Publications

Les familles d'Actinoptérygiens qui franchissent la limite Crétacé-Tertiaire et celles qui s'éteignent au Maastrichtiensont passées en revue. Pour quelques faunes du Crétacé supérieur et du Paléocène; un niveau évolutif moyen est calculé à partir des degrés évolutifs des familles qui composent ces faunes. Les familles représentées par des espèces pélagiques marines ont été beaucoup plus affectées lors de la limite Crétacé-Tertiaire que les familles dont les représentants étaient marins dans des milieux profonds; ou dulçaquicoles. Pour ces dernières; le niveau évolutif est beaucoup plus bas que les familles marines contemporaines. Cela correspond à la présence de nombreuses espèces “primitive” dans ces faunes.

A new genus and new species of an ichthyodectiform fish, a new species of the pachyrizodontid Goulmimichthys, as well as specimens of Araripichthys sp. are described from the Agua Nueva Formation (Turonian) of Vallecillo, State of Nuevo León, NE Mexico. The ichthyodectiform fish shows a combination of characters from different families, warranting the creation of a new genus and questioning the monophyly of these families. We report herein the first record of Goulmimichthys and Araripichthys in North America.

A very large cis-regulatory region of approximately 300 kb is responsible for the complex patterns of expression of the three homeotic genes of the bithorax complex Ubx, abd-A and Abd-B. This region can be subdivided in nine parasegment-specific regulatory subunits. Recent genetic and molecular analysis has revealed the existence of two novel cis-regulatory elements Mcp and Fab-7. Mcp is located between iab-4 and iab-5, the parasegment-specific regulatory subunits which direct Abd-B in parasegments 9 and 10. Similarly, Fab-7 is located between iab-6 and iab-7, the parasegment 11 and 12-specific regulatory units. Mcp and Fab-7 appear to function as domain boundaries that separate adjacent cis-regulatory units. We report the analysis of two new Mcp mutant deletions (McpH27 and McpB116) that allow us to localize sequences essential for boundary function to a approximately 0.4 kb DNA segment. These essential sequences closely coincide to a approximately 0.3 kb nuclease hypersensitive region in chromatin. We also show that sequences contributing to the Fab-7 boundary appear to be spread over a larger stretch of DNA, but like Mcp have an unusual chromatin structure.

Naturally occurring cell death (NOCD) is a prominent feature of the developing nervous system. During this process, neurons express bcl-2, a major regulator of cell death whose expression may determine whether a neuron dies or survives. To gain insight into the possible role of bcl-2 during NOCD in vivo, we generated lines of transgenic mice in which neurons overexpress the human BCL-2 protein under the control of the neuron-specific enolase (NSE) or phosphoglycerate kinase (PGK) promoters. BCL-2 overexpression reduced neuronal loss during the NOCD period, which led to hypertrophy of the nervous system. For instance, the facial nucleus and the ganglion cell layer of the retina had, respectively, 40% and 50% more neurons than normal. Consistent with this finding, more axons than normal were found in the facial and optic nerves. We also tested whether neurons overexpressing BCL-2 were more resistant to permanent ischemia induced by middle cerebral artery occlusion; in transgenic mice, the volume of the brain infarction was reduced by 50% as compared with wild-type mice. These animals represent an invaluable tool for studying the effects of increased neuronal numbers on brain function as well as the mechanisms that control the survival of neurons during development and adulthood.

Vertebrate Hox genes are essential for the proper organization of the body plan during development. Inactivation of these genes usually leads to important alterations, or transformations, in the identities of the affected developing structures. Hox genes are activated in a progressive temporal sequence which is colinear with the position of these genes on their respective complexes, so that 'anterior' genes are activated earlier than 'posterior' ones (temporal colinearity). Here, an hypothesis is considered in which the correct timing of activation of this gene family is necessary in order to properly establish the various expression domains. Slight modifications in the respective times of gene activation (heterochronies) may shift expression domains along the rostrocaudal axis and thus induce concurrent changes in morphologies. It is further argued that temporal colinearity only occurs in cells with high mitotic rates, which results in a strong linkage between patterning and growth control and makes the patterning process unidirectional, from anterior, proximal and early, to posterior, distal and late, a model referred to as the 'Einbahnstrasse'. While the nature of the mechanism(s) behind temporal and spatial colinearities is unknown, it is proposed that such a mechanism relies on meta-cis interactions, that is it may necessitate gene contiguity. Such a mechanism would be based on DNA-specific, rather than gene-specific, features such as chromatin configurations or DNA replication. The existence of such a meta-cis mechanism would explain the extraoridinary conservation of this genetic system during evolution as its basic properties would be linked to that of the genetic material itself.(ABSTRACT TRUNCATED AT 250 WORDS)