Control of cell fate in the tail region of C. elegans by the gene egl-5

The tail region of C. elegans contains a number of blast cell and neuron types that either are found only in the tail, or are different from more anterior homologues. In egl-5 mutants, the fates of many of these tail cells are abnormal or transformed to those of anterior homologues. The affected cells are related only by position and not by ancestry. egl-5 is also required for normal development of the somatic gonad and sex muscles in males. The function of egl-5 in all these tissues is cell autonomous. By genetic mapping, egl-5 lies very close to mab-5, a gene with an analogous role in the immediately anterior body region. egl-5 and mab-5 may constitute a ‘mini-cluster’ of regional determination genes, similar to those described in other animal phyla.

Etude expérimentale sur les premiers stades du développement du membre antérieur chez l'embryon du Chélonien Emys orbicularis L.: détermination en mosaïque et régulation

Experimental study on the early stages of development of the front limbs of the embryo of the chelonian Emys orbicularis L.: mosaic determination and regulation Ablation of postotic somites 6–13 on one side in embryos of Emys orbicularis L. or injury to the adjacent somatopleure at the developmental stage when 15–21 somite pairs were present, led to arrest of forelimb-bud development in this part of the somatopleure on the operated side. Limb development in the remaining part of prospective somatopleure on the operated side was investigated 5–11 days after the operation. When this part of somatopleure was adjacent to cranial somites 6–9 or 6–10, the development stopped at the start of the apical crest as in Anguis or Scelotes forelimb-buds. A part of somatopleure adjacent to caudal somites 8–12, 9–12 or 10–12 developed into a normal limb with three segments; a part of somatopleure adjacent to 1–2 somites only, developed into a reduced limb, scarcely swelling. Each somitic level developed in relation to its initial regional determination dependent on position in the cephalocaudal axis; to its environment (cranial or caudal bud) and to the quantity of somatopleural material in the bud.

A Statistical Analysis of Some Measures of the State of A Glacier’s “Health”

Data from Norwegian glaciers and statistical tests are presented which suggest that vertical net-budget gradient, ablation gradient and equilibrium-line altitude can be taken as characteristic for any particular glacier. The usefulness of these conceptual models as predictive techniques for the regional determination of glacier net budget when only a small sample is available, and in palaeo-net-budget studies, is shown to be limited.