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  • 1
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    Regulation of cell fate decision of undifferentiated spermatogonia by GDNF (2000)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2000-02-26
    Description: The molecular control of self-renewal and differentiation of stem cells has remained enigmatic. Transgenic loss-of-function and overexpression models now show that the dosage of glial cell line-derived neurotrophic factor (GDNF), produced by Sertoli cells, regulates cell fate decisions of undifferentiated spermatogonial cells that include the stem cells for spermatogenesis. Gene-targeted mice with one GDNF-null allele show depletion of stem cell reserves, whereas mice overexpressing GDNF show accumulation of undifferentiated spermatogonia. They are unable to respond properly to differentiation signals and undergo apoptosis upon retinoic acid treatment. Nonmetastatic testicular tumors are regularly formed in older GDNF-overexpressing mice. Thus, GDNF contributes to paracrine regulation of spermatogonial self-renewal and differentiation.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Meng, X -- Lindahl, M -- Hyvonen, M E -- Parvinen, M -- de Rooij, D G -- Hess, M W -- Raatikainen-Ahokas, A -- Sainio, K -- Rauvala, H -- Lakso, M -- Pichel, J G -- Westphal, H -- Saarma, M -- Sariola, H -- New York, N.Y. -- Science. 2000 Feb 25;287(5457):1489-93.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Research Programs of Developmental Biology, Molecular Neurobiology, Electron Microscopy Unit, Institute of Biotechnology, Viikki Biocenter, Finland.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10688798" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Apoptosis/drug effects ; Cell Cycle ; Cell Differentiation/drug effects ; Cobalt/metabolism ; *Drosophila Proteins ; Female ; Gene Expression ; Gene Targeting ; Glial Cell Line-Derived Neurotrophic Factor ; Glial Cell Line-Derived Neurotrophic Factor Receptors ; Male ; Mice ; Mice, Transgenic ; Mitosis ; *Nerve Growth Factors ; Nerve Tissue Proteins/genetics/*physiology ; Proto-Oncogene Proteins/genetics/metabolism ; Proto-Oncogene Proteins c-ret ; Receptor Protein-Tyrosine Kinases/genetics/metabolism ; Sertoli Cells/cytology/physiology ; *Spermatogenesis ; Spermatogonia/*cytology/drug effects ; Stem Cells/*cytology ; Testicular Neoplasms/pathology ; Testis/anatomy & histology ; Vitamin A/pharmacology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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    PAPER CURRENT
  • 2
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    Kinetics of Melting and Dissolution in Lunar Materials (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An understanding of the petrogenesis of lunar magmas, particularly mare basalts and the parent magmas to the Mg-rich suite, remains an unfulfilled goal. The fact is not surprising given the complexity of the problem. On the Moon, the source region for lunar magmas is not primitive mantle but rather a series of cumulate rocks that vary widely in both minerology and major and minor element contents. The stratigraphy of the cumulate mantle is not likely to be very regular given that the culumate pile is formed initially in an unstable configuration and subsequent thermal and compositional heterogeneities on a number of length scales. These lithologic heterogeneities, the large range of pressures and temperatures over which melts are generated on the Moon, and the close juxtaposition of cumulate rock with widely varying solidii introduce significant complications to the nature of the melting relations that control melt generation. These factors, coupled with the likelihood that polybaric fractional melting of varying efficiencies ultimately control the composition of planetary progress, are ample reasons why the lunar magmas remain the enigma they are. To make progress, phase equilibria studies must be coupled with a detailed understanding of the time scales and the dynamics of crystal and melt reequilibration processes.
    Keywords: Lunar and Planetary Science and Exploration
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Petrology and Physics of Magma Ocean Crystallization (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-11
    Description: Early Mars is thought to have been melted significantly by the conversion of kinetic energy to heat during accretion of planetesimals. The processes of solidification of a magma ocean determine initial planetary compositional differentiation and the stability of the resulting mantle density profile. The stability and compositional heterogeneity of the mantle have significance for magmatic source regions, convective instability, and magnetic field generation. Significant progress on the dynamical problem of magma ocean crystallization has been made by a number of workers. The work done under the 2003 MFRP grant further explored the implications of early physical processes on compositional heterogeneity in Mars. Our goals were to connect early physical processes in Mars evolution with the present planet's most ancient observable characteristics, including the early, strong magnetic field, the crustal dichotomy, and the compositional characteristics of the SNC meteorite's source regions as well as their formation as isotopically distinct compositions early in Mars's evolution. We had already established a possible relationship between the major element compositions of SNC meteorite sources and processes of Martian magma ocean crystallization and overturn, and under this grant extended the analysis to the crucial trace element and isotopic SNC signatures. This study then demonstrated the ability to create and end the magnetic field through magma ocean cumulate overturn and subsequent cooling, as well as the feasibility of creating a compositionally- and volumetrically-consistent crustal dichotomy through mode-1 overturn and simultaneous adiabatic melting.
    Keywords: Lunar and Planetary Science and Exploration
    Type: NRA-03-OSS-01-MFRP
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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