Efficient CRISPR Mutagenesis in Sturgeon Demonstrates Its Utility in Large, Slow-Maturing Vertebrates.

In the last decade, the CRISPR/Cas9 bacterial virus defense system has been adapted as a user-friendly, efficient, and precise method for targeted mutagenesis in eukaryotes. Though CRISPR/Cas9 has proven effective in a diverse range of organisms, it is still most often used to create mutant lines in lab-reared genetic model systems. However, one major advantage of CRISPR/Cas9 mutagenesis over previous gene targeting approaches is that its high efficiency allows the immediate generation of near-null mosaic mutants.

The origin and diversification of the developmental mechanisms that pattern the vertebrate head skeleton.

The apparent evolvability of the vertebrate head skeleton has allowed a diverse array of shapes, sizes, and compositions of the head in order to better adapt species to their environments. This encompasses feeding, breathing, sensing, and communicating: the head skeleton somehow participated in the evolution of all these critical processes for the last 500 million years. Through evolution, present head diversity was made possible via developmental modifications to the first head skeletal genetic program.

Embryonic expression of endothelins and their receptors in lamprey and frog reveals stem vertebrate origins of complex Endothelin signaling.

Neural crest cells (NCCs) are highly patterned embryonic cells that migrate along stereotyped routes to give rise to a diverse array of adult tissues and cell types. Modern NCCs are thought to have evolved from migratory neural precursors with limited developmental potential and patterning. How this occurred is poorly understood.

Mesodermal origin of median fin mesenchyme and tail muscle in amphibian larvae.

Mesenchyme is an embryonic precursor tissue that generates a range of structures in vertebrates including cartilage, bone, muscle, kidney, and the erythropoietic system. Mesenchyme originates from both mesoderm and the neural crest, an ectodermal cell population, via an epithelial to mesenchymal transition (EMT). Because ectodermal and mesodermal mesenchyme can form in close proximity and give rise to similar derivatives, the embryonic origin of many mesenchyme-derived tissues is still unclear.

A gene expression map of the larval Xenopus laevis head reveals developmental changes underlying the evolution of new skeletal elements.

The morphology of the vertebrate head skeleton is highly plastic, with the number, size, shape, and position of its components varying dramatically between groups. While this evolutionary flexibility has been key to vertebrate success, its developmental and genetic bases are poorly understood. The larval head skeleton of the frog Xenopus laevis possesses a unique combination of ancestral tetrapod features and anuran-specific novelties.

The evolution of the neural crest: new perspectives from lamprey and invertebrate neural crest-like cells.

The neural crest is an embryonic cell population that gives rise to an array of tissues and structures in adult vertebrates including most of the head skeleton. Because neural crest cells (NCCs), and many of their derivatives, are unique to vertebrates, the evolution of the neural crest is thought to have potentiated vertebrate origins and diversification. However, the lack of clear NCC homologs in invertebrate chordates has made it difficult to reconstruct the evolutionary history of modern NCCs.

Gene regulatory evolution and the origin of macroevolutionary novelties: insights from the neural crest.

The appearance of novel anatomic structures during evolution is driven by changes to the networks of transcription factors, signaling pathways, and downstream effector genes controlling development. The nature of the changes to these developmental gene regulatory networks (GRNs) is poorly understood. A striking test case is the evolution of the GRN controlling development of the neural crest (NC).

An essential role of variant histone H3.3 for ectomesenchyme potential of the cranial neural crest.

The neural crest (NC) is a vertebrate-specific cell population that exhibits remarkable multipotency. Although derived from the neural plate border (NPB) ectoderm, cranial NC (CNC) cells contribute not only to the peripheral nervous system but also to the ectomesenchymal precursors of the head skeleton. To date, the developmental basis for such broad potential has remained elusive.

New perspectives on pharyngeal dorsoventral patterning in development and evolution of the vertebrate jaw.

Patterning of the vertebrate facial skeleton involves the progressive partitioning of neural-crest-derived skeletal precursors into distinct subpopulations along the anteroposterior (AP) and dorsoventral (DV) axes. Recent evidence suggests that complex interactions between multiple signaling pathways, in particular Endothelin-1 (Edn1), Bone Morphogenetic Protein (BMP), and Jagged-Notch, are needed to pattern skeletal precursors along the DV axis. Rather than directly determining the morphology of individual skeletal elements, these signals appear to act through several families of transcription factors, including Dlx, Msx, and Hand, to establish dynamic zones of skeletal differentiation.

Novel Tfap2-mediated control of soxE expression facilitated the evolutionary emergence of the neural crest.

Gene duplication has been proposed to drive the evolution of novel morphologies. After gene duplication, it is unclear whether changes in the resulting paralogs' coding-regions, or in their cis-regulatory elements, contribute most significantly to the assembly of novel gene regulatory networks. The Transcription Factor Activator Protein 2 (Tfap2) was duplicated in the chordate lineage and is essential for development of the neural crest, a tissue that emerged with vertebrates.

A new mechanistic scenario for the origin and evolution of vertebrate cartilage.

The appearance of cellular cartilage was a defining event in vertebrate evolution because it made possible the physical expansion of the vertebrate "new head". Despite its central role in vertebrate evolution, the origin of cellular cartilage has been difficult to understand. This is largely due to a lack of informative evolutionary intermediates linking vertebrate cellular cartilage to the acellular cartilage of invertebrate chordates.

Evidence for the prepattern/cooption model of vertebrate jaw evolution.

The appearance of jaws was a turning point in vertebrate evolution because it allowed primitive vertebrates to capture and process large, motile prey. The vertebrate jaw consists of separate dorsal and ventral skeletal elements connected by a joint. How this structure evolved from the unjointed gill bar of a jawless ancestor is an unresolved question in vertebrate evolution.