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K Nübler-Jung

Publications and source records attributed to K Nübler-Jung.

9 recordsLinked to original sources
PubMed1999

Rearranging gastrulation in the name of yolk: evolution of gastrulation in yolk-rich amniote eggs.

Gastrulating birds and mammals form a primitive streak in lieu of a circular blastopore, and a conspicuous underlying tissue layer, the hypoblast. In an attempt to understand the evolution of these amniote characteristics, pregastrula and gastrulation stages in selected amniotes are compared with the more ancestral situation in amphibians. At blastula/blastoderm stages, the overall fate maps and the arrangement of tissues around the organizer are rather similar, as is exemplified by a comparison of gene expression and fate maps in the frog and chick. Compared with amphibians, however, the eggs of reptiles, birds and monotreme mammals have a disproportionately large yolk that alters gastrulation morphology. During amphibian gastrulation, the organizer moves from anterior to posterior, to lay down the dorsal axis around the vegetal hemisphere (Arendt, D., Nübler-Jung, K., 1997. Dorsal or ventral: similarities in fate maps and gastrulation patterns in annelids, arthropods and chordates. Mech. Dev. 61, 1-15). In contrast, in amniote eggs, the large yolk impedes the organizer from moving around the entire vegetal hemisphere so that axis formation begins and ends at the same side of the egg. This has apparently provoked an evolutionary transformation of an amphibian-like blastopore, first into the 'blastoporal canal' of reptiles, and then into the birds' and mammals' primitive streak. The blastopore divides into two functionally divergent parts, one as the site of mesoderm internalization ('intraembryonic blastopore') and the other as the site of ectodermal epiboly ('extraembryonic blastopore'). The hypoblast is proposed to derive from the 'endodermal wedge' that is seen already in the amphibian gastrula. Hypoblast formation would then represent a special kind of gastrulation movement that also exists in the amphibians, and for which the term 'hypoboly' is introduced.

Amnion↗
PubMed1999

Comparison of early nerve cord development in insects and vertebrates.

It is widely held that the insect and vertebrate CNS evolved independently. This view is now challenged by the concept of dorsoventral axis inversion, which holds that ventral in insects corresponds to dorsal in vertebrates. Here, insect and vertebrate CNS development is compared involving embryological and molecular data. In insects and vertebrates, neurons differentiate towards the body cavity. At early stages of neurogenesis, neural progenitor cells are arranged in three longitudinal columns on either side of the midline, and NK-2/NK-2.2, ind/Gsh and msh/Msx homologs specify the medial, intermediate and lateral columns, respectively. Other pairs of regional specification genes are, however, expressed in transverse stripes in insects, and in longitudinal stripes in the vertebrates. There are differences in the regional distribution of cell types in the developing neuroectoderm. However, within a given neurogenic column in insects and vertebrates some of the emerging cell types are remarkably similar and may thus be phylogenetically old: NK-2/NK-2.2-expressing medial column neuroblasts give rise to interneurons that pioneer the medial longitudinal fascicles, and to motoneurons that exit via lateral nerve roots to then project peripherally. Lateral column neuroblasts produce, among other cell types, nerve root glia and peripheral glia. Midline precursors give rise to glial cells that enwrap outgrowing commissural axons. The midline glia also express netrin homologs to attract commissural axons from a distance.

Animals↗
PubMed1997

Dorsal or ventral: similarities in fate maps and gastrulation patterns in annelids, arthropods and chordates.

The idea that chordates, during their evolution, have inverted their dorsoventral body axis has recently gained substantial support. It has been shown that various dorsoventral patterning genes that are evolutionarily conserved between insects and vertebrates are expressed dorsally in insects, and ventrally in vertebrates, or vice versa. The ventral body side of insects thus seems to correspond to the dorsal body side of vertebrates, and these are nerve cord-bearing, neural body sides in both groups. In order to exclude that the inverted polarity of gene patterning activity is purely accidental, we compare here vertebrate and invertebrate blastula fate maps and their gastrulation patterns in the framework of early gene expression. From this comparison it appears that the neural body sides, 'ventral' in annelids or arthropods, and 'dorsal' in chordates, develop at similar positions with respect to the initial egg asymmetry. In addition, the formation of the neural body sides involves similar movements during gastrulation. We further suggest that the deuterostome gastrulation seen in today's chordates can be derived from a more ancestral gastrulation pattern seen in today's annelids and arthropods, and that the ventral midline cells of insects correspond to the dorsal midline cells of vertebrates.

Animals↗
PubMed1996

Common ground plans in early brain development in mice and flies.

Comparing expression patterns of orthologous genes between insects and vertebrates, we have recently proposed that the ventral nerve cord in insects may correspond to the dorsal nerve cord in vertebrates. Here we show that the early development of the insect and vertebrate brain anlagen is indeed very similar. Insect and vertebrate brains express similar sets of genes in comparable areas with similar functions in the adult. In addition, early axogenesis establishes surprisingly similar patterns of axonal connectivity in both groups. We therefore propose that insect and vertebrate brains are built according to a common ground plan, and that specific areas of the insect and vertebrate brains be considered as homologous, meaning that these areas already existed, with their specific functions, in their common ancestor.

Animals↗
PubMed1990

Insect epidermis: polarity patterns after grafting result from divergent cell adhesions between host and graft tissue.

Insect epidermal cells display planar polarity (i.e. polarity in the plane of the cell sheet) by secreting oriented cuticular denticles and bristles before each moult. We investigate how cell polarities in an abdominal segment are uniformly oriented towards the posterior of the animal. Recently we have shown for the cotton bug Dysdercus that, in 180 degrees-rotated grafts pretreated with colchicine, graft cells tend to adopt the orientation prevailing in surrounding host cells via an intermediate stage with outward oriented denticles (Nübler-Jung and Grau, 1987). Here we show that, in untreated grafts that were transposed along the anteroposterior segment axis, the denticles also always tend to point outwards. This independence of the polarity pattern from the direction of transposition is compatible neither with a gradient model for polarity control, nor with the assumption that epidermal cells orient according to the local sequence of distinctly differentiated cells. Instead we found that outward orientation of graft denticles correlates with an elongation of epidermal cells along a host-graft border with divergent cell adhesiveness. We therefore propose that outward orientation in a graft results from a combination of two factors: epidermal cells stretch along an interface with divergent cell adhesiveness, and they form a denticle perpendicular to their long axis. By analogy, the normal anteroposterior orientation of denticles in a segment may result because epidermal cells tend to elongate parallel to the segment boundary and to form denticles perpendicular to this mediolateral cell elongation, i.e. along the anteroposterior segment axis.

Animals↗
PubMed1987

Cell polarity during wound healing in an insect epidermis.

The insect integument displays uniform posterior orientation of cuticular denticles or bristles formed by the epidermal cells. We want to understand how cell polarities become uniformly oriented in the plane of the epidermal sheet. Here we test whether directed cell migration disturbs the orientation of denticles. Burning a circular area of epidermal cells beneath the cuticle causes cells to migrate into the resulting wound and the cuticle pattern observed after the subsequent moult depends on the time interval between burning and ecdysis. After a short wound-healing period cuticular protrusions tend to point away from the wound. With increasing would healing periods they tend to point more and more towards the wound centre. These results suggest that the migrating cells tend to orient cuticular protrusions in the direction of cell movement while continued cell movement will bend nascent cuticular protrusions outwards. Cell shape may also determine denticle orientation. I propose that the asymmetric localization of cell components known to determine the orientation of cell migration may also determine denticle orientation in insect epidermal cells.

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