The morphogenesis of Wulst neurons in the pied flycatcher under conditions of limited afferent inflow]

Golgi preparations of the pied flycatcher Wulst region (the structure analogous to the mammalian visual cortex) were analyzed using the method of computerized morphometry, to study the influence of visual deprivation on the development of different types of neurons selected previously. Deprivation was accomplished by covering the young's eye with nontransparent caps. The experiments were carried out in 10-day-old nestlings (the onset of patterned vision) and 13-day-old nestlings (functioning patterned vision). In 10-day-old nestlings, the deprivation produced constructive changes in dendritic apparatus of projective stellate cells (among them, the most pronounced was more than three-fold increase in the number of foci of maximal branching) practically not affecting the small stellate-like cells. In 13-day-old nestlings, cells belonging to all selected cell types underwent destructive changes: their quantitative characteristics were decreased as compared to those in control nestlings. A large number of tree-like neurons were revealed in the Wulst in the deprived 10-day-old nestlings while in the control age-matched nestlings they were virtually never found. This phenomenon may be explained by the increased affinity to impregnation evoked by deprivation-induced biochemical changes in the tree-like neurons or to increase in their number. In the latter case, the phenomenon may be considered as compensatory, directed at the establishing of contacts with nonvisual afferents.     

Age-related changes in sensory neurons containing calcitonin gene-related peptide under conditions of afferentation deficit in rats

Morphological features of calcitonin gene-related peptide (CGRP)-immunoreactive neurons were studied in the sensory ganglia of the vagus and thoracic nerves in 3-, 10-, 20-, 30-, 60-, 90-, and 180-day-old rats under conditions of chemically-induced deafferentation. We found that, in rats, CGRP-containing neurons appeared in both ganglia immediately after they were born and their number decreased with aging. Most of CGRP-immunoreactive neurons were small in size, i.e., up to 600 ??m². Administration of capsaicin modified age-related changes in the number of CGRP-immunopositive neurons. In the thoracic nerve ganglion, the mean square of these cells and their number substantially decreased, whereas, in the vagus nerve ganglion, positive cells were not observed.     

Hofbauer-Buchner eyelet affects circadian photosensitivity and coordinates TIM and PER expression in Drosophila clock neurons

Extraretinal photoreception is a common input route for light resetting signals into the circadian clock of animals. In Drosophila melanogaster, substantial circadian light inputs are mediated via the blue light photoreceptor CRYPTOCHROME (CRY) expressed in clock neurons within the brain. The current model predicts that, upon light activation, CRY interacts with the clock proteins TIMELESS (TIM) and PERIOD (PER), thereby inducing their degradation, which in turn leads to a resetting of the molecular oscillations within the circadian clock. Here the authors investigate the function of another putative extraretinal circadian photoreceptor, the Hofbauer-Buchner eyelet (H-B eyelet), located between the retina and the medulla in the fly optic lobes. Blocking synaptic transmission between the H-B eyelet and its potential target cells, the ventral circadian pacemaker neurons, impaired the flies' ability to resynchronize their behavior under jet-lag conditions in the context of nonfunctional retinal photoreception and a mutation in the CRY-encoding gene. The same manipulation also affected synchronized expression of the clock proteins TIM and PER in different subsets of the clock neurons. This shows that synaptic communication between the H-B eyelet and clock neurons contributes to synchronization of molecular and behavioral rhythms and confirms that the H-B eyelet functions as a circadian photoreceptor. Blockage of synaptic transmission from the H-B eyelet in the presence of functional compound eyes and the absence of CRY also results in increased numbers of flies that are unable to synchronize to extreme photoperiods, supplying independent proof for the role of the H-B eyelet as a circadian photoreceptor.     

Binocular responses of neurons in the barn owl's visual Wulst

Binocular responses have been recorded extra-cellularly at 58 sites in the barn owl's (Tyto alba) visual Wulst. Neurons showed disparity tuning to stimulation with moving bars, moving sinewave gratings and a moving visual-noise stimulus. Responses to sinewave gratings as a function of disparity were cyclic, with the period of a cycle of the response being correlated to one cycle of the stimulus. Cyclic responses were also found when bars or noise were used as a stimulus, but, especially in response to visual noise, one response peak, the main peak, was different from the other peaks, the sidepeaks: usually, the main peak was either higher or narrower or both higher and narrower than the sidepeaks. When the responses to different spatial frequencies were compared, response maxima coincided at the main peak, but not at the other peaks. In analogy to auditory physiology the disparity at which the frequency-independent peak occurs is termed characteristic disparity. Spatial-frequency tuning revealed broad tuning, ranging from 1 to more than 3 octaves at 50% of the maximal response. Disparity tuning was broad at the onset of the response and sharpened later. The data are discussed within the framework of a model for the neural representation of visual disparity that was derived from a model proposed earlier for the representation of interaural time difference, the main cue for encoding sound-source azimuths in the barn owl.Abbreviations ITD interaural time difference - CD characteristic delay - RF receptive field     

The role of visual afferentation in the development of early defense behavior of pied flycatcher nestlings

The development of defense behavior in normal and visually deprived pied flycatcher nestlings was studied in the wild. It was demonstrated that the young deprived of the visual afferentation did not develop the freezing posture. In the majority of cases, specific alarm call suppressed begging in visually deprived nestlings less effectively than in the control ones. Visually deprived nestlings could not discriminate between the alarm call and other rhythmically organized acoustic signals even though the latter effectively suppressed begging.     

Incubation temperature affects growth and energy metabolism in blue tit nestlings

Because the maintenance of proper developmental temperatures during avian incubation is costly to parents, embryos of many species experience pronounced variation in incubation temperature. However, the effects of such temperature variation on nestling development remain relatively unexplored. To investigate this, we artificially incubated wild blue tit (Cyanistes caeruleus L.) clutches at 35.0°, 36.5°, or 38.0°C for two-thirds of the incubation period. We returned clutches to their original nests before hatching and subsequently recorded nestling growth and resting metabolic rate. The length of the incubation period decreased with temperature, whereas hatching success increased. Nestlings from the lowest incubation temperature group had shorter tarsus lengths at 2 weeks of age, but body mass and wing length were not affected by temperature. In addition, nestlings from the lowest temperature group had a significantly higher resting metabolic rate compared with mid- and high-temperature nestlings, which may partly explain observed size differences between the groups. These findings suggest that nest microclimate can influence nestling phenotype, but whether observed differences carry over to later life-history stages remains unknown.     

Mild stress during development affects the phenotype of great tit Parus major nestlings: a challenge experiment

Conditions experienced during early development may affect both adult phenotype and performance later during life. Phenotypic traits may hence be used to indicate past growing conditions and predict future survival probabilities. Relationships between phenotypic markers and future survival are, however, highly heterogeneous, possibly because poor‐ and high‐quality individuals cannot be morphologically discriminated when developing under good environmental conditions. Sub‐optimal breeding conditions, in contrast, may unmask poor‐quality individuals in a measurable way at the morphological level. We thus predict stronger associations between phenotype and performance under stress. In this field study, we test this hypothesis, experimentally challenging the homeostasis of great tit (Parus major) nestlings by short‐term deprivation of parental care, which had no immediate effect on nestling fitness. The experiment was replicated during two subsequent breeding seasons with contrasting ambient weather conditions. Experimental (short‐term) stress affected tarsus growth but not residual mass at fledging, whereas ambient (continuous) stress affected residual mass but not tarsus growth. Short‐term stress effects on tarsus length and tarsus fluctuating asymmetry were only apparent when ambient conditions were unfavourable. Residual mass and hatching date, but none of the other phenotypic traits, predicted local survival, whereby the strength of the relationship did not vary between both years. Because effects of stress on developmental homeostasis are likely to be trait‐specific and condition‐dependent, studies on the use of phenotypic markers for individual fitness should integrate multiple traits comprising different levels of developmental complexity. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 103–110.     

Improved development of rat embryos in culture during the period of craniofacial morphogenesis

To study the mammalian craniofacial development, the culture conditions of rat whole embryo during the period of major craniofacial morphogenesis were examined. The improved rotating apparatus which is gassed continuously was used. Rat embryos explanted at 11.5 days (plug day 0) developed in vitro for up to 72 hr, that is, throughout the period of major craniofacial morphogenesis, and cultured embryos showed normal facial formation. The medium was equilibrated with a gas mixture of 95% 02, 5% CO2. The 100% rat serum improved the protein content of embryos cultured for 48 hr compared with the medium consisting of 50% rat serum and 50% Tyrode solution, although somite number was not altered. Furthermore, 100% rat serum containing 2 mg/ml glucose was the best medium for supporting growth of embryos when it was measured by protein content. Thus, the best culture medium was pure rat serum containing 50 units/ml penicillin, 50 micrograms/ml streptomycin, and 2 mg/ml glucose. Protein content, body weight, craniofacial formation, and somite number of embryos cultured for 48 hr with continuous gassing were much better than those cultured with noncontinuous gassing.     

Laser ablation of the sonic hedgehog-a-expressing cells during fin regeneration affects ray branching morphogenesis

The zebrafish fin is an excellent system to study the mechanisms of dermal bone patterning. Fin rays are segmented structures that form successive bifurcations both during ontogenesis and regeneration. Previous studies showed that sonic hedgehog (shha) may regulate regenerative bone patterning based on its expression pattern and functional analysis. The present study investigates the role of the shha-expressing cells in the patterning of fin ray branches. The shha expression domain in the basal epidermis of each fin ray splits into two prior to ray bifurcation. In addition, the osteoblast proliferation profile follows the dynamic expression pattern of shha. A zebrafish transgenic line, 2.4shh:gfpABC#15, in which GFP expression recapitulates the endogenous expression of shha, was used to specifically ablate shha-expressing cells with a laser beam. Such ablations lead to a delay in the sequence of events leading to ray bifurcation without affecting the overall growth of the fin ray. These results suggest that shha-expressing cells direct localized osteoblast proliferation and thus regulate branching morphogenesis. This study reveals the fin ray as a new accessible system to investigate epithelial-mesenchymal interactions leading to organ branching.     

d-canavanine affects peptidoglycan structure,morphogenesis and fitness in Rhizobiales

The bacterial cell wall is made of peptidoglycan (PG), a polymer that is essential for maintenance of cell shape and survival. Many bacteria alter their PG chemistry as a strategy to adapt their cell wall to external challenges. Therefore, identifying these environmental cues is important to better understand the interplay between microbes and their habitat. Here, we used the soil bacterium Pseudomonas putida to uncover cell wall modulators from plant extracts and found canavanine (CAN), a non-proteinogenic amino acid. We demonstrated that cell wall chemical editing by CAN is licensed by P. putida BSAR, a broad-spectrum racemase which catalyses production of dl -CAN from l -CAN, which is produced by many legumes. Importantly, d -CAN diffuses to the extracellular milieu thereby having a potential impact on other organisms inhabiting the same niche. Our results show that d -CAN alters dramatically the PG structure of Rhizobiales (e.g., Agrobacterium tumefaciens, Sinorhizobium meliloti), impairing PG crosslinkage and cell division. Using A. tumefaciens, we demonstrated that the detrimental effect of d -CAN is suppressed by a single amino acid substitution in the cell division PG transpeptidase penicillin binding protein 3a. Collectively, this work highlights the role of amino acid racemization in cell wall chemical editing and fitness.     

Activated charcoal affects morphogenesis and enhances sporophyte regeneration during leaf cell suspension culture of Platycerium bifurcatum

In a leaf cell suspension culture of Platycerium bifurcatum, the incorporation of activated charcoal (AC) greatly increased the number of regenerated sporophytes even in growth regulator-free medium. The degree of improvement was dependent on cell aggregate sizes and medium composition. The maximal increase was observed in medium with 5.37 μM NAA and 4.44 μM BA, from 9 to 1520 sporophytes. The qualitative improvement by AC included: (1) regeneration of single sporophytes, which was relatively less frequent in non-AC media, (2) prevention of the formation of gametophyte clusters prior to sporophyte regeneration from 30- to 60-μm cells cultured in MS basal medium, (3) prevention of the formation of bud clusters, sporophytes with multiple bud primordia, `nodule'-like bud clusters in growth regulator containing media, and (4) prevention of the occurrence of hyperhydricity of regenerated sporophytes. Received: 9 December 1996 / Revision received: 18 April 1997 / Accepted: 5 July 1997     

The role of hyaluronate in morphogenesis of the neurons

The data about organization of the extracellular matrix (ECM) components and their interplay in the mammalian brain are rather limited. Hyaluronate (HA) is one of the main ECM glycosaminoglycans. Its location and function in the brain are believed to be mediated through its interaction with HA-binding proteins and proteoglycans. In this report, we describe distribution of the total HA-binding activity in the cells in the course of postnatal development of the rat brain and the effect of HA on cultured neurons. A high level of the HA-binding activity was found in the newborn cerebellum, but it quickly decreased after postnatal day 1. On postnatal day 5, strong HA-binding activity was demonstrated only in apical parts of growth cones of Purkinje cells. The data showed rapid down-regulation of HA-binding activity at the first stage of cerebellum maturation (migration of granule cells and beginning of differentiation of neurons). To obtain more information concerning a key role of HA in morphogenesis of neurons, low density cell cultures of the hippocampal neurons were used. The presence of HA in the substrate led to an increase in the cell adherence. However, a part of the cells got differentiated later. These data allow us to suggest that interactions between extracellular HA and cell-surface receptors can regulate motility and differentiation of the neurons.     

Disruption of sabR affects nikkomycin biosynthesis and morphogenesis in Streptomyces ansochromogenes

The gene, sabR, encoding a receptor for -butyrolactone, was cloned from the genomic DNA of Streptomyces ansochromogenes 7100. Its deduced protein shows strong homology to several -butyrolactone-binding proteins in Streptomyces. Disruption of sabR retarded nikkomycin production in liquid media containing glucose or glycerol as carbon source. Sporulation of sabR disruption mutants was earlier than the parent strain on solid media with glucose or glycerol as carbon source. However, disruption of sabR had no effect on either nikkomycin production or sporulation on media containing mannitol as carbon source, suggesting that sabR is a pleiotropic regulatory gene that controls the onset of nikkomycin production and sporulation in S. ansochromogenes and is related to the utilization of carbon source.     

Disruption of a DNA topoisomerase I gene affects morphogenesis in Arabidopsis

The genesis of phyllotaxis, which often is associated with the Fibonacci series of numbers, is an old unsolved puzzle in plant morphogenesis. Here, we show that disruption of an Arabidopsis topoisomerase (topo) I gene named TOP1alpha affects phyllotaxis and plant architecture. The divergence angles and internode lengths between two successive flowers were more random in the top1alpha mutant than in the wild type. The top1alpha plants sporadically produced multiple flowers from one node, and the number of floral organ primordia often was different. The mutation also caused the twisting of inflorescences and individual flowers and the serration of leaf margins. These morphological abnormalities indicate that TOP1alpha may play a critical role in the maintenance of a regular pattern of organ initiation. The top1alpha mutant transformed with the RNA interference construct for TOP1beta, another topo I gene arrayed tandemly with TOP1alpha, was found to be lethal at young seedling stages, suggesting that topo I activity is essential in plants.     

Experimentally increased nest temperature affects body temperature,growth and apparent survival in blue tit nestlings

The thermal environment experienced by birds during early postembryonic development may be an important factor shaping growth and survival. However, few studies have directly manipulated nest temperature (T _n) during the nestling phase, and none have measured the consequences of experimental heat stress on nestlings’ body temperature (T _b). It is therefore not known to what extent any fitness consequences of development in a thermally challenging environment arise as a direct, or indirect, effect of heat stress. We, therefore, studied how experimentally increased T _n affected T _b in 8–12 d old blue tit Cyanistes caeruleus nestlings, to investigate if increased thermoregulatory demands to maintain normothermic T _b influenced nestling growth and apparent long‐term survival. Nestlings in heated nest‐boxes had significantly higher T _b compared to unheated nestlings during most of the experimental period. Yet, despite facing T _n  50°C (as measured in the bottom of the nest cup below the nestlings), the highest nestling T _b recorded was 43.8°C with nestlings showing evidence of controlled facultative hyperthermia without any increased nestling mortality in heated nests. However, body mass gain was lower in these nestlings compared to nestlings from control nest‐boxes. Contrary to our prediction, a larger proportion of nestlings from heated nest‐boxes were recaptured during their first winter, or subsequently recruited into the breeding population as first‐ or second‐year breeders. This result should, however, be treated with caution because of low recapture rates. This study highlights the importance of the thermal environment during nestling development, and its role in shaping both growth patterns and possibly also apparent survival.     

Elimination of adult-born neurons in the olfactory bulb is promoted during the postprandial period

Granule cells (GCs) in the mouse olfactory bulb (OB) continue to be generated in adulthood, with nearly half incorporated and the remainder eliminated. Here, we show that elimination of adult-born GCs is promoted during a short time window in the postprandial period. Under restricted feeding, the number of apoptotic GCs specifically increased within a few hours after the start of feeding. This enhanced GC apoptosis occurred in association with postprandial behaviors that included grooming, resting, and sleeping, and was particularly correlated with the length of postprandial sleep. Further, deprivation of olfactory sensory experience in the local OB area potentiated the extent of GC elimination in that area during the postprandial period. Sensory experience-dependent enhancement of GC elimination also occurred during postprandial period under natural feeding condition. These results suggest that extensive structural reorganization of bulbar circuitry occurs during the postprandial period, reflecting sensory experience during preceding waking period.     

Oligodendrocyte ablation affects the coordinated interaction between granule and Purkinje neurons during cerebellum development

Oligodendrocytes (OLs) are the glial cells of the central nervous system (CNS) classically known to be devoted to the formation of myelin sheaths around most axons of the vertebrate brain. We have addressed the role of these cells during cerebellar development, by ablating OLs in vivo. Previous analyses had indicated that OL ablation during the first six postnatal days results into a striking cerebellar phenotype, whose major features are a strong reduction of granule neurons and aberrant Purkinje cells development. These two cell types are highly interconnected during cerebellar development through the production of molecules that help their proliferation, differentiation and maintenance. In this article, we present data showing that OL ablation has major effects on the physiology of Purkinje (PC) and granule cells (GC). In particular, OL ablation results into a reduction of sonic hedgehog (Shh), Brain Derived Neurotrophic Factor (BDNF), and Reelin (Rln) expression. These results indicate that absence of OLs profoundly alters the normal cerebellar developmental program.