Cloned interstitial stem cells grow as contiguous patches in hydra

The migration of interstitial cells was analyzed during the growth of stem cell clones in vivo. The spatial distribution of cloned cells was analyzed at a time by which extensive migration of interstitial cells could have occurred. All interstitial cell clones were found to form large contiguous patches of cells. The results indicate that there is little migration of large interstitial cells in undisturbed tissue during normal growth. This finding is surprising since numerous grafting experiments have shown extensive migration of these cells. The implications of finding nonrandomly distributed stem cells are discussed

Immunocompetence in Hydra. Epithelial cells recognize self-nonself and react against it

The evolution of effective immunologic defense mechanisms in multicellular organisms involves the ability of host cells to distinguish betweeen self and nonself and to react appropriately to eliminate foreign tissue. By producing interspecies grafts we have obtained evidence that immunorecognition followed by incompatibility reactions occur in Hydra. Our results demonstrate that epithelial cells of Hydra recognize and phagocytose foreign hydra cells, indicating that they are the effector cells in the incompatibility reactions. This observation is consistent with the idea that immunocompetence appeared early in the evolution of multicellular organisms

Male and female stem cells and sex reversal in Hydra polyps

Single interstitial stem cells of male polyps of Hydra magnipapillata give rise to clones that differentiate either male or female gametes. To test the sexual stability of these clones, stem cells were recloned. The results indicate that stem cells from female clones are stable in their sexual differentiation capacity; male stem cells, by comparison, switch sexual phenotype at the rate of 10-2 per cell per generation. As a result, female polyps contain only female stem cells; male polyps contain a mixture of male and female stem cells. A model is presented in which the sexual phenotype of Hydra polyps is controlled by (i) the switching rate of male and female stem cells and (ii) the repression of female differentiation by male stem cells

Growth regulation in Hydra. Relationship between epithelial cell cycle length and growth rate

The relationship between epithelial cell production and growth rate was investigated in Hydra attenuata under different feeding regimes. The increase of epithelial cell number was compared to the duration of the epithelial cell cycle using standard methods of cell cycle analysis. The results indicate that cell cycle changes accompanying changes in feeding regime are not sufficient to explain the altered growth rate. Under heavy feeding regimes, epithelial cell production equals tissue growth rate. At low feeding level or under starvation conditions the epithelial cell cycle lengthens and growth rate of epithelial cell population is slowed. However, the cell cycle changes are insufficient to account for the reduction in tissue growth and thus there is an effective overproduction of epithelial cells amounting to 10% per day. Evidence suggests that these excess cells are phagocytized by neighboring cells in the tissue. Thus phagocytosis is directly or indirectly involved in regulating the growth of hydra tissue

Shape Function Effects in B -> X_c l \nu_l

Owing to the fact that m_c^2 ~ m_b \Lambda_QCD, the endpoint region of the charged lepton energy spectrum in the inclusive decay B -> X_c l \nu_l is affected by the Fermi motion of the initial-state b quark bound in the B meson. This effect is described in QCD by shape functions. Including the mass of the final-state quark, we find that a different set of operators as employed in Ref. hep-ph/0205150 is needed for a consistent matching, when incorporating the subleading contributions in B -> X_q l \nu_l for both q = u and q = c. In addition, we modify the usual twist expansion in such a way that it yields a description of the lepton energy spectrum which is not just valid in the endpoint region, but over the entire phase space.Comment: 8 Pages, LaTeX, 2 figures; a few typos corrected and some clarifications added, final journal versio