The pharyngeal arches are one of the defining features of the vertebrates, with the first arch forming the mandibles of the jaw and the second forming jaw support structures. The cartilaginous elements of each arch are formed from separate migratory neural crest cell streams, which derive from the dorsal aspect of the neural tube. The second and more posterior crest streams are characterized by specific Hox gene expression. The zebrafish has a larger overall number of Hox genes than the tetrapod vertebrates, as the result of a duplication event in its lineage. However, in both zebrafish and mouse, there are just two members of Hox paralogue group 2 (PG2): Hoxa2 and Hoxb2. Here, we show that morpholino-mediated "knock-down" of both zebrafish Hox PG2 genes results in major defects in second pharyngeal arch cartilages, involving replacement of ventral elements with a mirror-image duplication of first arch structures, and accompanying changes to pharyngeal musculature. In the mouse, null mutants of Hoxa2 have revealed that this single Hox gene is required for normal second arch patterning. By contrast, loss-of-function of either zebrafish Hox PG2 gene individually has no phenotypic consequence, showing that these two genes function redundantly to confer proper pattern to the second pharyngeal arch. We have also used hoxb1a mis-expression to induce localized ectopic expression of zebrafish Hox PG2 genes in the first arch; using this strategy, we find that ectopic expression of either Hox PG2 gene can confer second arch identity onto first arch structures, suggesting that the zebrafish Hox PG2 genes act as "selector genes."

Hhex is required for early development of the liver. A null mutation of Hhex results in a failure to form the liver bud and embryonic lethality. Therefore, Hhex null mice are not informative as to whether this gene is required during later stages of hepatobiliary morphogenesis. To address this question, we derived Hhex conditional null mice using the Cre-loxP system and two different Cre transgenics (Foxa3-Cre and Alfp-Cre). Deletion of Hhex in the hepatic diverticulum (Foxa3-Cre;Hhex(d2,3/-)) led to embryonic lethality and resulted in a small and cystic liver with loss of Hnf4alpha and Hnf6 expression in early hepatoblasts. In addition, the gall bladder was absent and the extrahepatic bile duct could not be identified. Loss of Hhex in the embryonic liver (Alfp-Cre;Hhex(d2,3/-)) caused irregular development of intrahepatic bile ducts and an absence of Hnf1beta in many (cystic) biliary epithelial cells, which resulted in a slow, progressive form of polycystic liver disease in adult mice. Thus, we have shown that Hhex is required during multiple stages of hepatobiliary development. The altered expression of Hnf4alpha, Hnf6 and Hnf1beta in Hhex conditional null mice suggests that Hhex is an essential component of the genetic networks regulating hepatoblast differentiation and intrahepatic bile duct morphogenesis.

The pharyngeal arches give rise to multiple organs critical for diverse processes, including the thymus, thyroid and parathyroids. Several molecular regulators of thymus and thyroid organogenesis are strikingly conserved between mammals and zebrafish. However, land animals have parathyroids whereas fish have gills. The murine transcription factor Glial cells missing 2 (Gcm2) is expressed specifically in the parathyroid primordium in the endodermal epithelium of the third pharyngeal pouch, and in both mice and humans is required for normal development of parathyroid glands. The molecular regulation of fish gill organogenesis remains to be described. We report the expression of gcm2 in the zebrafish pharyngeal epithelium and a requirement for Hox group 3 paralogs for gcm2 expression. Strikingly, zebrafish gcm2 is expressed in the ectodermal portion of the pharyngeal epithelium and is required for the development of the gill filament buds, precursors of fish-specific gill filaments. This study identifies yet another role for a GCM gene in embryonic development and indicates a role for gcm2 during the evolution of divergent pharyngeal morphologies.

Highway safety evaluation has traditionally been performed by using crash data, although this method has limitations in terms of timeliness and efficiency. Previous studies show that the use of surrogate safety data allows for faster evaluation of safety in comparison with the significantly longer time horizon required for collecting crash data. However, the predictive capability of surrogate measures is still an area of ongoing research. Previous studies have often resulted in inconsistent findings for the relationship between surrogates and crashes, one of the primary reasons being inconsistent definitions of a conflict. This study evaluated the effectiveness of postencroachment time (PET) as a surrogate measure for the propensity of crashes between left-turning vehicles and opposing through vehicles at four-leg signalized intersections. The primary method of data collection was through video recording with postprocessing. Custom semiautomatic video processing software was used to reduce the video to a usable format for analysis. The study evaluated the effectiveness of PET as a surrogate measure by comparing three variations of the PET measure with crash history. This comparison showed that the threshold value of PET played an important role in establishing its correlation with crashes, with the best results at a threshold as low as 1 s.

Intersectins (ITSNs) represent a family of multi-domain adaptor proteins that regulate endocytosis and cell signaling. ITSN genes are highly conserved and present in all metazoan genomes examined thus far. Lower eukaryotes have only one ITSN gene, whereas higher eukaryotes have two ITSN genes. ITSN was first identified as an endocytic scaffold protein, and numerous studies reveal a conserved role for ITSN in endocytosis. Subsequently, ITSNs were found to regulate multiple signaling pathways including receptor tyrosine kinases (RTKs), GTPases, and phosphatidylinositol 3-kinase Class 2beta (PI3KC2β). ITSN has also been implicated in diseases such as Down Syndrome (DS), Alzheimer Disease (AD), and other neurodegenerative disorders. This review summarizes the evolutionary conservation of ITSN, the latest research on the role of ITSN in endocytosis, the emerging roles of ITSN in regulating cell signaling pathways, and the involvement of ITSN in human diseases such as DS, AD, and cancer.