Heparin-binding EGF-like growth factor interacts with mouse blastocysts independently of ErbB1: a possible role for heparan sulfate proteoglycans and ErbB4 in blastocyst implantation.
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Blastocyst implantation requires molecular and cellular interactions between the uterine luminal epithelium and blastocyst trophectoderm. We have previously shown that heparin-binding EGF-like growth factor (HB-EGF) is induced in the mouse luminal epithelium solely at the site of blastocyst apposition at 16:00 hours on day 4 of pregnancy prior to the attachment reaction (22:00-23:00 hours), and that HB-EGF promotes blastocyst growth, zona-hatching and trophoblast outgrowth. To delineate which EGF receptors participate in blastocyst activation, the toxicity of chimeric toxins composed of HB-EGF or TGF-(&agr;) coupled to Pseudomonas exotoxin (PE) were used as measures of receptor expression. TGF-(&agr;) or HB-EGF binds to EGF-receptor (ErbB1), while HB-EGF, in addition, binds to ErbB4. The results indicate that ErbB1 is inefficient in mediating TGF-(&agr;)-PE or HB-EGF-PE toxicity as follows: (i) TGF-(&agr;)-PE was relatively inferior in killing blastocysts, 100-fold less than HB-EGF-PE, (ii) analysis of blastocysts isolated from cross-bred egfr+/- mice demonstrated that HB-EGF-PE, but not TGF-(&agr;)-PE, killed egfr-/- blastocysts, and (iii) blastocysts that survived TGF-(&agr;)-PE were nevertheless killed by HB-EGF-PE. HB-EGF-PE toxicity was partially mediated by cell surface heparan sulfate proteoglycans (HSPG), since a peptide corresponding to the heparin-binding domain of HB-EGF as well as heparitinase treatment protected the blastocysts from the toxic effects of HB-EGF-PE by about 40%. ErbB4 is a candidate for being an HB-EGF-responsive receptor since RT-PCR analysis demonstrated that day 4 mouse blastocysts express two different erbB4 isoforms and immunostaining with anti-ErbB4 antibodies confirmed that ErbB4 protein is expressed at the apical surface of the trophectoderm cells. It is concluded that (i) HB-EGF interacts with the blastocyst cell surface via high-affinity receptors other than ErbB1, (ii) the HB-EGF interaction with high-affinity blastocysts receptors is regulated by heparan sulfate, and (iii) ErbB4 is a candidate for being a high-affinity receptor for HB-EGF on the surface of implantation-competent blastocysts. (+info)
Discrete roles for secreted and transmembrane semaphorins in neuronal growth cone guidance in vivo.
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From the initial stages of axon outgrowth to the formation of a functioning synapse, neuronal growth cones continuously integrate and respond to multiple guidance cues. To investigate the role of semaphorins in the establishment of appropriate axon trajectories, we have characterized a novel secreted semaphorin in grasshopper, gSema 2a. Sema 2a is expressed in a gradient in the developing limb bud epithelium during Ti pioneer axon outgrowth. We demonstrate that Sema 2a acts as chemorepulsive guidance molecule critical for axon fasciculation and for determining both the initial direction and subsequent pathfinding events of the Ti axon projection. Interestingly, simultaneous perturbation of both secreted Sema 2a and transmembrane Sema I results in a broader range and increased incidence of abnormal Ti pioneer axon phenotypes, indicating that different semaphorin family members can provide functionally distinct guidance information to the same growth cone in vivo. (+info)
Comparative anatomy of the vomeronasal organ complex in bats.
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The morphology of the vomeronasal organ complex was histologically described in eight out of fourteen chiropteran species investigated. Of the six families examined, all except the family Pteropodidae (suborder Megachiroptera) were found to have at least one member possessing the organ. The organ is best developed in phyllostomatids. It is absent in vespertilionids (including a Myotis embryo) except in Miniopterus. An accessory olfactory bulb is reported for the first time in the latter. The organ is described for the first time in Rhinopoma, Megaderma, and Hipposideros. The organ in Rhinolophus is also described. Homologous anterior nasal cartilages and patent nasopalatine ducts are present in all species. The organ occupies the anterior ventral nasal septum region. In Megaderma and Hipposideros it is level with the nasal cavity floor. Areas of epithelium similar to olfactory epithelium have been observed in some organs. Epithelia, vascular sinuses, vomeronasal nerves, paravomeronasal ganglia, accessory olfactory bulbs, and vomeronasal glands have been investigated. In bats with regressed or rudimentary organs (Megaderma, Rhinopoma, Rhinolophus, Hipposideros) accessory olfactory bulbs could not be identified. Thus, presence of the organ does not necessarily indicate presence of the accessory olfactory bulb. Septal pockets located superior to the organ complex and lined with pseudostratified columnar epithelium are described in Hipposideros and may play a part in nasophonation. A unique role is proposed for the organ in the feeding behaviour of Desmodus. The desirability of extending the useful terms 'diosmatic' and 'monosmatic' to all vertebrates in reference to their respective possession or lack of the vomeronasal organ is suggested. (+info)
Fine structure and cytochemistry of the intralobular ducts of the human parotid gland.
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An intralobular duct of a human parotid gland has two parts, an intercalated part and a striated part. Intercalated ducts are lined with low cuboidal cells endowed with scanty cytoplasmic organelles. Striated ducts are lined with columnar cells rich in mitochondria and glycogen particles, and are characterized by extensive infoldings of the basal plasma membrane. The apical cytoplasm of the cells of the striated ducts shows a number of membrane-bound granules having a diameter of about 0-15 mum. These granules contain material of varying electron density which does not react with silver or with the histochemical reagents employed in the present study. Thus, on the basis of their small size and histochemical characteristics, they are distinct from the large and dense secretory granules observed in the so-called granular striated ducts of some animals. In addition, cells of striated ducts contain lysosomes, peroxisomes, and large lipoid bodies which give histochemical reactions typical of lipofuscins. Bodies of myoepithelial cells have been observed only in intercalated ducts. Their processes, however, extend into the proximal parts of striated ducts. (+info)
Secretory cells of the peripheral pulmonary epithelium as targets for toxic agents.
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The extracellular lining of the pulmonary peripheral airways is of vital importance to the lung. In this report, some aspects of the pulmonary extracellular lining and the epithelial cells believed to be responsible for its formation and secretion have been briefly reviewed. The influence of a number of toxic agents on the extracellular lining either directly or via those cells involved in its formation indicates that the extracellular lining may be important in understanding numerous toxic agent interactions with the lung. (+info)
Biochemical studies of isolated hamster tracheal epithelium.
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The epithelial lining of respiratory air passageways is a primary target tissue for toxicity and carcinogenesis in man and in animal models of human disease. The importance of this target tissue was the basis for development of methods to study its biochemistry, and with this information to distinguish the unique properties of this tissue from properties common to all cell types. Biochemical methods employed labeling of macromolecules in isolated hamster treacheas during brief (less than 4 hr) incubation in vitro. Studies of RNA metabolism in isolated tracheas demonstrated a pattern of maturation of ribosomal RNA like that shown for other cell types. Alterations in RNA metabolism were observed in isolated tracheas obtained from vitamin A-deficient hamsters and hamsters previously treated by intratracheal administration of benzo[a]pyrene (BP) plus ferric oxide (Fe2O3) in vivo. Studies with toyocamycin, actinomycin D, and alpha-amanitin, all inhibitors of RNA metabolism, were performed to characterize the class of RNA molecules with a decreased proportion of labeling in tracheas from vitamin A deficient hamsters. In another series of experiments, BP was shown to bind to DNA in epithelial cells of isolated tracheas. The quantity of BP binding was increased by prior intratracheal treatment of hamsters with BP plus Fe2O3 in vivo, this induced binding was inhibited by addition of 7,8-benzoflavone to the incubation medium. Increased BP binding was also observed in isolated tracheas from hamsters believed to be in states of increased susceptibility to respiratory carcinogenesis in vivo. The results show that biochemical studies are feasible with this tissue. Furthermore, a number of questions of importance with regard to this target epithelium are best studied directly in its constituent cells. (+info)
Association between mouse nude gene expression and the initiation of epithelial terminal differentiation.
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Loss-of-function mutations in Whn (Hfh 11), a winged-helix/forkhead transcription factor, result in the nude mouse phenotype. To determine the whn expression pattern during development, we utilized mice in which a beta-galactosidase reporter gene was placed under the control of the wild-type whn promoter by homologous recombination (M. Nehls et al., 1996, Science 272, 886-889). Sites of reporter expression were confirmed by immunohistochemical staining for Whn protein or by in situ hybridization for whn mRNA. At all developmental stages, whn expression is restricted to epithelial cells. In addition to the skin and thymus, whn is expressed in the developing nails, nasal passages, tongue, palate, and teeth. In embryonic epidermis, suprabasal cells induce whn expression at the same time that terminal differentiation markers first appear. As the epidermis matures, whn promoter activity is found primarily in the first suprabasal layer, which contains keratinocytes in the early stages of terminal differentiation. In developing and mature anagen hair follicles, whn is expressed at high levels in the postmitotic precursor cells of the hair shaft and inner root sheath. Though principally associated with terminal differentiation, whn expression is also detected in progenitor cell compartments; in the hair bulb matrix and basal epidermal layer, a small subclass of cells expresses whn, while in the outer root sheath, whn promoter activity is induced as the follicle completes its elongation. Within these compartments, rare cells exhibit both whn expression and the nuclear proliferation marker Ki-67. The results suggest that whn expression encompasses the transition from a proliferative to a postmitotic state and that whn regulates the initiation of terminal differentiation. (+info)
Apoptosis is a pathway responsible for the resolution of endotoxin-induced alveolar type II cell hyperplasia in the rat.
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Previous studies showed that intratracheal instillation of endotoxin induces transient type II cell hyperplasia in the rat lung and described some of the mechanisms involved in the proliferative response of type II cells. The purpose of the present study was to investigate how long the type II cell hyperplasia persists and how it is resolved. The portion of epithelial cells in hyperplastic lesions of the rat lung expressing cyclin D1, an indicator for cells in the G1 phase of the cell cycle, was greatest at 3 d post instillation and decreased after 4 and 6 d. The fate of the proliferating epithelial cells was traced by injecting the rats with 5-bromo-2' deoxy uridine (BrdU) 2 d post instillation, the peak time point for maximum incorporation of BrdU. Exfoliated BrdU-positive epithelial cells were detected in the alveolar spaces in tissue sections from rats 4, 5, and 6 d post instillation. BrdU-positive epithelial cells showed flattened nuclei at 6 and 10 d post instillation. Expression of the 116 kD poly(ADP-ribose) polymerase (PARP) was low in type II cells from control rats, and was increased at 3, 4, and 6 d post instillation. In cells obtained by lavage, only a 35 kD cleavage product of PARP was detected, which is an indicator of necrotic cell death. In isolated type II cells from rats 3, 4, and 6 d post endotoxin instillation, progressive cleavage of the PARP to its 89 kD residual fragment was detected, which is a direct evidence for the activation of caspases. Furthermore, apoptotic epithelial cells with condensed nuclei were identified by electron microscopy in rats 4 d post instillation. These results indicate that apoptosis is an additional mechanism for the resolution of endotoxin-induced lung epithelial hyperplasias. (+info)