Fungi on the hair of large mammals in Egypt

Several isolates of Candida albicans were tested for production of chlamydoconidia and metabolic changes when grown on several different solid and liquid media. A liquid medium, consisting solely of sterilized skimmed milk and a solid medium containing processed cheese stimulated more rapid and greater production of chlamydoconidia than the corn meal agar and the other media tested.     

Studies in symbiosis: hair follicle mites of mammals and man

A programme of study using hair follicle mites of man, dog, and other mammals is presented which has been successful in stimulating student interest in symbiosis. Brief background information on these mites, with illustrations, is provided as well as details of laboratory procedures for secondary school through college level classes. Suggestions for more advanced or independent studies using these mites are also made so that exceptional, career-oriented students and their teachers can explore adaptations to symbiosis in depth.     

Notch signaling regulates the pattern of auditory hair cell differentiation in mammals

The development of the mammalian cochlea is an example of patterning in the peripheral nervous system. Sensory hair cells and supporting cells in the cochlea differentiate via regional and cell fate specification. The Notch signaling components shows both distinct and overlapping expression patterns of Notch1 receptor and its ligands Jagged1 (Jag1) and Jagged2 (Jag2) in the developing auditory epithelium of the rat. On embryonic day 16 (E16), many precursor cells within the K?lliker's organ immunostained for the presence of both Notch1 and Jag1, while the area of hair cell precursors did not express either Notch1 and Jag1. During initial events of hair cell differentiation between E18 and birth, Notch1 and Jag1 expression predominated in supporting cells and Jag2 in nascent hair cells. Early after birth, Jag2 expression decreased in hair cells while the pattern of Notch1 expression now included both supporting cells and hair cells. We show that the normal pattern of hair cell differentiation is disrupted by alteration of Notch signaling. A decrease of either Notch1 or Jag1 expression by antisense oligonucleotides in cultures of the developing sensory epithelium resulted in an increase in the number of hair cells. Our data suggest that the Notch1 signaling pathway is involved in a complex interplay between the consequences of different ligand-Notch1 combinations during cochlear morphogenesis and the phases of hair cell differentiation.     

Solar heating of mammals: Observations of hair transmittance

The transmission of solar radiation through animal coats by diffuse scattering is well known, but the part played by hair structure has not been examined. Transmittance of light through single guard hairs of 6 marine and 5 terrestrial mammals was measured through a microscope and values ranging from 0.29 to 0.94 were found. The hair transmittance was negatively correlated with pigmentation and medullation. Stepwise regression analysis indicates that solar heating at skin level is correlated with both hair transmittance and coat reflectance besides being coupled with coat thickness.     

Development of the clavicles in birds and mammals

Clavicles (collar bones) are variably present in mammals. Furculae (wishbones)--which may or may not be homologous with clavicles--are variably present and/or fused in birds and present in theropod dinosaurs. In this overview the development of clavicles and furculae is discussed with special attention to modes of skeletogenesis (whether intramembranous or endochondral), numbers of centres of ossification (one in chick furculae; two in murine clavicles), presence of cartilage (primary in clavicles, secondary in furculae), evidence from experimental analysis and from mutations for dependence of both clavicular and furcular growth on mechanical stimulation, and syndromes and mutations affecting clavicular development leading to both under and over development. J. Exp. Zool. 289:153-161, 2001.     

Survival of bundleless hair cells and subsequent bundle replacement in the bullfrog's saccule

Our senses of hearing and balance depend upon hair cells, the sensory receptors of the inner ear. Millions of people suffer from hearing and balance deficits caused by damage to hair cells as a result of exposure to noise, aminoglycoside antibiotics, and antitumor drugs. In some species such damage can be reversed through the production of new cells. This proliferative response is limited in mammals but it has been hypothesized that damaged hair cells might survive and undergo intracellular repair. We examined the fate of bullfrog saccular hair cells after exposure to a low dose of the aminoglycoside antibiotic gentamicin to determine whether hair cells could survive such treatment and subsequently be repaired. In organ cultures of the bullfrog saccule a combination of time‐lapse video microscopy, two‐photon microscopy, electron microscopy, and immunocytochemistry showed that hair cells can lose their hair bundle and survive as bundleless cells for at least 1 week. Time‐lapse and electron microscopy revealed stages in the separation of the bundle from the cell body. Scanning electron microscopy (SEM) of cultures fixed 2, 4, and 7 days after antibiotic treatment showed that numerous new hair bundles were produced between 4 and 7 days of culture. Further examination revealed hair cells with small repaired hair bundles alongside damaged remnants of larger surviving bundles. The results indicate that sensory hair cells can undergo intracellular self‐repair in the absence of mitosis, offering new possibilities for functional hair cell recovery and an explanation for non‐proliferative recovery. © 2002 Wiley Periodicals, Inc. J Neurobiol 50: 81–92, 2002; DOI 10.1002/neu.10002     

Development of the hair bundle and mechanotransduction

This review focuses on the cellular and molecular mechanisms underlying the development of the sensory hair bundle, an apical specialisation of the hair cell that is essential for mechanotransduction. The structure, function and development of the hair bundle is described, with an emphasis on the properties and possible roles played by the different link types that interconnect the individual elements of the hair bundle - the multiple stereocilia and the single kinocilium. Studies of mouse and zebrafish mutants have revealed that several classes of molecule are required for the genesis and maintenance of hair-bundle structure. These include cell surface molecules that are associated with the different hair-bundle links, along with myosin motors, scaffolding proteins and an actin cross-linker. Finally we consider how differences in the form and shape of hair bundles within and between different sensory organs are generated.     

IGF系统与雌性哺乳动物生殖

胰岛素样生长因子(insulin-like growth factor,IGF)是一类多肽类生长因子。IGF-I、IGF-II以及各自受体和胰岛素生长因子结合蛋白(IGF-binding proteins, IGFBPs)构成了IGF系统。IGF系统在多个组织器官中均有表达,具有调节动物生殖,细胞增殖和凋亡等方面的功能。本文综述了IGF系统在雌性动物生殖激素分泌、卵泡闭锁、胚胎和胎盘发育等方面的作用,为进一步研究IGF系统对动物生殖的调控提供参考。     

Stem cells for the replacement of inner ear neurons and hair cells

Stem cells in the nervous system have some capacity to restore damaged tissue. Proliferation of stem cells endows them with self-renewal ability and accounts for in vitro formation of neurospheres, clonally derived colonies of floating cells. However, damage to the nervous system is not readily repaired, suggesting that the stem cells do not provide an easily recruited source of cells for regeneration. The vestibular and auditory organs, despite their limited ability to replace damaged cells, appear to contain cells with stem cell properties. These inner ear stem cells, identified by neurosphere formation and by their expression of markers of inner ear progenitors, can differentiate to hair cells and neurons. Differentiated cells obtained from inner ear stem cells expressed sensory neuron markers and, after co-culture with the organ of Corti, grew processes that extended to hair cells. The neurons expressed synaptic vesicle markers at points of contact with hair cells. Exogenous stem cells have also been used for hair cell and neuron replacement. Embryonic stem cells are one potential source of both hair cells and sensory neurons. Neural progenitors made from embryonic stem cells, transplanted into the inner ear of gerbils that had been de-afferented by treatment with a toxin, differentiated into cells that expressed neuronal markers and grew processes both peripherally into the organ of Corti and centrally. The regrowth of these neurons suggests that it may be possible to replace auditory neurons that have degenerated with neurons that restore auditory function by regenerating connections to hair cells.     

Local sequence dependence of rate of base replacement in mammals.

I have analysed the local sequence context of base replacement changes in 78 processed pseudogenes. Transversions occur more often than transitions in a ratio of 3.37 to 1, and G:C is replaced 1.4 times more frequently than A:T. In addition, the bases to the 5' and 3' of the mutating base also influence the rate at which bases change, purine:pyrimidine and pyrimidine:purine pairs changing 1.2 times as fast as purine:purine and pyrimidine:pyrimidine pairs. I discuss implications of this for the mechanism of DNA polymerization in mammals.     

Survival of bundleless hair cells and subsequent bundle replacement in the bullfrog's saccule.

Our senses of hearing and balance depend upon hair cells, the sensory receptors of the inner ear. Millions of people suffer from hearing and balance deficits caused by damage to hair cells as a result of exposure to noise, aminoglycoside antibiotics, and antitumor drugs. In some species such damage can be reversed through the production of new cells. This proliferative response is limited in mammals but it has been hypothesized that damaged hair cells might survive and undergo intracellular repair. We examined the fate of bullfrog saccular hair cells after exposure to a low dose of the aminoglycoside antibiotic gentamicin to determine whether hair cells could survive such treatment and subsequently be repaired. In organ cultures of the bullfrog saccule a combination of time-lapse video microscopy, two-photon microscopy, electron microscopy, and immunocytochemistry showed that hair cells can lose their hair bundle and survive as bundleless cells for at least 1 week. Time-lapse and electron microscopy revealed stages in the separation of the bundle from the cell body. Scanning electron microscopy (SEM) of cultures fixed 2, 4, and 7 days after antibiotic treatment showed that numerous new hair bundles were produced between 4 and 7 days of culture. Further examination revealed hair cells with small repaired hair bundles alongside damaged remnants of larger surviving bundles. The results indicate that sensory hair cells can undergo intracellular self-repair in the absence of mitosis, offering new possibilities for functional hair cell recovery and an explanation for non-proliferative recovery.