Developmental alterations in the appearance of hatching activity inIlyanassa obsoleta embryos

Embryos of the marine gastropodIlyanassa obsoleta are enclosed within a maternally-produced egg capsule for the first eight days of development. Embryos escape from the capsule by releasing a hatching substance that dissolves the egg capsule plug found at the apex of the capsule. Although hatching was determined to occur at 171 h of development, hatching activity could be detected in homogenates of 96 h embryos and premature hatching of embryos was initiated as early as 90 h of development when capsules were incubated in KCl. Therefore, the hatching substance is stored for over 80 h before its release. Appearance of hatching activity during the fourth day of development required that transcription and then translation occur between 70-76 h of development. Inhibition of either of these processes after 76 h did not prevent the appearance of hatching activity on schedule. In addition, removal of the third polar lobe formed at first cleavage, reduced the quantity of the hatching substance present in day eight lobeless embryos, when compared with control embryos. These results demonstrate a requirement for embryonic gene activity as well as maternal information placed in the egg during oogenesis and segregated into the polar lobe during cleavage for appearance of hatching activity in theIlyanassa embryo.