Scanning microscopy of collagen in the basement lamella of normal and regenerating frog tadpoles

The arrangement of collagen fibers over the body surface in the basement lamella of Pseudaeris and Xenopus tadpoles is described. It can be viewed by scanning microscopy after removal of epidermis and basal lamina by trypsin treatment of alcohol fixed tissue. The orthogonal array is modified in regions where fiber direction changes extensively such as the base of the ventral fin or the posterior part of the head. In these regions “exceptional points” in the orthogonal pattern occur, as described by Rosin (1946). The pattern is bilaterally symmetrical. In the region of the nasal opening the orthogonal pattern is replaced by a mat of randomly oriented fibers. In tail regeneration the wound area is marked by aberrant disposition of collagen anteriorly then a mat of randomly disposed fibers followed posteriorly with a sharp transition to the orthogonal pattern of the regenerate. No fiber terminations could be seen in normal or regenerating regions of the lamella.     

Length and sequence heterogeneity of the histone gene repeat unit of the sea urchin, S. purpuratus

Histone gene repeats in S. purpuratus are shown to be of variable length and sequence. Two recombinant plasmids containing the full-length 6.3 kb histone repeat unit are found to differer in length at two sites in the repeating structure and in the occurrence of two restriction enzyme recognition sites. Variation in repeat length is also demonstrated in the unfractionated DNA of five sea urchins and in a sample of DNA enriched for histone gene sequences by density gradient methods. The repeats in each individual are of a very limited number of major classes, which may differ from one another in overall length or in distribution and presence of particular restriction enzyme sites. Variations are found to occur at many regions of the repeat; some have been mapped specifically to spacer regions. Repeats may differ dramatically from individual to individual since there is no one type of repeat class common to all, although the absolute length differences of the repeats that are found are small.     

Classical and molecular genetic analyses of his-3 mutants of Neurospora crassa. II. Southern blot analyses and molecular mechanisms of mutagenicity

Previous studies (Overton et al., Mutation Res., 1989) on specific revertibility of 81 his-3 mutants have shown a correlation between complementation pattern and presumed genetic alteration similar to that shown by ad-3B mutants. In the present study, restriction enzyme analyses were used to further characterize the genetic alterations in individual his-3 mutants. The restriction fragment banding patterns of the majority of mutants were identical with that shown by wild-type 74-OR23-1A and were consistent with expectations based on previous data suggesting that they resulted from single base-pair alterations (Overton et al., Mutation Res., 1989). His-3 mutants with altered banding patterns were only found among those with polarized complementation patterns or noncomplementing mutants. One of the mutants with a polarized complementation pattern, 1-189-83, and another noncomplementing mutant, 1-189-85, are associated with genetic alterations proximal to the his-3 locus. In one other mutant, 1-226-565 (with a polarized complementation pattern), an insertion of approx. 2 kb has occurred in the proximal region of the his-3 locus. Two other mutants, 1-155-270 and 1-155-276 (both noncomplementing), contained a large insertion of approx. 12.8 kb in the proximal region of the his-3 locus.     

Central nervous system actions of corticotropin-releasing factor on cardiovascular function in the absence of locomotor activity

Studies were performed in conscious and anesthetized Sprague-Dawley rats to examine whether the cardiovascular responses to intracerebroventricular (i.c.v.) administration of corticotropin-releasing factor (CRF) required concomitant locomotor activation. I.c.v. administration of CRF to conscious animals elicited significant increases in arterial pressure, heart rate, mesenteric resistance, and iliac blood flow, as well as intermittent locomotor, grooming and chewing activity. Intravenous infusion of the anesthetic agent, Saffan, at the minimal dose required to abolish locomotor activity caused slight but significant elevations of heart rate and mesenteric vascular resistance. I.c.v. administration of CRF to anesthetized animals produced delayed, yet significant and sustained increases in the heart rate and arterial pressure, without altering regional blood flow. These results demonstrate that locomotor activation is not requisite for the expression of CRF-induced pressor and tachycardic responses. It is concluded that CRF acts within the central nervous system to influence cardiovascular function in the absence of locomotor activity.