“Highlights” is a feature that calls attention to exciting advances in developmental biology that have recently been reported in Developmental Dynamics. Development is a broad field encompassing many important areas. To reflect this fact, the section will spotlight significant discoveries that occur across the entire spectrum of developmental events and problems: from new experimental approaches, to novel interpretations of results, to noteworthy findings utilizing different developmental organisms.

Macrophages and morphology (Dev Dyn 235:3222–3229). If you think that macrophages are just gluttons that gobble up cellular debris and foreign material, think again. According to Pollard's group, macrophages also shape mammary gland branching morphology. During female puberty, rudimentary ducts in mammary glands start to grow. At the leading edge of growing ducts are epithelial structures called terminal end buds (TEBs), whose surrounding stromal layer is collagen-rich. Here, the authors show that mice deficient in macrophages have abnormal TEB morphology, but its total amount of collagen I is unchanged. This finding demonstrates that macrophages regulate TEB morphology, but not by producing monomeric collagen. The fascinating observation that macrophages travel along the TEB collagen matrix in vivo agrees with their conclusion that macrophages instead promote the organization of collagen into fibrillar bundles.

It takes guts (Dev Dyn 235:3259–3267). Sea cucumbers (Holothuria glaberrima) eject their intestines to distract or repel predators. Before you get any ideas, be advised that while they have the remarkable capacity to regenerate their internal organs, humans do not. In documenting intestine regeneration, this study focuses on a population of sphere-shaped, vesicle-filled cells called spherulocytes. With the help of spherulocyte-specific antibodies, the authors track the cells during the regeneration process. Found in connective tissue throughout the organism, spherulocytes increase in number, change morphology, appear to fuse with intestinal extracellular matrix, and dispel their vesicular contents. These data are highly suggestive that spherulocytes participate in regeneration and/or wound healing. Identifying the vesicular contents may be key to understanding exactly what these mysterious cells do.

Sugar coated fish (Dev Dyn 235:3423–3431, 3432–3437). In back-to-back papers, Cadwallader and Yost present compelling evidence that sugar does not deserve such a bad rap. Heparin sulfate (HS) proteoglycans bind to extracellular molecules, modulating several biological processes, including cell adhesion and cell signaling. HS ligand binding specificity is influenced by O-sulfotransferases (OSTs), which position sulfates on HS sugar chains. Here, the authors detail the zebrafish developmental expression patterns of two OST families, 3- and 6-OSTs, most members of which are conserved in humans. Interestingly, they find that the enzymes show unique tissue distribution patterns, suggesting that each plays a specialized role in development.