Adult neurogenesis in the brain of the Mozambique tilapia, Oreochromis mossambicus.

Although the generation of new neurons in the adult nervous system ('adult neurogenesis') has been studied intensively in recent years, little is known about this phenomenon in non-mammalian vertebrates. Here, we examined the generation, migration, and differentiation of new neurons and glial cells in the Mozambique tilapia (Oreochromis mossambicus), a representative of one of the largest vertebrate taxonomic orders, the perciform fish. The vast majority of new cells in the brain are born in specific proliferation zones of the olfactory bulb; the dorsal and ventral telencephalon; the periventricular nucleus of the posterior tuberculum, optic tectum, and nucleus recessi lateralis of the diencephalon; and the valvula cerebelli, corpus cerebelli, and lobus caudalis of the cerebellum. As shown in the olfactory bulb and the lateral part of the valvula cerebelli, some of the young cells migrate from their site of origin to specific target areas. Labeling of mitotic cells with the thymidine analog 5-bromo-2'-deoxyuridine, combined with immunostaining against the neuron-specific marker protein Hu or against the astroglial marker glial fibrillary acidic protein demonstrated differentiation of the adult-born cells into both neurons and glia. Taken together, the present investigation supports the hypothesis that adult neurogenesis is an evolutionarily conserved vertebrate trait.

Apoptotic cell death, long-term persistence, and neuronal differentiation of aneuploid cells generated in the adult brain of teleost fish.

Aneuploidy, caused by segregation defects during mitosis, has previously been identified in adult-born cells of mammals and teleosts. In the present study, we have examined the fate of these cells in the brain of the teleost fish Apteronotus leptorhynchus. By immunostaining against active caspase-3, we have shown that both cells with normal nuclear morphology and cells with mitotic segregation defects undergo apoptosis, but the relative number of apoptotic cells is higher among cells of the latter category. Long-term survival of cells with mitotic segregation defects could be demonstrated by incorporation of 5-bromo-2'-deoxyuridine into newly synthesized DNA during the S-phase of mitosis, and by employment of postadministration survival times of up to 860 days. Moreover, by combining 5-bromo-2'-deoxyuridine immunolabeling with immunostaining against the neuron-specific marker protein Hu, we have shown that among the long-term persistent cells with mitotic segregation defects a similar portion develops into neurons as does among the long-term persistent cells without such defects. It is possible that aneuploid cells play a role in the regulation of gene expression by somatic genomic alterations during postnatal development.

Proteome analysis identifies novel protein candidates involved in regeneration of the cerebellum of teleost fish.

In contrast to mammals, adult teleost fish exhibit an enormous potential to regenerate neuronal tissue after injuries to the CNS. By combining a well-defined cerebellar lesion paradigm with differential proteome analysis at a post-lesion survival time of 3 days, we screened for protein candidates involved in repair of the fish brain. Out of nearly 900 protein spots detected on 2-D gels, spot intensity was significantly increased at least twofold in 30 spots and decreased to at least half the intensity of control tissue in 23 spots. The proteins associated with 24 of the spots were identified by PMF and MS/MS fragmentation. The cellular localization and the spatiotemporal patterns of two of these proteins, beta-actin and beta-tubulin, were further characterized through immunohistochemistry. Comparison of the observed changes in protein abundance with the previously characterized events underlying regeneration of the cerebellum suggests that the proteins identified are especially involved in cellular proliferation and survival, as well as axonal sprouting.

Spatio-temporal distribution of microglia/macrophages during regeneration in the cerebellum of adult teleost fish, Apteronotus leptorhynchus: a quantitative analysis.

In contrast to mammals, adult teleost fish exhibit an enormous capacity to replace damaged neurons with newly generated ones after injuries in the central nervous system. In the present study, the role of microglia/macrophages, identified by tomato lectin binding, was examined in this process of neuronal regeneration in the corpus cerebelli of the teleost fish Apteronotus leptorhynchus. In the intact corpus cerebelli, or after short survival times following application of a mechanical lesion to this cerebellar subdivision, microglia/macrophages were virtually absent. Conversely, approximately 3 days after application of the lesion, the areal density of microglia/macrophages started to increase at and near the lesion site in the ipsilateral hemisphere, as well as in the contralateral hemisphere, and reached maximum levels at approximately 10 days post lesion. The density remained elevated until it reached background levels approximately one month after the injury. By comparing the time course of the appearance of microglia/macrophages with that of other regenerative events occurring within the first few weeks of wound healing in this model system, we hypothesize that one possible function of microglia/macrophages might be to remove debris of cells that have undergone apoptotic cell death at the lesion site.