Distinguishing Drift and Selection Empirically: “The Great Snail Debate” of the 1950s

Biologists and philosophers have been extremely pessimistic about the possibility of demonstrating random drift in nature, particularly when it comes to distinguishing random drift from natural selection. However, examination of a historical case – Maxime Lamotte’s study of natural populations of the land snail, Cepaea nemoralis in the 1950s – shows that while some pessimism is warranted, it has been overstated. Indeed, by describing a unique signature for drift and showing that this signature obtained in the populations under study, Lamotte was able to make a good case for a significant role for␣drift. It may be difficult to disentangle the causes of drift and selection acting in a population, but it is not (always) impossible.     

Differential response to hepatic differentiation stimuli of amniotic epithelial cells isolated from four regions of the amniotic membrane

Human Amniotic Epithelial Cells (hAEC) isolated from term placenta are a promising source for regenerative medicine. However, it has long been debated whether the hAEC population consists of heterogeneous or homogeneous cells. In a previous study, we investigated the characteristics of hAEC isolated from four different regions of the amniotic membrane finding significant heterogeneity. The aim of this study was to evaluate the hepatic differentiation capability of hAEC isolated from these four regions. Human term placentae were collected after caesarean section and hAEC were isolated from four regions of the amniotic membrane (R1-R4, according to their relative distance from the umbilical cord) and treated in hepatic differentiation conditions for 14 days. hAEC-derived hepatocyte-like cells showed marked differences in the expression of hepatic markers: R4 showed higher levels of Albumin and Hepatocyte Nuclear Factor (HNF) 4α whereas R1 expressed higher Cytochrome P450 enzymes, both at the gene and protein level. These preliminary results suggest that hAEC isolated from R1 and R4 of the amniotic membrane are more prone to hepatic differentiation. Therefore, the use of hAEC from a specific region of the amniotic membrane should be taken into consideration as it could have an impact on the outcome of therapeutic applications.     

Involvement of Carrot Cell Surface Proteins in Attachment of Agrobacterium tumefaciens

The initial step in tumor formation by Agrobacterium tumefaciens is the site-specific attachment of the bacteria to plant cells. A similar attachment to plant tissue culture cells has been observed. Binding to carrot suspension culture cells was not dependent on the presence of divalent cations and was not inhibited by the addition of mannose, α-methyl mannoside, galactose, arabinose, glucosamine, 2-deoxyglucose, or 0.25 molar NaCl to the culture medium. The ability of the carrot cells to bind A. tumefaciens was markedly reduced by elution of the cells with dilute detergent or CaCl₂ or by incubation of the cells with proteolytic enzymes. The carrot cells were not killed by these treatments and recovered the ability to bind A. tumefaciens within 3 to 6 hours. A. tumefaciens did not bind to carrot cells which had been induced to form embryos (AG Matthysse, RHG Gurlitz 1982 Physiol Plant Pathol 21: 381-387). A comparison of the peptides eluted from embryos and from uninduced cells using sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that there were several changes in extractable polypeptides after embryo induction. One or more of the polypeptides present before embryo induction and absent from embryos may be involved in the binding of A. tumefaciens to the carrot cell surface.     

Identification of somatic hybrids in plant protoplast fusions with monoclonal antibodies to plasma-membrane antigens

Monoclonal antibodies generated by immunization with a plasma-membrane preparation from suspension-cultured cells of Nicotiana glutinosa L. were used in combination with fluoresceinor rhodamine-labeled goat anti-mouse immunoglobulins to identify heterokaryons in protoplast fusion procedures. Antibody labeling did not inhibit callus formation nor plantlet regeneration. The antibodies are non-invasive and surface labeling provides clear optical discrimination of true heterokaryons from unfused aggregates as well as from parental protoplasts and homokaryons. Labeling is stable throughout fusion and hence by pre-labeling parental protoplast populations the strategy is both versatile and of general applicability.