No abstract

We present a DNA extraction technique that does not require the destruction of the insect exoskeleton. This technique is, therefore, of great utility for extracting from museum specimens DNA suitable for the polymerase chain reaction and subsequent DNA sequencing.

No abstract

Hypotheses of homology are the basis of phylogenetic analysis. All character data are considered to be equivalent regardless of the source of those characters. Putative homology statements are designated based on observations of similarity. Pairwise sequence alignment using the Needleman-Wunsch algorithm is the basis for similarity maximization between molecular sequences. Multiple sequence alignment uses this algorithm in a topologically hierarchical framework. The resulting hypotheses of homology are tested in conjunction with character congruence through parsimony. This review introduces some underlying principles of phylogenetic analysis as they pertain homology testing and DNA sequence alignment.

Netrins are secreted, diffusible proteins that direct axonal growth. To study the functions of netrins in the relatively simple and easily accessible nervous system of the leech Hirudo medicinalis, we have cloned a leech netrin and have characterized its expression during embryogenesis. By probing a leech cDNA library at low stringency with chick netrin probes, we have identified a complete cDNA clone that bears significant sequence similarity to netrins of other species. In situ hybridization and dye filling of individual neurons show that this leech netrin is expressed by several identifiable central neurons in every segmental ganglionic primordium during early stages of embryogenesis. Some of these neurons, including the bipolar cells which are thought to be involved in setting up longitudinal tracts, express this gene only transiently during embryogenesis, while others continue to express it in the adult. In addition, leech netrin is expressed by ventral but not dorsal longitudinal muscle cells in each segment before central neurons project their axons to the periphery. These highly specific expression patterns are consistent with the hypothesis that leech netrin plays a role in forming the major interganglionic neuronal tracts and in defining ventral versus dorsal domains of peripheral innervation.