Members of the TGF-β superfamily are important regulators of skeletal development. TGF-βs signal through heteromeric type I and type II receptor serine/threonine kinases. When over-expressed, a cytoplasmically truncated type II receptor can compete with the endogenous receptors for complex formation, thereby acting as a dominant-negative mutant (DNIIR). To determine the role of TGF-βs in the development and maintenance of the skeleton, we have generated transgenic mice (MT-DNIIR-4 and -27) that express the DNIIR in skeletal tissue. DNIIR mRNA expression was localized to the periosteum/perichondrium, syno-vium, and articular cartilage. Lower levels of DNIIR mRNA were detected in growth plate cartilage. Transgenic mice frequently showed bifurcation of the xiphoid process and sternum. They also developed progressive skeletal degeneration, resulting by 4 to 8 mo of age in kyphoscoliosis and stiff and torqued joints. The histology of affected joints strongly resembled human osteo-arthritis. The articular surface was replaced by bone or hypertrophic cartilage as judged by the expression of type X collagen, a marker of hypertrophic cartilage normally absent from articular cartilage. The synovium was hyperplastic, and cartilaginous metaplasia was observed in the joint space.We then tested the hypothesis that TGF-β is required for normal differentiation of cartilage in vivo. By 4 and 8 wk of age, the level of type X collagen was increased in growth plate cartilage of transgenic mice relative to wild-type controls. Less proteoglycan staining was detected in the growth plate and articular cartilage matrix of transgenic mice. Mice that express DNIIR in skeletal tissue also demonstrated increased Indian hedgehog (IHH) expression. IHH is a secreted protein that is expressed in chondrocytes that are committed to becoming hypertrophic. It is thought to be involved in a feedback loop that signals through the periosteum/ perichondrium to inhibit cartilage differentiation. The data suggest that TGF-β may be critical for multifaceted maintenance of synovial joints. Loss of responsiveness to TGF-β promotes chondrocyte terminal differentiation and results in development of degenerative joint disease resembling osteoarthritis in humans.

The incidence of marginal biotin deficiency in normal human gestation is approximately one in three. In ICR mice, maternal biotin deficiency results in cleft palate, micrognathia, microglossia and limb hypoplasia. However, the relationships among the severity of maternal biotin deficiency, fetal biotin status and malformations have not been reported. This study utilized validated indices of biotin status to investigate the relationships among maternal biotin status, fetal biotin status and the rate of fetal malformations in ICR mice. Biotin status was controlled by feeding diets with varying egg white concentration. In dams and fetuses, biotin status was assessed by hepatic biotin content and hepatic activity of the biotin-dependent enzyme propionyl-CoA carboxylase; in dams, status was also assessed by urinary excretion of biotin and 3-hydroxyisovaleric acid. Malformations were assessed morphologically. Biotin was measured by HPLC/avidin-binding assay. Propionyl-CoA carboxylase (PCC) activity was determined by H(14)CO(3) incorporation. 3-Hydroxyisovaleric acid concentration was determined by GC/MS. Although no overt signs of deficiency appeared, metabolic disturbances caused by biotin deficiency were detectable in dams and fetuses. These disturbances increased with increasing egg white. Fetal biotin status correlated significantly with maternal biotin status (fetal vs. dam hepatic biotin, r = 0.671; fetal vs. dam PCC activity, r = 0.70). The incidences of malformations were strikingly dependent on egg white concentration. We conclude that in ICR mice, marginal maternal biotin deficiency causes fetal biotin deficiency. We speculate that the fetal malformations are primarily the consequence of fetal biotin deficiency. Because murine malformations appeared at degrees of biotin deficiency that are similar to those in human gestation, we speculate that some human fetal malformations may be caused by biotin deficiency.

ABSTRAC~Fumonisins are mycotoxins produced worldwide by Fusnriion fungi, principally F. nzonilifonne. The fungus is present in virtually all harvested corn, but the toxins produced are variable. The toxins, especially fumonisin B,, cause mild to fatal diseases in animals, with peculiar species specificity for the dominant signs of toxicity. The mechanism of toxicity is poorly understood, but it appears to be related to interference with sphingolipid biosynthesis in multiple organs. Whereas brain, lung, and liver are well-known target organs, toxic effects on the kidney are also widespread and have only recently begun to be characterized. Increased urine volume and decreased osmolarity are early changes associated with the toxin, as are increased excretions of high-and low-molecular-weight proteins. Enzymuria in vivo, reduced ion transport in who, and elevation of free sphinganine in renal tissue and in urine are present. An increase in serum creatinine and blood urea nitrogen and histopathologic change in renal tubules occur later and at higher doses. The morphologic change principally affects the junction of cortex and medulla and includes prGminent apoptosis of epithelial cells of proximal convoluted tubules. Nephrotoxicity has been reported in several species, and in rats and rabbits, the kidney appears to be the most sensitive target organ.

SummaryThis study describes the baseline haematology and serum chemistry values found in nonpregnant, pregnant (gestational days [GO] 2-211 and lactating (postnatal days 1-9) Sprague Dawley rats (n =3-10/dayl from the NCTR breeding colony of Crl:COBS CD(SD)BRstrain. Maternal body weights on GOO ranged from 250 to 300 g. Multiple analytes were measured in both whole blood and serum of dams. Amniotic fluid, fetal serum, and postnatal pup serum analyte values were also acquired. Maternal blood was collected from the heart under subterminal carbon dioxide (C02) anaesthesia. Most pregnant dam blood values were not appreciably different from values for non-pregnant dams until near term; near-term values for some analytes (red blood cells, haemoglobin, haematocrit, mean corpuscular haemoglobin concentration, alkaline phosphatase, albumin, total protein, glucose, total bilirubin, sodium, and chloridel decreased but returned to near-normal values soon after delivery. The most dramatic change was a three-fold elevation of serum triglyceride levels near term with a subsequent decrease at birth. Most serum chemistry analytes measured in progeny increased after birth except for alkaline phosphatase, calcium and potassium levels which decreased.

Two of five pregnant rabbits gavaged with purified fumonisin B1 at 1.75 mg/kg/day died, one after 9 and one after 13 doses. Microscopic examination revealed focal small hemorrhages in cerebral white matter in both animals, with malacia and hemorrhage also present in the hippocampus of one. The lesions were bilateral. Both animals also had marked degeneration of renal tubule epithelium and of hepatocytes. Apoptosis was the dominant degenerative change in kidney and liver. Fumonisin is known to cause leukoencephalomalacia and hemorrhage in equines, but CNS changes associated with exposure to fumonisins apparently have not been reported in other species. This preliminary observation in rabbits is reported to alert other investigators of a potential model of the disease in equines, as well as for investigation of potential mechanisms of toxicity to the CNS.