bluuebunny/crossref_metadata_2025 huggingface dataset:
Patterns of tenascin expression during tail regeneration of the amphibian urodele Pleurodeles waltl
Authors: Arsanto Jean-Pierre , Diano Monique , Thouveny Yves , Thiery Jean Paul , Levi Giovanni
Published: April 2021

We have determined the patterns of expression of tenascin, an extracellular matrix (ECM) glycoprotein, by indirect immunohistofluorescence and immunoblots during the post-traumatic regeneration of the tail distal part of the amphibian urodele Pleurodeles waltl. In normal tails of adult Pleurodeles, tenascin expression is mostly restricted to few connective tissues including the periosteum, the ligaments of vertebral articulation, myotendinous structures, the perimysium and the pia mater; the extracellular matrix is virtually negative. In certain areas of the adult skin the molecule is expressed around cells of the inner epidermal layer, apparently associated with the cell surface. In the first 4-6 days following tail amputation, tenascin expression increases in the stump region in areas surrounding dedifferentiating tendons; the early blastemic epithelium does not express the molecule. The local increase of tenascin in areas where cells dedifferentiate and start to migrate, precedes the increase in fibronectin that occurs later in the mesenchyme of the blastema. From the 8th day of regeneration, there is a sharp increase of the level of expression of the molecule in the extracellular matrix of the loose mesenchyme underlying the epithelium of the blastema which remains negative. The maximal expression in the matrix is reached in 4-to 6-week-old regenerates and then gradually decreased. High levels of tenascin are present in sites of muscle condensation as fibrils oriented parallel to the direction of alignment of myogenic cells and in sites of chondrogenesis particularly in regions of precartilage formation. After the second week of regeneration, tenascin is strongly expressed in the basal lamina of the regenerated skin and, after the fourth week, also at the level of epidermaldermal junctional areas. Like in normal tail ends, in regenerates older than 8 – 9 weeks, tenascin expression is nearly restricted to the muscle connective tissue and myotendinous structures.

These results are discussed in view of the possible multiple morphogenetic roles of tenascin in tissue regeneration and repair.
Molecular analysis of the Mov 34 mutation: transcript disrupted by proviral integration in mice is conserved in Drosophila
Authors: Gridley Thomas , Gray Douglas A. , Orr-Weaver Terry , Soriano Philippe , Barton David E. , Francke Uta , Jaenisch Rudolf
Published: April 2021

The Mov 34 mutation is a recessive embryonic lethal mutation caused by retroviral integration in the murine germline. This integration disrupts a transcription unit that appears to encode a novel protein. The Mov 34 proviral integration is located on mouse chromosome 8 and the human homolog of this gene has been mapped to chromosome region 16q23-q24. An evolutionarily conserved syntenic relationship exists between this region of human chromosome 16 and a region of mouse chromosome 8 that also contains oligosyndactyly (Os), another recessive lethal mutation. Genetic studies have ruled out Os as residing at the same locus as the Mov 34 integration.

The Mov 34 transcript is conserved in evolution, and a Drosophila homolog appears to encode a protein with 62 % amino acid identity to the murine protein. In situ hybridization to Drosophila polytene chromosomes localizes the Drosophila homolog to 60B,C on chromosome 2. Several Drosophila lethal mutations also map to this region.
A positional marker for the dorsal embryonic retina is homologous to the high-affinity laminin receptor
Authors: Rabacchi Sylvia A. , Neve Rachael L. , Dräger Ursula C.
Published: April 2021

In a search for determinants of positional information in the embryonic eye, we isolated two monoclonal anti bodies that label strongly the dorsal part of the undifferentiated embryonic retina in mammals, bird and cold blooded vertebrates. In the chick, the optic tectum is labeled in a corresponding fashion, the ventral tectum more heavily than the dorsal tectum. Through biochemical and molecular analysis both antibodies were found to recognize a protein that has been cloned repeatedly, first in a screen with antibodies to the ‘68K-laminin receptor’ (Wewer et al. (1986)Cancer Res. 47, 5691–5698), a name that may not exhaustively describe its function. Western blots show the protein to be present in most or all tissues, and Western and Southern blots reveal a high degree of conservation in the detected signals up to invertebrates and bacteria. Despite the very strong and selective labeling of the dorsal retina in conventional immunohistochemical preparations, the protein and its mRNA are present in even amounts throughout the embryonic retina, as demonstrated by Western and Northern blots of bisected retinas, and immunohistochemically in retinas fixed with ethylene glycole bissuccinimide (EGS), an NH2-group crosslinker with very long spacer arm. This indicates that the dorsoventral asymmetry in the embryonic retina is not in the amount but in the configuration of this protein; whether this difference relates to laminin binding is not known.
Early onset of phenotype and cell patterning in the embryonic zebrafish retina
Authors: Larison Karen D. , Bremiller Ruth
Published: April 2021

The regular arrangement of retinal cone cells in a mosaic pattern is a common feature of teleosts. In the zebrafish, Brachydanio rerio, the retinal cone mosaic comprises parallel rows consisting of a repeating motif of four cone types. In order to elucidate the temporal and spatial aspects of the genesis of the cone mosaic in the developing retina, we generated a monoclonal antibody that specifically binds to the double cone photoreceptor of the adult. We first saw staining in the developing retina with this antibody, FRet 43, at 48 hours postfertilization, the time at which the first photoreceptor cells undergo their final mitotic division. We then injected embryonic fish with the thymidine analog, 5-bromo-2‘-deoxyuridine (BrdU), confirming with a double-labeling experiment that the onset of FRet 43 antigenicity occurs within three hours of the cellular division that generates the double cone photoreceptors. Then we stained tangential sections of the 54-hour embryonic retina with FRet 43, further showing that cells devoid of staining alternate with stained pairs of cells in a pattern that is consistent with the arrangement of photoreceptors in the adult cone mosaic. These results indicate that a marker of the double cone phenotype is expressed at approximately the same time as cellular birthday and that the mosaic patterning is present within 6 hours of this expression.
Experimental Studies on the Origin of the Cartilage of the Auditory Capsule and Columella in Ambystoma
Authors: Toerien M. J.
Published: April 2021

The ear capsule chondrocytes are derived from three sources, viz. neural crest, ear placode and surrounding ectoderm, and also cranial mesentoderm. Under experimental conditions the crest ectomesenchyme is the least significant and the placode the most important source of cartilage cells. Ectomesenchyme of placodal origin predominates more often in capsules which developed into normal structures than in those that developed somewhat abnormally. The cartilaginous wall separating the internal ear from the brain is essentially of axial origin although it receives a contribution from the ecto-mesenchyme. Axial and capsular cartilage is separated along a fairly definite line ventral to the medial wall of the capsule. The presence or absence of the ear capsule affects the shape of the foot-plate of the columella, but not its existence. The footplate and stylus columellae share an origin with the visceral skeleton. The columella is most likely a part of the hyoid arch.
Environmental Factors Determining the Growth and Development of Whole Bone Transplants
Authors: Mawdsley R. , Harrison G. Ainsworth
Published: April 2021

Intrinsic factors are known to play an integral part in skeletal morphogenesis (Willis, 1936; Fell, 1956). In particular, it has recently been demonstrated that the humerus (Felts, 1959) and femur (Chalmers & Ray, 1962) of the mouse develop, grow, and in many ways preserve their distinctive form when transplanted to non-functional sites. However, it is also widely recognized that internal and external environmental factors are important in determining skeletal growth and form (Sissons, 1956). The aim of this paper is to examine some of these extrinsic factors in terms of the effects of various types of host on the growth of subcutaneous transplants of the mouse humerus. The factors studied were environmental temperature, age and genotype including sex.
The Effects of Vitamin A and Citral on Epithelial Differentiation in vitro 2. The Chick Oesophageal and Corneal Epithelia and Epidermis
Authors: Aydelotte Margaret B.
Published: April 2021

Differentiation of the oesophageal and corneal epithelia and epidermis of the chick embryo was studied in organ cultures in normal medium and in media containing added vitamin A and/or citral. In normal medium the oesophageal epithelium developed well for the first 6 days, but between 6 and 12 days many superficial layers of cells were sloughed and large mucous cells from the glands spread over the remaining epithelium. Vitamin A inhibited the normal stratification, and the oesophageal epithelium became pseudostratified and folded, with tall, columnar, ciliated cells and many small mucous glands. Citral inhibited the differentiation of ciliated and mucous cells and the epithelium became thicker than in normal medium. Vitamin A and citral together produced either a vitamin A or a citral effect, depending upon the relative concentrations of the two compounds. The corneal epithelium differentiated normally in the control cultures, but under the influence of additional vitamin A it remained thin and the superficial cells secreted mucus. In + citral medium the corneal epithelium became thicker than usual and the conjunctival epithelium keratinized. When both vitamin A and citral were added to the medium the corneal cultures showed a mild vitamin A effect. Skin cultures keratinized well in normal medium, but the epithelium remained thin and became mucus-secreting in response to high concentrations of vitamin A. Citral alone had little effect on epidermis, but it suppressed the vitamin A response almost completely when both compounds were added together. Citral produced changes resembling those of vitamin A deficiency in cultures of oesophagus and cornea, and it reduced the effects of added vitamin A. The results of these experiments therefore give further evidence of antagonism between vitamin A and citral. It is suggested that either deficiency of vitamin A or treatment with citral stimulates, whilst high concentrations of vitamin A inhibit, mitosis in the corneal epithelium. The results of these experiments indicate that each epithelium achieves its maximal synthesis of mucus at a characteristic concentration of vitamin A.
The Drosophila segment polarity gene patched is involved in a position-signalling mechanism in imaginal discs
Authors: Phillips Roger G. , Roberts Ian J. H. , Ingham Philip W. , Whittle J. Robert S.
Published: April 2021

We demonstrate the role of the segment polarity gene patched (ptc) in patterning in the cuticle of the adult fly. Genetic mosaics of a lethal allele of patched show that the contribution of patched varies in a position-specific manner, defining three regions in the wing where ptc clones, respectively, behave as wild-type cells, affect vein formation, or are rarely recovered. Analysis of twin clones demonstrates that the reduced clone frequency results from a proliferation failure or cell loss. In the region where clones upset venation, they autonomously fail to form veins and also non-autonomously induce ectopic veins in adjacent wild-type cells. In heteroallelic combinations with lethal alleles, two viable alleles produce distinct phenotypes: (1) loss of structures and mirror-image duplications in the region where patched clones fail to proliferate; (2) vein abnormalities in the anterior compartment. We propose that these differ-enees reflect independently mutable functions within the gene. We show the pattern of patched transcription in the developing imaginal wing disc in relation to the expression of certain other reporter genes using a novel double-labelling method combining non-radioactive detection of in situ hybridization with β-galactosidase detection. The patched transcript is present throughout the anterior compartment, with a stripe of maximal intensity along the A/P compartment border extending into the posterior compartment. We propose that the patched product is a component of a cell-to-cell positionsignalling mechanism, a proposal consistent with the predicted structure of the patched protein.
Orientation of commissural axons in vitro in response to a floor plate-derived chemoattractant
Authors: Placzek Marysia , Tessier-Lavigne Marc , Jessell Thomas , Dodd Jane
Published: April 2021

Developing axons are guided to their targets by molecular cues in their local environment. Some cues are shortrange, deriving from cells along axonal pathways. There is also increasing evidence for longer-range guidance cues, in the form of gradients of diffusible chemoattractant molecules, which originate from restricted populations of target cells. The guidance of developing commissural axons within the spinal cord depends on one of their intermediate cellular targets, the floor plate. We have shown previously that floor plate cells secrete a diffusible factor(s) that can alter the direction of commissural axon growth in vitro. Here we show that the factor is an effective chemoattractant for commissural axons. It can diffuse considerable distances through a collagen gel matrix and through dorsal and ventral neural epithelium in vitro to reorient the growth of virtually all commissural axons. The orientation of axons occurs in the absence of detectable effects on the survival of commissural neurons or on the rate of commissural axon extension. The regionally restricted expression of the factor suggests that it is present in the embryonic spinal cord in a gradient with its high point at the floor plate. These observations support the idea that the guidance of commissural axons to the ventral midline of the spinal cord results in part from the secretion of a chemoattractant by the floor plate.
A Dictyostelium morphogen that is essential for stalk cell formation is generated by a subpopulation of prestalk cells
Authors: Kwong Linda , Xie Yinjuan , Daniel Juliet , Robbins Stephen M. , Weeks Gerald
Published: April 2021

The stalk cell differentiation inducing factor (DIF) has the properties required of a morphogen responsible for pattern regulation during the pseudoplasmodial stage of Dictyostelium development. It induces prestalk cell formation and inhibits prespore cell formation, but there is as yet no strong evidence for a morphogenetic gradient of DIF. We have measured DIF accumulation by monolayers of isolated prestalk and prespore cells in an attempt to provide evidence for such a gradient. DIF is accumulated in the largest quantities by a subpopu lation of prestalk cells that specifically express the DIF-inducible genes pDd56 and pDd26. Since it has been shown recently that cells that express pDd56 are localized in the central core of the prestalk cell region of the pseudoplasmodia, our current results suggest a morphogenetic gradient generated by this region.
daughterless-abo-like, a Drosophila maternal-effect mutation that exhibits abnormal centrosome separation during the late blastoderm divisions
Authors: Sullivan William , Minden Jonathan S. , Alberts Bruce M.
Published: April 2021

daughterless-abo-like (dal) is a maternal-effect semilethal mutation in Drosophila. The nuclear divisions of embryos derived from homozygous dal females are normal through nuclear cycle 10. However, during nuclear cycles 11, 12 and 13, a total of about half of the nuclei in each embryo either fail to divide or fuse with a neighboring nucleus during telophase. These abnormal nuclei eventually sink into the interior of the embryo, leaving their centrosomes behind on the surface. The loss of about one-half of the peripheral nuclei into the interior of the embryo results in these embryos cellularizing during nuclear cycle 14 with about one-half the normal number of cells. Surprisingly, many of these embryos develop a nearly normal larval cuticle and 8 % develop to adulthood.

Observations of live embryos doubly injected with tubulin and histones that have been fluorescently labeled allows nuclear and centrosomal behavior to be directly followed as the embryo develops. We find that the abnormal nuclei arise from nuclei whose centrosomes have failed to separate normally in the previous interphase. These incompletely separated centrosomes can cause a non-functional spindle to form, leading to a nuclear division failure. Alternatively, they can form an abnormal spindle with a centrosome from a neighboring nucleus, causing two nuclei to share a common spindle pole. Such nuclei with a shared centrosome will undergo telophase fusions, unequal divisions, or division failures later in mitosis. These findings have helped us to understand the function of the centrosome in the Drosophila embryo.
The cellular retinoic-acid-binding protein is expressed in tissues associated with retinoic-acid-induced malformations
Authors: Vaessen Marie-Josée , Meijers J. H. Carel , Bootsma Dirk , Van Kessel Ad Geurts
Published: April 2021

Retinoic acid (RA) is thought to play a role in embryonic pattern formation in vertebrates. A naturally occurring gradient of endogenous RA has been demonstrated in the developing chick limb bud, while local application of RA leads to the formation of additional digits. In mammals, a well-defined spectrum of birth defects has been reported as a result of fetal exposure to excess RA. In analogy to the chick limb bud, it may be speculated that these malformations are the result of disturbance of morphogenetic RA concentration gradients.

A candidate gene involved in the regulation of endogenous RA concentrations is the gene encoding cellular RA binding protein (CRABP). We have isolated a partial cDNA clone corresponding to the chicken homolog of CRABP, and performed in situ hybridization experiments on sections of embryos at various stages of development. CRABP expression was detected in the CNS, the craniofacial mesenchyme, ganglia of the peripheral nervous system, the limb bud, and the visceral arch area. Our results indicate that the spatiotemporally specified expression pattern displayed by the CRABP gene exhibits a striking correspondence to the tissues that are affected by exposure of avian or mammalian embryos to RA. We hypothesize that CRABP plays an important role in normal embryogenesis and that embryonic tissues showing high CRABP expression are susceptible to the adverse effects of excess RA.
Pathfinding during spinal tract formation in the chick-quail chimera analysed by species-specific monoclonal antibodies
Authors: Tanaka Hideaki , Kinutani Masae , Agata Akemi , Takashima Youichiro , Obata Kunihiko
Published: April 2021

In order to analyse the spinal tract formation at early stages of development in avian embryos, chick-quail spinal cord chimeras were prepared and species-specific monoclonal antibodies (MAb) were developed. MAbs CN, QN and CQN uniquely stained chick, quail, and both chick and quail nervous tissues, respectively. All three antibodies appeared to bind to the same membrane molecule, but to different epitopes. Cord reversal revealed the features of axonal growth of both cord interneurons and dorsal root ganglion cells. Quail cord interneurons grew along an originally ventral marginal layer in the quail cord transplanted in a reversed position, then turned toward the ventral side at the boundary between the graft and the host, and grew along the host chick ventral marginal layer. Central axons of dorsal root ganglia were restricted to the ventrolateral region of the cord which originally formed the dorsal funiculus. These results suggest that cord interneurons and dorsal root ganglion cells actively select to grow along specific regions of the cord and that spinal tract formation appears to be determined by cord cells, and not by sclerotome cells.
In situ hybridization analysis of TGFβ3 RNA expression during mouse development: comparative studies with TGFβ1 and β2
Authors: Pelton Ron W. , Dickinson Mary E. , Moses Harold L. , Hogan Brigid L. M.
Published: April 2021

To date, three closely-related TGFβ genes have been found in the mouse; TGFβ1, TGFβ2 and TGFβ3. Previous experiments have indicated that TGFβ1 and TGFβ2 may play important roles during mouse embryo-genesis. The present study now reports the distribution of transcripts of TGFβ3 in comparison to the other two genes and reveals overlapping but distinct patterns of RNA expression. TGFβ3 RNA is expressed in a diverse array of tissues including perichondrium, bone, intervertebral discs, mesenteries, pleura, heart, lung, palate, and amnion, as well as in central nervous system (CNS) structures such as the meninges, choroid plexus and the olfactory bulbs. Furthermore, in several organ systems, TGFβ3 transcripts are expressed during periods of active morphogenesis suggesting that the protein may be an important factor for the growth and differentiation of many embryonic tissues.
Establishment of germ-line-competent embryonic stem (ES) cells using differentiation inhibiting activity
Authors: Nichols Jennifer , Evans Edward P. , Smith Austin G.
Published: April 2021

The regulatory factor Differentiation Inhibiting Activity/Leukaemia Inhibitory Factor (DIA/LIF) suppresses the differentiation of cultured embryonic stem (ES) cells. In the present study, it is shown that ES cell lines can be derived and maintained in the absence of feeder layers using medium supplemented with purified DIA/LIF. These cells can differentiate normally in vitro and in vivo and they retain the capacity for germ-line transmission. DIA/LIF therefore fulfils the essential function of feeders in the isolation of pluripotential stem cells.
α-actin proteins and gene transcripts are colocalized in embryonic mouse muscle
Authors: Lyons Gary E. , Buckingham Margaret E. , Mannherz Hans G.
Published: April 2021

The α-actins are among the earliest muscle-specific mRNAs to appear in developing cardiac and skeletal muscle. To determine if there is coexpression of the α-actin proteins at early stages of myogenesis, we have used an α-actins-specific polyclonal antibody and in situ hybridization with specific cRNA probes to cardiac and skeletal α-actins transcripts on serial slides of mouse embryo sections. As soon as we can detect α-actins mRNAs in embryonic striated muscle, we also detect the protein suggesting that α-actins transcripts are translated very rapidly after transcription during myogenesis. In skeletal muscle, this colocalization of α-actins mRNA and protein was observed both in the myotomes of somites and in developing muscles in the limbs. In cardiac muscle, α-actins transcripts and proteins are abundantly expressed as soon as a cardiac tube forms.
Early expression of the myogenic regulatory gene, myf-5, in precursor cells of skeletal muscle in the mouse embryo
Authors: Ott Marie-Odile , Bober Eva , Lyons Gary , Arnold Hans , Buckingham Margaret
Published: April 2021

We have analysed by in situ hybridization the expression of myf-5, the murine homologue of the human myogenic regulatory sequence myf5, during embryogenesis in the mouse, myf-5 sequences were first detected in the earliest somites (from about 8 days p.c.) in the dermomyotome, before formation of the dermatome, myotome and sclerotome. The dermomyotome is classically considered to give rise to the precursor muscle cells of body and limb skeletal muscle. myf-5 -positive cells were also detected early in the visceral arches and limb buds. In this case, as in somites, myf-5 expression precedes that of the two related myogenic regulatory sequences, myogenin and MyoDl, and indeed any other skeletal muscle marker examined to date, myf-5 is not detected at any stage in developing cardiac muscle. From 11.5 days p.c., the level of myf-5 transcripts begins to decrease to become undetectable (by in situ hybridization) from 14 days p.c. Both the appearance and disappearance of myf-5 follow the anteroposterior gradient of somite formation and maturation in the embryo. The time and place of myf-5 expression are consistent with a role in the early events of myogenic differentiation, possibly during determination of the myogenic lineage.
Mis-regulating segmentation gene expression in Drosophila
Authors: Parkhurst Susan M. , Ish-Horowicz David
Published: April 2021

We have used the hunchback (hb) gap-gene promoter to drive ectopic expression of the pair-rule genes fushi tarazu (fiz), even-skipped (eve) and hairy (h). Unexpectedly, flies transformed with such constructs are viable, despite spatial and temporal mis-regulation of pair-rule expression caused by the fusion genes. We show that fusion gene expression is transcriptionally regulated, such that ectopic expression is suppressed when pattern is established, and present evidence indicating that interstripe hb – fiz expression is repressed by eve. These results are considered in terms of redundant control of pair-rule gene striping. We also discuss the potential dangers of using mis-regulated gene expression to analyse normal function.
Differentiating and mature neurons express the acidic fibroblast growth factor gene during chick neural development
Authors: Schnürch Harald , Risau Werner
Published: April 2021

We have previously isolated and characterized acidic fibroblast growth factor (aFGF) from the embryonic chick brain. To analyze the expression of the gene encoding this growth factor a cDNA clone was isolated. The predicted amino acid sequence was found to be highly conserved (90 %) between human and chick. Using single-stranded DNA probes, aFGF gene expression was detectable at day 3.5 in the embryonic chick brain. The mRNA level of the 1.7 kb transcript increased during embryonic development and reached the highest level in the adult brain. In situ hybridization results confirmed these developmental changes and revealed a localized expression in neurons. In the adult, Purkinje cells, deep cerebellar and brainstem neurons showed a high level of aFGF mRNA. In the embryonic brain, localized expression in neurons was detectable from day 6 onward. aFGF mRNA was also present in neurons of the peripheral nervous system. In dorsal root ganglia, aFGF was found to be expressed after embryonic day 6. Cells of blood vessels and the ependyma did not express detectable amounts of aFGF mRNA. These results suggest that aFGF may have a function as a differentiation or maintenance factor for postmitotic neurons or as a growth or differentiation factor for other cells in the nervous system mainly in later stages of development.
The transient expression of type II collagen at tissue interfaces during mammalian craniofacial development
Authors: Wood Andrew , Ashhurst Doreen E. , Corbett Andrew , Thorogood Peter
Published: April 2021

Using immunocytochemical techniques, the spatiotemporal distribution of the major collagen isoform of cartilage, type II collagen, has been investigated during early craniofacial development in the mouse embryo. Early and transient expression was associated with the otic and optic vesicles, the ventrolateral surfaces of the developing brain, olfactory conchi, endocardial and mesocardial tissues, the lateral and basal surfaces of the pharyngeal endoderm and beneath the ectoderm of the branchial arches. A number of these locations are sites of epithelial-mesenchymal tissue interaction believed to generate the component parts of the chondrocranium; here, type II collagen appears transiently in advance of overt chondrogenesis in the mesenchyme. At such sites, immunofluorescence is typically localised along the basal surface of the epithelial partner, with the strongest reaction detected between the basal aspects of the otic and rhombencephalic epithelia. Immunoelectron microscopy, using pre-embedding immunostaining and a protein G-gold technique, reveals that the type II collagen is adjacent to, but not integral with, the basal laminae. Gold particles are clearly associated with 10-15 nm fibrils of the extracellular matrix in the reticulate lamina region.

The pattern of type II collagen expression in the mouse closely correlates with that demonstrated previously in the quail, indicating a high degree of phylogenetic conservation between these two vertebrate species. These findings are consistent with the hypothesis that the pattern of epithelial secretion of type II collagen, or a coexpressed matrix molecule, constitutes a morphogenetic signal, realised as a matrix-mediated tissue interaction, and specifying the form of the vertebrate chondrocranium. Three-dimensional reconstruction of early type II collagen distribution, and of the subsequent chondrocranial cartilages, reveals that chondrocranial form can be derived from a ‘pre-pattern’ of epithelially derived type n collagen expressed at epithelial-mesenchymal tissue interfaces.
Genetic interactions among floral homeotic genes of Arabidopsis
Authors: Bowman John L. , Smyth David R. , Meyerowitz Elliot M.
Published: April 2021

We describe allelic series for three loci, mutations in which result in homeotic conversions in two adjacent whorls in the Arabidopsis thaliana flower. Both the structure of the mature flower and its development from the initial primordium are described by scanning electron microscopy. New mutations at the APETALA2 locus, ap2-2, ap2-8 and ap2-9, cause homeotic conversions in the outer two whorls: sepals to carpels (or leaves) and petals to stamens. Two new mutations of PISTILLATA, pi-2 and pi-3, cause second and third whorl organs to differentiate incorrectly. Homeotic conversions are petals to sepals and stamens to carpels, a pattern similar to that previously described for the apetala3-l mutation. The AGAMOUS mutations, ag-2 and ag-3, affect the third and fourth whorls and cause petals to develop instead of stamens and another flower to arise in place of the gynoecium. In addition to homeotic changes, mutations at the APETALA2, APETALAS and PISTILLATA loci may lead to reduced numbers of organs, or even their absence, in specific whorls. The bud and flower phenotypes of doubly and triply mutant strains, constructed with these and previously described alleles, are also described. Based on these results, a model is proposed that suggests that the products of these homeotic genes are each active in fields occupying two adjacent whorls, AP2 in the two outer whorls, PI and AP3 in whorls two and three, and AG in the two inner whorls. In combination, therefore, the gene products in these three concentric, overlapping fields specify the four types of organs in the wild-type flower. Further, the phenotypes of multiple mutant lines indicate that the wild-type products of the AGAMOUS and APETALA2 genes interact antagonistically. AP2 seems to keep the AG gene inactive in the two outer whorls while the converse is likely in the two inner whorls. This field model successfully predicts the phenotypes of all the singly, doubly and triply mutant flowers described.
A secreted 80 × 103M
r protein mediates sensing of cell density and the onset of development in Dictyostelium
Authors: Gomer Richard H. , Yuen Ita S. , Firtel Richard A.
Published: April 2021

In submerged monolayer culture, Dictyostelium cells can differentiate into prespore and prestalk cells at high cell densities in response to cAMP but not at low cell densities. However, cells at low densities will differentiate in medium taken from developing cells starved at a high density. The putative factor in the medium was designated CMF for conditioned medium factor (Mehdy and Firtel, Molec. cell. Biology 5, 705 – 713,1985). In this report, we size-fractionate conditioned medium and show that the activity that allows low density cells to differentiate can be separated into high and low Mr (relative molecular mass) fractions. Interestingly, the two fractions both have the same activity and do not need to be combined to allow differentiation. The large conditioned medium factor is a protein, as determined by trypsin sensitivity, that can be purified to a single 80 × 103Mr band on a silver-stained SDS-polyacrylamide gel, and has CMF activity at a concentration of ∼ 4pM (0.3 ng ml-1). Our results suggest that CMF is a secreted factor that functions in vivo as an indicator of cell density in starved cells. At high cell densities, the concentration of CMF is sufficient to enable cells to enter the multicellular stage of the developmental cycle. When present below a threshold concentration, cells do not initiate the expression of genes required for early development. This factor plays an essential role in the regulatory pathway necessary for cells to obtain the developmental competence to induce prestalk and prespore gene expression in response to cAMP.
The maternal gene nanos has a central role in posterior pattern formation of the Drosophila embryo
Authors: Lehmann Ruth , Nüsslein-Volhard Christiane
Published: April 2021

A group of maternal genes, the posterior group, is required for the development of the abdominal region in the Drosophila embryo. We have used genetic as well as cytoplasmic transfer experiments to order seven of the posterior group genes (nanos, pumilio, oskar, valois, vasa, staufen and tudor) into a functional pathway. An activity present in the posterior pole plasm of wild-type embryos can restore normal abdominal development in posterior group mutants. This activity is synthesized during oogenesis and the gene nanos most likely encodes this activity. The other posterior group genes have distinct accessory functions: pumilio acts downstream of nanos and is required for the distribution or stability of the nanos-dependent activity in the embryo. Staufen, oskar, vasa, valois and tudor act upstream of nanos. Embryos from females mutant for these genes lack the specialized posterior pole plasm and consequently fail to form germ-cell precursors. We suggest that the products of these genes provide the physical structure necessary for the localization of nanos-dependent activity and of germ line determinants.
Stereotyped pathway selection by growth cones of early epiphysial neurons in the embryonic zebrafish
Authors: Wilson Stephen W. , Easter Stephen S.
Published: April 2021

In this report we have examined the development of one of the earliest projections in the embryonic zebrafish brain, that from the epiphysis. Epiphysial axons and growth cones were labelled anterogradely in wholemounted brains, using either the carbocyanine dye, dil, or horseradish peroxidase (HRP). Some embryos were also either stained with anti-acetylated tubulin or HNK-1 antibodies to reveal other axons in the brain, or were secondarily sectioned for light and electron microscopy.

The epiphysial axons have a very specific projection pattern and virtually all axons grow precisely to their target regions without error. The first epiphysial growth cone extends ventrally from the epiphysis into the dorsoventral diencephalic tract at 19 –20 h post-fertilisation (h PF). Several hours later, it turns rostrally to grow alongside axons in the tract of the postoptic commissure. The morphology of the leading growth cone changes in predictable ways at different locations along its pathway and these changes correlate with differences in the local environment that it encounters. In contrast to other published descriptions of other developing systems, the epiphysial growth cone is no more complex either when pioneering a pathway, or when encountering divergent axonal pathways. Indeed, it is most complex (i.e. has the greatest number of processes) when it first starts to follow the tract of the postoptic commissure. The presence and selective retention of filopodia within other axonal pathways suggests that growth cones have access to these pathways but do not select them. These observations support the notion that local guidance cues exist within the early scaffold of brain tracts.

Subsequent epiphysial axons form a tight fascicle within the dorsoventral diencephalic tract, but abruptly defasciculate from each other upon turning rostrally into the tract of the postoptic commissure. Epiphysial growth cones that enter this tract at abnormal locations still turn in the appropriate direction. Therefore, guidance cues are not restricted solely to the normal intersections but may be distributed along the length of the tracts.

The epiphysial growth cones and axons have very characteristic spatial relations to other axons in the tracts of the developing brain. They are restricted to the dorsal region of the tract of the postoptic commissure and the rostral region of the postoptic commissure. At early developmental stages, the epiphysial axons are the only axons within the dorsoventral diencephalic tract and they are located very superficially within the neuroepithelium. At later stages, they are displaced to deeper regions of the neuropil by non-epiphysial axons.
Restrictin: a chick neural extracellular matrix protein involved in cell attachment co-purifies with the cell recognition molecule F11
Authors: G. Rathjen Fritz , Wolff Michael , Chiquet-Ehrismann Ruth
Published: April 2021

We report here the characterization of restrictin, a novel chick neural extracellular matrix glycoprotein associated with the cell recognition molecule F11. hnmunoaffinity chromatography using monoclonal antibody 23-13 directed to restrictin yield a maior relative .molecular mass band at 170×103 animmorWas al and 320 ×103 w“ich are immunologically related to each other. Neural cells attach on immobilized restrictin in a short-term adhesion assay. This adhesion can be blocked specifically by monoclonal or polyclonal antibodies to restrictin but not by antibodies to Fll or by the peptide GRGDSP. Antibodies to restrictin do not interfere with the fasciculation of retinal axons and the isolated restrictin does not stimulate the outgrowth of axons. In the developing nervous system, restrictin is localized in very restricted regions and is found within areas of Fll expression. The timing and pattern of expression of restrictin and its cell attachment activity suggest that it participates in developmental events of the nervous system.
The Drosophila extramacrochaetae protein antagonizes sequence-specific DNA binding by daughterless/achaete-scute protein complexes
Authors: Van Doren M. , Ellis H.M. , Posakony J.W.
Published: April 2021

In Drosophila, a group of regulatory proteins of the helix-loop-helix (HLH) class play an essential role in conferring upon cells in the developing adult epidermis the competence to give rise to sensory organs. Proteins encoded by the daughterless (da) gene and three genes of the achaete-scute complex (AS-C) act positively in the determination of the sensory organ precursor cell fate, while the extramacrochaetae (emc) and hairy (h) gene products act as negative regulators. In the region upstream of the achaete gene of the AS-C, we have identified three ‘E box’ consensus sequences that are bound specifically in vitro by hetero-oligomeric complexes consisting of the da protein and an AS-C protein. We have used this DNA-binding activity to investigate the biochemical basis of the negative regulatory function of emc. Under the conditions of our experiments, the emc protein, but not the h protein, is able to antagonize specifically the in vitro DNA-binding activity of da/AS-C and putative da/da protein complexes. We interpret these results as follows: the heterodimerization capacity of the emc protein (conferred by its HLH domain) allows it to act in vivo as a competitive inhibitor of the formation of functional DNA-binding protein complexes by the da and AS-C proteins, thereby reducing the effective level of their transcriptional regulatory activity within the cell.
Expression of the mouse anti-Müllerian hormone gene suggests a role in both male and female sexual differentiation
Authors: Münsterberg Andrea , Lovell-Badge Robin
Published: April 2021

We describe here the isolation of cDNA and genomic clones corresponding to the mouse gene encoding anti-Müllerian hormone, and the use of these clones as molecular probes to study AMH gene expression. We constructed a 14.5 days post coitum (dpc) mouse fetal testes library and isolated a cDNA clone using bovine, human and rat partial cDNAs as probes. This clone contained a 1 kb insert, which was confirmed by sequencing to be the mouse homologue of AMH. Probes derived from the mouse cDNA clone were used to screen genomic libraries and a 12 kb DNA fragment containing the complete coding region of mouse AMH was isolated. In situ hybridisation was used to determine the precise timing and localisation of AMH expression in male and female embryos and postnatal testes and ovaries. AMH transcripts were first detected in fetal testes at 12.5 Ape when differences between testes and ovaries first become visible. The signal was specific for the Sertoli cells of the testes. Other fetal tissues or female embryos were negative for AMH transcripts. During male development, AMH expression is shut off postnatally. In the female, the expression of AMH was first detected at day 6 after birth and is restricted to granulosa cells. We have correlated the pattern of AMH expression in both sexes with cellular events occurring in gonadal development and discuss some implications that this may have for its function and regulation.
Influence of paternally imprinted genes on development
Authors: Barton Sheila C. , Ferguson-Smith Anne C. , Fundele Reinald , Surani M. Azim
Published: April 2021

The parental origin of chromosomes is critical for normal development in the mouse because some genes are imprinted resulting in a predetermined preferential expression of one of the alleles. Duplication of the paternal (AG: androgenones) or maternal (GG/PG: gynogenones/parthenogenones) genomes will result in an excess or deficiency of gene dosage with corresponding phenotypic effects. Here, we report on the effects of paternally imprinted genes on development following introduction of the AG inner cell mass into normal blastocysts. There was a striking increase in embryonic growth by up to 50%, and a characteristic change in embryonic shape, partly because of the corresponding increase in length of the anterior –posterior axis. These changes, between el2 –el5, were proportional to the contribution from AG cells to the embryo. However, a contribution of AG cells in excess of 50 % was invariably lethal as development progressed to el5. A limited number of chimeras were capable of full-term development provided there was a relatively low contribution from AG cells. The distribution of AG cells in chimeras was not uniform, especially later in development when there was a disproportionate presence of AG cells in the mesodermally derived tissues. Their contribution was consistently greater in the heart and skeletal muscle, but was considerably lower in the brain. Chimeras detected after birth were either dead or developed severe abnormalities of the skeletal elements, particularly of the ribs which were enlarged, distorted and fused, with greatly increased cartilaginous material with an absence of normal ossification. These phenotypic effects in chimeras are reciprocal to those observed in the presence of GG/PG cells, which resulted in a substantial size reduction approaching 50%. Moreover, the GG/PG cells made a relatively substantial contribution to the brain but rarely contributed to skeletal muscle. These observations suggest that the imprinting of some parental alleles establishes a balance of gene dosage which is required for normal embryonic growth regulation and for the development of some lineages. When this balance is altered by duplication of the parental chromosomes, the cumulative effects of imprinted genes are reflected in the phenotypic traits described here. At least part of the phenotypic effects are likely to be due to the imprinting of genes involved in cell interactions as well as for the short-range autocrine/ paracrine factors.
Angiogenesis during human extraembryonic development involves the spatiotemporal control of PDGF ligand and receptor gene expression
Authors: Holmgren Lars , Glaser Anna , Pfeifer-Ohlsson Susan , Ohlsson Rolf
Published: April 2021

We have examined the role of platelet-derived growth factor (PDGF) ligand and receptor genes in the angiogenic process of the developing human placenta. In situ hybridization analysis of first trimester placentae showed that most microcapillary endothelial cells coexpress the PDGF-B and PDGF β-receptor genes. This observation indicates that PDGF-B may participate in placental angiogenesis by forming autostimulatory loops in capillary endothelial cells to promote cell proliferation. Endothelial cells of macro blood vessels maintained high PDGF-B expression, whereas PDGF β-receptor mRNA was not detectable. In contrast, PDGF β-receptor mRNA was readily detectable in fibroblastlike cells and smooth muscle cells in the surrounding intima of intermediate and macro blood vessels. Taken together, these data suggest that the PDGF-B signalling pathway appears to switch from an autocrine to a paracrine mechanism to stimulate growth of surrounding PDGF β-receptor-positive mesenchymal stromal cells.Smooth muscle cells of the blood vessel intima also expressed the PDGF-A gene, the protein product of which is presumably targeted to the fibroblast-like cells of the mesenchymal stroma as these cells were the only ones expressing the PDGF α-receptor. PDGF-A expression was also detected in columnar cytotrophoblasts where it may have a potential role in stimulating mesenchymal cell growth at the base of the growing placental villi. We discuss the possibility that the regulation of the PDGF-B and β-receptor gene expression might represent the potential targets for primary angiogenic factors.