bluuebunny/crossref_metadata_2025 huggingface dataset:
Pathfinding in the central nervous system and periphery by identified embryonic Drosophila motor axons
Authors: Sink Helen , Whitington Paul M.
Published: April 2021

We have studied the pattern of axon outgrowth from the identified embryonic Drosophila motorneurons, RP1, RP3, RP4 and RP5, from the onset of axonogenesis to the time of arborization over target muscles. Lucifer Yellow was intracellularly injected into each of these neurons to obtain a detailed description of the morphology of their growth cones and of the pathways that they follow. We have divided the sequence of axon growth from these neurons into five major phases. In the first phase, the growth cone of each RP axon grows medially along its contralateral homologue along the anterior commissure. Each RP axon follows a separate path across the midline in the anterior commissure. After crossing the ventral midline, the axons wrap around specific contralateral RP somata. In the second phase, each axon grows posteriorly and dorsally down the contralateral longitudinal connective, fasciculating with the other RP axons. In the third phase, the axons turn into the intersegmental nerve via the anterior nerve root, then cross over to the segmental nerve, before contacting the external surfaces of intermediate muscles 15/16. They do not fasciculate with the pioneering aCC and RP2 axons at this time. In the fourth phase, the axons advance laterally across the ventral muscle group. During this phase, each axon extends processes over a number of inappropriate muscles as well as contacting its correct, target muscle. In the final phase, the processes to inappropriate muscles are withdrawn, generating the mature pattern of motor axon projections. There is no consistent, clear difference between the RP motorneurons in the relative timing of axon outgrowth.
Normal segmentation and size of the primary sympathetic ganglia depend upon the alternation of rostrocaudal properties of the somites
Authors: Goldstein Ronald S. , Kalcheim Chaya
Published: April 2021

Metameric organization of the dorsal root ganglia (DRG) and ventral roots depends on the alternation of rostrocaudal properties within the somites. In addition, the size of DRG is likely to be regulated by the adjacent mesoderm, because unilateral creation of a paraxial mesoderm with only rostral somitic (RS) halves, leads to the development of non-segmented DRG that are larger and contain more cells than the sum of the contralateral, control DRG. We have now extended our studies of the role of the paraxial mesoderm in the morphogenesis of the peripheral nervous system (PNS) to another metameric PNS component, the sympathetic ganglia (SG). The development of the primary sympathetic chain was studied in chick-quail chimeras with multiple half-somite grafts using quantitative morphometric analysis. In the presence of an exclusively rostral or caudal somitic mesoderm, segmentation of the initially homogeneous primary sympathetic chain into ganglia is prevented. Therefore, the SG, like the DRG and ventral roots, require the normal rostrocaudal alternation of the somitic mesoderm for segmental morphogenesis.

On embryonic day 4 (E4), there is a 38% average decrease in the volume of the primary sympathetic chain opposite a RS mesoderm, compared with the primary chain on the unoperated side. This is in contrast to the average increase of 27% in the volume of the DRG opposite the grafted mesoderm in the same embryos. Our results, and classical observations, have led us to propose a model in which the mesoderm controls DRG and SG size by modulating the partition of migrating NC precursors between the anlage of these two ganglion types. According to this model, the reduction in SG volume and concomitant increase in DRG volume observed opposite RS grafts, results from the arrest in the DRG anlage of neural crest cells that normally migrate to the SG.
Analysis of high PSA N-CAM expression during mammalian spinal cord and peripheral nervous system development
Authors: Boisseau Sylvie , Nedelec Joël , Poirier Véronique , Rougon Geneviève , Simonneau Michel
Published: April 2021

Using a monoclonal antibody that recognizes specifically a high polysialylated form of N-CAM (high PSA N-CAM), the temporal and spatial expression of this molecule was studied in developing spinal cord and neural crest derivatives of mouse truncal region. Temporal expression was analyzed on immunoblots of spinal cord and dorsal root ganglia (DRGs) extracts microdissected at different developmental stages. Analysis of the ratio of high PSA N-CAM to total N-CAM indicated that sialylation and desialylation are independently regulated from the expression of polypeptide chains of N-CAM. Motoneurons, dorsal root ganglia cells and commissural neurons present a homogeneous distribution of high PSA N-CAMs on both their cell bodies and their neurites. Sialylation of N-CAM can occur in neurons after their aggregation in peripheral ganglia as demonstrated for dorsal root ganglia at E12. Furthermore, peripheral ganglia express different levels of high PSA N-CAM. With in vitro models using mouse neural crest cells, we found that expression of high PSA N-CAM was restricted to cells presenting an early neuronal phenotype, suggesting a common regulation for the expression of high PSA N-CAM molecules, neurofilament proteins and sodium channels. Using perturbation experiments with endoneuraminidase, we confirmed that high PSA N-CAM molecules are involved in fasciculation and neuritic growth when neurons derived from neural crest grow on collagen substrata. However, we demonstrated that these two parameters do not appear to depend on high PSA N-CAM molecules when cells were grown on a fibronectin substratum, indicating the existence of a hierarchy among adhesion molecules.
cactus, a maternal gene required for proper formation of the dorsoventral morphogen gradient in Drosophila embryos
Authors: Roth Siegfried , Hiromi Yasushi , Godt Dorothea , Nüsslein-Volhard Christiane
Published: April 2021

The dorsoventral pattern of the Drosophila embryo is mediated by a gradient of nuclear localization of the dorsal protein which acts as a morphogen. Establishment of the nuclear concentration gradient of dorsal protein requires the activities of the 10 maternal ‘dorsal group’ genes whose function results in the positive regulation of the nuclear uptake of the dorsal protein. Here we show that in contrast to the dorsal group genes, the maternal gene cactus acts as a negative regulator of the nuclear localization of the dorsal protein.

While loss of function mutations of any of the dorsal group genes lead to dorsalized embryos, loss of cactus function results in a ventralization of the body pattern. Progressive loss of maternal cactus activity causes progressive loss of dorsal pattern elements accompanied by the expansion of ventrolateral and ventral anlagen. However, embryos still retain dorsoventral polarity, even if derived from germline clones using the strongest available, zygotic lethal cactus alleles. In contrast to the loss-of-function alleles, gain-of-function alleles of cactus cause a dorsalization of the embryonic pattern. Genetic studies indicate that they are not overproducers of normal activity, but rather synthesize products with altered function. Epistatic relationships of cactus with dorsal group genes were investigated by double mutant analysis. The dorsalized phenotype of the dorsal mutation is unchanged upon loss of cactus activity. This result implies that cactus acts via dorsal and has no independent morphogen function. In all other dorsal group mutant backgrounds, reduction of cactus function leads to embryos that express ventrolateral pattern elements and have increased nuclear uptake of the dorsal protein at all positions along the dorsoventral axis. Thus, the cactus gene product can prevent nuclear transport of dorsal protein in the absence of function of the dorsal group genes. Genetic and cytoplasmic transplantation studies suggest that the cactus product is evenly distributed along the dorsoventral axis. Thus the inhibitory function that cactus product exerts on the nuclear transport of the dorsal protein appears to be antagonized on the ventral side. We discuss models of how the action of the dorsal group genes might counteract the cactus function ventrally.
Induction of brain and sensory pigment cells in the ascidian embryo analyzed by experiments with isolated blastomeres
Authors: Nishida Hiroki
Published: April 2021

Tadpole larvae of ascidians have a brain and two kinds of sensory pigment cells within the brain. These neural tissues are formed through folding of the neural plate and, as in vertebrates, neural induction is involved in the formation of the nervous system. The brain and pigment cells are derived from anterior-animal (a-line) blastomeres, and inductive interaction with anterior-vegetal (A-line) blastomeres is necessary for formation of neural tissues from the a-line cells. In order to investigate the characteristics of this process in detail, blastomeres were isolated from embryos of Halocynthia roretzi at the 110cell (late blastula) stage, and then their developmental capacity was examined. In the first set of experiments, brain- and pigment-lineage cells, isolated prior to neural induction, failed to develop three specific features of epidermis (epithelial morphology, secretion of larval tunic and expression of epidermis-specific antigen). These observations suggested a process different from amphibian neural induction, indicative perhaps of a permissive type of induction in ascidian embryogenesis.

Next, in order to identify which type of tissueprecursor cell is the inducer of the sensory pigment cells, various sets of blastomeres were isolated from 110-cell embryos, in which the fates of most of the blastomeres are restricted to a single type of tissue. The results suggested that spinal-cord precursor blastomeres, which are cells of the A-line, are sufficient to induce the a-line cells to form pigment cells. In addition, embryos from which all spinal cord precursors had been ablated, failed to form sensory pigment cells as well as a brain structure. Therefore, it is probable that the inducers of the ascidian sensory pigment cells are the spinal-cord precursor cells.
Hyaluronan as a propellant for epithelial movement: the development of semicircular canals in the inner ear ofXenopus
Authors: Haddon Catherine M. , Lewis Julian H.
Published: April 2021

The membranous labyrinth of the inner ear, with its three semicircular canals, originates from a simple spheroidal otic vesicle. The process is easily observed in Xenopus. The vesicle develops three dorsal outpocketings; from the two opposite faces of each outpocketing pillars of tissue are protruded into the lumen; and these paired ‘axial protrusions’ eventually meet and fuse, to form a column of tissue spanning the lumen of the outpocketing like the hub of a wheel, with a tube of epithelium forming the semicircular canal around the periphery. Each axial protrusion consists of epithelium encasing a core of largely cell-free extracellular matrix that stains strongly with alcian blue. In sections, at least 60 % of the stainable material is removed by treatment with Streptomyces hyaluronidase. When Streptomyces hyaluronidase is microinjected into the core of a protrusion in vivo, the protrusion collapses and the corresponding semicircular canal fails to form. Hyaluronan (hyaluronic acid) in the core of the protrusion therefore seems to be essential in driving the extension of the protrusion. Autoradiography with tritiated glucosamine indicates that the hyaluronan-rich matrix is synthesised by the epithelium covering the tip of the protrusion; the basal lamina here appears to be discontinuous. These findings indicate that the epithelium of the axial protrusion propels itself into the lumen of the otocyst by localised synthesis of hyaluronan. Hyaluronan may be used in a similar way in the development of other organs, such as the heart and the secondary palate.
Diversity of expression of engrailed-like antigens in zebrafish
Authors: Hatta Kohei , Bremiller Ruth , Westerfield Monte , Kimmel Charles B.
Published: April 2021

We have studied developmental expression of zebrafish engrailed-like (Eng) antigens. Many cell types are reproducibly labeled by two antibodies that recognize the Eng homeodomain, but other cells are labeled by only one or the other, suggesting a hitherto unrecognized complexity of Eng proteins. Expression patterns vary remarkably according to cell type and location. In the undifferentiated primordia of the brain and of each myotome, expression by a stripe of cells spatially subdivides the primordium at a location where a morphological boundary forms later, suggesting expression may be required for development of the boundaries. Supporting this hypothesis, trunk myotomal cells that express Eng are absent in spt-1 mutant embryos, just where the myotomal boundaries fail to form. Another pattern is present in rhombomeres, pharyngeal arches, and the pectoral girdle. In each of these cases, cells (neuron, muscle, cartilage) generating a subset of a series of repeated elements selectively express Eng. These subsets then form specialized derivatives, suggesting Eng homeoproteins are involved in determining the specializations. Epidermal expression is present in the ventral half of the pectoral fin rudiment, precisely ‘compartmentalizing’ the fin. Neuronal cells at a certain dorsoventral level in each hindbrain and spinal cord segment selectively express Eng, suggesting segmental control of neuronal identity. Specific expression patterns are observed in taste buds, otic vesicles and teeth. Thus we propose that eng genes function in diverse cell types in zebrafish, but play selector roles that can be classified into a few basic types.
F-actin localization during trochoblast differentiation in Patella vulgata embryos
Authors: Serras Florenci , Speksnijder Johanna E.
Published: April 2021

We have studied the development of the ciliated, locomotory organ of Patella vulgata trochophore larvae. This organ, the prototroch, arises from different clones of trochoblasts. In each of these trochoblasts, a band of filamentous (F-) actin is formed at the time that ciliogenesis starts. This band, which we visualized with TRITC-phalloidin, is positioned at the base of the row of cilia that crosses each trochoblast. Isolated trochoblasts, as well as isolated quartets of animal micromeres (from which the trochoblasts are derived), similarly form rows of cilia and F-actin bands at the proper time in development. In whole embryos, the trochoblasts shift their position following ciliogenesis, and finally form a ring of differentiated prototroch cells with a continuous band of F-actin encircling the entire larva. At the dorsal side, a double row of prototroch cells and thus a double band of F-actin is present. In contrast, multiple regions with a double F-actin band are found in trochophores in which the establishment of a dorsoventral axis is inhibited experimentally. Confocal laser scanning microscopy shows that the F-actin band extends from the apical surface deep into the cytoplasm of the prototroch cells. At the ultrastructural level, a single striated rootlet connected to the basal body of each cilium can be seen to extend deep into the cytoplasm toward the nucleus, and a band of actin-like filaments is found to interconnect neighboring basal apparatus. Treatment of trochophores with cytochalasin B disrupts the organization of the F-actin band as visualized with TRITC-phalloidin, affects the angle of the effective stroke of ciliary beat and reduces their swimming capacity. This suggests that the F-actin band is essential for the normal locomotory behavior of the Patella trochophore larva.
The development of the sensory neuron pattern in the antennal disc of wild-type and mutant (lz
3, ss
a
) Drosophila melanogaster
Authors: Lienhard M. C. , Stocker R. F.
Published: April 2021

The development of the sensory neuron pattern in the antennal disc of Drosophila melanogaster was studied with a neuron-specific monoclonal antibody (22C10). In the wild type, the earliest neurons become visible 3h after pupariation, much later than in other imaginai discs. They lie in the center of the disc and correspond to the neurons of the adult aristal sensillum. Their axons join the larval antennal nerve and seem to establish the first connection towards the brain. Later on, three clusters of neurons appear in the periphery of the disc. Two of them most likely give rise to the Johnston’s organ in the second antennal segment. Neurons of the olfactory third antennal segment are formed only after eversion of the antennal disc (clusters tl-t3). The adult pattern of antennal neurons is established at about 27 % of metamorphosis.

In the mutant lozenge3(Iz3), which lacks basiconic antennal sensilla, cluster t3 fails to develop. This indicates that, in the wild type, a homogeneous group of basiconic sensilla is formed by cluster t3. The possible role of the lozenge gene in sensillar determination is discussed.

The homoeotic mutant spineless-aristapedia (ssa) transforms the arista into a leg-like tarsus. Unlike leg discs, neurons are missing in the larval antennal disc of ssa. However, the first neurons differentiate earlier than in normal antennal discs. Despite these changes, the pattern of afferents in the ectopic tarsus appears leg specific, whereas in the non-transformed antennal segments a normal antennal pattern is formed. This suggests that neither larval leg neurons nor early aristal neurons are essential for the outgrowth of subsequent afferents.
Phosphorylation, expression and function of the Ultrabithorax protein family in Drosophila melanogaster
Authors: Gavis Elizabeth R. , Hogness David S.
Published: April 2021

Alternative splicing of the Ultrabithorax homeotic gene transcript generates a family of five proteins (UBX isoforms) that function as transcription factors. All isoforms contain a homeodomain within a common 99 aa C-terminal region (C-constant region) which is joined to a common 247 aa N-terminal (N-constant) region by different combinations of three small optional elements. Unlike the UBX proteins expressed in E. coli, UBX isoforms expressed in D. melanogaster cells are phosphorylated on serine and threonine residues, located primarily within a 53 aa region near the middle of the N-constant region, to form at least five phosphorylated states per isoform. Similar, if not identical states can be generated in vitro from purified E. coli UBX protein by a kinase activity in nuclear extracts from D. melanogaster cells. Temporal developmental profiles of UBX isoforms parallel those for the respective mRNAs, and all isoforms are similarly phosphorylated throughout embryogenesis. Analysis by cotransfection assays of the promoter activation and repression functions of mutant UBX proteins with various deletions in the N-constant region shows that repression is generally insensitive to deletion and, hence, presumably to phosphorylation. By contrast, the activation function is differentially sensitive to the different deletions in a manner indicating the absence of a discrete activating domain and instead, the presence of multiple activating sequences spread throughout the region.
Roles of wingless in patterning the larval epidermis of Drosophila
Authors: Bejsovec Amy , Arias Alfonso Martinez
Published: April 2021

The larval epidermis of Drosophila shows a stereotyped segmentally repeating pattern of cuticular structures. Mutants deficient for the wingless gene product show highly disrupted patterning of the larval cuticle. We have manipulated expression of the wg gene product to assess its role in this patterning process. We present evidence for four distinct phases of wg function in epidermal cells: (1) an early requirement in engrailed- expressing cells to establish and maintain stable expression of en, (2) a discrete period when wg and en gene products act in concert to generate positional values in the anterior portion of the ventral segment and all values of the dorsal and lateral epidermis, (3) a progressive function (dependent on prior interaction with the en- expressing cells) in conferring positional values to cells within the posterior portion of the segment, and (4) a late continuous requirement for maintaining some ventral positional values.
The nuclear-cytoplasmic distribution of the Xenopus nuclear factor, xnf7, coincides with its state of phosphorylation during early development
Authors: Miller Mill , Reddy Bramham A. , Kloc Malgorzata , Li Xiao Xia , Dreyer Christine , Etkin Laurence D.
Published: April 2021

We describe the characterization in Xenopus laevis of a nuclear protein, xnf7, which is first detected in the oocyte GV and is eventually enriched in nuclei of cells of the adult brain. Previous studies have shown that this protein contains zinc-finger-like structures and acidic domains typical of transcriptional activators, and is phosphorylated in vitro by p34cdc2 protein kinase. The protein also binds to double-stranded DNA. These data suggest that xnf7 may function as a transcription factor. During oocyte maturation, xnf7 is released into the cytoplasm and is not detectable in nuclei until the mid-blastula-gastrula stage of development. Western blot analysis of xnf7 isolated from oocytes and eggs showed the existence of multiple bands or isoforms of the protein. Unique isoforms that are generated during oocyte maturation are the result of phosphorylation. The phosphorylated isoforms remain in the cytoplasm until the mid-blastula stage. The re-accumulation of protein in the embryonic nuclei at this time correlates with the increase in abundance of the less phosphorylated isoforms. The xnf7 protein possesses a nuclear localization signal (NLS) similar to the bipartite signal found in nucleoplasmin. Newly synthesized xnf7 accumulated in the oocyte GV to detectable levels within a few hours following synthesis suggesting that retention of the protein in the cytoplasm during early cleavage may be due to a process that interferes with the function of the NLS. These data suggest that compartmentalization and/or post-translational modification of the nuclear protein xnf7 may be involved in regulating its function during early development.
Basic fibroblast growth factor induces retinal pigment epithelium to generate neural retina in vitro
Authors: Pittack C. , Jones M. , Reh T. A.
Published: April 2021

During embryogenesis, the cells of the eye primordium are initially capable of giving rise to either neural retina or pigmented epithelium (PE), but become restricted to one of these potential cell fates. However, following surgical removal of the retina in embryonic chicks and larval amphibians, new neural retina is generated by the transdifferentiation, or phenotypic switching, of PE cells into neuronal progenitors. A recent study has shown that basic fibroblast growth factor (bFGF) stimulates this process in chicks in vivo. To characterize further the mechanisms by which this factor regulates the phenotype of retinal tissues, we added bFGF to enzymatically dissociated chick embryo PE. We found that bFGF stimulated proliferation and caused several morphological changes in the PE, including the loss of pigmentation; however, no transdifferentiation to neuronal phenotypes was observed. By contrast, when small sheets of PE were cultured as aggregates on a shaker device, preventing flattening and spreading on the substratum, we found that a large number of retinal progenitor cells were generated from the PE treated with bFGF. These results indicate that bFGF promotes retinal regeneration in vitro, as well as in ovo, and suggest that the ability of chick PE to undergo transdifferentiation to neuronal progenitors appears to be dependent on the physical configuration of the cells.
FGFR-4, a new member of the fibroblast growth factor receptor family, expressed in the definitive endoderm and skeletal muscle lineages of the mouse
Authors: Stark Kevin L. , McMahon Jill A. , McMahon Rew P.
Published: April 2021

We have used the polymerase chain reaction to clone from fetal cerebellar RNA a novel member of the fibroblast growth factor receptor family, FGFR-4. cDNAs encoding a full-length receptor were isolated and RNA expression examined in adult and fetal tissues by RNA blot analysis. Transcripts were detected in adult lung, liver and kidney and in fetal RNAs from 11.5 to 16.5 days post coitum (p.c.). In situ hybridization was performed to examine developmental expression. FGFR-4 RNA was expressed in definitive endoderm of the developing gut and extraembryonic endoderm of the yolk-sac from 8.5 to 14.5 days p.c. At early somite stages, FGFR-4 was also expressed in the myotomal component of the somite, and by 14.5 days p.c. in the myotomally derived skeletal muscle. No expression was seen at any stage in cardiac muscle. Several endodermal derivatives, the liver, lung and pancreas, expressed FGFR-4 at 14.5 days p.c. In addition, FGFR-4 RNA was detected in the adrenal cortex, collecting tubules of the kidney and condensing cartilage at this time. These results suggest that FGFR-4 is likely to have diverse roles in development, which may include regulation of definitive endoderm and skeletal muscle lineages.
Expression of the cut locus in the Drosophila wing margin is required for cell type specification and is regulated by a distant enhancer
Authors: Jack Joseph , Dorsett Dale , Delotto Yvonne , Liu Su
Published: April 2021

The cut locus is a complex gene whose function is necessary for specification of a number of cell types, including the external sensory organs. The cut wing class of mutations of the cut locus are homozygous viable and lack tissue from the wing margin, which is normally composed of external sensory organs and noninnervated bristles. Expression of cut was examined in the developing wings of wild-type and mutant pupae using an antiserum against Cut protein. Cut is expressed in all of the external sensory organs of the wing and the noninnervated bristles of the posterior margin. The cut wing class of mutations prevents Cut expression specifically in the wing margin mechanoreceptors and noninnervated bristles, apparently preventing neural differentiation. The transformed cells die soon after differentiation would have occurred. We identify an enhancer, located about 80 kb upstream of the cut gene promoter, that confers expression in the cells of the mechanoreceptors and noninnervated bristles from a heterologous promoter. The 27 gypsy retrotransposon insertions that prevent expression in these margin cells, all occur between this enhancer and the promoter. These, gypsy insertions probably interfere with the interaction between the enhancer and the cut gene promoter.
Human acrosome biogenesis: immunodetection of proacrosin in primary spermatocytes and of its partitioning pattern during meiosis
Authors: Escalier Denise , Gallo Jean-Marc , Albert Martine , Meduri Geri , Bermudez Diego , David Georges , Schrevel Joseph
Published: April 2021

Proacrosin biosynthesis timing during human spermatogenesis has been studied using the monoclonal antibody 41)4 (mAb 4D4). Frozen and paraffin-embedded sections of testicular biopsies were labelled by standard indirect immunofluorescence and avidin-biotin immunoperoxidase procedures. The labelling specificity was checked by immunochemistry assays on unrelated tissues and by western blotting of testis extracts showing that only the 50–55×103 Mr proacrosin was recognized by mAb 4D4. Proacrosin was first observed in the Golgi region of midpachytene primary spermatocytes. In late pachytene primary spermatocytes, proacrosin was observed in two regions located at opposite nuclear poles. During the subsequent steps of the first meiotic division, the two bodies containing proacrosin were located: (i) on opposite sides of the equatorial plate during metaphase; along the microtubular spindle during anaphase; and close to each chromosomal aggregate during telophase. Two bodies containing proacrosin were still observed in interphasic secondary spermatocytes. The single labelled area observed in early spermatids was found to increase considerably in size during spermiogenesis. Anomalies of proacrosin scattering were observed in patients with Golgi complex partitioning failure. These data’ reveal proacrosin biosynthesis during diploid and haploid phases of human spermatogenesis and the proacrosin partitioning pattern during meiosis.
Embryogenesis of the murine endocrine pancreas; early expression of pancreatic polypeptide gene
Authors: Herrera Pedro-Luis , Huarte Joaquin , Sanvito Francesca , Meda Paolo , Orci Lelio , Vassalli Jean-Dominique
Published: April 2021

By immunofluorescence on cytospin preparations and on semithin sections of mouse pancreatic buds, we have found glucagon and pancreatic polypeptide (PP)-containing cells at embryonal day 10.5 (E 10.5) in dorsal buds and at E 11.5 in ventral buds. Insulin-containing cells appear in dorsal buds at E 11.5, and one to two days later in ventral buds. Somatostatin-containing cells are detectable from E 13.5 in both dorsal and ventral buds. A quantitative analysis shows that up to E 15.5, PP-containing cells are relatively abundant in both buds. By PCR amplification of oligo(dT)-primed cDNAs prepared from total pancreatic RNA, we also detect PP mRNA from E 10.5 onwards, thus confirming the early expression of the PP gene in the developing mouse pancreas.

Analysis of endocrine cells in situ suggests three major patterns of cell distribution in embryonic pancreas. First, individual hormone-containing cells are located within the epithelium of pancreatic ducts. In both dorsal and ventral buds, the majority of these endocrine cells contain PP, but many also contain glucagon, insulin or somatostatin. Secondly, clusters of endocrine cells are found in the pancreatic interstitium. Many of these cells contain both glucagon and PP which, by inununogold labelling of consecutive thin sections, can be shown to co-exist within individual secretory granules. Finally, starting on E 18.5, typical islets are formed with centrally located B cells and with the adult ‘one cell – one hormone’ phenotype. These results suggest an intriguing ontogénie relationship between A- and PP-cells, and also indicate that PP-containing cells may occupy a hitherto unexpected place in the lineage of endocrine islet cells.
Dosage dependence of maternal contribution to somatic cell division in Drosophila melanogaster
Authors: Carmena Mar , Gonzalez Cayetano , Casalf Jose , Ripoll Pedro
Published: April 2021

Most mitotic mutants in Drosophila do not lead to lethality in early development despite the highly abnormal chromosome behaviour that they elicit. This has been explained as being the effect of maternally provided wild-type products. We have tested this hypothesis by studying cuticular clones derived from cells in which there has been loss of a marked Y chromosome due to chromosome nondisjunction in individuals homozygous for the mutation abnormal spindle who are progeny of heterozygous mothers. We have found that the size and frequency of these clones are higher than in control flies. Furthermore, by analysing flies whose female parents have different doses of the asp+ gene, we have found that there is a correlation between the amount of maternally contributed asp+ product and the frequency and size of cuticular clones. We have also estimated the time in development when the first mitotic mistakes take place, i.e. the time when maternal products are no longer sufficient to carry out normal cell division.
Cell lineage analysis of the gynoecium of maize using the transposable element Ac
Authors: Dellaporta Stephen L. , Moreno Maria A. , Delong Alison
Published: April 2021

The maize gynoecium develops from a primordium comprising two distinct cell lineages: an epidermal LI and a subepidermal LII lineage. We have analyzed somatic gynoecial sectors marked with red flavonoid pigments by excision of Ac from the P locus. Somatic sector analysis indicates the epidermal lineage starts as a single cell layer at the base of the ovary and thickens into several cell layers, presumably by periclinal divisions, near the silk attachment point. The silk attachment point appears to be mainly an epidermal outgrowth of two of three fused carpels and presumably the silk contains only LI, or mostly LI, with only traces of subepidermal LII cells. The third carpel, covering the germinal face of the kernel, retains a multicellular LII and unicellular LI organization but fails to contribute substantially to stylar outgrowth. Ac transpositions in subepidermal somatic sectors are transmitted to the archesporial cell lineage. Ac transpositions that occur in epidermal sectors are not transmitted to offspring. These results demonstrate that the female megasporocyte is derived from subepidermal (LII) cells.
Homeotic genes controlling flower development in Antirrhinum
Authors: Coen Enrico S. , Doyle Sandra , Romero JOse M. , Elliott Robert , Magrath Ruth , Carpenter Rosemary
Published: April 2021

In order to study genes controlling flower development, we have carried out an extensive transposon-mutagenesis experiment in Antirrhinum majus. More than 15 independent homeotic mutations were obtained, allowing three categories of genes to be defined. The first includes floricaula (flo), a primary gene required for the initiation of the floral developmental pathway. In the absence of the wild-type flo product, proliferating inflorescence meristems arise in place of flowers. The flo gene has been isolated and shown to be expressed transiently in a subset of organ primordia in the floral meristem. The second category includes genes that affect the identity, and also sometimes the number, of whorls of organs in the flower. These genes act in overlapping domains so that each whorl has a distinct combination of gene functions, suggesting a model for the genetic control of whorl identity and number. Genes of the third category control differences between organs in the same whorl and hence the overall symmetry of the flower. We discuss how the basic plan of the flower and inflorescence may arise through the interactions between the three categories of genes.
Properties of deficiens, a homeotic gene involved in the control of flower morphogenesis in Antirrhinum majus
Authors: Sommer Hans , Nacken Wolfgang , Beltran Pio , Huijser Peter , Pape Heike , Hansen Rolf , Flor Peter , Saedler Heinz , Schwarz-Sommer Zsuzsanna
Published: April 2021

deficiens, together with other homeotic genes, is involved in the genetic control of floral morphogenesis in A. majus. Mutations in this gene cause homeotic transformations of petals to sepals and stamens to carpels, thus producing male sterile flowers.

The deduced DEF A protein shows homology to the DNA-binding domain of the transcription factors SRF of mammals (activating c-fos) and MCM1 of yeast (regulating mating type), suggesting that DEF A has a possible regulatory function as a transcription factor. Interestingly, DEF A belongs to a family of putative transcription factors, called the MADS box genes, whose DNA-binding domains show conserved homology.

Two members of this family correlate with known morphogenetic mutants of Antirrhinum.

DEF A is constantly expressed during flower development in all floral organs; it is strongly expressed in petals and stamens, but only at a low basal level in the other organs. Molecular, genetic and morphological observations with deficiens morphoalleles indicate that transcriptional and post-transcriptional control of deficiens specifies and diversifies its function in space and time.
Genetic analysis of pattern formation in the Arabidopsis embryo
Authors: Jürgens Gerd , Mayer Ulrike , Ruiz Ramon A. Torres , Berleth Thomas , Miséra Simon
Published: April 2021

Virtually nothing is known about the mechanisms that generate the basic body pattern in plant embryogenesis. As a first step towards the analysis of pattern formation, we have isolated and begun to characterise putative pattern mutants in the flowering plant, Arabidopsis thaliana. A large-scale screen for morphologically abnormal seedling mutants yielded about 250 lines for further study, and genetic evidence suggests saturation of the genome for this kind of mutation. The phenotypes of putative pattern mutants fall into distinct categories, classes and groups, which may reflect specific aspects of embryonic pattern formation. Mutant seedling phenotypes result from abnormal development in the early embryo. The implications of our findings are discussed with regard to the prospects for a mechanistic understanding of pattern formation in the plant embryo.
Gene activation in the amphibian mesoderm
Authors: Hopwood N. D. , Gurdon J. B.
Published: April 2021

Cell potency is progressively restricted in amphibian development by a series of cellular interactions called inductions. The mesoderm is believed to develop in response to the earliest known induction, in which vegetal cells of the blastula divert overlying animal hemisphere cells away from epidermal and towards mesodermal fates. We describe two early markers of mesodermal differentiation in Xenopus laevis, both mRNAs that encode DNA-binding proteins of the helixloop-helix family. One is a frog homologue of MyoD, a gene that in transfection experiments can convert cultured fibroblasts into myoblasts. Xenopus MyoD (XMyoD) is expressed in the early myotomes, from which the axial musculature develops. The accumulation of XMyoD RNA precedes that of transcripts from the cardiac actin gene, until now the earliest known marker of the muscle lineage, this result indicating that XMyoD could play a role in initiating muscle differentiation in normal development. We show by microinjection of synthetic RNA that XMyoD can indeed activate musclespecific gene expression in animal cap cells, which would normally form only ectoderm. However, the XMyoD-injected animal caps did not produce differentiated muscle, suggesting that additional specific factors are required for full myogenesis. The other mRNA is a relative of the twist gene of Drosophila, which is required for mesodermal differentiation in flies. This gene (Xtwi) is expressed widely in the early frog mesoderm, but not, however, in the myotomes, where XMyoD is expressed. Later, the Xtwi gene is activated, in response to a second induction, in the developing neural crest.
Isolation of temperature-sensitive diphtheria toxins in yeast and their effects on Drosophila cells
Authors: Bellen Hugo J. , D’Evelyn Diana , Harvey Michele , Elledge Stephen J.
Published: April 2021

We have isolated temperature-sensitive diphtheria toxins (DT-At5) to develop a method that allows temporal impedement of cellular functions. Four DT-Ats genes were isolated in a mutagenesis screen using the yeast, Saccharomyces cerevisiae. When expressed in yeast, these DT-Ats arrest growth at 18°C but not at 30°C. Three DT-At5 were subsequently tested in the R1-R6 photoreceptor cells of transgenic fruit flies, Drosophila melanogaster. The toxins show similar temperature dependence in both organisms, suggesting that they may be useful in a wide range of non-homeothermic species. DNA sequence analysis revealed that three of the four DT-At5 mutations are novel. Interestingly, the fourth DT-Ats carries the same point mutation as the extensively characterized CRM197, an ADP ribosyltransferase-defective form of diphtheria toxin.
Synthesis and phosphorylation of uvomorulin during mouse early development
Authors: Sefton Mark , Johnson Martin H. , Clayton Lesley
Published: April 2021

The cell adhesion molecule, uvomorulin, is synthesised in both the 135×103Mr precursor and 120×103Mr mature forms on maternal mRNA templates in unfertilized and newly fertilized mouse oocytes. Synthesis on maternal message ceases during the 2-cell stage to resume later on mRNA encoded presumptively by the embryonic genome. Uvomorulin is detectable by immunoblotting at all stages upto the blastocyst stage, but shows variations in its total amount and processing with embryonic stage. Whilst only trace levels of phosphorylated uvomorulin are detectable in early and late 4-cell embryos, uvomorulin in 8-cell embryos is phosphorylated.
Development of surface pattern during division in Paramecium II. Defective spatial control in the mutant kin241
Authors: Jerka-Dziadosz Maria , Loubresse Nicole Garreau De , Beisson Janine
Published: April 2021

kin241 is a monogenic nuclear recessive mutation producing highly pleiotropic effects on cell size and shape, generation time, thermosensitivity, nuclear reorganization and cortical organization. We have analyzed the nature of the cortical disorders and their development during division, using various specific antibodies labelling either one of the cortical cytoskeleton components, as was previously done for analysis of cortical pattern formation in the wild type.

Several abnormalities in basal body properties were consistently observed, although with a variable frequency: extra microtubules in either the triplets or in the lumen; nucleation of a second kinetodesmal fiber; abnormal orientation of the newly formed basal body with respect to the mother one. The latter effect seems to account for the major observed cortical disorders (reversal, intercalation of supplementary ciliary rows). The second major effect of the mutation concerns the spatiotemporal map of cortical reorganization during division. Excess basal body proliferation occurs and is correlated with modified boundaries of some of the cortical domains identified in the wild type on the basis of their basal body duplication pattern.

This is the first mutant described in a ciliate in which both the structure and duplication of basal bodies and the body plan are affected. The data support the conclusion that the mutation does not alter the nature of the morphogenetic signal(s) which pervade the dividing cell, nor the competence of cytoskeletal structures to respond to signalling, but affects the local interpretation of the signals.
Gonad formation and development requires theabd-Adomain of the bithorax complex inDrosophila melanogaster
Authors: Cumberledge Susan , Szabad Janos , Sakonju Shigeru
Published: April 2021

The abdominal-A (abd-A) gene, a member of the bithorax complex, is required for the correct identity of parasegments (PS) 7 through 13. Mutations in iab-4, one of the crs-regulatory regions of abd-A, transform epidermal structures of PS 9 and also cause loss of gonads in adult flies. Here, we describe a developmental and molecular analysis of the role of iab-4 functions in gonadal development. In flies homozygous for a strong iab-4 allele, gonadogenesis is not initiated in the embryo because the mesodermal cells fail to encapsulate the pole cells. Flies homozygous for weaker iab-4 mutations sometimes form ovaries. The ovary-oviduct junctions are abnormal, however, and egg transfer from the ovary to the uterus is blocked in the adult. To localize the sites that require iab-4 function, we have analyzed animals chimeric for the mutant and wild-type cells. These chimeras were generated by three kinds of transplantation experiments: pole cells, embryonic somatic nuclei or larval ovaries. Our results suggest that iab-4 is required in the somatic cells of the gonadal primordia, but not the germ line. In addition, the formation of functional ovary-oviduct junctions and egg transfer also requires iab-4 functions in the somatic cells of the ovary and in at least one additional somatic tissue.
A transgene containing lacZ is expressed in primary sensory neurons in zebrafish
Authors: Bayer Thomas A. , Campos-Ortega José A.
Published: April 2021

In order to screen for developmentally active chromosomal domains during zebrafish embryogenesis, we generated transgenic fish by microinjecting two different lacZ reporter constructs into fertilized eggs. Transgenic fish were screened among the progeny of injected fish (Fo) crossed to non-injected fish. Groups of 15 to 20 progeny of each cross were tested for lacZ expression and/or transmission of injected sequences using PCR and Southern hybrizations. Progeny from 2 of 102 fish injected with super coiled constructs containing Rous sarcoma virus promoter sequences showed apparently spatially regulated β-galactosidase (β-Gal) activity. However, we were not able to detect this reporter construct in DNA from fins of F, fish. Injections of a linear reporter construct containing mouse heat-shock promoter sequences revealed transmission of injected sequences to Fi progeny in about 6% of cases (8 of 129 fish, tested with PCR). We found one ZacZ-expressing line that showed a spatially and temporally restricted expression of lacZ and, therefore, features typical characteristics of ‘enhancer trap’lines. In this line, lacZ expression starts at 16 hours post-fertilization in trigeminal ganglion cells. At about 24 hours lacZ expression can be detected in trigeminal ganglion neurons and Rohon-Beard neurons, indicating that the development of these two cell types shows common features. The reporter gene has integrated as a single copy. The founder fish was mosaic: 19% of its offspring (3 of 16 tested animals) carried the reporter construct in their fins; about 51% (13 of 27 tested animals) of the progeny of F, fish were β-Gal positive indicating full hemizygosity. We traced the heritability up to the 4th generation and showed that the reporter construct is stably integrated and inherited in a Mendelian manner. These results demonstrate that it is possible to generate “enhancer trap” lines in zebrafish, albeit with low efficiency.
Spatial and temporal expression of an epithelial mucin, Muc-1, during mouse development
Authors: Braga V. M. M. , Pemberton L. F. , Duhig T. , Gendler S. J.
Published: April 2021

The Muc-1 mucin is found as a transmembrane protein in the apical surface of glandular epithelia. To provide insight into possible functions, we have assessed the timing of expression and the distribution of the Muc-1 protein during mouse embryogenesis using three different techniques: RT-PCR, northern blots and immunohistochemistry. Our results indicate that Muc-1 expression correlates with epithelial differentiation in stomach, pancreas, lung, trachea, kidney and salivary glands. Once started, Muc-1 synthesis continually increases with time, mainly due to epithelial area growth. Our data suggest that expression of the Muc-1 gene is under spatial and temporal control during organogenesis. Although Muc-1 is present in different organs, its expression is not induced systemically, but according to the particular onset of epithelial polarization and branching morphogenesis of each individual organ. It is of particular interest that Muc-1 protein can be detected lining the apical surfaces of the developing lumens when the epithelium of these organs is still undergoing folding and branching, and glandular activity has not yet started. We speculate that Muc-1 may participate in epithelial sheet differentiation/lumen formation during early development of the organs known to express it. This speculation is based on: (1) the detection of Muc-1 expression early during organogenesis, (2) the defined apical localization in different epithelia, (3) the decrease in cell-cell interactions when Muc-1 protein is highly expressed and (4) the possible interaction of its cytoplasmic tail with the actin cytoskeleton. However, it remains to be established using in vitro systems, whether the temporal and local expression of the Muc-1 gene coincident with the morphogenetic events described here is relevant for the process.