Publications

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)

The abdominal A (abdA) gene is one of three transcription units in the Bithorax Complex of Drosophila encoding a homeo box protein; it is flanked by Ultrabithorax (Ubx) and Abdominal B (AbdB). The abdA gene is required for segmental identity of the second through eighth abdominal segments. The transcription unit of abdA is approximately 20 kb long and encodes a protein of 330 amino acids. The abdA homeo box is almost identical to the homeo box of Ubx but is quite different from the AbdB homeo box. A polyclonal antibody to abdA protein stains embryonic nuclei in segments A1-A7 (parasegments 7-13). The iab-2, 3, and 4 mutant classes define positive cis-regulatory elements that induce expression of abdA in segments A2-A4 (parasegments 7-9), respectively. Once a pattern of abdA expression is turned on in a given parasegment, it remains on in the more posterior parasegments, so that the complex pattern of expression is built up in the successive parasegments. The abdA product appears to repress expression of Ubx whenever they appear in the same cell, but abdA is repressed by AbdB only in the eighth and ninth abdominal segments.

The alpha-crystallin-related heat shock (stress) protein hsp27 is expressed in absence of heat shock during Drosophila melanogaster development. Here, we describe the tissue distribution of this protein using an immunoaffinity-purified antibody. In embryos, hsp27 translated from maternal RNA is uniformly distributed, except in the yolk. During the first, second, and early third larval stages, hsp27 expression is restricted to the brain and the gonads. These tissues are characterized by a high level of proliferating cells. In late third instar larvae and early pupae, in addition to the central nervous system and the gonads, all the imaginal discs synthesize hsp27. The disc expression seems restricted to the beginning of their differentiation since it disappears during the second half of the pupal stage: no more hsp27 is observed in the disc-derived adult organs. In adults, hsp27 is still present in some regions of the central nervous system, and is also expressed in the male and female germ lines where it accumulates in mature sperm and oocytes. The transcript and the protein accumulate in oocytes since the onset of vitellogenesis with a uniform distribution similar to that found in embryos. The adult germ lines transcribe hsp27 gene while no transcript is detected in the late pupal and adult brain. These results suggest multiple roles of hsp27 during Drosophila development which may be related to both the proliferative and differentiated states of the tissues.