bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differential reaction of crossing and non-crossing rat retinal axons on cell membrane preparations from the chiasm midline: an in vitro study
Authors: Wizenmann A. , Thanos S. , Boxberg Y. v. , Bonhoeffer F. 
Published: April 2021

ABSTRACT
In the rat, a small subpopulation of retinal ganglion cell axons forms a persistent projection to the ipsilateral half of the brain. These fibres originate almost exclusively from the ventrotemporal margin of the retina. In contrast to all other retinal axons they seem to be deflected from the midline of the optic chiasm and thereby led into the ipsilateral optic tract.
In order to analyse the interactions between growing fibres and chiasm midline, we have developed the following in vitro model. Axons of the embryonic rat retina are grown on a carpet of tectal cell membranes used as a general growth-permissive substratum. At a certain distance from the explant (200-450 μ m), the advancing fibres are confronted with two stripes of cell membranes prepared from the chiasm midline. Such chiasm membranes are shown to act as a barrier for the presumptive non-crossing axons, while they do not influence growth of fibres originating from any other regions of the retina, including the dorsotemporal part. The repulsion of non-crossing fibres by chiasm membranes is observed in vitro only when retinal explants from embryonic day (E) 17/18 and chiasm preparations from E14/15 are used. Fibres and tissue from different regions of the brain as well as from different developmental ages, and even from different species, can be combined in this assay system. In a first attempt to characterize the molecular basis of the repulsive effect of chiasm membranes on ventrotemporal fibres, similar assays were performed with membranes derived from other regions of the central nervous system midline, some of which are known to have repulsive properties against certain axon populations. Since these cell membranes did not act as a barrier for the ventrotemporal retinal axons, we suggest that the guidance cues at the chiasm are very specific.
Our results are consistent with the hypothesis that certain cells at the chiasm midline (very likely radial glial cells) express ‘repulsive or inhibitory’ molecules, which act in a specific way on ipsilaterally projecting axons.
Sex determination in Drosophila: sis-b, a major numerator element of the X:A ratio in the soma, does not contribute to the X:A ratio in the germ line
Authors: Steinmann-Zwicky Monica 
Published: April 2021

ABSTRACT
In soma and germ cells of Drosophila, the X:A ratio builds a primary signal for sex determination, and in both tissues Sex-lethal (Sxl) function is required for cells to enter the female pathway.
In somatic cells of XX animals, the products of X-chromosomal elements of the X:A ratio activate Sxl. Here I show that sisterless-b (sis-b), which is the X-chro-mosomal element of the somatic X:A ratio that has best been analysed, is not required for oogenesis. I also present evidence that Sxl function might not be suffi-cient to direct germ cells into the female pathway. These results show that the elements forming the X:A ratio in the germ line are different from the elements forming the X:A ratio in the soma and they suggest that, in the germ line, Sxl might not be regulated by the X:A ratio.
A role for subplate neurons in the patterning of connections from thalamus to neocortex
Authors: Ghosh Anirvan , Shatz Carla J. 
Published: April 2021

ABSTRACT
During cerebral cortical development, ingrowing axons from different thalamic nuclei select and invade their cortical targets. The selection of an appropriate target is first evident even before thalamic axons grow into the cortical plate: initially axons accumulate and wait below their cortical target area in a zone called the subplate. This zone also contains the first postmitotic neurons of the cerebral cortex, the subplate neurons. Here we have investigated whether subplate neurons are involved in the process of target selection by thalamic axons by ablating them from specific cortical regions at the onset of the waiting period and examining the subsequent thalamocortical axon projection patterns.
Subplate neurons were ablated at the onset of the waiting period by intracortical injections of kainic acid. The effect of the ablation on the thalamocortical projection from visual thalamus was examined by DiI-labeling of the LGN days to weeks following the lesion. At two to four weeks post-lesion, times when LGN axons would have normally invaded the cortical plate, the axons remained below the cortical plate and grew past their appropriate cortical target in an anomalous pathway. Moreover, examination of LGN axons at one week post-lesion, a time when they would normally be waiting and branching within the visual subplate, indicated that the axons had already grown past their correct destination. These observations suggest that visual subplate neurons are involved in the process by which LGN axons select and subsequently grow into visual cortex. In contrast, subplate neurons do not appear to play a major role in the initial morphological development of the LGN itself. Subplate ablations did not alter dendritic growth or shapes of LGN projection neurons during the period under study, nor did it prevent the segregation of retinal ganglion cell axons into eye-specific layers. However, the overall size of the LGN was reduced, suggesting that there may be increased cell death of LGN neurons in the absence of subplate neurons.
To examine whether subplate neurons beneath other neocortical areas play a similar role in the formation of thalamocortical connections, subplate neurons were deleted beneath auditory cortex at the onset of the waiting period for auditory thalamic axons. Subsequent DiI labeling revealed that in these animals the majority of MGN axons had grown past auditory cortex instead of innervating it. Taken together these observations underscore a general requirement for subplate neurons throughout neocortex in the process of cortical target selection and ingrowth by thalamic axons. Moreover, they imply that the cortical plate alone has insufficient information to direct the formation of specific sets of thalamocortical connections: interactions involving subplate neurons must also be present.
A unique pattern of expression of the four muscle regulatory factor proteins distinguishes somitic from embryonic, fetal and newborn mouse myogenic cells
Authors: Smith Timothy H. , Block, Nancy E. , Rhodes, Simon J. , Miller Jeffrey Boone 
Published: April 2021

ABSTRACT
A unique pattern of expression of the four muscle regulatory factor (MRF) proteins was found to distinguish early somitic from embryonic, fetal and newborn limb myogenic cells in vitro. Expression of the myosin heavy chain (MHC), MyoD, myogenin, Myf-5, and MRF4 proteins was examined by immunocytochemistry in cultures of four distinct types of mouse myogenic cells: somitic (E8.5), embryonic (E11.5), fetal (E16.5) and newborn limb. In embryonic, fetal and newborn cultures, the MRF proteins were expressed in generally similar patterns: MyoD was the first MRF expressed; MyoD and myogenin were expressed by more cells than Myf-5 or MRF4; and each of the four MRFs was found both in cells that expressed MHC and in cells that did not express MHC. In cultures of somitic cells, in contrast, Myf-5 was expressed first and by more cells than MyoD or myogenin; MRF4 was not detected; and the MRFs were never found to be coexpressed with MHC in the same cell. Thus, some somitic cells had the unexpected ability to maintain MHC expression in the absence of detectable MRF protein expression. The different myogenic programs of embryonic, fetal and newborn myogenic cells are not, therefore, a simple result of qualitatively different MRF expression patterns, whereas myogenesis by somitic cells does include a unique pattern of MRF expression.
Tight junction protein cingulin is expressed by maternal and embryonic genomes during early mouse development
Authors: Javed Qamar , Fleming Tom P. , Hay Mark , Citi Sandra 
Published: April 2021

ABSTRACT
The expression of the tight junction peripheral membrane protein, cingulin (140 103Mr), was investigated in mouse eggs and staged preimplantation embryos by immunoblotting and immunoprecipitation. Polyclonal antibody to chicken brush border cingulin detected a single 140 103Mr protein in immunoblots of unfertilised eggs and all preimplantation stages. Relative protein levels were high in eggs and early cleavage stages, declined during later cleavage and increased again in expanding blastocysts. Quantitative immunoprecipitation of metabolically labelled eggs and staged embryos also revealed a biphasic pattern for cingulin synthesis with relative net levels being high in unfertilised eggs, minimal during early cleavage, rising 2.3-fold specifically at the onset of compaction (8-cell stage, when tight junction formation begins), and increasing further at a linear rate during morula and blastocyst stages. Cingulin synthesis in eggs is not influenced by fertilisation (or aging, if unfertilised), but this level declines sharply after first cleavage. These results indicate that cingulin is expressed by both maternal and embryonic genomes. The turnover of maternal cingulin (unfertilised eggs) and embryonic cingulin at a stage before tight junction formation begins (4-cell stage) is higher (t ∼4 hours) than cingulin synthesised after tight junction formation (blastocysts; t ∼10 hours). This increase in cingulin stability is reversed in the absence of extracellular calcium. Cingulin synthesis is also tissue-specific in blastocysts, being up-regulated in trophectoderm and down-regulated in the inner cell mass. Taken together, the results suggest that (i) cingulin may have a role during oogenesis and (ii) cell-cell contact patterns regulate cingulin biosynthesis during early morphogenesis, contributing to lineage-specific epithelial maturation.
Developmental role of endogenous retinoids in the determination of morphallactic field in budding tunicates
Authors: Kawamura Kazuo , Hara Kenji , Fujiwara Shigeki 
Published: April 2021

ABSTRACT
We have extracted retinoids from the budding tunicate Polyandrocarpa misakiensis and, using HPLC, identified some major peaks as cis-retinal, all-trans-retinal and all-trans-retinoic acid, of which cis-retinal was most abundant (∼2 M). In developing buds, the amount of cis-retinal was about one-fifth that of the adult animals. In those buds, aldehyde dehydrogenase, which could metabolize retinal in vitro, was expressed in epithelial cells and then in mesenchymal cells at the proximal extremity, that is, the future developmental field of the bud. Exogenous retinoic acid comparable to the endogenous level could induce an additional field at the distal end of the bud, resulting in a double monster. The induction always accompanied an ectopic expression of aldehyde dehydrogenase. The results of this work suggest that retinoic acid or related molecule(s) act as an endogenous trigger of morphallactic development of Polyandrocarpa buds.
Cell lineage analysis of the expression of an engrailed homolog in leech embryos
Authors: Lans Deborah , Wedeen Cathy J. , Weisblat David A. 
Published: April 2021

ABSTRACT
ht-en is an engrailed-class gene that is expressed during early development and neurogenesis in embryos of the leech Helobdella triserialis. During the early development of this annelid (stages 7-9), ht-en is expressed in each of the ectodermal and mesodermal teloblast lineages that contributes progeny to the definitive segments. ht-en is expressed transiently by individually identified cells within the segmentally iterated primary blast cell clones. Its expression is correlated with the age of the primary blast cell clone. After consegmental primary blast cell clones from the different teloblast lineages have come into segmental register, cells that express ht-en during stages 7-9 are clearly confined to a transverse region corresponding to the posterior portion of the segmental anlage, but not all cells within this region express ht-en. Only a minority of the identified cells that express ht-en during terminal differentiation of the segmental ganglia and body wall (stages 10-11) are descendants of cells that express ht-en in early development (stages 7-9).
Characterization of the unusually rapid cell cycles during rat gastrulation
Authors: Auley Alasdair Mac , Werb Zena , Mirkes Philip E. 
Published: April 2021

ABSTRACT
The onset of gastrulation in rodents is associated with the start of differentiation within the embryo proper and a dramatic increase in the rate of growth and proliferation. We have determined the duration of the cell cycle for mesodermal and ectodermal cells of rat embryos during gastrulation (days 8.5 to 9.5 of gestation) using a stathmokinetic analysis. These embryonic cells are the most rapidly dividing mammalian cells yet described. Most cells of the ectoderm and mesoderm had a cell cycle time of 7 to 7.5 hours, but the cells of the primitive streak divided every 3 to 3.5 hours. Total cell cycle time was reduced by shortening S and G2, as well as G1, in contrast to cells later in development, when cell cycle duration is modulated largely by varying the length of G1. In the ectoderm and mesoderm, G1 was 1.5 to 2 hours, S was 3.5 to 4 hours, and G2 was 30 to 40 minutes. G1, S and G2 were shortened even further in the cells of the primitive streak: G1 was less than 30 minutes, S was 2 to 2.75 hours, and G2 was less than 20 minutes. Thus, progress of cells through all phases of the cell cycle is extensively modified during rodent embryogenesis. Specifically, the increased growth rate during gastrulation is associated with radical changes in cell cycle structure and duration. Further, the commitment of cells to become mesoderm and endoderm by entering the primitive streak is associated with expression of a very short cell cycle during transit of the primitive streak, such that developmental decisions determining germ layer fate are reflected in differences in cell cycle regulation.
Gene expression during imaginal disc regeneration detected using enhancer-sensitive P-elements
Authors: Brook William J. , Ostafichuk Lisa M. , Piorecky Jana , Wilkinson Mark D. , Hodgetts Daralyn J. , Russell Michael A. 
Published: April 2021

Abstract
When imaginal disc fragments from Drosophila are cultured in adult female hosts, they either duplicate the part of the pattern specified by the fate map, or regenerate to replace the missing part. The new tissue is added by proliferation of a small number of cells from the cut edge, brought together when the wound heals to form a regeneration blastema. Specification of the new pattern has been explained by assuming interactions among cells of different positional value in the regeneration blastema. In order to identify genes which might mediate these events, we screened over eight hundred independently isolated autosomal insertions of an enhancer-sensitive P-element, for altered lac-z expression in regenerating discs following cell death induced by a temperature-sensitive cell-lethal mutation. Two further screens divided the positive lines into four groups based on appropriate timing of the lac-z response in the cell-lethal mutant background and the expected response to an alternate source of cell death. Expression in wing disc fragments cultured in vivo was most frequent in the target class defined by the screens. In this direct test, lac-z expression was found in 23 lines and in most cases was spatially and temporally correlated with the formation of the regeneration blastema. Our results suggest a very substantial transcriptional response during the early stages of imaginal disc regeneration. lac-z expression in control imaginal discs, embryos and adult ovaries of the positive lines was also assayed. The selected insertions included: a small class expressed only in discs undergoing regeneration and apparently not at any other stage, possibly representing genes active exclusively in regeneration; a larger class expressed in the embryo or during oogenesis, but not normally in imaginal discs, as expected for functions recruited from earlier stages of the developmental program; and finally a class with spatially patterned expression in normal discs. This class included several insertions with expression associated with compartment boundaries, including one at the decapentaplegic (dpp), and one at the crumbs (crb) locus, a growth factor homologue, and an EGF-repeat gene respectively. Some of the expression patterns observed in cultured disc fragments provide evidence for cell communication in the regeneration blastema.
The cell adhesion molecule M-cadherin is specifically expressed in developing and regenerating, but not denervated skeletal muscle
Authors: Moore Robert , Walsh Frank S. 
Published: April 2021

Abstract
The spatiotemporal distribution of M-cadherin mRNA has been determined by in situ hybridization in the mouse embryo and in adult skeletal muscle following experimental regeneration and denervation. M-cadherin mRNA is highly tissue specific and is found only in developing skeletal muscle. In contrast, N-cadherin mRNA has a broader tissue distribution in the embryo, being found on both neural elements and skeletal and cardiac muscle. M-cadherin is expressed in the myotomes shortly after they form, along with the myo-genic regulatory factor myogenin. M-cadherin is expressed in muscles derived from the myotomes and is detected in forelimb bud precursor cells at embryonic day 11.5. In the latter case M-cadherin expression appears co-ordinately with that of myogenin and cardiac-actin. Shortly before birth, M-cadherin expres-sion is down regulated. M-cadherin can, however, be re-expressed following experimental regeneration of skele-tal muscle. Here M-cadherin is transiently expressed on regenerating myoblasts but not myotubes. Following muscle denervation no evidence was found for re-expression of M-cadherin under conditions where there was strong expression of the nicotinic acetylcholine receptor on myofibres.
The highly specific tissue distribution and unique developmental profile distinguishes M-cadherin from other cadherins and suggests a role in cell surface events during early myogenesis.
Multiple extracellular signals are required for long-term oligodendrocyte survival
Authors: Barres B. A. , Schmid R. , Sendnter M. , Raff M. C. 
Published: April 2021

ABSTRACT
We showed previously that oligodendrocytes and their precursors require continuous signalling by protein trophic factors to avoid programmed cell death in culture. Here we show that three classes of such trophic factors promote oligodendrocyte survival in vitro: (1) insulin and insulin-like growth factors (IGFs), (2) neurotrophins, particularly neurotrophin-3 (NT-3), and (3) ciliary-neurotrophic factor (CNTF), leukemia inhibitory factor (LIF) and interleukin 6 (IL-6). A single factor, or combinations of factors within the same class, promote only short-term survival of oligodendrocytes and their precursors, while combinations of factors from different classes promote survival additively. Long-term survival of oligodendrocytes in vitro requires at least one factor from each class, suggesting that multiple signals may be required for long-term oligodendrocyte survival in vivo. We also show that CNTF promotes oligodendrocyte survival in vivo, that platelet-derived growth factor (PDGF) can promote the survival of oligodendrocyte precursors in vitro by acting on a novel, very high affinity PDGF receptor, and that, in addition to its effect on survival, NT-3 is a potent mitogen for oligodendrocyte precursor cells.
The spatial organization of epidermal structures: hairy establishes the geometrical pattern of Drosophila leg bristles by delimiting the domains of achaete expression
Authors: Orenic Teresa V. , Held Lewis I. , Paddock Stephen W. , Carroll Sean B. 
Published: April 2021

ABSTRACT
The spatial organization of Drosophila melanogaster epidermal structures in embryos and adults constitutes a classic model system for understanding how the two dimensional arrangement of particular cell types is generated. For example, the legs of the Drosophila melanogaster adult are covered with bristles, which in most segments are arranged in longitudinal rows. Here we elucidate the key roles of two regulatory genes, hairy and achaete, in setting up this periodic bristle pattern. We show that achaete is expressed during pupal leg development in a dynamic pattern which changes, by approximately 6 hours after puparium formation, into narrow longitudinal stripes of 3–4 cells in width, each of which represents a field of cells (proneural field) from which bristle precursor cells are selected. This pattern of gene expression foreshadows the adult bristle pattern and is established in part through the function of the hairy gene, which also functions in patterning other adult sense organs. In pupal legs, hairy is expressed in four longitudinal stripes, located between every other pair of achaete stripes. We show that in the absence of hairy function achaete expression expands into the interstripe regions that normally express hairy, fusing the two achaete stripes and resulting in extra-wide stripes of achaete expression. This misexpression of achaete, in turn, alters the fields of potential bristle precursor cells which leads to the misalignment of bristle rows in the adult. This function of hairy in patterning achaete expression is distinct from that in the wing in which hairy suppresses late expression of achaete but has no effect on the initial patterning of achaete expression. Thus, the leg bristle pattern is apparently regulated at two levels: a global regulation of the hairy and achaete expression patterns which partitions the leg epidermis into striped zones (this study) and a local regulation (inferred from other studies on the selection of neural precursor cells) that involves refinement steps which may control the alignment and spacing of bristle cells within these zones.
Multiple cell interactions are required for fate specification during male spicule development in Caenorhabditis elegans
Authors: Chamberlin Helen M. , Sternberg Paul W. 
Published: April 2021

ABSTRACT
The B blast cell divides postembryonically in C. elegans males to produce 47 progeny that include all of the cells of the copulatory spicules. During the early development of the B lineage, the anterior daughter of B, B.a, generates eight cells. These cells migrate to form four pairs of cells that flank the developing cloaca (ventral, dorsal, and two identical lateral pairs). For each pair, the more anterior cell produces a distinct lineage (‘anterior fate’) from the posterior cell (‘posterior fate’). For the ventral and dorsal pairs, either cell can migrate to the anterior position and produce the anterior lineage, and the other cell migrates posterior and produces the posterior lineage (Sulston and Horvitz, 1977, Dev. Biol. 56, 110–156). The migration is variable, although the resultant fate pattern is invariant. In the two lateral pairs, both the migration and fate pattern are invariant. Using a laser microbeam to selectively ablate neighboring cells we have found that the cells of the lateral pair also respond to positional cues. For all four pairs other male-specific blast cells provide extracellular cues. In general, F and U promote anterior fates, Y promotes some posterior fates, and the B.a progeny promote posterior fates. Several of these cues are redundant. By ablating combinations of cells we have deduced how these signals may act in concert to specify the fates of the B.a progeny. We propose that fate specification in these pairs depends on three general classes of extracellular cues: positional cues, modulators of positional cues, and lateral signals. The B lineage thus provides an opportunity to study with single cell resolution the integration of multiple intercellular signals.