Development and migration of the zebrafish rhombencephalic octavolateral efferent neurons.

In vertebrate animals, motor and sensory efferent neurons carry information from the central nervous system (CNS) to peripheral targets. These two types of efferent systems sometimes bear a close resemblance, sharing common segmental organization, axon pathways, and chemical messengers. Here, we focus on the development of the octavolateral efferent neurons (OENs) and their interactions with the closely-related facial branchiomotor neurons (FBMNs) in zebrafish. Using live-imaging approaches, we investigate the birth, migration, and projection patterns of OENs. We find that OENs are born in two distinct groups: a group of rostral efferent neurons (RENs) that arises in the fourth segment, or rhombomere (r4), of the hindbrain and a group of caudal efferent neurons (CENs) that arises in r5. Both RENs and CENs then migrate posteriorly through the hindbrain between 18 and 48 hrs postfertilization, alongside the r4-derived FBMNs. Like the FBMNs, migration of the r4-derived RENs depends on function of the segmental identity gene hoxb1a; unlike the FBMNs, however, both OEN populations move independently of prickle1b. Further, we investigate whether the previously described "pioneer" neuron that leads FBMN migration through the hindbrain is an r4-derived FBMN/REN or an r5-derived CEN. Our experiments verify that the pioneer is an r4-derived neuron and reaffirm its role in leading FBMN migration across the r4/5 border. In contrast, the r5-derived CENs migrate independently of the pioneer. Together, these results indicate that the mechanisms OENs use to navigate the hindbrain differ significantly from those employed by FBMNs.

From head to tail: regionalization of the neural crest.

The neural crest is regionalized along the anteroposterior axis, as demonstrated by foundational lineage-tracing experiments that showed the restricted developmental potential of neural crest cells originating in the head. Here, we explore how recent studies of experimental embryology, genetic circuits and stem cell differentiation have shaped our understanding of the mechanisms that establish axial-specific populations of neural crest cells. Additionally, we evaluate how comparative, anatomical and genomic approaches have informed our current understanding of the evolution of the neural crest and its contribution to the vertebrate body.

Rapid image deconvolution and multiview fusion for optical microscopy.

The contrast and resolution of images obtained with optical microscopes can be improved by deconvolution and computational fusion of multiple views of the same sample, but these methods are computationally expensive for large datasets. Here we describe theoretical and practical advances in algorithm and software design that result in image processing times that are tenfold to several thousand fold faster than with previous methods. First, we show that an 'unmatched back projector' accelerates deconvolution relative to the classic Richardson-Lucy algorithm by at least tenfold. Second, three-dimensional image-based registration with a graphics processing unit enhances processing speed 10- to 100-fold over CPU processing. Third, deep learning can provide further acceleration, particularly for deconvolution with spatially varying point spread functions. We illustrate our methods from the subcellular to millimeter spatial scale on diverse samples, including single cells, embryos and cleared tissue. Finally, we show performance enhancement on recently developed microscopes that have improved spatial resolution, including dual-view cleared-tissue light-sheet microscopes and reflective lattice light-sheet microscopes.

Neural crest development: insights from the zebrafish.

Our understanding of the neural crest, a key vertebrate innovation, is built upon studies of multiple model organisms. Early research on neural crest cells (NCCs) was dominated by analyses of accessible amphibian and avian embryos, with mouse genetics providing complementary insights in more recent years. The zebrafish model is a relative newcomer to the field, yet it offers unparalleled advantages for the study of NCCs. Specifically, zebrafish provide powerful genetic and transgenic tools, coupled with rapidly developing transparent embryos that are ideal for high-resolution real-time imaging of the dynamic process of neural crest development. While the broad principles of neural crest development are largely conserved across vertebrate species, there are critical differences in anatomy, morphogenesis, and genetics that must be considered before information from one model is extrapolated to another. Here, our goal is to provide the reader with a helpful primer specific to neural crest development in the zebrafish model. We focus largely on the earliest events-specification, delamination, and migration-discussing what is known about zebrafish NCC development and how it differs from NCC development in non-teleost species, as well as highlighting current gaps in knowledge.

Excess SMAD signaling contributes to heart and muscle dysfunction in muscular dystrophy.

Disruption of the dystrophin complex causes muscle injury, dysfunction, cell death and fibrosis. Excess transforming growth factor (TGF) ß signaling has been described in human muscular dystrophy and animal models, where it is thought to relate to the progressive fibrosis that characterizes dystrophic muscle. We now found that canonical TGFß signaling acutely increases when dystrophic muscle is stimulated to contract. Muscle lacking the dystrophin-associated protein γ-sarcoglycan (Sgcg null) was subjected to a lengthening protocol to produce maximal muscle injury, which produced rapid accumulation of nuclear phosphorylated SMAD2/3. To test whether reducing SMAD signaling improves muscular dystrophy in mice, we introduced a heterozygous mutation of SMAD4 (S4) into Sgcg mice to reduce but not ablate SMAD4. Sgcg/S4 mice had improved body mass compared with Sgcg mice, which normally show a wasting phenotype similar to human muscular dystrophy patients. Sgcg/S4 mice had improved cardiac function as well as improved twitch and tetanic force in skeletal muscle. Functional enhancement in Sgcg/S4 muscle occurred without a reduction in fibrosis, suggesting that intracellular SMAD4 targets may be important. An assessment of genes differentially expressed in Sgcg muscle focused on those encoding calcium-handling proteins and responsive to TGFß since this pathway is a target for mediating improvement in muscular dystrophy. These data demonstrate that excessive TGFß signaling alters cardiac and muscle performance through the intracellular SMAD pathway.

Cellular basis of differential limb growth in postnatal gray short-tailed opossums (Monodelphis domestica).

While growth has been studied extensively in invertebrates, the mechanisms by which it is controlled in vertebrates, particularly in mammals, remain poorly understood. In this study, we investigate the cellular basis of differential limb growth in postnatal Monodelphis domestica, the gray short-tailed opossum, to gain insights into the mechanisms regulating mammalian growth. Opossums are an ideal model for the study of growth because they are born with relatively large, well-developed forelimbs and small hind limbs that must "catch up" to the forelimb before the animal reaches adulthood. Postnatal Days 1-17 were identified as a key period of growth for the hind limbs, during which they undergo accelerated development and nearly quadruple in length. Histology performed on fore- and hind limbs from this period indicates a higher rate of cellular differentiation in the long bones of the hind limbs. Immunohistochemical assays indicate that cellular proliferation is also occurring at a significantly greater rate in the long bones of the hind limb at 6 days after birth. Taken together, these results suggest that a faster rate of cellular proliferation and differentiation in the long bones of the hind limb relative to those of the forelimb generates a period of accelerated growth through which the adult limb phenotype of M. domestica is achieved. Assays for gene expression suggest that the molecular basis of this differential growth differs from that previously identified for differential pre-natal growth in opossum fore- and hind limbs.