Involvement of Glucocorticoids in the Development of the Secondary Palate

Genetic differences between various inbred strains of mice in the levels of glucocorticoid receptors embryonic in maxillary mesenchyme cells appear to be reflected in the magnitude of the responses to steroids in these cells. High levels of glucocorticoids cause significant growth inhibition in maxillary mesenchyme cells with subsequent alterations in the production of extracellular matrix components. The presence of higher levels of cytoplasmic glucocorticoid receptor proteins may be one factor which could predispose those strains such as A/J to a greater inhibition of craniofacial growth in vivo by glucocorticoids and therefore increase the frequency of cleft palate production. Furthermore, women with infertility treated with glucocorticoids to support pregnancy give birth to infants with a marked decrease in birth weight [98]. Pharmacologic doses of glucocorticoids can also cause a dramatic reduction in the growth of a number of fetal tissues in mice and humans. In fact, there is evidence that glucocorticoids may be a causative factor in the production of cleft palate in primates [52]. The nature of the molecular elements which determine the biochemical and physiologic responses to glucocorticoids in the palate still remains largely unknown. Although in the mouse there is some evidence to suggest that the major histocompatibility locus (H-2) might be involved, the level(s) at which this control is exerted is unknown. It is possible that this locus may regulate in some manner the level of glucocorticoid receptors and the response to glucocorticoids in the secondary palate. Moreover, there is evidence to suggest that other genes distinct from, but closely linked to the H-2 locus may be important in determining both the strain-dependent differences in susceptibility to glucocorticoid-induced cleft palate and the intracellular levels of cyclic AMP in the secondary palate. It is also apparent that glucocorticoids in conjunction with other hormones or growth factors such as epidermal growth factor and agents which regulate cyclic nucleotide metabolism are essential for the normal development of the secondary palate. Excesses or deficiencies in either the level of these growth regulators and/or in their receptors in specific fetal tissues at defined periods in development are likely to lead to certain fetal malformations. Definition and integration of the genetic, biochemical, and endocrine factors which are involved in the control of cellular growth as influenced by alterations in the composition of cell surface and extracellular matrix components should provide some insights into the events associated with normal palatogenesis.     

Partial Purification and Characterization of Naegleria fowleriβ-Glucosidase1

Naegleria fowleri cells, grown axenically, contain high levels of β-D-glucosidase which catalyzes the hydrolysis of 4-methylumbelliferyl-β-D-glucopyranoside (4MUGlc) (K_m, 0.9 mM), octyl-β-D-glucoside (K_m, 0.17 mM), and p-nitrophenyl-β-D-glucopyranoside at relative rates of 1.00, 2.88, and 1.16, respectively (substrate concentration, 3.0 mM). When the amebae are subjected to freeze-thawing, sonication, and centrifugation (100,000 g, 1 h), 85% of the β-glucosidase activity appears in the supernatant fraction. The β-glucosidase was purified 40-fold (34% yield) using a combination of chromatographic steps involving DE-52 cellulose, concanavalin A-Sepharose, and hydroxylapatite followed by isoelectric focusing. The predominant soluble β-D-galactosidase activity in the Naegleria extract copurifies with the β-D-glucosidase; the two activities have the same isoelectric point (pI, 6.9), similar heat stabilities, are both inhibited by lactobionic acid (K_i, 0.40 mM), and exhibit optima at pH 4.5, indicating that they are probably the same enzyme. The Naegleriaβ-D-glucosidase has an apparent molecular weight of 66,000, a Stokes radius of 25 Å, and a sedimentation coefficient of 4.2S. The β-glucosidase is not inhibited by conduritol β-epoxide or galactosylsphingosine but is completely inhibited by 1.25 mM bromo conduritol β-epoxide. The latter compound, when present in the growth medium, inhibits the growth of the organism and profoundly alters its ultrastructure, the main effect being the apparent inhibition of cytokinesis and the generation of multinucleate cells. The issue of the role of the β-glucosidase in the metabolism of the ameba and its possible role in pathogenic mechanisms are discussed.     

Plant Haemoglobins,Nitric Oxide and Hypoxic Stress

It is now known that there are several classes of haemoglobins in plants. A specialized class of haemoglobins, symbiotic haemoglobins, were discovered 62 years ago and are found only in nodules of plants capable of symbiotic nitrogen fixation. Plant haemoglobins, with properties distinct from symbiotic haemoglobins were discovered 18 years ago and are now believed to exist throughout the plant kingdom. They are expressed in different organs and tissues of both dicot and monocot plants. They are induced by hypoxic stress and by oversupply of certain nutrients. Most recently, truncated haemoglobins have been shown to also exist in plants. While hypoxic stress‐induced haemoglobins are widespread in the plant kingdom, their function has not been elucidated. This review discusses the recent findings regarding the function of these haemoglobins in relation to adaptation to hypoxia in plants. We propose that nitric oxide is an important metabolite in hypoxic plant cells and that at least one of the functions of hypoxic stress‐induced haemoglobins is to modulate nitric oxide levels in the cell.     

Emergence of Zoonotic Canine Leishmaniasis in the United States: Isolation and Immunohistochemical Detection of Leishmania infantum from Foxhounds from Virginia.

ABSTRACT. Previously considered an exotic disease, canine leishmaniasis caused by Leishmania infantum has recently been detected within the foxhound population in the United States and parts of Canada. Leishmania infantum is the etiologic agent of visceral leishmaniasis in many areas of the world and dogs are considered a major reservoir host for human Leishmania infections. Human visceral leishmaniasis has recently emerged as an opportunistic infection among individuals co-infected with HIV/AIDS and in persons taking immunosuppressive drugs. We report the isolation of L. infantum from 3 naturally infected foxhounds from Virginia by culture of popliteal lymph node and bone marrow, and the development of an immunohistochemical test to detect the parasite in tissues.     

萌发后食松幼苗淀粉粒结合与可溶性淀粉合酶的研究

裸子植物食松 (PinusedulisEngelm .)幼苗在萌发后具有淀粉积累的独特特征 ,而淀粉合酶在裸子植物中尚未有研究。这项研究对在室温下暗中萌发的食松幼苗的淀粉合酶进行了提取和研究 ,结果显示 :5 8kD和 91kD的淀粉粒结合蛋白均为豌豆淀粉合酶Ⅱ抗体所识别。5 8kD淀粉粒结合蛋白被纯化出来 ,其N端序列与其他几种被子植物淀粉粒结合的淀粉合酶Ⅰ的N端序列有很高的相似性 ,并与豌豆、大麦、马铃薯淀粉粒结合淀粉合酶Ⅰ有免疫相似性 ,被鉴定为淀粉粒结合的淀粉合酶Ⅰ。从DEAE_Sepharose柱上洗脱出来的可溶性淀粉合酶表现出两个淀粉合酶活性峰 ,表明至少有两类可溶性淀粉合酶同工酶。对可溶性淀粉合酶的前体亲和特性进行了研究。以兔肝糖原为前体时 ,可溶性淀粉合酶的亲和性最高。裸子植物淀粉合酶的酶学特性表现与已研究的被子植物相似。     

Landscape discontinuities influence gene flow and genetic structure in a large, vagile Australian mammal, Macropus fuliginosus

Large vagile mammals typically exhibit little genetic structuring across their range, particularly when their habitat is essentially continuous. We investigated the population genetic structure of a large vagile Australian macropodid, Macropus fuliginosus, which is continuously distributed across most of southern Australia, using nine highly polymorphic nuclear microsatellite loci. Five distinct genetic units were identified across the range, four on the mainland and one on Kangaroo Island. In addition to the predicted historic Nullarbor Plain Barrier, two unexpected mainland barriers to gene flow were identified. Both were associated with landscape discontinuities (Swan River, Flinders Ranges), which appear within the dispersal capabilities of M. fuliginosus. Typical of large vagile mammals, M. fuliginosus displays high genetic diversity (with the exception of an insular population) and weak genetic structuring (within genetic units). However, the expansion of M. fuliginosus from southwestern Australia during the Pleistocene has resulted in significantly reduced genetic diversity in eastern populations. No significant sex-biased dispersal was detected, although differences in habitat, densities and climatic conditions between the eastern and western regions of the range appear to influence dispersal with the effects of isolation by distance only evident in the west. These results suggest that the biogeography of southern Australia is more complex than previously thought and reveal that seemingly minor landscape features can significantly impact genetic structuring in large vagile mammals.     

Fire frequency and biodiversity conservation in Australian tropical savannas: implications from the Kapalga fire experiment

Abstract Every year large proportions of northern Australia's tropical savanna landscapes are burnt, resulting in high fire frequencies and short intervals between fires. The dominant fire management paradigm in these regions is the use of low‐intensity prescribed fire early in the dry season, to reduce the incidence of higher‐intensity, more extensive wildfire later in the year. This use of frequent prescribed fire to mitigate against high‐intensity wildfire has parallels with fire management in temperate forests of southern Australia. However, unlike in southern Australia, the ecological implications of high fire frequency have received little attention in the north. CSIRO and collaborators recently completed a landscape‐scale fire experiment at Kapalga in Kakadu National Park, Northern Territory, Australia, and here we provide a synthesis of the effects of experimental fire regimes on biodiversity, with particular consideration of fire frequency and, more specifically, time‐since‐fire. Two recurring themes emerged from Kapalga. First, much of the savanna biota is remarkably resilient to fire, even of high intensity. Over the 5‐year experimental period, the abundance of most invertebrate groups remained unaffected by fire treatment, as did the abundance of most vertebrate species, and we were unable to detect any effect of fire on floristic composition of the grass‐layer. Riparian vegetation and associated stream biota, as well as small mammals, were notable exceptions to this general resilience. Second, the occurrence of fire, independent of its intensity, was often the major factor influencing fire‐sensitive species. This was especially the case for extinction‐prone small mammals, which have suffered serious population declines across northern Australia in recent decades. Results from Kapalga indicate that key components of the savanna biota of northern Australia favour habitat that has remained unburnt for at least several years. This raises a serious conservation concern, given that very little relatively long unburnt habitat currently occurs in conservation reserves, with most sites being burnt at least once every 2 years. We propose a conservation objective of increasing the area that remains relatively long unburnt. This could be achieved either by reducing the proportion of the landscape burnt each year, or by setting prescribed fires more strategically. The provision of appropriately long unburnt habitat is a conservation challenge for Australia's tropical savanna landscapes, just as it is for its temperate forests.     

Testing for selection on the androgen-binding protein in the Danish mouse hybrid zone

The three peripheral subspecies of the house mouse Mus musculus have fixed specific variants of the androgen-binding protein (ABP) that have been proposed to be part of a recognition mechanism that could participate in sexual isolation between the subspecies. We tested for selection on Abpa by characterizing the pattern of Abpa introgression across a transect of the hybrid zone between M. m. musculus and M. m. domesticus in Jutland. On the musculus side, the cline for Abpa resembled that of a nearly neutral allozyme more than that of strongly selected X and Y chromosome markers. However, the high central step which displaces the tail of introgression of Abpa to higher frequencies was best accounted for by linkage to a locus under strong selection against hybrids. Still, we cannot exclude that this pattern results from weak selection against Abpa in the tail of introgression, which would be compatible with an assortative choice mechanism. On the domesticus side there was little introgression close to the hybrid zone, presumably due to a geographical barrier to migration. However, substantial frequencies of musculus alleles occurred further away, suggesting mixed colonization patterns as well as flow across the hybrid zone.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 447–459.