Frank N. Low

Microdissection by Ultrasonication: Application to Early Chick Embryos

A technique utilizing microdissection by ultrasonication was applied to scanning electron microscopy of chick embryos during the first three days of incubation. Using a tank cleaner operating at 80 kHz, whole embryos immersed in pure acetone were sonicated until fragmentation became evident. At 12 hr incubation disintegration occurred by one second or less. At 18 hr, three sonic bursts of one second each produced only partial fragmentation. All three germ layers retained their original relationships to each other. During the second day of incubation, large pieces of integument were removed and somites began to microdissect after 10-20 seconds of sonication. Late in the third day of incubation, sonication for 1 min or more was required to produce significant microdissection. Living embryos exposed to 0.1% collagenase for 10 min prior to standard fixation fragmented in a different manner. Lamellipodia and filopodia were most sensitive and were largely destroyed. The three major germ layers (ectoderm, endoderm, mesoderm), however, retained their structural integrity and original relationships to each other. Factors contributing to the results reported here include: 1) extracellular fibrils of varying chemical composition, 2) primitive cell junctions, 3) biomechanical stability in the nonfibrillar portions of the extracellular matrix, and 4) effects of technical procedures performed prior to sonication. Sonicated tissues of early embryos reveal features that are difficult to demonstrate in other ways and may be unrecognized in conventional preparations.

Morphological changes in the developing alimentary canal: A review by scanning electron microscopy

The complex series of developmental events leading to the mature alimentary mucosa in higher mammals has interested investigators for over a century (1). Villi in the small intestine were discovered as early as 1861 by von Kolliker and somewhat later in 1868 in the developing large intestine by Barth. But systematic studies of the developmental process did not get underway until the twentieth century when Hilton (2) described the ontogeny of a large number of species in his doctoral thesis. Attention was turned somewhat later to a series of human embryos by Johnson (3,4).