EARLY MESSENGER-RNAS, SPATIALLY RESTRICTED ALONG THE ANIMAL-VEGETAL AXIS OF SEA-URCHIN EMBRYOS, INCLUDE ONE ENCODING A PROTEIN RELATED TO TOLLOID AND BMP-1

The cloning and characterization of cDNAs representing four genes or s mall gene families that are coordinately expressed in a spatially rest ricted pattern during the very early blastula (VEB) stage of sea urchi n development are presented. The VEB genes encode multiple transcripts that are expressed transiently in embryos of Strongylocentrotus purpu ratus between 16-cell stage and hatching, with peak abundance 12 to 15 hours post-fertilization (approximately 150-250 cells). The VEB trans cripts share the same spatial pattern in the early blastula embryo: th ey are asymmetrically distributed along the animal-vegetal axis but th eir distribution around this axis is uniform. Thus, the VEB transcript s are the earliest messages to reveal asymmetry along the primary axis in the sea urchin embryo. The temporal and spatial patterns of VEB tr anscript accumulation are not consistent with involvement of these gen e products in cell division or in tissue-specific functions. Furthermo re, VEB messages cannot be detected in either ovary or adult tissues, suggesting that these genes function exclusively during embryogenesis. We suggest that the VEB genes function in constructing the early blas tula. Two VEB genes encode metalloendoproteases: one (SpHE) is hatchin g enzyme and the other (SpAN) is similar to bone morphogenetic protein -1 (BMP-1; Wozney et al., Science 242: 1528-1534, 1988) and the Tolloi d gene product (tld) (Shimell et al., Cell 67: 459-482, 1991). Several lines of evidence suggest that the VEB genes are regulated directly b y factors or regulatory activities localized along the maternally spec ificed animal-vegetal axis.