SummaryThe identity and behavior of mouse spermatogenic stem cells have been a long-standing focus of interest. In the prevailing “As model,” stem cell function is restricted to singly isolated (As) spermatogonia. By examining single-cell dynamics of GFRα1+ stem cells in vivo, we evaluate an alternative hypothesis that, through fragmentation, syncytial spermatogonia also contribute to stem cell function in homeostasis. We use live imaging and pulse labeling to quantitatively determine the fates of individual GFRα1+ cells and find that, during steady-state spermatogenesis, the entire GFRα1+ population comprises a single stem cell pool, in which cells continually interconvert between As and syncytial states. A minimal biophysical model, relying only on the rates of incomplete cell division and syncytial fragmentation, precisely predicts the stochastic fates of GFRα1+ cells during steady state and postinsult regeneration. Thus, our results define an alternative and dynamic model for spermatogenic stem cell function in the mouse testis.

SUMMARY Chromosomal inversion between 3q21 and 3q26 results in high-risk acute myeloid leukemia (AML). Here, we identified a mechanism whereby a GATA2 distal hematopoietic enhancer (G2DHE or −77-kb enhancer) is brought into close proximity to the EVI1 gene in inv(3)(q21;q26) inversions, leading to leukemogenesis. We examined the contribution of G2DHE to leukemogenesis by creating a bacterial artificial chromosome (BAC) transgenic model that recapitulates the inv(3)(q21;q26) allele. Transgenic mice harboring a linked BAC developed leukemia accompanied by EVI1 overexpression, neoplasia that was not detected in mice bearing the same transgene but missing the GATA2 enhancer. These results establish the mechanistic basis underlying the pathogenesis of a severe form of leukemia through aberrant expression of the EVI1 proto-oncogene.

No abstract

Xylene monooxygenase, encoded by the TOL plasmid of Pseudomonas putida, catalyzes the oxidation of toluene and xylenes and consists of two different subunits encoded by xylA and xylM. In this study, the complete nucleotide sequences of these genes were determined and the amino acid sequences of the xylA and xylM products were deduced. The XylM sequence had a 25% homology with alkane hydroxylase, which catalyzes the w-hydroxylation of fatty acids and the terminal hydroxylation of alkanes. The sequence of the first 90 amino acids of XylA exhibited a strong similarity to the sequence of chloroplast-type ferredoxins, whereas the rest of the XylA sequence resembled that of ferredoxin-NADP+ reductases. Based on this information, the structure and function of xylene monooxygenase were deduced. Xy1M may be a catalytic component for the hydroxylation of the carbon side chain of toluene and xylenes and, as is the alkane hydroxylase protein, may be a membrane-bound protein containing ferrous ion as a prosthetic group. XylA may have two domains consisting of an N-terminal region similar to chloroplast-type ferredoxins and a C-terminal region similar to ferredoxin-NADP+ reductases. The ferredoxin portion of XylA may contain a [2Fe-2S] cluster and reduce the oxidized form of the XylM hydroxylase. The activity determined by the C-terminal region of the XylA sequence may be the reduction of the oxidized form of ferredoxin by concomitant oxidation of NADH.