French Flag Research Articles

Cell size and proportional distance assessment during determination of organelle position in the cortex of the ciliate Tetrahymena.

Developing oral organelles of dividing Tetrahymena corlissi appear to be positioned by mechanisms which assess distances as a proportion of the organism's overall dimensions. In some respects, the cortex of this protozoan obeys the 'French flag' rule formulated by Wolpert for describing regulation of spatial proportions during differentiation of metazoan embryos. Dividing Tetrahymena of markedly different sizes occur when division is synchronized by starvation and refeeding. At the start of cell division, the distance between old and new mouthparts varies proportionately with respect to cell length. In addition, determination of the site where new oral organelles will develop is apparently not directly related to the number of ciliated basal bodies which separate the 2 sets of mouthparts; the greater the distance between the old and developing sets of mouthparts, the greater the number of ciliated basal bodies in the rows between them. It is suggested that 2 distinct mechanisms are largely responsible for defining organelle position in ciliates. The new terms structural positioning and chemical signalling are defined to describe these mechanisms.

A stochastic approach to the French Flag problem

A stochastic approach to the French Flag problem

A stochastic approach to the French Flag problem

An abstract is not available for this content so a preview has been provided. Please use the Get access link above for information on how to access this content.

The daughter of Celia, the French flag, and the firing squad

In earlier work we have reported on CELIA, a program for simulating the behavior of linear iterative arrays of cells. The action of a cell is influenced by both its neighbors. Our main application area was biology, where the program can be used to test hypotheses about the developmental rules for organisms. More recently we have been applying our program to test proposed solutions to some fairly complicated biozogically-based problems. We have investigated whether one can achieve regulative global polarity in organisms without polarity in individual cells, by solving the French flag problem of Wolpert, using only symmetric elements. In our attempted simulation of pigmentation patterns on the shells of sea-snails, we have found it necessary to find a solution to a generalized version of the firing squad synchronization problem, in which the firing squad is growing while it is trying to synchronize itself. We found that our original program CELIA was some what awkward for simulating such complicated situa tions. A new program has been devised in which the state of the individual ceZZs is described by a set of attributes and each attribute itself may be a list structure. The present paper reports on these changes and ex plains how they turn out to be useful in the appli cations mentioned above.

Positional information and the spatial pattern of cellular differentiation

The problem of pattern is considered in terms of how genetic information can be translated in a reliable manner to give specific and different spatial patterns of cellular differentiation. Pattern formation thus differs from molecular differentiation which is mainly concerned with the control of synthesis of specific macromolecules within cells rather than the spatial arrangement of the cells. It is suggested that there may be a universal mechanism whereby the translation of genetic information into spatial patterns of differentiation is achieved. The basis of this is a mechanism whereby the cells in a developing system may have their position specified with respect to one or more points in the system. This specification of position is positional information. Cells which have their positional information specified with respect to the same set of points constitute a field. Positional information largely determines with respect to the cells' genome and developmental history the nature of its molecular differentiation. The specification of positional information in general precedes and is independent of molecular differentiation. The concept of positional information implies a co-ordinate system and polarity is defined as the direction in which positional information is specified or measured. Rules for the specification of positional information and polarity are discussed. Pattern regulation, which is the ability of the system to form the pattern even when parts are removed, or added, and to show size invariance as in the French Flag problem, is largely dependent on the ability of the cells to change their positional information and interpret this change. These concepts are applied in some detail to early sea urchin development, hydroid regeneration, pattern formation in the insect epidermis, and the development of the chick limb. It is concluded that these concepts provide a unifying framework within which a wide variety of patterns formed from fields may be discussed, and give new meaning to classical concepts such as induction, dominance and field. The concepts direct attention towards finding mechanisms whereby position and polarity are specified, and the nature of reference points and boundaries. More specifically, it is suggested that the mechanism is required to specify the position of about 50 cells in a line, relatively reliably, in about 10 hours. The size of embryonic fields is, surprisingly, usually less than 50 cells in any direction.

Les Français de Grande Bretagne

MONSIEUR ANDRÉ LABARTHE, director-general of the Department of Armaments and Scientific Research in General de Gaulle's Legion, addressed a meeting of “Les Français de Grande Bretagne” on August 31, at the Central Hall, Westminster. Courage, decision and tenacity begin to bear fruit, he said. The French Empire is awakening from its stupefaction, and coming back to life. It is rallying to that French flag which General de Gaulle has raised again, to that flame which he has known how to shield from all blasts of misconception, carping and discouragement. This is the meaning of the re-entry into the war of French Equatorial Africa, the Cameroons and Lake Chad Territory, a re-entry of which the importance, material and moral, strategic and political, no one can overlook. In France itself, the rulers have sought to save their country from destruction by begging for a shameful armistice, and have opened the way to the most disastrous concessions. On one hand, the Germans are methodically pillaging the richest and most productive parts of the country, on the other the flood of refugees and the scarcity of transport are creating chaos and famine. Workers have left their factories and hungry children wander along the roads. Bit by bit, defeated France is handed over to the tender mercies of the conqueror. She can no longer even remain neutral; she is being dragged into the war on the side of the Germans.

The french flag and the trinitarian order

Journal Article The french flag and the trinitarian order Get access John B. Wainewright John B. Wainewright Search for other works by this author on: Oxford Academic Google Scholar Notes and Queries, Volume s11-XI, Issue 270, 27 February 1915, Pages 167–168, https://doi.org/10.1093/nq/s11-XI.270.167a Published: 27 February 1915

The French flag

Journal Article The French flag Get access Ed. Ed. Search for other works by this author on: Oxford Academic Google Scholar Notes and Queries, Volume s5-II, Issue 46, 14 November 1874, Page 384, https://doi.org/10.1093/nq/s5-II.46.384b Published: 14 November 1874