N-Acetyl-d-Glucosamine Induces Germination in Candida albicans through a Mechanism Sensitive to Inhibitors of cAMP-Dependent Protein Kinase

The present study examines the involvement of cAMP-dependent protein kinase (PKA) in the dimorphic transition of Candida albicans by assessing the in vivo effect of two permeable PKA inhibitors on N-acetyl-d-glucosamine (GlcNAc)- and serum-induced differentiation. The permeable myristoylated derivative of the heat-stable PKA inhibitor (MyrPKI), which inhibited C. albicans PKA in vitro, caused a concentration-dependent inhibition of germ-tube formation in cultures induced to germinate by GlcNAc; germination halted irrespective of the time of addition of the inhibitor. MyrPKI also blocked dibutyryl-cAMP (dbcAMP)- and glucagon-stimulated germination but did not affect serum-induced germination. H-89, another highly specific PKA inhibitor, displayed the same effect on germination. Neither MyrPKI nor H-89 had any effect on budding of yeast cells. In conclusion, our results indicate that cAMP-mediated activation of PKA plays a pivotal role in the biochemical mechanism underlying morphogenesis.     

A novel strategy for the induction and maintenance of shoot regeneration from callus derived from established shoots of apple [Malus×Domestica Borkh.] cv. Golden Delicious

A novel strategy for the production and maintenance of morphogenic callus for 1 year from mature leaf explants of apple has been developed using micropropagated primary leaves of cv. Golden Delicious. The technique required second generation adventitious buds produced from cultured primary leaves also produced from established shoot cultures. The age at which buds were capable of producing morphogenic callus was critical and found to be when leaflets were 2–3 mm in length. Medium composition affected the maintenance but not the induction of shoot regeneration from callus and the best combination was found to be high calcium, low ammonium and low hormone levels. Adventitious shoots were rooted in vitro and established glasshouse-grown plants showed no phenotypic differences from the plants derived from shoot proliferation. The great advantage of this technique for an increased efficiency of recovery of transgenic plants from transformed cells is discussed and the acquisition and maintenance of cell competence with respect to the formation of shoots in culture is explained. Received: 13 August 1996 / Revision received: 13 November 1996 / Accepted: 6 December 1996     

Development of the brain in staged embryos of the long-tailed monkey (Macaca fascicularis)

The external characteristics and successive morphological changes of the brain and its derivatives were studied in 69 long-tailed monkey embryos representing developmental stages 8 through 16. This morphogenesis follows a similar pattern to those of the rhesus, baboon, and human. Minor differences in the temporal sequence of specific developmental events include: 1) otic disc, adenohypophyseal pouch, and hippocampal internal sulcus formation in the long-tailed macaque occur at stage 10, stage 11, and after stage 16 respectively, which is comparable to human stages 9, 10, and 16; 2) formation of the trigeminal primordium and the motor root of the trigeminal nerve and evagination of the neurohypophysis occur at stage 12, stage 14, and stage 15, while in the human embryo these features are observed at stage 14, stage 15, and stage 16, respectively; and 3) closure of the lens pore, like in the rhesus monkey, occurs during stage 15, while in the baboon and human it takes place during stage 14. These temporal differences in the embryonic period are important factors to be taken into consideration in any embryological and teratological studies when usingM. fascicularis as a primate model.     

Resumption of growth of heat inactivated embryonic epiphyses by grafting

Summary This communication describes a new experimental model for the study of the role of the extracellular matrix (ECM) in morphogenesis. In a preceding paper (Markson et al. 1991) we demonstrated that isolated epiphyses from femora of 6-day-old chick embryos grow during the first days in organ culture almost as well as their intact counterparts. Heating femora for 1 h at 45.2° C caused complete cessation of growth and proteoglycan biosynthesis. When the cut surface of a heat-inactivated (HI) epiphysis was brought into apposition with the cut surface of a live epiphysis and the attached pair placed in organ culture, the HI epiphysis began to grow and reached almost the same size as its live partner. The different possible interpretations of this finding are discussed. When a HI epiphysis of a certain shape (from humerus) is attached to a live epiphysis of a very different shape (from femur) and the attached pair is cultured for 6–7 days, the typical resumption of growth can be observed and the HI epiphysis that doubled or tripled its size retains its original characteristic form. The possibility that the existing infrastructure of the cartilaginous ECM directs the pattern of deposition of newly synthesized ECM by the chondroblasts is discussed, and it is suggested that stretch-activated channels participate in a process by which cells sense the topography of their ECM. Offprint requests to: F. Doljanski     

Morphogenesis induction and organogenic nodule differentiation in <Emphasis Type="Italic">Populus euphratica</Emphasis> Oliv. leaf explants

Populus euphratica Oliv. is a deciduous poplar species, occurring mainly in riparian areas of China and Middle Eastern countries, and presenting high tolerance to extreme temperatures and high soil salinity. In this study, an optimized protocol for development and propagation of P. euphratica from leaf explants is reported, based on a morphogenic process that involves organogenic nodule differentiation. Adventitious shoot regeneration of P. euphratica from organogenic nodules of leaf explants was achieved within a range of concentrations of α-naphtalenacetic acid and 6-benzylaminopurine, at a fixed 2:1 ratio. Cambial cells started to divide 5 days after inoculation on culture medium and, after 12 days, several organizing centres were already formed. Non-friable callus tissue, together with organization centres, formed structures that evolved to nodules after about 40 days which were, then, able to regenerate new shoots after 50–60 days. The nodules did not separate from the mother explants and were able to successfully give rise to new adventitious shoots. These were rescued and successfully grown and rooted in different culture media, and fully developed plants were obtained. The regeneration system here described for P. euphratica is innovative, reproducible and data from histological studies of the morphogenic process support the classification of the regenerative structures as organogenic nodules.     

Reproduction,Chromosome Number,and Postembryonic Development of Panagrellus redivivus (Nematoda: Cephalobidae)

Panagrellus redivivus (L.) T. Goodey reproduced amphimictically; the sexual primordia of males had nine chromosomes, those of females had ten. Eggs contained five chromosomes, sperm four or five. There were four molts, all after hatching. The sexes could be separated at the second molt by development of a lobe of somatic cells in the gonad, anteriorly in males, posteriorly in females. The lobe in males reflexed posteriorly at the third molt and joined the rectum at the fourth molt. Third molt females had a thickened vaginal primordium and at the fourth molt the spermathecal and uterine primordia were evident. The uterus elongated enormously in the adult. The 15 ventral chord nuclei between esophagus and rectum in the first stage increased to approximately 63 during the first molt; specialized nuclei, not evident until the third molt, participate in vaginal lining formation in fourth molt females. Sperm were first produced at the late fourth molt. Eggs, not produced until after copulation, hatched within the uterus.     

Patterns of leaf size and morphology in relation to shoot length in Tsuga canadensis

Summary Pattern of change in leaf character was assessed along the length and around the circumference of Tsuga canadensis (L.) Carr. shoots of different length classes. Leaf size decreased, and number of leaves per unit length of shoot increased, with decrease in shoot length. Acropetally along the shoots, lamina length and width decreased, relative petiole length increased, apices became more pointed, and leaf margins bore more teeth. Around the shoot, from upper to side, and to lower surfaces, leaf size and number of marginal teeth in the proximal halves of leaves increased. These patterns were related both to production of preformed versus neoformed leaves, though their separation was indistinct, and to secondary orientation of leaves by twisting in their petiolar regions into two major bi-lateral ranks. An additional minor rank occurred along the upper surfaces of the shoots where secondary orientation of the leaves was minimal. Surface features of leaves did not differ in any obvious manner. Leaves on sylleptic shoots, which by definition were all neoformed, exhibited similar patterns, but were generally smaller than those on their parent shoots.     

Adventitious shoot formation is not inherent to micropropagation of banana as it is in maize

Despite their similar morphology, banana and maize shoot tips responded strikingly different with respect to the in vitro formation of homogeneous multiple shoot clusters. While up to 50 small shoots per maize explant could be induced within 1 month, zero to one additional shoot formed starting from a banana shoot tip. Subsequently, banana shoot tips were subjected to different combinations of five cytokinins (0–100 μM) and five auxins (0–5 μM). The cytokinins thidiazuron and benzylaminopurine stimulated multiplication to a higher extent compared to zeatin, kinetin and isopentenyl adenine. The addition of indoleacetic acid, naphthalene acetic acid or indolebutyric acid to cytokinin containing medium did not affect the in vitro response. In contrast, 2,4-dichlorophenoxyacetic acid (1 and 5 μM) and a higher concentration of picloram (5 μM) had a detrimental effect on shoot formation and resulted in explant death and globule development. When small (0.1 cm) shoot tips were grown on cytokinin medium without an auxin source, the average number of shoots was generally two to three times lower compared to bigger (0.5 cm) shoot tips. Based on our experience in maize and this large-scale study with banana shoot tips, we conclude that banana is extremely recalcitrant towards adventitious shoot formation. This recalcitrance could not be overcome by any of the 173 different plant growth regulator combinations tested. In vitro multiplication of banana thus appears solely restricted to axillary shoot formation.     

Les éléments cytoplasmiques au cours de la spermiogenèse du TritonPleurodeles waltlii Michah

Résume La morphogenèse des éléments caudaux: filament de soutien, membrane ondulante, flagelle et filament marginal, est décrite durant les différents stades de la spermiogenèse. L'absence de cytochrome cytochimiquement décelable, prouve que l'acidophilie marquée du filament de soutien provient de protéines basiques cytoplasmiques ne dérivant pas des mitochondries. Leur origine nucléaire éventuelle est discutée.Le filament de soutien est homologué à la fibre dense externe n^o 3 du spermatozoïde des mammifères. Le filament marginal à structure périodique pourrait correspondre à la colonne dense longitudinale n^o 8 de la gaine fibreuse. A la fin de la spermiogenèse, le spermatozoïde présente une symétrie bilatérale. Une face ventrale et une face dorsale peuvent être définies par comparaison avec le spermatozoïde de mammifère.

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The cytoplasmic elements during spermiogenesis in the triturusPleurodeles waltlii michahIII. Tail structures evolution

Summary The morphogenesis of the tail components: supporting filament, axial rod, undulating membrane, and marginal filament, are described through the differents spermiogenesis steps. The cytochemical cytochrome fate, demonstrated that the pronounced acidophilic properties of the supporting filament are related to the presence of the other cytoplasmic basic proteins. Their eventual nuclear origine is discussed.The supporting filament is homologous to the mammalian sperm outer dense fiber n^o 3. The marginal filament which shows a periodic structure, may correspond to the longitudinal column n^o 8 of the fibrous sheath. At the end of spermiogenesis, the spermatozoon shows a bilaterally symmetrical structure. A ventral face and a dorsal face may be defined by comparison with the insect and mammalian spermatozoon.

Equipe de Recherche Associée au C.N.R.S., E.R.A. n^o 129.     

Continuous Models for Cell Migration in Tissues and Applications to Cell Sorting via Differential Chemotaxis

Chemotaxis, the guided migration of cells in response to chemical gradients, is vital to a wide variety of biological processes, including patterning of the slime mold Dictyostelium, embryonic morphogenesis, wound healing, and tumor invasion. Continuous models of chemotaxis have been developed to describe many such systems, yet few have considered the movements within a heterogeneous tissue composed of multiple subpopulations. In this paper, a partial differential equation (PDE) model is developed to describe a tissue formed from two distinct chemotactic populations. For a “crowded” (negligible extracellular space) tissue, it is demonstrated that the model reduces to a simpler one-species system while for an “uncrowded” tissue, it captures both movement of the entire tissue (via cells attaching to/migrating within an extracellular substrate) and the within-tissue rearrangements of the separate cellular subpopulations. The model is applied to explore the sorting of a heterogeneous tissue, where it is shown that differential-chemotaxis not only generates classical sorting patterns previously seen via differential-adhesion, but also demonstrates new classes of behavior. These new phenomena include temporal dynamics consisting of a traveling wave composed of spatially sorted subpopulations reminiscent of Dictyostelium slugs.