It has long been known that during the closed mitosis of many unicellular eukaryotes, including the fission yeast (Schizosaccharomyces pombe), the nuclear envelope remains intact while the nucleus undergoes a remarkable sequence of shape transformations driven by elongation of an intranuclear mitotic spindle whose ends are capped by spindle pole bodies embedded in the nuclear envelope. However, the mechanical basis of these normal cell cycle transformations, and abnormal nuclear shapes caused by intranuclear elongation of microtubules lacking spindle pole bodies, remain unknown. Although there are models describing the shapes of lipid vesicles deformed by elongation of microtubule bundles, there are no models describing normal or abnormal shape changes in the nucleus. We describe here a novel biophysical model of interphase nuclear geometry in fission yeast that accounts for critical aspects of the mechanics of the fission yeast nucleus, including the biophysical properties of lipid bilayers, forces exerted on the nuclear envelope by elongating microtubules, and access to a lipid reservoir, essential for the large increase in nuclear surface area during the cell cycle. We present experimental confirmation of the novel and non-trivial geometries predicted by our model, which has no free parameters. We also use the model to provide insight into the mechanical basis of previously described defects in nuclear division, including abnormal nuclear shapes and loss of nuclear envelope integrity. The model predicts that (i) despite differences in structure and composition, fission yeast nuclei and vesicles with fluid lipid bilayers have common mechanical properties; (ii) the S. pombe nucleus is not lined with any structure with shear resistance, comparable to the nuclear lamina of higher eukaryotes. We validate the model and its predictions by analyzing wild type cells in which ned1 gene overexpression causes elongation of an intranuclear microtubule bundle that deforms the nucleus of interphase cells.

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Using the plainfin midshipman fish Porichthys notatus, a species with alternative reproductive tactics (ARTs), we investigated how sperm maturation shapes sperm competitive abilities. We compared sperm performance and morphology before and after final sperm maturation by sampling sperm from the testes and stripped ejaculates of guarders and sneakers. In accordance with sperm competition risk theory, ejaculates from sneaker males had three times as much sperm as ejaculates from guarder males and sneaker males produced faster swimming sperm than guarder males, but this was only the case after final sperm maturation had occurred. Additionally, fully mature sperm found in ejaculates had larger heads and midpieces than sperm found in the testes. These results emphasize the important role played by non‐sperm components of an ejaculate in mediating sperm performance and potentially also morphology.

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This is the third in a series of articles on the spine. The first reviewed the anatomy of the neck. The second reviewed the upper thoracic spine and chest (T1-T4). A fourth article is planned for the lower thoracic spine. Procedures in the midthoracic spine include chest tube placement, trigger point injections, chemodenervation with botulinum toxin, video-assisted thoroscopic surgery, and spinal injections. Complications include pneumothorax, hemothorax, diaphragmatic irritation, sympathetic trunk irritation, postthoracotomy pain, and intradural abscesses. This article provides anatomically accurate schematics of innervations of the middle thoracic chest and spine (T5-T8) that can be used to interpret magnetic resonance images of the muscles and nerves. Cross-sectional schematics of the middle thoracic chest and spine were drawn as they appear on imaging projections. The relevant nerves were color coded. The muscles and skin surfaces were labeled and assigned the color of the appropriate nerves. An organized comprehensive map of the motor innervation of the middle thoracic chest and spine allows the physician to increase the accuracy and efficacy of interventional procedures. This could also assist the electromyographer in correlating the clinical and electrophysiologic findings with magnetic resonance images.