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During female meiotic prophase in many organisms, a specialized chromatin structure is formed in the oocyte nucleus. This structure is known as the karyosome, and has been proposed to be important for the formation of the female meiotic bipolar spindle. However, how the karyosome is formed and maintained is not very well understood. To identify proteins involved in the formation and maintenance of the karyosome, I carried out a cytological screen on a collection of 220 mutant fly lines for mutants that were defective in karyosome morphology. The screen identified 46 mutants on the X and 2nd chromosome with abnormal karyosomes. Genetic analysis of these 46 mutants, followed by molecular analysis of one mutant, identified SRPK (SR Protein Kinase) as a protein that is important for the proper formation of the karyosome. NHK-1 (Nucleosomal Histone Kinase 1) was previously identified as a protein that is essential for the formation of the karyosome via its phosphorylation of BAF (Barrier-to-Autointegration Factor). NHK-1 phosphorylation of BAF leads to the release of chromatin from the nuclear membrane, an essential step for the formation of the karyosome, however, the regulation of this process is unclear. In order to identify genes that interact with NHK-1, I carried out a genetic modifier screen using a semi-lethal allele of NHK-1, NHK-1trip. After screening a collection of 44 deficiencies located on the 2nd chromosome, I identified a genetic region (44B8-44D1) containing a gene that interacts with NHK-1 and, when gene dosage is halved, enhanced the semi-lethal phenotype of NHK-1trip.

Developmental nicotine exposure (DNE) is associated with increased risk of cardiorespiratory, intellectual, and behavioral abnormalities in neonates, and is a risk factor for apnea of prematurity, altered arousal responses and Sudden Infant Death Syndrome. Alterations in nicotinic acetylcholine receptor signaling (nAChRs) after DNE lead to changes in excitatory neurotransmission in neural networks that control breathing, including a heightened excitatory response to AMPA microinjection into the hypoglossal motor nucleus. Here, we report on experiments designed to probe possible postsynaptic and presynaptic mechanisms that may underlie this plasticity. Pregnant dams were exposed to nicotine or saline via an osmotic mini-pump implanted on the 5th day of gestation. We used whole-cell patch clamp electrophysiology to record from hypoglossal motoneurons (XIIMNs) in thick medullary slices from neonatal rat pups (N = 26 control and 24 DNE cells). To enable the translation of our findings to breathing-related consequences of DNE, we only studied XIIMNs that were receiving rhythmic excitatory drive from the respiratory central pattern generator. Tetrodotoxin was used to isolate XIIMNs from presynaptic input, and their postsynaptic responses to bath application of L-glutamic acid (glutamate) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were studied under voltage clamp. DNE had no influence on inward current magnitude evoked by either glutamate or AMPA. However, in cells from DNE animals, bath application of AMPA was associated with a right shift in the amplitude distribution (P = 0.0004), but no change in the inter-event interval distribution of miniature excitatory postsynaptic currents (mEPSCs). DNE had no influence on mEPSC amplitude or frequency evoked by glutamate application, or under (unstimulated) baseline conditions. Thus, in the presence of AMPA, DNE is associated with a small but significant increase in quantal size, but no change in the probability of glutamate release.

The area most widely associated with osmoreception has been the lateral preoptic nucleus. However, Hatton (1976) proposed that the nucleus circularis could be the actual osmoreceptor in the hypothalamus. The present study supported Hatton by using 30 rats which were randomly assigned to sham, lateral preoptic, and nucleus circularis lesion groups. After a 2-week post-operative period, half of each group was injected with isotonic saline while the other half was injected with hypertonic saline. Water consumption was measured at 10-minute intervals for one hour. Following a 4-day recovery period, the injection procedure was reversed. Analysis of difference scores, computed by subtracting the amount of water consumed after isotonic injection from the amount of water consumed after hypertonic injection, revealed a significant difference between the nucleus circularis group and the other two groups.

Substantial evidence suggests that serotonin (5-HT) activation within the brain modulates anxiety-like behavior. The bed nucleus of the stria terminalis (BNST) has been argued to mediate anxiety-like behavioral responding, and the activation of 5-HT systems may modulate anxiety-like behavior via the release of 5-HT within the BNST. Prior studies have suggested that the 5-HT1, 7 agonist 5-carboxyamidotrytamine (5-CT) is anxiolytic, which is consistent with a reduction in BNST activity via the activation of postsynaptic 5- HT1A receptors. However the anxiolytic effects of 5-CT could also have been mediated by 5-HT7 receptor activation. Hence, to isolate the effects of 5-HT1A on anxiety-like behavior, we infused the 5-HT1A antagonist WAY-100635 (0, 0.04, 0.4, and 4.0 μg/μl in saline vehicle) into the BNST of rats immediately before social interaction or acoustic startle testing. For social interaction testing pairs of rats were administered two 5-sec 1- mA footshocks immediately after infusion, removed from the chamber and measured for social interaction in a separate testing apparatus. For acoustic startle testing, rats were placed in boxes and measured for the percentage increase in test (post-infusion) startle from baseline (pre-infusion) startle. Anxiety levels were operationalized as the amount of social interaction per line cross and the percentage increase in startle following drug infusion. WAY-100635 dose dependently decreased social interaction, indicative of an anxiogenic effect. Interestingly, 0.4μg/μl of WAY-100635 decreased startle, indicative of an anxiolytic effect. These data suggest that activation of the 5-HT systems modulates anxiety-like behavior by altering activity within the BNST.

Thesis advisor: Eric S. Folker / Thesis advisor: David R. Burgess / During muscle development, myonuclei undergo a complex set of movements that result in evenly spaced nuclei throughout the muscle cell. In many muscle diseases mispositioned myonuclei have been used as a hallmark phenotype of disease. A number of studies over the last decade have started to piece together the cytoskeletal elements that govern these movements. In Drosophila, two separate pools of Kinesin and Dynein work in synchrony to drive nuclear movement. However, it is still not clear how these two pools of microtubule motors become specified. In addition, it is not clear how nuclear position impacts the other defining feature of the muscle cell, which is the highly organized contractile network of sarcomeres. Previously, mispositioned myonuclei have been correlated with improper muscle function, yet no direct link between nuclear position and sarcomere development or function has been demonstrated. In this thesis, we show a role for Aplip1 (the Drosophila homolog of JIP1), a known regulator of both Kinesin and Dynein, in myonuclear positioning. Aplip1 localizes to the myotendinous junction and has genetically separable roles in myonuclear positioning and muscle stability. Furthermore, we show that a number of sarcomeric proteins, including ZASP, Actin and β-integrin localize to the nucleus prior to being incorporated into the sarcomere, regardless of nuclear position. Finally, we show that the LINC complex is required for nuclear dependent sarcomere assembly and that disruption of nuclear dependent sarcomere assembly or nuclear position resulted in a compromised sarcomeric network. Together, this thesis adds to the mechanisms that are important in positioning nuclei and shows the first direct link between the nucleus and sarcomere assembly. / Thesis (PhD) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Biology.

by Lui Po Yee Pauline. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (p. 211-222). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web.

The first stage of mammalian auditory processing occurs within the dorsal and ventral divisions of the cochlear nucleus. The dorsal cochlear nucleus (DCN) is remarkable in that it shares striking similarities with the cerebellum in terms of its development, gene expression patterns, and anatomical organization. Notably, principal cells of the DCN integrate auditory nerve input with a diverse array of signals conveyed by a mossy fiber- granule cell system. Yet how the elaborate cerebellum-like circuitry of DCN contributes to early auditory processing has been a longstanding puzzle. The work in this thesis shows that, in mice, that the DCN functions to cancel responses to self-generated sounds. While the DCN and ventral cochlear nucleus (VCN) neurons respond similarly to externally-generated acoustic stimuli, sounds generated by licking behavior evoke much weaker responses in DCN than in VCN. Recordings in deafened mice revealed non- auditory signals related to licking in Purkinje-like neurons of DCN. Moreover, silencing somatosensory mossy fiber inputs revealed prominent DCN responses to sounds generated by licking, suggesting that these inputs normally function to cancel responses to self-generated sounds. Finally, I show that this cancellation is not fixed, but involves an adaptive process whereby neural responses correlated with the animal’s own behavior are gradually reduced. Together, these findings suggest that the fundamental process of distinguishing self-generated from external stimuli begins at the very first stage of mammalian auditory processing. Related adaptive filtering functions have been described for cerebellum-like sensory structures in fish and hypothesized for the mammalian cerebellum. Hence our findings also suggest that, despite their wide phylogenetic separation, different cerebellum-like structures and the cerebellum itself may all perform a similar computation.

Studies of cerebellum-like circuits in fish have demonstrated that synaptic plasticity shapes the motor corollary discharge responses of granule cells into highly-specific predictions of self- generated sensory input. However, the functional significance of such predictions, known as negative images, has not been directly tested. Here we provide evidence for improvements in neural coding and behavioral detection of prey-like stimuli due to negative images. In addition, we find that manipulating synaptic plasticity leads to specific changes in circuit output that disrupt neural coding and detection of prey-like stimuli. These results link synaptic plasticity, neural coding, and behavior and also provide a circuit-level account of how combining external sensory input with internally-generated predictions enhances sensory processing. In addition, the mammalian dorsal cochlear nucleus (DCN) integrates auditory nerve input with a diverse array of sensory and motor signals processed within circuity similar to the cerebellum. Yet how the DCN contributes to early auditory processing has been a longstanding puzzle. Using electrophysiological recordings in mice during licking behavior we show that DCN neurons are largely unaffected by self-generated sounds while remaining sensitive to external acoustic stimuli. Recordings in deafened mice, together with neural activity manipulations, indicate that self-generated sounds are cancelled by non-auditory signals conveyed by mossy fibers. In addition, DCN neurons exhibit gradual reductions in their responses to acoustic stimuli that are temporally correlated with licking. Together, these findings suggest that DCN may act as an adaptive filter for cancelling self-generated sounds. Adaptive filtering has been established previously for cerebellum-like sensory structures in fish suggesting a conserved function for such structures across vertebrates.

The study of cerebellum-like circuits allows many points of entry. These circuits are often involved in very specific systems not found in all animals (for example electrolocation in weakly electric fish) and thus can be studied with a neuroethological approach in mind. There are many cerebellum-like circuits found across the animal kingdom, and so studies of these systems allow us to make interesting comparative observations. Cerebellum-like circuits are involved in computations that touch many domains of theoretical interest - the formation of internal predictions, adaptive filtering, cancellation of self-generated sensory inputs. This latter is linked both conceptually and historically to philosophical questions about the nature of perception and the distinction between the self and the outside world. The computation thought to be performed in cerebellum-like structures is further related, especially through studies of the cerebellum, to theories of motor control and cognition. The cerebellum itself is known to be involved in much more than motor learning, its traditionally assumed function, with particularly interesting links to schizophrenia and to autism. The particular advantage of studying cerbellum-like structures is that they sit at such a rich confluence of interests while being involved in well-defined computations and being accessible at the synaptic, cellular, and circuit levels. In this thesis we present work on two cerebellum-like structures: the electrosensory lobe (ELL) of mormyrid fish and the dorsal cochlear nucleus (DCN) of mice. Recent work in ELL has shown that a temporal basis of granule cells allows the formation of predictions of the sensory consequences of a simple motor act - the electric organ discharge (EOD). Here we demonstrate that such predictions generalize between electric organ discharge rates - an ability crucial to the ethological relevance of such predictions. We develop a model of how such generalization is made possible at the circuit level. In a second section we show that the DCN is able to adaptively cancel self-generated sounds. In the conclusion we discuss some differences between DCN and ELL and suggest future studies of both structures motivated by a reading of different aspects of the machine learning literature.