Agrin-induced reorganization of extracellular matrix components on cultured myotubes: relationship to AChR aggregation.

Agrin, an extracellular matrix-associated protein extracted from synapse-rich tissues, induces the accumulation of acetylcholine receptors (AChRs) and other synaptic components into discrete patches on cultured myotubes. The appearance of agrin-like molecules at neuromuscular junctions suggests that it may direct synaptic organization in vivo. In the present study we examined the role of extracellular matrix components in agrin-induced differentiation. We used immunohistochemical techniques to visualize the spatial and temporal distribution of laminin, a heparan sulfate proteoglycan (HSPG), fibronectin, and type IV collagen on cultured chick myotubes during agrin-induced aggregation of AChRs. Myotubes displayed significant amounts of laminin and HSPG, lesser amounts of type IV collagen, and little, if any, fibronectin. Agrin treatment caused cell surface laminin and HSPG to patch, while collagen and fibronectin distributions were generally unaffected. Many of the agrin-induced laminin and HSPG patches colocalized with AChR patches, raising the possibility of a causal relationship between matrix patching and AChR accumulations. However, patching of AChRs (complete within a few hours) preceded that of laminin or HSPG (not complete until 15-20 h), making it unlikely that matrix accumulations initiate AChR patching at agrin-induced sites. Conversely, when AChR patching was blocked by treatment with anti-AChR antibody mAb 35, agrin was still able to effect patching of laminin and HSPG. Taken together, these findings suggest that agrin-induced accumulations of AChR and laminin/HSPG are not mechanistically linked.

Effects of diethylstilbestrol exposure in utero on the genital tracts of female ACI rats.

Aspects of development and morphology were studied in the reproductive tract of female ACI rats exposed prenatally to diethylstilbestrol (DES) and followed to 10 months of age. Pregnant ACI rats were injected with vehicle or DES (0.8 microgram = low DES or 8.0 micrograms = high DES) on Days 15 and 18 of gestation. At 12 weeks of age, half of the female offspring in each prenatal exposure group received a subcutaneous implant of a pellet containing 2.5 mg DES and 17.5 mg cholesterol; the remaining offspring received a control cholesterol pellet. Maternal reproductive performance was significantly impaired in DES-treated dams compared to controls. In female offspring mean time of vaginal opening was accelerated from 50.3 +/- 2.7 days in the vehicle-exposed group to 46.2 +/- 2.6 and 47.1 +/- 2.3 days in the low and high DES groups, respectively. Prior to pellet implantation, none of the rats exposed to DES prenatally was in "persistent estrus." At necropsy, rats exposed to DES in utero and implanted with the cholesterol pellet showed an increased frequency of atypical uterine epithelia, cystically dilated uterine glands, and a thickened vaginal epithelium. Among groups implanted with the DES pellet, prenatal exposure to DES increased the incidence of squamous metaplasia of the luminal epithelium and of cystically dilated uterine glands. Collectively, groups implanted with the DES pellet had higher incidences of squamous metaplasia of the uterine lumen, cystically dilated uterine glands, and patches of multilayered uterine epithelium than groups bearing the cholesterol pellet. DES pellet-bearing rats were also found to display a pronounced thickening and vacuolation of the vaginal epithelium. Cervical tissue from 98% of the DES-treated litters was characterized by a markedly convoluted epithelium with numerous squamous cell nests. There were no apparent effects of prenatal DES exposure or postnatal DES treatment on ovarian or oviductal histology. However, ovarian wet weights were significantly reduced as a result of postnatal DES treatment. Thus, the epithelial tissues of the uterus, cervix, and vagina in the ACI rat show a sensitivity to DES whether administered prenatally, postnatally, or in combination.

Transplacental effects of diethylstilbestrol on mammary development and tumorigenesis in female ACI rats.

Female ACI rats were exposed to diethylstilbestrol (DES) transplacentally and followed to 10 months of age to assess the effect of the drug on mammary development and tumorigenesis. Pregnant rats were given injections of vehicle (sesame oil) or DES (total dose, 0.8 micrograms = low DES or 8.0 micrograms = high DES) on days 15 and 18 of gestation. Pellets containing 2.5 mg DES + 17.5 mg cholesterol (DES pellet) or 20 mg cholesterol (chol pellet) were implanted s.c. into 12-week-old female offspring, creating 6 experimental groups: vehicle exposure + chol pellet (1) or + DES pellet (2); low DES exposure + chol pellet (3) or + DES pellet (4); high DES exposure + chol pellet (5) or + DES pellet (6). At sacrifice, representative mammary tissue and all palpable mammary tumors were removed for histopathological analysis. Each of the 6 experimental groups contained a minimum of 32 rats from at least 14 litters. In computation of data, the unit of analysis was the litter. Groups which had received any DES (prenatally or postnatally) were found to have elongated nipples and enlarged pituitaries. The mammary gland whole mounts from all rats in groups 4 and 6 displayed extensive lobuloalveolar proliferation comparable to that seen in DES pellet controls (group 2). Mammary glands of approximately 75% of rats in groups 3 and 5 were categorized as showing the lowest grade of differentiation while this undifferentiated condition was seen in only 36% of group I controls. No palpable mammary tumors were found in rats exposed to vehicle in utero (group 1). But in group 5, a total of 6 tumors in 5 animals derived from 4 different litters were obtained, a difference shown to be statistically significant. Group 3 had 1 rat with 8 tumors. Among rats bearing the DES pellet, tumor latency was shortened significantly in both groups exposed to DES in utero. By 22 weeks after pellet implantation, 100% of the DES-exposed litters (groups 4 and 6) contained at least 1 tumor-bearing rat compared to about 50% of the tumor-bearing litters in group 2. Tumor multiplicity at sacrifice was increased significantly in the group exposed prenatally to the higher dose of DES. Histologically, the overwhelming majority of palpable mammary tumors from all tumor-bearing treatment groups were classified as adenocarcinomas. Prenatal exposure to DES did not alter the ratio of malignant to benign lesions observed, nor did it affect the degree of differentiation noted in the adenocarcinomas.(ABSTRACT TRUNCATED AT 400 WORDS)

Genital tract abnormalities in female rats exposed to diethylstilbestrol in utero.

Genital tract morphology in 14-month old female rats exposed prenatally to diethylstilbestrol (DES) was analyzed as part of an examination of the effects of transplacental exposure to DES on estrogen sensitive tissues. Pregnant Sprague-Dawley rats were injected with sesame oil alone or with DES in sesame oil on days 10 and 13 of gestation (total dose 1.2 micrograms DES) or on days 15 and 18 (total dose 1.2 micrograms or 120 micrograms DES). Female offspring (9-15 per group) were sacrificed at 14 months of age. Effects of DES exposure varied with the dose given and with the stage of differentiation of the fetal tissues. In the ovaries of rats exposed to 120 micrograms of DES on days 15 and 18 of gestation, follicular elements were reduced and replaced by dense sheets of stromal cells; oophoritis was noted in five of nine rats. Hypercellularity of oviductal stroma was another common feature, as was suppurative salpingitis. Ovaries of rats exposed to 1.2 micrograms DES on days 10 and 13 of gestation were more likely to contain numerous corpora lutea than the other DES-exposed groups of controls. An increased incidence of benign uterine abnormalities was observed in DES-exposed offspring, including squamous metaplasia and suppurative endometritis. In the cervices of all nine rats exposed to 120 micrograms DES on days 15 and 18 of gestation, the epithelial surface showed a convoluted pattern, lined by stratified squamous and stratified cuboidal cells. Thus, prenatal exposure to DES, especially at the higher dose used, has long-term consequences on reproductive tract morphology in Sprague-Dawley rats.