Nitrification by plants that also fix nitrogen (original) (raw)
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Journal of Anatomy, 1998
Careful histological observation of the development of the anlage of the inner ear in chicken embryos led us to question the traditional view of otic placode (OP) formation. First, morphological studies in the cephalic region carried out on stages preceding the appearance of the placodal epithelium revealed that the medial placodal cells are continuous temporally and spatially with cells belonging to the neural fold (NF). Second, both the formation of the basal lamina between the dorsal region of the neural tube (NT) and ectoderm and the pattern of formation of the neural crest present distinctive characteristics between otic levels and regions located anteriorly and posteriorly. Third, numerical comparisons of parameters for the NT and the OP between different levels of the rhombencephalon allowed us to assign a differential behaviour in the growth pattern of the otic region. These results indicated that the medial part of the OP is not derived from already independent ectoderm that increases in thickness under the influence of the NT (as previously accepted) but that it develops directly from the NFs. Although we do not exclude other possibilities, we propose that at least a proportion of the OP cells originate directly from cells committed to be neural crest. After this incorporation, basal laminal formation would delimit the NT from the OP without transition of the otic cells to ectoderm. This hypothesis would imply that part of the otic cells originate directly from neuroepithelial cells having a neuroectodermal (rather than the previously established ectodermal) origin.
Neural Tube Biology With Emphasis on Early Neurulation; A Narrative Review
Anatomical Sciences Journal, 2022
Neurulation, as the formation of the basis of the nervous system, is the earliest and crucial stage of embryonic development, affecting the development of other parts of the embryonic body. During neurulation, the neural plate is formed through morphological changes. At the end of this stage, the neural tube is established and the central nervous system could be formed in the future. Although this embryonic process occurs morphologically, the precise study of nervous system evolution can be considered by different gene mutations in rodent embryos. Genetic assessments of embryos can finally cause the accurate discovery of the role of genes in embryo development, the stages of nervous system development, and possible associated diseases. Explanation of new findings in the field of neurulation with emphasis on genetics can be helpful in future embryonic studies, abnormalities, and treatments. Thus, the study of neural plate formation can play an important role in increasing the insight of embryological researchers in this field. In this review article, we aimed to collect basic embryonic data in rodent neurulation to provide important information for more laboratory investigations in this field.
Determination of the embryonic inner ear
Journal of Neurobiology, 2002
Inner ear induction, like induction of other tissues examined in recent years, is likely to be comprised of several stages. The process begins during gastrulation when the ectoderm is competent to respond to induction. It appears that a signal from the endomesoderm underlying the otic area during gastrulation initiates induction complemented by a signal from presumptive neural tissue. By the neural plate stage, a region of ectoderm outside the neural plate is "biased" toward ear formation; this process may be part of a more general "placodal" bias shared by several sensory tissues. Induction continues during neurulation when a signal from neural tissue (possibly augmented by mesoderm underlying the otic area) results in ectoderm committed to otic vesicle formation at the time of neural tube closure. Studies on several gene families implicate them in the ear determination process. Fibroblast Growth Factor (FGF) family members are clearly involved in induction: FGFs are appropriately expressed for such a role, and have been shown to be essential for inner ear development. FGFs also have inductive activity, although it is not clear if they are sufficient for ear induction. Activation of transcription factors in the otic ectoderm, for example, by Pax gene family members, provides evidence for important changes in the responding ectoderm beginning during gastrulation and continuing through specification at the end of neurulation, although few functional tests have defined the role of these genes in determination. The challenge remains to merge embryologic data with gene function studies to develop a clear model for the molecular basis of inner ear induction.
Journal of Neuroscience, 2006
In the mouse, Frizzled3 (Fz3) and Frizzled6 (Fz6) have been shown previously to control axonal growth and guidance in the CNS and hair patterning in the skin, respectively. Here, we report that Fz3 and Fz6 redundantly control neural tube closure and the planar orientation of hair bundles on a subset of auditory and vestibular sensory cells. In the inner ear, Fz3 and Fz6 proteins are localized to the lateral faces of sensory and supporting cells in all sensory epithelia in a pattern that correlates with the axis of planar polarity. Interestingly, the polarity of Fz6 localization with respect to the asymmetric position of the kinocilium is reversed between vestibular hair cells in the cristae of the semicircular canals and auditory hair cells in the organ of Corti. Vangl2, one of two mammalian homologs of the Drosophila planar cell polarity (PCP) gene van Gogh/Strabismus, is also required for correct hair bundle orientation on a subset of auditory sensory cells and on all vestibular sensory cells. In the inner ear of a Vangl2 mutant (Looptail; Lp), Fz3 and Fz6 proteins accumulate to normal levels but do not localize correctly at the cell surface. These results support the view that vertebrates and invertebrates use similar molecular mechanisms to control a wide variety of PCP-dependent developmental processes. This study also establishes the vestibular sensory epithelium as a tractable tissue for analyzing PCP, and it introduces the use of genetic mosaics for determining the absolute orientation of PCP proteins in mammals.
The postnodal piece (PNP) of the chick embryo as a model system for studying organ differentiation
Toxicology in Vitro, 1995
Ah&&-The postnodal piece of the chick embryo is prepared by cutting the blastoderm 0.6 mm behind Hensen's node at the primitive streak stage. The explants with their area opaca can be maintained in flat culture (New's method) for 24-30 hr. With this method the polarity and the connections between various sheets are maintained, but the explants are stretched and difficult to handle for histology and immunostaining. Several PNPs from which the area opaca had been trimmed were cultured on one vitelline membrane (Niu and Deshpande's method) for up to 4 days without stretching effects. The polarity and connections between the embryonic sheets are hard to recognize, but explants can be easily processed for histology and immunofluorescence. In both culture types the explants can be easily treated, even with high molecular weight substances. Although the flat culture was useful for the induction of somites and of neural plates, we describe the advantages of culture without the area opaca of neural plates induced by tubulin mRNA or by TPA, which can differentiate into neural tubes. We also demonstrated that TPA is a powerful neural inducer in the chick embryo and stimulates cell proliferation in ectoderm and endoderm.
Teratology, 1997
Quail embryos (embryonic days 2-2.5) with spontaneous neural tube defects (NTDs), along with age-matched normal embryos, were examined immunocytochemically for the extracellular matrix (ECM) molecules laminin, fibronectin, and chondroitin sulfate proteoglycan, the cell adhesion molecules (CAMs) E-and N-cadherin and neural CAM (NCAM), and the neural crest marker HNK-1. The embryos with NTDs were at the lower limit of the normal stage range and the affected region was about 25% shorter than in normal embryos. Open NTDs occurred in cervical and upper thoracic level, although often the ventral neural tube was morphologically normal. Widened, irregular but closed neural tubes (lower thoracic to sacral levels) showed disorganized mesenchyme-like cells centrally and often multiple lumens. Finger-like tabs projecting from the ectoderm over the neural tube also occurred at lower thoracic to sacral levels. In open NTDs, the E-cadherin-labeled epidermis was incomplete dorsally, and was continuous with the N-cadherin-labeled neural tissue, with a sharp demarcation between E-and N-cadherin-expressing regions, as in the early stages of normal primary neurulation. A sharp inverted peak of epidermis extended ventrally, closely applied to the side of the neural tissue. The intervening matrix labeled less intensely for chondroitin sulfate proteoglycan relative to laminin and fibronectin, in comparison to control embryos. In closed NTDs, the dorsal superficial cell layer (i.e., positionally epidermis) was not separated from the underlying neural tissue by a band of matrix as in control embryos. In addition, this layer expressed E-cadherin (as in normal embryos), but coexpressed N-cadherin and NCAM, which are not normally found here at this stage. This overlap region resembled the mid-dorsal tissue at earlier stages in normal secondary neurulation in the tail-bud. The tabs of tissue appeared to be localized hypertrophy of the epidermal and neural ectoderm, and also showed codistribution of E-and N-cadherin. In all these defects, matrix molecules occurred within (rather than around) the neural and epidermal epithelia. HNK-1-labeled neural crest cells were frequently absent in regions of NTDs, in contrast to control embryos. These results show that matrix and cell adhesion molecules are disturbed in spontaneous NTDs at the time of neurulation, and therefore could be
Hearing Research, 1991
Cochleae from fetal guinea-pigs (37 to 64 gestation days, gd) were used to correlate the appearance of motile properties of isolated outer hair cells (OHCs) with the development of specific morphological features. Both the 'fast' electrically-driven and the 'slow' calcium-induced motilities appeared first in OHCs from basal turn of 52 gd fetuses. At 56 gd, most of basal and some apical OHCs responded positively to both types of stimulation. All tested cells were positive at 64 gd. It is noteworthy that this period closely corresponds to the onset and maturation of the gross cochlear potentials. Some structural changes in the organ of Corti may be correlated with the development of OHC motile properties: the acquisition of an adult-like cylindrical shape by the OHC, its lateral detachment from neighboring Deiters cells, and its surrounding by fluid spaces. At the ultrastructural level, the formation of a first layer of laminated cisternae regularly aligned along the OHC plasma membrane from the cuticular plate down to the nuclear level, temporally coincided with the onset of in vitro motility (52 gd). The following days, pillars and a sub-membrane lattice were clearly noticed between the outermost cisternal membrane and the plasma membrane. The results support the ideas that: motile properties observed in vitro reflect the in vivo active mechanisms, and that one single layer of laminated cisternae and its associated sub-plasma membrane material may be needed for OHC motility. Cochlear development; Outer hair cell motilities; Outer hair cell ultrastructure
Current Biology, 2003
Drosophila together with frizzled, dishevelled, prickle, strabismus/van gogh, and rhoA [2, 3]. The identification of mouse mutants of Celsr1 provides the first evidence for the function of the Celsr family in planar cell polarity in mammals and further supports the Two mutants, spin cycle (Scy) and crash (Crsh), were 2 MRC Institute of Hearing Research identified from independent ENU mutagenesis experi-University Park ments ([4] and B.C., unpublished data) by their head-Nottingham, NG7 2RD shaking behavior and subsequently were shown to ex-3 MRC Mammalian Genetics Unit hibit belly curling and spinning during tail suspension. Harwell These heterozygous phenotypes suggest some vestibu-Oxon, OX11 0RD lar dysfunction, although we have found no clear defect 4 Neural Development Unit in the peripheral vestibular system of adult Scy or Crsh Institute of Child Health mutants (data not shown). Both mutants exhibit a posi-University College London tive Preyer reflex in response to a 20 kHz, 90 dB SPL tone 30 Guilford Street burst; this finding indicates that they are not profoundly London, WC1N 1EH deaf. However, examination of the adult cochlea re-5 Institute of Human Genetics vealed that both Scy and Crsh heterozygotes contain an University of Newcastle upon Tyne excess of misoriented outer hair cell (OHC) stereociliary International Centre for Life bundles (Figures 1A and 1B), particularly in the apical Central Parkway turn of the cochlea (in Scy/ϩ, apex 3.60%, base 1.68% Newcastle upon Tyne, NE1 3BZ rotated; in ϩ/ϩ, apex 0.66%, base 0.18% rotated). Inner 6 Department of Obstetrics and Gynaecology hair cell stereociliary bundles appeared to be unaffected Institute of Reproductive and Developmental (Figures 1A and 1B). Crsh heterozygotes showed a Biology slightly milder phenotype than Scy, with fewer hair cells Imperial College School of Medicine affected (data not shown). The general organization into Hammersmith Campus three rows of outer and one row of inner hair cells ap-London, W12 0NN pears to be normal in Scy and Crsh heterozygotes, al-7 Department of Neurodegenerative Disease though there was a small amount of OHC degeneration Institute of Neurology in the basal turn (see the Supplemental Data available Queen Square with this article online). Furthermore, the upper surfaces London, WC1N 3BG of supporting cells immediately surrounding the af-United Kingdom fected hair cells showed abnormal shapes (Figures 1A and 1B). We examined cochleae from embryonic day (E) 16.5 and 18.5 ( ) and found that, even Summary at the earliest stages of OHC differentiation (E16.5 in the apex), bundle misorientation was observed in the We identified two novel mouse mutants with abnormal mutants, while controls showed normal orientation. The head-shaking behavior and neural tube defects during phenotype is particularly pronounced in homozygotes, the course of independent ENU mutagenesis experiwith apparently random orientation of OHC bundles,