Targeted disruption of semaphorin 3C leads to persistent truncus arteriosus and aortic arch interruption.

Semaphorin 3C is a secreted member of the semaphorin gene family. To investigate its function in vivo, we have disrupted the semaphorin 3C locus in mice by targeted mutagenesis. semaphorin 3C mutant mice die within hours after birth from congenital cardiovascular defects consisting of interruption of the aortic arch and improper septation of the cardiac outflow tract. This phenotype is similar to that reported following ablation of the cardiac neural crest in chick embryos and resembles congenital heart defects seen in humans. Semaphorin 3C is expressed in the cardiac outflow tract as neural crest cells migrate into it. Their entry is disrupted in semaphorin 3C mutant mice. These data suggest that semaphorin 3C promotes crest cell migration into the proximal cardiac outflow tract.     

COPROMYXELLA: A NEW GENUS OF ACRASIDAE

A new genus of cellular slime molds, Copromyxella, is described together with four species that comprise it. Since it resembles Zopf's Copromyxa more than any genus presently recognized, but differs from it in important characteristics such as the smaller dimensions of its cellular elements and the delicacy of its fructifications, the name Copromyxella is chosen for the new taxon. Four species are included: C. silvatica, C. filamentosa, C. spicata, and C. coralloides. All are characterized by small myxamoebae with lobose and potentially “explosive” pseudopodia and may assume limax forms in liquid media; all possess nuclei with centrally positioned nucleoli; all lack true contractile vacuoles (with a single possible exception); all aggregate without stream formation; and all form fructifications with no demarcation into stalks and sori. Taxonomically the genus belongs in the Acrasidae with Copromyxa, Guttulinopsis and Acrasis rosea rather than in the better known Dictyostelidae that includes Dictyostelium and Polysphondylium.