Hindbrain development and evolution: past, present, and future.
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Biomedical subjects
Eduardo Rosa-Molinar
Publications and source records attributed to Eduardo Rosa-Molinar.
The development of the hindbrain afferent projections in the axolotl: evidence for timing as a specific mechanism of afferent fiber sorting.
The aim of this study is to reveal the timing and growth pattern of central octavolateral projection development in the Mexican axolotl, Ambystoma mexicanum. In this amphibian species the development of the inner ear occurs first, followed by mechanosensory lateral line organs, and finally by ampullary electroreceptors. Several hypotheses have been proposed about how the development of peripheral organs, including differential projections of the ear, might relate to the development of central projections. Our data suggest that the sequence of maturation of the ear, mechanosensory lateral line, and ampullary electroreceptive organs is closely accompanied by the timed development of the trigeminal, inner ear, mechanosensory lateral line organs, and the ampullary electroreceptor afferent projections in the axolotl. Our data suggest that segregation of central termination within the alar plate is a function of time and space: later forming organs are likely innervated by later forming ganglia that project centrally later and to more dorsal areas of the alar plate that have not yet received any other afferents. Later forming ganglia of the same type may grow along existing pathways of earlier formed neurons.
Afferent Pathways↗
Starting from fins: parallelism in the evolution of limbs and genitalia: the fin-to-genitalia transition.
Organizers of the symposium Starting from Fins: Parallelism in the Evolution of Limbs and Genitalia intended it 1) to begin debates and discussions about parallelism, serial homology and transitions in development, as well as evolution of gene function and theories of origins and 2) to examine closely the potential significance of serial homology in understanding the evolution of morphology. This issue of Evolution and Development focuses on unpaired fin to genitalia transitions; the July-August issue will focus on paired fins to limbs, revisit the issues raised in the symposium, and point to future directions. Minelli's opening presentation introduced the central theme of the symposium by suggesting that body appendages such as arthropod and vertebrate limbs, chordate tails and external genitalia are evolutionarily divergent duplicates (paramorphs) of the main body axis. Suzuki's and Podlasek's presentations focused on the development of mammalian genitalia. Suzuki presented Suzuki et al investigations of the role of fibroblast growth factor (Fgf) and Sonic hedgehog (Shh) as signaling molecules during murine external genitalia formation, and Podlasek presented Podlasek et al investigations to elucidate a rudimentary pathway of essential developmental genes and transcriptional regulators such as Hox genes, Sonic hedgehog (Shh), and Bone morphogenetic proteins 2 and 4 (BMP-2; BMP-4), found in the limb. Discussions and questions emerging from the symposium point to the need to recognize that claims of phylogenetic cause must be based on something more than similarities; research must focus on the extent to which comparisons can be taken as well as on the evolutionary significance of similarities.
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Starting from fins: parallelism in the evolution of limbs and genitalia. The fin-to-limb transition.
The March/April 2002 issue of Evolution and Development focused on three presentations made at the Starting from Fins: Parallelism in the Evolution of Limbs and Genitalia symposium held as part of the 2001 Chicago meeting of the Society of Integrative and Comparative Biology. The intention of the symposium and the publication of the presentations was to extend discussion of the potential and the limits of using serial homologues to understand developmental aspects of morphological evolution. The March/April 2002 issue concentrated on unpaired fin to genitalia transitions. This issue focuses on paired fins to limbs and highlights the need for developmental data to be integrated with data from fossil materal, phylogenetic analysis, and explicitly comparative studies. Coates et al. use phylogenetic methods to explore the limb/fin characters of taxa, but their analysis departs somewhat from the usual in that the reference group for organisms includes sister group taxa not usually considered true tetrapods. They state that including finned taxa from the stem group permits an attempt to distinguish the primitive condition of the characteristics demonstrated by the crown group, that is, "limbed tetrapods." In focusing on limb characters specifically and including aspects of the appendicular girdles, Coates et al. highlight morphological details and trends within a given phylogeny. They also demonstrate the degree of relevance of limb characters during the establishment of lineages and their branching patterns by using only limb characters to generate a tree and use a direct comparison of serial versus special homologies to explore the degree of evolutionary parallelism between fore-and hindlimbs. The preliminary conclusions indicate a high level of independence between the serially homologous fore-and hindlimb. Innes et al. present outcomes from the use of cutting edge molecular genetic approaches to understand developmental aspects of limb morphology. In a manner conceptually similar to Coates et al.'s use of fossil characters, Innes et al. use the serial analysis of gene expression to sort differences from similarities in the gene expression profiles of fore-and hindlimbs of the same embryos. Although these gene expression pattems are likely to reflect the serial homology of the paired limbs, they are silent in terms of our understanding both the profound and subtle differences between fore- and hindlimbs in any given species. Innes et al. point out the volume of data generated by SAGE far exceeds our ability to interpret its biological meaning. The studies presented here and in the March/April issue are excellent examples of the need to interpret complex data in light of collective knowledge of evolutionary history. We hope the insights gained from the symposium and papers contribute to a dialogue on how to integrate different approaches and assist in moving forward the field of Evolution and Development.
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