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Abstract: The zebrafish muscle segment homeobox genes msxB, msxC and msxE are expressed in partially overlapping domains in the neural crest and preplacodal ectoderm. We examined the roles of these msx genes in early development. Disrupting individual msx genes causes modest variable defects, whereas disrupting all three produces a reproducible severe phenotype, suggesting functional redundancy. Neural crest differentiation is blocked at an early stage. Preplacodal development begins normally, but placodes arising from the msx expression domain later show elevated apoptosis and are reduced in size. Cell proliferation is normal in these tissues. Unexpectedly, Msx-deficient embryos become ventralized by late gastrulation whereas misexpression of msxB dorsalizes the embryo. These effects appear to involve Distal-less (Dlx) protein activity, as loss of dlx3b and dlx4b suppresses ventralization in Msx-depleted embryos. At the same time, Msx-depletion restores normal preplacodal gene expression to dlx3b-dlx4b mutants. These data suggest that mutual antagonism between Msx and Dlx proteins achieves a balance of function required for normal preplacodal differentiation and placement of the neural–nonneural border. [Copyright &y& Elsevier]

The vertebrate inner ear is a marvel of structural and functional complexity, which is all the more remarkable because it develops from such a simple structure, the otic placode. Analysis of inner ear development has long been a fascination of experimental embryologists, who sought to understand cellular mechanisms of otic placode induction. More recently, however, molecular and genetic approaches have made the inner ear a useful model system for studying a much broader range of basic developmental mechanisms, including cell fate specification and differentiation, axial patterning, epithelial morphogenesis, cytoskeletal dynamics, stem cell biology, neurobiology, physiology, etc. Of course, there has also been tremendous progress in understanding the functions and processes peculiar to the inner ear. The goal of this review is to recount how historical approaches have shaped our understanding of the signaling interactions controlling early otic development; to discuss how new findings have led to fundamental new insights; and to point out new problems that need to be resolved in future research. [Copyright &y& Elsevier]

Abstract: The Caenorhabditis elegans distal tip cell (DTC) provides a niche for germline stem cells in both hermaphrodites and males. The hermaphrodite distal tip cell (hDTC) also provides “leader” function to control gonadal elongation and shape, while in males, leader function is allocated to the linker cell (LC). Therefore, the male distal tip cell (mDTC) serves as a niche but not as a leader. The C. elegans homolog of E/Daughterless, HLH-2, was previously implicated in hDTC specification. Here we report that HLH-2 is also critical for hDTC maintenance, hDTC niche function and hDTC expression of a lag-2/DSL ligand reporter. We also find that HLH-2 functions in males to direct linker cell specification and to promote both mDTC maintenance and the mDTC niche function. We conclude that HLH-2 functions in both sexes to promote leader cell specification and DTC niche function. [Copyright &y& Elsevier]

[Display omitted] • Regulated aggregation affects protein storage, activity and spatial distribution. • Many "bodies" historically connected to cell and development are protein condensates. • Physiological aggregates are regulated, reversible, and often multifunctional. • Chaperones, protein modification, local milieu and co-aggregates alter aggregation. • Exploring multiple experimental systems helps identify regulators of aggregation. Protein aggregation is a feature of numerous neurodegenerative diseases. However, regulated, often reversible, formation of protein aggregates, also known as condensates, helps control a wide range of cellular activities including stress response, gene expression, memory, cell development and differentiation. This review presents examples of aggregates found in biological systems, how they are used, and cellular strategies that control aggregation and disaggregation. We include features of the aggregating proteins themselves, environmental factors, co-aggregates, post-translational modifications and well-known aggregation-directed activities that influence their formation, material state, stability and dissolution. We highlight the emerging roles of biomolecular condensates in early animal development, and disaggregation processing proteins that have recently been shown to play key roles in gametogenesis and embryogenesis. [ABSTRACT FROM AUTHOR]