Endochondral and intramembranous fetal bone development: osteoblastic cell proliferation, and expression of alkaline phosphatase, m-twist, and histone H4

We have previously studied the expression of alkaline phosphatase (ALP) and alpha2(I) collagen (two phenotypic markers of osteoblastic cell differentiation) during development of the rat mandible, and the spatial and temporal distribution of the respective transcripts. Our current studies utilize the rat mandible and hind foot as in vivo model systems to investigate the relationship between osteoblastic differentiation and proliferation during intramembranous and endochondral bone formation. Pregnant rats, at 15.17, and 19 days of gestation were intraperitoneally injected with various doses of [3H]-thymidine, and sacrificed at various time intervals in order to label dividing embryonic osteoblastic and preosteoblastic cells. Cross sections through the mid-body of 15-day embryos showed [3H-thymidine dose-dependent labeling of a relatively high percentage of cells in the liver (49 +/- 8% at 440 muCi) and a lower percentage of cells of the developing vertebral cartilage (29 +/- 6% at 440 muCi). ALP-positive condensed mesenchyme--consisting of mandibular preosteoblast (15 days of gestation) showed a relatively high (32 +/- 5%) level of [3H]-thymidine labeling, compared to surrounding ALP-negative loose mesenchymal cells (22 +/- 1%). Similar results were observed in the developing hind foot of 19-day embryos for ALP-positive cells (15 +/- 6%) and surrounding ALP-negative cells (13 +/- 5%). In both the hind foot and the mandible an overall decrease in labeling was observed during bone development. RNA samples from these tissues show increasing amounts of ALP mRNA, and decreasing amounts of histone H4 mRNA between days 15 and 19 of gestation. These data indicate that a general inverse correlation between osteoblastic differentiation and proliferation, similar to the correlation previously described in cultured osteogenic cells, is also present in developing bones in vivo. However, these results indicate that ALP-positive preosteoblasts, committed to the osteoblastic lineage, maintain their proliferative capacity. In an attempt to elucidate underlying molecular mechanisms, we further investigated the levels of expression of m-twist in these tissues. This member of the basic helix-loop-helix family of transcription regulators has been previously implied as playing a role in osteoblast differentiation in culture. Our results demonstrate a decrease in m-twist levels during bone development in both the mandible and the hind foot.

Evolution and replacement of Candida albicans strains during recurrent vaginitis demonstrated by DNA fingerprinting

Southern blot hybridization with the Ca3 probe and the C fragment of the Ca3 probe was used to assess the genetic relatedness of Candida albicans strains from one patient with recurrent C. albicans infection in whom the same strain was maintained, one patient in whom the infecting strain was replaced, and their male sexual partners. In the patient in whom the infecting strain was maintained, the infecting strain exhibited a minor genetic change in each successive episode of Candida vaginitis. These genetic changes occurred in the C-fragment bands of the Ca3 hybridization pattern. In the patient in whom the infecting strain was replaced by another infecting strain, a transition infection involved a genetically mixed infecting population, and the replacement strain appeared to have originated from the oral cavity of the male partner. The results demonstrate that the infecting strains of recurrent Candida vaginitis are not genetically stable, that drug treatment can result in the selection of variants of the previously infecting strain or replacement by a genetically unrelated strain, and that the male partner can be the source of a replacement strain.

Genetic dissimilarity of commensal strains of Candida spp. carried in different anatomical locations of the same healthy women

Candida spp. carriage and strain relatedness were assessed in 52 healthy women at 17 anatomical locations by using an isolation procedure which assesses carriage intensity and by using a computer-assisted DNA fingerprinting system which computes genetic similarity between strains on the basis of the patterns of Southern blots probed with the moderately repetitive sequence Ca3. Candida spp. were cultured from 73% of the test individuals, most frequently from the oral (56%), vulvovaginal (40%), and anorectal (24%) regions. Half of the test individuals with Candida spp. carried the organism simultaneously in more than one of the three general areas of carriage. Isolates from different body locations of the same individual were either completely unrelated, identical, or highly similar but nonidentical. In 11 cases in which Candida spp. were simultaneously isolated from the oral cavity and vaginal canal, seven pairs of isolates were genetically unrelated and four pairs were similar but nonidentical. In the latter cases, the isolate pairs each appear to have arisen by genetic divergence from a single progenitor. A comparison of the genetic relatedness of isolates from different individuals further uncovered a single strain which was vaginospecific in the Iowa City, Iowa area and reduced genetic diversity among vulvovaginal strains compared with those isolated from other body locations. These results suggest that strains adapt to different anatomical locations and, conversely, that in a healthy individual there is anatomical selection of vaginotropic, anotropic and orotropic strains of Candida spp.

Switching of Candida albicans during successive episodes of recurrent vaginitis

Strain relatedness and switching were monitored in Candida albicans strains isolated from different body locations through three episodes of recurrent vulvovaginal candidiasis separated by two treatment-latency periods in a single patient. Strain relatedness was assessed by comparing Southern blot hybridization patterns with the relatively immobile mid-repeat sequence Ca3. The following conclusions are demonstrated. (i) Three different strains of C. albicans colonized the mouth, the area under the breasts, and the vulvovaginal, anal, and rectal regions, respectively, at the time of the first infection. (ii) The same strain of C. albicans was responsible for the three vaginal infections. (iii) Switching of colony phenotype occurred with each new vaginal infection. (iv) Enrichment of drug-resistant switch phenotypes (assessed in vitro) was unlikely the basis for the changes in the switch phenotypes of the strain found in the vulvovaginal, anal, and rectal areas after treatment of the first infection with clotrimazole. (v) The same strain of C. albicans was responsible for the recurrent increases in mouth colonization and was distinct from the recurrent vaginal strain. The results of this case study demonstrate the need for further detailed analyses of full-body mycofloras, strain relatedness, switching repertoires, and changes in drug susceptibility during successive episodes of recurrent vulvovaginal candidiasis.