Explore the vast range of titles available.

While the role of cholinergic neurotransmission from motoneurons is well established during neuromuscular development, whether it regulates central nervous system development in the spinal cord is unclear. Zebrafish presents a powerful model to investigate how the cholinergic system is set up and evolves during neural circuit formation. In this study, we carried out a detailed spatiotemporal analysis of the cholinergic system in embryonic and larval zebrafish. In 1-day-old embryos, we show that spinal motoneurons express presynaptic cholinergic genes including choline acetyltransferase ( chata ) , vesicular acetylcholine transporters ( vachta , vachtb ) , high-affinity choline transporter ( hacta ) and acetylcholinesterase ( ache ), while nicotinic acetylcholine receptor (nAChR) subunits are mainly expressed in interneurons. However, in 3-day-old embryos, we found an unexpected decrease in presynaptic cholinergic transcript expression in a rostral to caudal gradient in the spinal cord, which continued during development. On the contrary, nAChR subunits remained highly expressed throughout the spinal cord. We found that protein and enzymatic activities of presynaptic cholinergic genes were also reduced in the rostral spinal cord. Our work demonstrating that cholinergic genes are initially expressed in the embryonic spinal cord, which is dynamically downregulated during development suggests that cholinergic signaling may play a pivotal role during the formation of intra-spinal locomotor circuit.

Interferons (IFNs) are ancient cytokines that arose in jawed vertebrates ∼400-500 million years ago. IFN systems are present with conserved antiviral functions across vertebrate lineages, including zebrafish (Danio rerio). In mammals, antiviral IFNs are divided between type I interferons (IFN-I), which drive systemic responses, and type III interferons (IFN-III), which protect barrier mucosal epithelia, owing to the specific distribution of their respective receptors. Although zebrafish lack IFN-III, they have IFN-Is which subdivide into 2 groups with distinct receptors, providing a unique opportunity to study how antiviral immunity has evolved in the absence of IFN-III. Whilst previous work has suggested complementary, non-redundant roles for IFNs from these groups, the tissue specificity has not yet been resolved. As larvae, zebrafish only express one group 1 (IFNφ1) and one group 2 IFN (IFNφ3). Using viral infection assays and reporter transgenics, we found that IFNs from group 1 (IFNφ1) and group 2 (IFNφ3) are produced by distinct subsets of cells, with no detectable co-expression. To assess tissue and cell-type-specific responses to these two IFNs, we used ISG reporter fish imaging and whole-larva single cell RNA sequencing after injection of recombinant IFNφ1 and IFNφ3. Despite a similar core ISG response, distinct downstream ISG programs across multiple tissues and organ systems were found. In particular, barrier epithelial cells, such as enterocytes, responded more strongly to IFNφ1, while myeloid cells responded more strongly to IFNφ3. Our results indicate that zebrafish IFN-I families have functionally diversified their antiviral immune responses by tissue context, driven by cellular partitioning of both IFN-I production and response. These results mirror the division of labour between mammalian IFN-I and IFN-III, emphasising the evolutionary importance of tissue division of immune responses, as well as deepening our understanding of the zebrafish as a model for host-pathogen interactions.

Modular organization of spinal neural circuits control dynamic regulation of locomotion. However, it is unknown when or how the distinct microcircuits emerge during development. We carried out high-resolution calcium imaging of neural activity driving the first motor behavior in one day old zebrafish embryo. During this period, at least two waves of neurogenesis occur to generate primary and secondary motoneurons. We found that embryos first display a single highly synchronized rhythmic neuronal circuit containing interneurons and motoneurons. Later, two distinct interneuron-motoneuron circuits emerge with one containing early-born motoneurons displaying low-frequency activity and the other containing later-born motoneurons with high-frequency activity. The results indicate a mode of birth order determined microcircuits where neurons that are born together are recruited together. Nicotine affected neuronal activity frequency, revealing a functional role for cholinergic signaling in the emergence of patterned spinal circuits. Indeed, we found aberrant arrhythmic synchronized activity in mutants for cholineacetyltransferase-a where acetylcholine is no longer synthesized. Overall, we reveal the sequential recruitment of birth order specified microcircuits during the emergence of the earliest motor behavior and highlight a conserved role for cholinergic signaling in regulating rhythmic neural activity in the embryonic spinal cord.