Migration-related changes in the cytoskeleton of cultured neural crest cells visualized by the monoclonal antibody I-5G9

An epitope recognized by the monoclonal antibody I-5G9 was expressed by all neural crest cells shortly after explantation into culture. At this time all neural crest cells actively migrated away from the neural tube. Immunoreactivity was localized intracellularly and organized into stress fiber-like filaments. Often, immunofluorescence was particularly high in short fibers in the lamellipodia of the leading edge of migrating cells. Two-week-old cultures had a diameter of 8-10 mm. At that stage a ring of immunoreactive cells was present at the periphery of each culture, an area where cells were still migratory. An inner concentric circle had reduced and more granular staining. In this area cells had ceased to migrate. In the center of the culture cells were multilayered, nonmigratory, and did not bind I-5G9. After creating a lesion in the nonreactive central region, some cells resumed migration into the lesioned area and reexpressed the epitope. I-5G9 staining and phalloidin fluorescence colocalized partially in some cells and completely in others. It is concluded that the epitope recognized by I-5G9 is expressed in a migration-dependent manner. The partial colocalization of I-5G9 and phalloidin fluorescence supports the notion that the epitope recognized by I-5G9 is specifically expressed in stress fibers of migratory cells, possibly in one of the actin-associated proteins or an F actin-associated protein complex.

Echolocation by young bats on their initial and subsequent flights

This study documents developmental changes in the vocal reaction of bats to obstacles and describes the pulse patterns of young bats on their 1st and subsequent flights. The pulse repetition rate of young bats showed an increase just before the bats approached obstacles. This pattern differs from that of older bats. The distance at which the change in pulse repetition rate occurs is roughly twice as far from the obstacle in adults as it is in young bats. Even on their 1st flights young bats (25-29 days old) seemed to perform better than chance. This capability seems to be resistant to environmental manipulation during the preweaning period.