within, the twI8 and the th20 deletions. A comparison of the t and wild forms of the gene reveals a high degree of sequence conservation. This gene is associated with a CpG-rich island at its 5’ end. It encodes a novel protein with extensive α-helical structure indicative of coiled-coil interactions.
Inherited type of allelic methylation variations in a mouse chromosome region where an integrated transgene shows methylation imprinting
Authors: Sasaki Hiroyuki , Hamada Tsuyoshi , Ueda Takayuki , Seki Ritsuko , Higashinakagawa Toru , Sakaki Yoshiyuki
Published: April 2021

It is still unclear whether or not parent-of-origin-dependent differential methylation observed in some transgenes reflects genomic imprinting of endogenous genes. We have characterized a transgene locus showing such methylation imprinting together with the corresponding-native chromosome region. We show that only part of the transgene is affected by methylation imprinting and the methylation pattern is established before early prophase I during spermatogenesis. Interestingly, the native genomic region, which is mapped to the proximal chromosome 11, shows no evidence of methylation imprinting but displays heri-table, strain-specific type of allelic methylation differences. The results demonstrate that transgenes do not necessarily reflect the methylation status of either the surrounding or corresponding chromosome region. In addition, inherited type of allelic methylation variations previously described in human may be widespread in mammals.
Mitogenic activity of chicken chorioallantoic fluid is temporally correlated to vascular growth in the chorioallantoic membrane and related to fibroblast growth factors
Authors: Flamme Ingo , Schulze-Osthoff Klaus , Jügen Jacob Heinz
Published: April 2021

The chorioallantoic membrane (CAM) is one of the most vascularized tissues in the chicken embryo. Capillary growth proceeds until day 10 of development and thereafter abruptly regresses. As it is generally accepted that the formation of new blood vessel is regulated by growth factors, we have investigated the presence of angiogenic and mitogenic factors in the chicken chorioallantois.

In the present study, we show that chorioallantoic fluid (CAF) contains angiogenic substances that are probably synthesized in the CAM or the embryonic kidney. When applied in the chorioallantoic membrane assay, CAF from 9 day chicken embryos elicits a strong angiogenic response. This angiogenic activity of CAF is associated with pronounced mitogenic effects in vitro. Comparison of different embryonic fluids reveals that mitogenic activity is particularly evident in the CAF but not detectable in embryonic serum and amnion fluid. Expression of mitogenic activity is found to be temporally correlated with vascular growth in the CAM. High activity is detected in CAF prior to day 10 and then sharply decreases, thus preceding termination of capillary growth by one day.

Heparin–sepharose affinity chromatography suggests that the biological activities of CAF probably correspond to the presence of acidic and basic fibroblast growth factor (aFGF and bFGF). In Western blot analyses of CAF, an immunoreactive bFGF-like protein of about 17×103Mr is recognized by a monospecific anti-bFGF antiserum. This protein elutes at 2.4 M NaCl from the heparin-sepharose. The mitogenic activity of the CAF can be specifically blocked by the anti-bFGF antibody indicating bFGF to be the active mitogenic principle of the CAF.

These results strongly suggest that basic and probably acidic FGF play an important role in the regulation of chorioallantoic vascular growth.
Differential expression of type I and type III collagen genes during tooth development
Authors: Andujar Mauricio B. , Couble Pierre , Couble Marie-Lise , Magloire Henri
Published: April 2021

Collagen gene expression during mouse molar tooth development was studied by quantitative in situ hybridization techniques. Different expression patterns of type I and type HI collagen mRNAs were observed in the various mesenchymal tissues that constitute the tooth germ. High concentration for pro-alpha 1(1) and proalpha 2(1) collagen mRNAs were found within the osteoblasts. We found that the cellular content of type I collagen mRNAs in the odontoblasts varies throughout the tooth formation: whereas mRNA concentration for pro-alpha 1(1) collagen decreases and that of pro-alpha 2(1) increases, during postnatal development. Moreover, different amounts of pro-alpha 1(1) and pro-alpha 2(1) collagen mRNAs were observed in crown and root odontoblasts, respectively. Type HI collagen mRNAs were detected in most of the mesenchymal cells, codistributed with type I collagen mRNAs, except in odontoblasts and osteoblasts.

Finally, this study reports differential accumulation of collagen mRNAs during mouse tooth development and points out that type I collagen gene expression is regulated by distinct mechanisms during odontoblast differentiation process. These results support the independent expression of the collagen genes under developmental tissue-specific control.
The Drosophila gene Serrate encodes an EGF-like transmembrane protein with a complex expression pattern in embryos and wing discs
Authors: Thomas Ulrich , Speicher Stephan A. , Knust Elisabeth
Published: April 2021

We describe the molecular characterization of the Drosophila gene Serrate (Ser), which encodes an integral membrane protein. The extracellular domain contains two cysteine-rich regions, one of which is organized in a tandem array of 14 EGF-like repeats. Antibodies directed against part of the extracellular region confirm the localization of the protein in the membrane. In the wing imaginai discs, the protein is detected in those regions that are affected in the wings of two dominant mutations, SerD and SerBd. Both mutations as well as three out of eight newly induced revertants of SerD could be mapped molecularly to the transcribed region, confirming the identity between the gene Ser and the transcription unit characterized. During embryonic development, RNA and protein exhibit a complex expression pattern, which is, however, not correlated with an appropriate embryonic phenotype. Phenotypic interactions of Ser alleles with the neurogenic genes Notch and Delta coupled with the structural similarity of the proteins encoded by these three genes suggest close interactions at the protein level.
Patterns of microtubule polymerization relating to cortical rotation in Xenopus laevis eggs
Authors: Houliston Evelyn , Elinson Richard P.
Published: April 2021

Following fertilization, the Xenopus egg cortex rotates relative to the cytoplasm by 30° about a horizontal axis. The direction of rotation, and as a result the orientation of the embryonic body axes, is normally specified by the position of sperm entry. The mechanism of rotation appears to involve an array of aligned microtubules in the vegetal cortex (Elinson and Rowning, 1988, Devi Biol. 128, 185–197). We performed anti-tubulin immunofluorescence on sections to follow the formation of this array. Microtubules disappear rapidly from the egg following fertilization, and reappear first in the sperm aster. Surprisingly, astral microtubules then extend radially through both the animal and vegetal cytoplasm. The cortical array arises as they reach the vegetal cell surface. The eccentric position of the sperm aster gives asymmetry to the formation of the array and may explain its alignment since microtubules reaching the cortex tend to bend away from the sperm entry side. The radial polymerization of cytoplasmic microtubules is not dependent on the sperm aster or on the female pronucleus: similar but more symmetric patterns arise in artificially activated and enucleate eggs, slightly later than in fertilized eggs.

These observations suggest that the cortical microtubule array forms as a result of asymmetric microtubule growth outward from cytoplasm to cortex and, since cortical and cytoplasmic microtubules remain connected throughout the period of the rotation, that the microtubules of the array rotate with the cytoplasm.
The effect of age on motor neurone death following axotomy in the mouse
Authors: Pollin M. M. , Mchanwell S. , Slater C. R.
Published: April 2021

The ability of mouse motor neurones to survive axotomy during the first month of life was studied. The motor neurones that lie in the dorsolateral columns of spinal segments C7 and C8 and supply the flexor muscles of the forepaw were axotomized by cutting and removing part of the median and ulnar nerves above the elbow. The number and position of cell bodies with axons in these nerves were confirmed by retrograde labelling of the cut axons with horseradish peroxidase. The ability of these neurones to survive axotomy varies with the age of the animal at the time of axotomy. When the axons are sectioned within the first four postnatal days, 80—90 % of the cell bodies will die, more than half of this death occurring in less than one week after axotomy. If the animals are one week old at the time the nerves are cut, a significantly smaller number (50 %) die (P=0.013), and the time-course of death is different, with eight to ten days elapsing before half the death has occurred. 40 % of the neurones will die if sectioned at two weeks of age, and it is not until four weeks of age that more than 90 % of the cells can survive axotomy.

We conclude, therefore, that the kinetics of motor neurone death, as well as the final extent of neuronal loss, are affected by the age at which the animal is axotomized.
Changes in the expression of laminin during intestinal development
Authors: Simo P. , Simon-Assmann P. , Bouziges F. , Leberquier C. , Kedinger M. , Ekblom P. , Sorokin L.
Published: April 2021

The expression of laminin, a major glycoprotein constituent of basement membranes, was investigated in the rat developing intestine. The biosynthesis of laminin was studied after metabolic labeling of intestinal segments taken at various stages of development; the neosynthesized laminin was purified by affinity chromatography on heparin–Sepharose. Immunoblotting and immunoprecipitation experiments allowed us to analyze its constitutive chains. The data show that laminin is synthesized in very large amounts at 16–18 days of gestation concomitant with the onset of intestinal morphogenetic movements, i.e. villus emergence. Evaluation of the relative proportion of individual laminin polypeptides shows that laminin B1/B2 chains are produced in excess of A chains whatever the developmental stage considered. Interestingly at 17 days of gestation, levels of laminin A subunits are maximal. A second rise in the A/B chain ratio starts around birth and continues until adulthood. These quantitative data are corroborated by the immunocytochemical detection of laminin A and B chains, which revealed a specific spatiotemporal pattern. The finding that laminin A chains are located in the basement membrane of growing villi and of adult crypts raises the possibility that they may be involved in the process of cell growth and/or in the establishment of cell polarity by creating a specialized extracellular microenvironment.
Macrophages in haemopoietic and other tissues of the developing mouse detected by the monoclonal antibody F4/80
Authors: Morris Lynn , Graham Christopher F. , Gordon Siamon
Published: April 2021

Macrophages are widely distributed in lymphohaemo-poietic and other tissues of the normal and diseased adult, where they play an important role in host defence and repair. Although the development of haemopoiesis has been well studied in several species, the ontogeny of the mononuclear phagocyte system remains poorly understood. We have used a highly specific mAh, F4/80, to examine the distribution of mature macrophages in the developing mouse, with special reference to their presence in the haemopoietic microenvironment. Monocytes and macrophages were first seen in embryos on day 10 in the yolk sac and liver as well as in mesenchyme. In liver, spleen and bone marrow, there was expansion of this population associated with the initiation of haemopoietic on days 11,15 and 17, respectively. Macrophages in these sites formed part of the haemopoietic stroma and their extensively spread plasma membrane processes could be seen making intimate contacts with clusters of differentiating haemopoietic cells. F4/80+ cells were widely dispersed in undifferentiated mesenchymal tissue in organs such as lung, kidney and gut.

Numbers of F4/80-labefled cells increased concomitantly with organ growth and local mitoses were evident, as well as actively phagocytic macrophages. Our studies establish that macrophages are among the earliest haemopoietic cells to be produced during development and that they are relatively abundant in fetal tissues in the absence of overt inflammatory stimuli. Their distribution is correlated with the sequential migration of haemopoiesis and they constitute a prominent component of the stroma in fetal liver, spleen red pulp and bone marrow. Apart from a role in haemopoietic cellular interactions, their highly developed endocytic and biosynthetic activities suggest that macrophages contribute major undefined functions during growth, turnover and modelling of fetal tissues.

Abbreviations: Ab, antibody; ag, antigen; mAb, monoclonal antibody; MΦ, macrophage.
Potential role of RGD-binding integrins in mammalian lung branching morphogenesis
Authors: Roman Jesse , Little Candice W. , McDonald J. A.
Published: April 2021

Cell–matrix interactions are generally considered critical for normal lung development. This is particularly likely to be true during the glandular stage, when the primitive airways are formed through a process termed branching morphogenesis. Integrins, transmembrane receptors that bind to extracellular matrices, are likely to mediate important interactions between embryonic cells and their matrices during branching morphogenesis. In this report, we examine the role of integrin receptors in this process. Immunohistochemical studies revealed that the integrins VLA 3, VLA 5 and integrin receptors to vitronectin are expressed in the epithelium and/or mesenchyme during the glandular stage of murine lung development. To correlate expression with function, an in vitro model of murine lung branching morphogenesis was utilized to examine branching in the presence of inhibitors of ligand binding to integrin receptors. One such reagent, a hexapeptide containing the RGD (Arg-Gly-Asp) sequence, diminished branching and resulted in an abnormal morphology, whereas a control peptide RGESP (Arg-Gly-Glu-Ser-Pro) had no effect. These findings suggest a critical role for cell–matrix interactions mediated via integrin receptors in early stages of mammalian lung development.
Fate mapping and cell lineage analysis of Hensen’s node in the chick embryo
Authors: Selleck Mark A. J. , Stern Claudio D.
Published: April 2021

Fate maps of chick Hensen’s node were generated using Dil and the lineage of individual cells studied by intracellular injection of lysine-rhodamine-dextran (LRD). The cell types contained within the node are organized both spatially and temporally. At the definitive primitive streak stage (Hamburger and Hamilton stage 4), Hensen’s node contains presumptive notochord cells mainly in its anterior midline and presumptive somite cells in more lateral regions. Early in development it also contains presumptive endoderm cells. At all stages studied (stages 3–9), some individual cells contribute progeny to more than one of these tissues.

The somitic precursors in Hensen’s node only contribute to the medial halves of the somites. The lateral halves of the somites are derived from a separate region in the primitive streak, caudal to Hensen’s node.
Autonomy and nonautonomy of sex determination in triploid intersex mosaics of C. elegans
Authors: Schedin Pepper , Hunter Craig P. , Wood William B.
Published: April 2021

The primary sex-determining signal in Caenorhabditis elegans is the ratio of X chromosomes to sets of autosomes (X/A ratio), normally 1.0 in hermaphrodites (XX) and 0.5 in males (XO). XX triploids (X/A=0.67) are males, but if these animals carry a partial duplication of the X chromosome such that X/A ≅ 0.7, they develop as intersexes that are sexually mosaic. We have analyzed these mosaics using Nomarski microscopy and in situ hybridization to obtain information on whether sex determination decisions can be made independently in different cells and tissues, and when these commitments are made. The observed patterns of male and female cells in individual animals indicate that sex determination decisions can be influenced by anterior-posterior position and that sex determination decisions can be made as late as the third larval stage of postembryonic development. Although these decisions clearly can be made independently in different lineages, they show substantial biases toward one sex or the other in individual animals. We interpret these results to suggest that sex determination in C. elegans is not entirely cell autonomous.
Autonomous differentiation of dorsal axial structures from an animal cap cleavage stage blastomere in Xenopus
Authors: Gallagher Betty C. , Hainski Alexandra M. , Moody Sally A.
Published: April 2021

Dorsal or ventral blastomeres of the 16- and 32-cell stage animal hemisphere were labeled with a lineage dye and transplanted into the position of a ventral, vegetal midline blastomere. The donor blastomeres normally give rise to substantial amounts of head structures and central nervous system, whereas the blastomere which they replaced normally gives rise to trunk mesoderm and endoderm. The clones derived from the transplanted ventral blastomeres were found in tissues appropriate for their new position, whereas those derived from the transplanted dorsal blastomeres were found in tissues appropriate for their original position. The transplanted dorsal clones usually migrated into the host’s primary axis (D1.1, 92 %; DI.1.1, 69 %; DI.1.2, 100 %), and in many cases they also induced and populated a secondary axis (D1.1, 43%; DI.1.1, 67%; DI.1.2, 63%). Bilateral deletion of the dorsal blastomeres resulted in partial deficits of dorsal axial structures in the majority of cases, whereas deletions of ventral midline blastomeres did not. When the dorsal blastomeres were cultured as explants they elongated. Notochord and cement glands frequently differentiated in these explants. These studies show that the progeny of the dorsal, midline, animal blastomeres: (1) follow their normal lineage program to populate dorsal axial structures after the blastomere is transplanted to the opposite pole of the embryo; (2) induce and contribute to a secondary axis from their transplanted position in many embryos; (3) are important for the normal formation of the entire length of the dorsal axis; and (4) autonomously differentiate in the absence of exogenous growth factor signals. These data indicate that by the 16cell stage, these blastomeres have received instructions regarding their fate, and they are intrinsically capable of carrying out some of their developmental program.
Curvature of the caudal region is responsible for failure of neural tube closure in the curly tail (ct) mouse embryo
Authors: Brook Frances A. , Shum Alisa S. W. , Straaten Henny W. M. Van , Copp Andrew J.
Published: April 2021

Delayed closure of the posterior neuropore (PNP) occurs to a variable extent in homozygous mutant curly tail (ct) mouse embryos, and results in the development of spinal neural tube defects (NTD) in 60 % of embryos. Previous studies have suggested that curvature of the body axis may delay neural tube closure in the cranial region of the mouse embryo. In order to investigate the relationship between curvature and delayed PNP closure, we measured the extent of ventral curvature of the neuropore region in ct/ct embryos with normal or delayed PNP closure. The results show significantly greater curvature in ct/ct embryos with delayed PNP closure in vivo than in their normal littermates. Reopening of the posterior neuropore in non-mutant mouse embryos, to delay neuropore closure experimentally, did not increase ventral curvature, suggesting that increased curvature in ct/ct embryos is not likely to be a secondary effect of delayed PNP closure. Experimental prevention of ventral curvature in ct/ct embryos, brought about by implantation of an eyelash tip longitudinally into the hindgut lumen, ameliorated the delay in PNP closure. We propose, therefore, that increased ventral curvature of the neuropore region of ct/ct embryos imposes a mechanical stress, which opposes neurulation and thus delays closure of the PNP. Increased ventral curvature may arise as a result of a cell proliferation imbalance, which we demonstrated previously in affected ct/ct embryos.
Regulation and processing of a secreted protein that mediates sensing of cell density in Dictyostelium
Authors: Yuen Ita S. , Taphouse Carl , Halfant Kerri A. , Gomer Richard H.
Published: April 2021

During Dictyostelium development, the expression of some genes is dependent on cell density. This effect is mediated by soluble factors referred to as conditioned medium factors (CMFs) which the developing cells secrete at very low rates and simultaneously sense. There are at least two classes of CMFs: one is an 80 × 103Mr glycoprotein and the other is a heterogeneous group of molecules, with relative molecular masses between 6.5X103 and 0.65 X103. Interestingly, the two classes of molecules do not need to be combined for activity. We find that the 80x103Afr CMF but not the small CMF is sequestered in vegetative cells. The 80x103Air CMF is then secreted by cells during early development, while the small CMF appears only during late development. Like the 80x103Afr CMF, the small CMFs are trypsin-sensitive and contain N- and O-linked glycosylation. The breakdown products of a fraction containing SOxlO3 CMF cochromatographed from a Sephadex G-50 column and a reverse-phase HPLC column with small CMFs. The specific activity of CMF increases roughly 100-fold upon breakdown. The results suggest that, during differentiation, the slowly diffusing 80 × 103 Afr CMF is first produced from a precursor pool already present in vegetative cells, allowing differentiation of only those cells in the immediate vicinity of the aggregation center. The breakdown of SOxlfpAf,. CMF to a faster-diffusing, higher specific activity form then might enable cells farther from the aggregation center to differentiate.
Transient expression of XMyoD in non-somitic mesoderm of Xenopus gastrulae
Authors: Frank Dale , Harland Richard M.
Published: April 2021

XMyoD is the earliest marker of muscle development in Xenopus embryos and is expressed in presumptive somites in the late gastrula. In the early gastrula, in situ hybridization showed XMyoD transcripts in precursors of both muscle and non-muscle mesoderm. Embryos ventralized by UV irradiation made no muscle, but expressed XMyoD transiently. Embryo explants that differentiated ventral mesoderm also expressed XMyoD transiently. These results show that the initiation of XMyoD expression is not sufficient to convert cells to muscle and suggest that XMyoD is expressed in response to a general mesodermalizing signal; expression is stabilized and enhanced only in muscle precursors that have received a dorsalizing signal.
The effects of retinoic acid on heart formation in the early chick embryo
Authors: Osmond Mark K. , Butler Andrew J. , Voon Francis C. T. , Bellairs Ruth
Published: April 2021

The vitamin A derivative retinoic acid has previously been shown to have teratogenic effects on heart development in mammalian embryos. The craniomedial migration of the precardiac mesoderm during the early stages of heart formation is thought to depend on a gradient of extracellular fibronectin associated with the underlying endoderm. Here, the effects of retinoic acid on migration of the precardiac mesoderm have been investigated in the early chick embryo. When applied to the whole embryo in culture, the retinoid inhibits the craniomedial migration of the precardiac mesoderm resulting in a heart tube that is stunted cranially, while normal or enlarged caudally. Similarly, a local application of retinoic acid to the heart-forming area disrupts the formation of the cardiogenic crescent and the subsequent development of a single mid-line heart tube. This effect is analogous to removing a segment of endoderm and mesoderm across the heart-forming area and results In various degrees of cardia bifida. At higher concentrations of retinoic acid and earlier developmental stages, two completely separate hearts are produced, while at lower concentrations and later stages there are partial bifurcations. The controls, in which the identical operation is carried out except that dimethyl sulphoxide (DMSO) is used instead of the retinoid, are almost all normal. We propose that one of the teratogenic effects of retinoic acid on the heart is to disrupt the interaction between precardiac cells and the extracellular matrix thus inhibiting their directed migration on the endodermal substratum.
Developmental expression of two murine fibroblast growth factor receptors, fig and bek
Authors: Orr-Urtreger Avi , Givol David , Yayon Avner , Yarden Yosef , Lonai Peter
Published: April 2021

Developmental expression of two closely related fibroblast growth factor receptors, bek and fig, is described from early postimplantation until advanced organogenesis. Transcripts of bek and fig were first seen in the primitive ectoderm of egg-cylinder-stage embryos. Later, starting with somitogenesis, and then throughout embryogenesis, they were actively transcribed both in the mesoderm and neuroectoderm. Bek was expressed also in the surface ectoderm and in various epithelia, whereas flg expression was restricted mainly to the mesenchyme. In the limb bud bek transcripts displayed a gradient-like distribution and appeared earlier than flg. The two receptors, in contrast to their almost identical ligand binding specificity, displayed distinct spatial specificities throughout development, suggesting that developmental localization may contribute to functional specificity. The role of bek and flg in gastrulation and in epithelial-mesenchymal interactions of organogenesis will be discussed.
A chondroitin sulfate proteoglycan may influence the direction of retinal ganglion cell outgrowth
Authors: Snow D. M. , Watanabe M. , Letourneau P. C. , Silver J.
Published: April 2021

In the developing retina, retinal ganglion cell (RGC) axons elongate toward the optic fissure, even though no obvious directional restrictions exist. Previous studies indicate that axon-matrix interactions are important for retinal ganglion cell axon elongation, but the factors that direct elongation are unknown. Chondroitin sulfate proteoglycan (CS-PG), a component of the extracellular matrix, repels elongating dorsal root ganglion (DRG) axons in vitro and is present in vivo in the roof plate of the spinal cord, a structure that acts as a barrier to DRG axons during development. In this study, we examined whether CS-PG may regulate the pattern of retinal ganglion cell outgrowth in the developing retina.

Immunocytochemical analysis showed that CS-PG was present in the innermost layers of the developing rat retina. The expression of CS-PG moved peripherally with retinal development, always remaining at the outer edge of the front of the developing axons. CS-PG was no longer detectable with immunocytochemical techniques when RGC axon elongation in the retina is complete.

Results of studies in vitro showed that CS-PG, isolated from bovine nasal cartilage and chick limb, was inhibitory to elongating RGC axons and that RGC growth cones were more sensitive to CS-PG than were DRG neurites tested at the same concentrations of CS-PG. The behavior of retinal growth cones as they encounter CS-PG was characterized using time-lapse video microscopy. Filopodia of the RGC growth cones extended to and sampled the CS-PG repeatedly. With time, the growth cones turned to avoid outgrowth on the CS-PG and grew only on laminin.

While numerous studies have shown the presence of positive factors within the retina that may guide developing RGC axons, this is the first demonstration of an inhibitory or repelling molecule in the retina that may regulate axon elongation. Taken together, these data suggest that the direction of RGC outgrowth in the retina may be regulated by the proper ratio of growthpromoting molecules, such as laminin, to growthinhibiting molecules, like CS-PG, present in the correct pattern and concentrations along the retinal ganglion cell pathway.
Positive and negative control of the Antennapedia promoter P2
Authors: Riley George R. , Jorgensen Erik M. , Baker Robert K. , Garber Richard L.
Published: April 2021

To understand the nature of the regulatory signals impinging on the second promoter of the Antennapedia gene (Antp P2), analysis of its expression in mutants and in inhibitory drug injected embryos has been carried out. The maternally-active gene osk is identified as one of two general repressors of P2 which prevent Antp transcription until division cycle 14. Products of the zygoticaliy-active segmentation genes ftz, hb, Kr, gt and kni then act as activators or repressors of Antp P2 in a combinatorial fashion. The timing of these events, and their positive versus negative nature, is critical for generating the expression patterns normal for Antp.
Genetic analysis of leaf development in cotton
Authors: Dolan Liam , Poethig R. Scott
Published: April 2021

Leaf shape in cotton is regulated by the developmental age of the shoot and by several major genes that affect leaf lobing. The effect of these factors was investigated by allometric analysis, cell lineage analysis, and by studying the expression of the leaf shape mutation, Okra, in genetic mosaics. Allometric analysis of leaf growth suggests that leaf shape is determined during the initiation of the primordium rather than during the expansion phase of leaf growth. Clonal analysis demonstrates that both the rate and duration of cell division are fairly uniform throughout the leaf. Cells in the marginal region of the developing cotton leaf contribute more to the growth of the lamina than they do in tobacco. The Okra mutation acts early in the development of a leaf and appears to accentuate a developmental pattern that is also responsible for heteroblastic variation in leaf shape. The expression of this mutation in genetic mosaics demonstrates that its effect does not diffuse laterally within the leaf primordium.
Expression of the L14 lectin during mouse embryogenesis suggests multiple roles during pre- and post-implantation development
Authors: Poirier Francoise , Timmons Paula M. , Chan C.-T. J. , Guénet Jean-Louis , Rigby Peter W. J.
Published: April 2021

A cDNA encoding L14, the lactose-binding, soluble lectin of relative molecular mass 14 × 103, has been isolated in a differential screen designed to identify genes that are regulated during the differentiation of murine embryonic stem cells in vitro. The expression patterns of the gene and of the encoded protein during mouse embryogenesis are consistent with the lectin playing a role at several stages of development. Firstly, it is initially synthesised in the trophectoderm of expanded blastocysts immediately prior to implantation, suggesting that it may be involved in the attachment of the embryo to the uterine epithelium. Secondly, in the postimplantation embryo, the lectin is abundantly expressed in the myotomes of the somites. This observation, when taken together with data indicating a role for the lectin in myoblast differentiation in culture, suggests that the protein is important in muscle cell differentiation. Finally, within the nervous system expression of this gene is activated early during the differentiation of a particular subset of neurones.
A 102 base pair sequence of the nicotinic acetylcholine receptor delta-subunit gene confers regulation by muscle electrical activity
Authors: Chahine Kenneth G. , Walke Wade , Goldman Daniel
Published: April 2021

Muscle electrical activity suppresses expression of the embryonic-type (α, β, γ and δ) nicotinic acetylcholine receptor (nAChR) genes. The molecular mechanism by which electrical activity regulates these genes is not known. One approach to this problem is to identify regions of the nAChR genes that mediate electrical regulation. Here we report results from such a study of the nAChR δ-subunit gene. We cloned the rat δ-subunit promoter region and created an expression vector in which this DNA controlled the expression of a down-stream luciferase structural gene. The effect that muscle electrical activity had on the expression from this promoter was assayed by introducing this expression vector into electrically stimulated and tetrodotoxin (TTX)-treated rat primary myotubes, and assaying for luciferase activity. These myotubes, when stimulated with extracellular electrodes, suppressed endogenous embryonic-type nAChR gene expression compared to those treated with TTX. Transfection of these cells with δ-promoter-luciferase expression vectors resulted in the δ-promoter conferring electrical regulation on luciferase expression. Additional experiments using deletions from the 5’ end of theδ-promoter region have identified an element between −677 and −550 bp that suppressed δ-promoter activity and a minimal 102 bp sequence that promotes and regulates luciferase expression in response to muscle electrical activity. This latter sequence also contains all the necessary elements to confer tissue and developmental stage-specific expression.
Dynamic expression of the cell adhesion molecule fasciclin I during embryonic development in Drosophila
Authors: Mcallister Linda , Goodman Corey S. , Zinn Kai
Published: April 2021

A number of different cell surface glycoproteins expressed in the central nervous system (CNS) have been identified in insects and shown to mediate cell adhesion in tissue culture systems. The fasciclin I protein is expressed on a subset of CNS axon pathways in both grasshopper and Drosophila. It consists of four homologous 150-amino acid domains which are unrelated to other sequences in the current databases, and is tethered to the cell surface by a glycosyl-phosphatidylinositol linkage. In this paper we examine in detail the expression of fasciclin I mRNA and protein during Drosophila embryonic development. We find that fasciclin I is expressed in several distinct patterns at different stages of development. In blastoderm embryos it is briefly localized in a graded pattern. During the germ band extended period its expression evolves through two distinct phases. Fasciclin I mRNA and protein are initially localized in a 14-stripe pattern which corresponds to segmentally repeated patches of neuroepithelial cells and neuroblasts. Expression then becomes confined to CNS and peripheral sensory (PNS) neurons. Fasciclin I is expressed on all PNS neurons, and this expression is stably maintained for several hours. In the CNS, fasciclin I is initially expressed on all commissural axons, but then becomes restricted to specific axon bundles. The early commissural expression pattern is not observed in grasshopper embryos, but the later bundle-specific pattern is very similar to that seen in grasshopper. The existence of an initial phase of expression on all commissural bundles helps to explain the loss-of-commissures phenotype of embryos lacking expression of both fasciclin I and of the D-abl tyrosine kinase. Fasciclin I is also expressed in several nonneural tissues in the embryo.
Activation of the easter zymogen is regulated by five other genes to define dorsal-ventral polarity in the Drosophila embryo
Authors: Chasan Rebecca , Jin Yishi , Anderson Kathryn V.
Published: April 2021

The product of the Drosophila easter gene, a member of the trypsin family of serine proteases, must be more active ventrally than dorsally to promote normal embryonic polarity. The majority of the easter protein in the embryo is present in the unprocessed zymogen form and appears to be evenly distributed in the extracellular space, indicating that the asymmetric activity of wildtype easter must arise post-translationally. A dominant mutant form of easter that does not require cleavage of the zymogen for activity (ea ▵N) is active both dorsally and ventrally. The ea ▵N mutant bypasses the requirement for five other maternal effect genes, indicating that these five genes exert their effects on dorsal-ventral patterning solely by controlling the activation of the easter zymogen. We propose that dorsal-ventral asymmetry is initiated by a ventrally-localized molecule in the vitelline membrane that nucleates an easter zymogen activation complex, leading to the production of ventrally active easter enzyme.