Ectopic head and foot formation in Hydra: Diacylglycerol-induced increase in positional value and assistance of the head in foot formation

In wild type Hydra magnipapillata, daily application of the protein kinase C activator diacylglycerol (DAG) evokes sprouting of periodically spaced ectopic heads along the body column and leads to loss of the ability to regenerate proximal structures including the foot. The present transplantation studies show that the appearance of ectopic heads is preceded by an early increase in the 'positional value' (P-value) or 'head activation potential' of the gastric column. Long before ectopic head structures emerge, pieces of DAG-treated tissue transplanted into the corresponding positional level of untreated hosts induce head formation instead of being integrated, whereas pieces implanted from untreated donors into DAG-treated hosts form feet. Foot formation implies a decrease in the P-value. This down-regulation is promoted through long-range assistance by the head. Thus, after termination of the DAG treatment ectopic feet are intercalated midway between the periodically spaced heads; moreover, untreated polyps onto which additional distal heads have been grafted regenerate feet faster than do one-headed polyps and may form supernumerary feet. Multiheaded animals can also be produced using two substances (K-252a and xanthate D609) that interfere with signal transduction, but the mode by which secondary heads arise is different from DAG-induced ectopic head formation. Presumably because the assistance by the parental head is impaired, buds fail to form a foot and detach and instead give rise to stable secondary body axes. It is assumed that the P-value along the body varies according to the number of cellular receptors for factors serving as intercellular signals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Expression and evolutionary conservation of nanos-related genes in Hydra

The Drosophila gene nanos encodes two particular zinc finger motifs which are also found in germline-associated factors from nematodes to vertebrates. We cloned two nanos (nos)-related genes, Cnnos1 and Cnnos2 from Hydra magnipapillata. Using whole-mount in situ hybridization, the expression of Cnnos1 and Cnnos2 was examined. Cnnos1 was specifically expressed in multipotent stem cells and germline cells, but not in somatic cells. Cnnos2 was weakly expressed in germline cells and more specifically in the endoderm of the hypostome where it appears to be involved in head morphogenesis. In addition to structural conservation in the zinc finger domain of nanos-related genes, functional conservation of Cnnos1 was also demonstrated by the finding that a Cnnos1 transgene can partially rescue the nos ^RC phenotype that is defective in the egg production of Drosophila. Thus, the function of nanos-related genes in the germline appears to be well conserved from primitive to highly evolved metazoans. Received: 28 April 2000 / Accepted: 1 July 2000     

Genetic regulation of developmental phases in winter wheat

The orderly development of winter wheat through its life cycle can be marked at three stages: stem elongation, heading date, and physiological maturity. The duration of a developmental phase between two stages is important in yield component generation. In this study the three developmental stages were characterized and 350 markers were mapped in a population of recombinant inbred lines (RILs) generated from a cross between two winter wheat cultivars (‘Jagger’ and ‘2174’). Three major QTLs were found to control variation in developmental process, and each of them was tightly associated with a known flowering gene, VRN-A1 on chromosome 5A, PPD-D1 on chromosome 2D, and VRN-D3 on chromosome 7D. The average contribution of the gene marker for each QTL to the total phenotypic variation (R ²) was evaluated over 3 years. The effect of VRN-A1 ranged from 21.5% at stem elongation to 17.4% at physiological maturity. The effect of PPD-D1 was minor (6.7%) at stem elongation but increased to 29.7% at heading and 20.1% at physiological maturity. The effect of VRN-D3 was not detected at stem elongation but increased to 14.6% at heading and to 20.5% at physiological maturity. Hence, the VRN-A1 locus, the PPD-D1 locus, and the VRN-D3 locus had greatest impact on development at stem elongation, heading date, and physiological maturity, respectively. Whereas the Jagger VRN-A1 and VRN-D3 alleles accelerated development, the Jagger PPD-D1 allele delayed the developmental process due to its sensitivity to photoperiod. Our findings suggest that through the appropriate combination of alleles at these three loci one would be able to regulate the various developmental phases to accommodate different agricultural needs.     

The Hydra genome: insights, puzzles and opportunities for developmental biologists

The sequencing of a Hydra genome marked the beginning of a new era in the use of Hydra as a developmental model. Analysis of the genome sequence has led to a number of interesting findings, has required revisiting of previous work, and most importantly presents new opportunities for understanding the developmental biology of Hydra. This review will de-scribe the history of the Hydra genome project, a selection of results from it that are relevant to developmental biologists, and some future research opportunities provided by Hydra genomics.     

Expression of annexin VI (p68, 67 kDa-calelectrin) in normal human tissues: evidence for developmental regulation in B- and T-lymphocytes

This paper describes the tissue distribution of annexin VI, a Ca²⁺-dependent phospholipid binding protein, and a member of the annexin super-gene family. In order to determine whether annexin VI expression correlated with a particular functional phenotype, an extensive series of non-pathological human tissues were examined, in which annexin VI was detected either immunohistochemically or by immunofluorescence, using a rabbit polyclonal anti-(human annexin VI)-IgG of known specificity. Although most tissues investigated were found to express annexin VI, the protein was usually confined to highly specific cell types within each tissue, the staining generally appearing cytoplasmic and diffuse. There was particularly good correlation between annexin VI expression and hormone secreting cells, with positive staining in the islet cells of the pancreas, the Leydig cells of the testis and the cells of the adrenal cortex. A notable exception was the parathyroid gland, which lacked detectable annexin VI. Although the protein was absent in most epithelia, it was expressed strongly in certain secretory epithelia; e.g. the ductal epithelial cells of the salivary glands and non-lactating breast, and the sweat glands and their ducts. The observation that the epithelial cells of lactating breast failed to stain for annexin VI suggests functional regulation of protein expression in this tissue. However, the most interesting finding was that annexin VI expression appeared to be developmentally regulated in B- and T-lymphocyte differentation, with negative staining in the proliferating B cells of the germinal centre of the lymph nodes, but strong staining in the mature small lymphocytes of the cortex, mantle zone and paracortex.     

Expression of transfected human interferon-gamma DNA: evidence for cell-specific regulation

The production of interferon-gamma (IFN-gamma) has been limited to two specific cell types of the immune system, T cells and large granular lymphocytes. Interleukin 2 (IL 2) appears to be the primary physiologic stimulus for IFN-gamma production in vitro, but other agents, such as antigens, phorbol myristic acetate, concanavalin A, or other plant lectins, may also act as effective inducing agents for IFN-gamma production. Little is known, however, as to the role, if any, that genetic factors may play in the induction process. We now report that, on stable transfection of the genomic human IFN-gamma 8.6 Kb BamH DNA fragment into a mouse T lymphoblast cell line, both mRNA expression and synthesis of human IFN-gamma were stimulated by both the physiologic ligand IL 2 and phorbol ester. In contrast, we have been unable to induce with extracellular stimulants IFN-gamma production or cytoplasmic mRNA after introduction of this gene into NIH 3T3 fibroblasts, thus suggesting that the extracellular regulation of the expression of IFN-gamma may be controlled by a developmental mechanism(s) intrinsic for cells of lymphoid lineage.     

Notch-signalling is required for head regeneration and tentacle patterning in Hydra

Local self-activation and long ranging inhibition provide a mechanism for setting up organising regions as signalling centres for the development of structures in the surrounding tissue. The adult hydra hypostome functions as head organiser. After hydra head removal it is newly formed and complete heads can be regenerated. The molecular components of this organising region involve Wnt-signalling and β-catenin. However, it is not known how correct patterning of hypostome and tentacles are achieved in the hydra head and whether other signals in addition to HyWnt3 are needed for re-establishing the new organiser after head removal. Here we show that Notch-signalling is required for re-establishing the organiser during regeneration and that this is due to its role in restricting tentacle activation. Blocking Notch-signalling leads to the formation of irregular head structures characterised by excess tentacle tissue and aberrant expression of genes that mark the tentacle boundaries. This indicates a role for Notch-signalling in defining the tentacle pattern in the hydra head. Moreover, lateral inhibition by HvNotch and its target HyHes are required for head regeneration and without this the formation of the β-catenin/Wnt dependent head organiser is impaired. Work on prebilaterian model organisms has shown that the Wnt-pathway is important for setting up signalling centres for axial patterning in early multicellular animals. Our data suggest that the integration of Wnt-signalling with Notch-Delta activity was also involved in the evolution of defined body plans in animals.     

Expression of annexin VI (p68, 67 kDa-calelectrin) in normal human tissues: evidence for developmental regulation in B- and T-lymphocytes.

This paper describes the tissue distribution of annexin VI, a Ca(2+)-dependent phospholipid binding protein, and a member of the annexin super-gene family. In order to determine whether annexin VI expression correlated with a particular functional phenotype, an extensive series of non-pathological human tissues were examined, in which annexin VI was detected either immunohistochemically or by immunofluorescence, using a rabbit polyclonal anti(human annexin VI)-IgG of known specificity. Although most tissues investigated were found to express annexin VI, the protein was usually confined to highly specific cell types within each tissue, the staining generally appearing cytoplasmic and diffuse. There was particularly good correlation between annexin VI expression and hormone secreting cells, with positive staining in the islet cells of the pancreas, the Leydig cells of the testis and the cells of the adrenal cortex. A notable exception was the parathyroid gland, which lacked detectable annexin VI. Although the protein was absent in most epithelia, it was expressed strongly in certain secretory epithelia; e.g. the ductal epithelial cells of the salivary glands and non-lactating breast, and the sweat glands and their ducts. The observation that the epithelial cells of lactating breast failed to stain for annexin VI suggests functional regulation of protein expression in this tissue. However, the most interesting finding was that annexin VI expression appeared to be developmentally regulated in B- and T-lymphocyte differentiation, with negative staining in the proliferating B cells of the germinal centre of the lymph nodes, but strong staining in the mature small lymphocytes of the cortex, mantle zone and paracortex.