Developmental phenotypic plasticity: Where ecology and evolution meet molecular biology

The plastic response of phenotypic traits to environmental change is a common research focus in several disciplines - from ecology and evolutionary biology to physiology and molecular genetics. The use of model systems such as the flowering plant Arabidopsis thaliana has facilitated a dialogue between developmental biologists asking how plasticity is controlled (proximate causes) and organismal biologists asking why plasticity exists (ultimate causes). Researchers studying ultimate causes and consequences are increasingly compelled to reject simplistic, ‘black box’ models, while those studying proximate causes and mechanisms are increasingly obliged to subject their interpretations to ecological ‘reality checks.’ We review the successful multidisciplinary efforts to understand the phytochrome-mediated shade-avoidance and light-seeking responses of flowering plants as a pertinent example of convergence between evolutionary and molecular biology. In this example, the two-way exchange between reductionist and holist camps has been essential to rapid and sustained progress. This should serve as a model for future collaborative efforts towards understanding the responses of organisms to their constantly changing environments.     

Tlie Two Milpas of Chan Kom: A Study of Socioeconomic and Political Transformations in a Maya Community

Tlie Two Milpas of Chan Kom:. Study of Socioeconomic and Political Transformations in. Maya Community. Alicia Re Cruz. Albany: State University of New York Press, 1996. 203 pp.     

Oxytocin Release by Infused Prostaglandin

Plasma oxytocin levels were measured serially in 22 women receiving prostaglandin E₂ or F_2α intravenously for the induction of labour. Oxytocin was detected in the plasma of 19 of the 22 women; positive levels were found in 60 (43%) of 139 plasma samples, an incidence similar to that in the late first stage of spontaneous labour. Oxytocin was found in the maternal plasma even when the fetus was dead, and in the plasma of two men receiving prostaglandin infusions. This indicates that prostaglandins stimulate the pituitary directly and suggests that this mechanism may play a part in the oxytocic action of infused prostaglandins.     

Motricity of the female genital apparatus in mammals. Hormonal correlations]

The motility and the pharmacological reactivity of the uterine tract of mammals are linked with the ovarian cycle and the gestation. In the birds, the study of general scheme of the hormonal mechanism and the uterine motility involued in the ovulation, the egg formation and the uterine dilatation can be used as an experimental model of the mammalian gestation.     

Ultrastructural visualization of the internalization of low density lipoprotein by human placental cells

Low density lipoproteins (LDL) were conjugated to colloidal gold to visualize the route for internalization of LDL in the cultured cells of human term placenta. Cells were obtained from placental villi (caesarian section) by a standard trypsin-DNase dispersion method followed in some cases by a Percoll gradient centrifugation step. Employing electron microscopy it was observed that after 3 days of culture, cells obtained by trypsin-DNase dispersion were a mixture of macrophages, mononucleated cells and large multinucleated cells. When the cells were incubated for 3 days after the Percoll purification, essentially multinucleated cells identical to the syncytiotrophoblast were present. The number of LDL receptor was increased by preincubation in medium with lipoprotein depleted serum. In binding experiments cells incubated at 4 degrees C for 2 h with medium containing gold LDL conjugates showed gold LDL attached to the plasma membrane without characteristic localization. After incubation with gold LDL at 37 degrees C for various times, the three cellular types showed ligand internalization. Gold LDL endocytosis involved first coated pits but also uncoated plasmalemmal invaginations. Then gold LDL was further observed in coated and non coated vesicles, smooth walled endosomes, multivesicular bodies and tubular vesicles. Lastly free gold particles were observed in lysosome like dense bodies. These results prove the internalization of gold LDL conjugates by human cultured placental cells, particularly by syncytiotrophoblast like multinucleated cells. This accumulation of LDL (the major cholesterol carrying protein in humans) is recognised to be responsible for the exogenous cholesterol supply indispensable to the progesterone biosynthesis and cellular growth of the placenta.