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No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

The Acipenseridae comprises the largest group of non-teleostean actinopterygians and has served a central role in evolutionary studies of the Actinopterygii, and yet no comprehensive study of morphology and systematics of the family has ever been made. The family includes twenty-four species within four traditionally recognized genera, but the traditional generic designations lack rigorous definition within a cladistic scheme and are confounded by plesiomorphic characters. As background, revised diagnoses, synonymy lists, and overviews of life history are provided for every acipenserid species and genus. The systematics of the Acipenseridae are addressed with emphasis on generic-level relationships based on characters from examinations of skeletal morphology. A complete description of the skeleton of the shovelnose sturgeon Scaphirhynchus platorynchus provides a template of the skeleton of acipenserids. Skeletal comparisons with representatives of the remaining three acipenserid genera (Huso, Acipenser, and Pseudoscaphirhynchus), as well as Polyodontidae, $\dagger$Chondrosteidae, $\dagger$Peipiaosteidae, and other actinopterygians were used to identify, define, and test putative synapomorphies. Ninety-six synapomorphies are identified defining all major nodes within Acipenseriformes. A novel phylogeny of Acipenseridae is proposed, with Huso recognized as the sister group to a newly redefined subfamily Acipenserinae comprising all other acipenserids. The shovelnose sturgeons (genera Scaphirhynchus and Pseudoscaphirhynchus) compose a monophyletic Scaphirhynchini. No synapomorphies are recognized defining Acipenser, leaving the genus as a potentially untenable assemblage within Acipenseridae. The proposed phylogeny suggests that evolution within Acipenseridae followed a markedly different course than typically assumed, with progressive increase in morphological specializations for benthic life. Huso and polyodontids (as immediate outgroups) define an outgroup morphology and life history founded on mid-water habitats and piscivory. In contrast, most acipenserines, and more markedly in scaphirhynchines, are more benthic as exemplified by their ventral jaws and substrate-oriented diets. This phylogeny further suggests that peramorphosis, not paedomorphosis, played a central role in acipenserid evolution, exemplified by progressive acquisition of novel bones, increased scalation, and stronger dermal ornament. While putative paedomorphic characters are coincident with these peramorphic characters, addition of characters through peramorphosis belies the historical idea that paedomorphic or degenerate features dominate acipenserid evolution.

The organization of retinal ganglion cell (RGC) axons within the optic nerve (ON), chiasm (OCh), and tract of the frog, Rana pipiens, was examined using both light and electron microscopy. In one group of experiments, anterograde and retrograde transport of horseradish peroxidase (HRP) revealed the spatial reorganizations of RGC axons between the retina and central retinorecipient targets. Optic axons form a concentric representation or map of the retinal surface across the distal ON cross-section. Within this map, the distal ON contains two representations of the temporal and nasal retinal quadrants. Fiber reorganizations within the proximal ON result in axons from central RGCs becoming positioned within the dorsal region of the nerve and in axons of more peripheral RGC becoming localized to the ventral, anterior, and posterior margins of the nerve. As a result of this proximal ON fiber reorganization, age-related RGC axons become grouped in laminae that are aligned perpendicular to the posterodorsal-anteroventral axis of the optic projection. Axons occupying complementary positions in different retinal representations converge in a dorsal-to-ventral sequence as the projection passes through the perichiasm. Within the prechiasm, axons separate from the laminated optic projection to form four fascicles; the projection to corpus geniculatum, the projection to the neuropil of Bellonci, the basal optic root, and the marginal optic tract (MOT). In addition, electron microscopic examination of the optic fiber spectrum revealed the morphological organization of the retinofugal projection within the ON and the lateral division of the marginal optic tract (lMOT). Within the ON, myelinated and unmyelinated axons of various sizes are homogeneously distributed. Optic axons are reorganized within the MOT such that within the lMOT large myelinated optic axons become concentrated within ventromedial regions and small myelinated axons become concentrated within the dorsolateral regions. In rostral lMOT larger unmyelinated axons are also concentrated along the ventromedial regions. The morphological organization of the optic axons within lMOT, established by the reorganization of the retinofugal projection within MOT, anticipates the innervation pattern of the optic axons within the laminated, superficial layers of the optic tectum.

The tumor-suppressor gene, TP53, plays a major role in surveillance of cellular and genomic integrity, functioning in cell cycle regulation, repair of damaged DNA, and deletion of malfunctioning or defective cells. The latter is achieved through apoptosis, a mechanism of programmed cell death, which is important in both normal morphogenesis and suppression of tumorigenesis. The loss of p53 function in breast cancer has been the subject of intensive study, however, not much is known about how p53 functions in the normal mammary gland to mediate its protective apoptotic responses. The aim of this dissertation was to examine p53-mediated cell death in the murine mammary epithelial cells in response to two distinct apoptotic stimuli: exposure to ionizing radiation and detachment from an appropriate substratum. The first component of this work examined the role p53 plays in mediating apoptosis in response to gamma-radiation during distinct stages of post-natal mammary gland. The second part of this dissertation focused on whether detachment of epithelial cells from their extracellular matrix results in cell death that is p53-dependent or -independent. Results from these experiments demonstrate a requirement for functionally active p53 in radiation-induced cell death, and show that the proliferative capacity of the mammary gland at time of radiation exposure predicts the robustness of this apoptotic response. In contrast, detachment from substratum can trigger both p53-dependent and -independent cell death in mammary epithelial cells. However, apoptosis induced by the specific abrogation of β1 integrin-ligand interaction appears to proceed through a p53-dependent mechanism.