Epidermal growth factor can replace thymic mesenchyme in induction of embryonic thymus morphogenesis in vitro

The thymus is surrounded by a thin layer of mesenchyme and the epithelial-mesenchymal interaction is known to be essential for the thymus development. To clarify the roles of mesenchyme in the thymus lobule formation that occurs around embryonic days 14–15 in vivo, we set up a three-dimensional organ culture system. The epithelium of embryonic day 13 thymic primordium was separated from the mesenchyme and cultured in Matrigel (reconstituted basement membrane). Addition of the mesenchyme to a chamber separated by a membrane filter induced the lobule formation of the thymic epithelium in vitro. We found that epidermal growth factor (EGF) can replace the mesenchyme for lobulation of the embryonic thymus in vitro. Among other growth factors tested, only transforming growth factor (TGF)-α was as effective as EGF, in agreement with the fact that EGF and TGF-α bind to the same receptor. These results suggest that EGF or its family members may be involved in morphogenesis and differentiation of the thymus gland epithelium, although we cannot exclude the possibility that other unknown factors are required in vivo.     

Immunogenotypes of Lymphoid Malignancies; the Rearrangement of T Cell Receptor β Chain Gene Can Occur before the γ Chain Gene Rearrangement

Immunoglobulin (Ig) and T cell receptor (TcR) gene rearrangements were analyzed in 101 cases of lymphoid malignancies in association with a surface phenotype study. In leukemias/lymphomas with mature phenotype, there is a good correlation between phenotypes and genotypes. However, in leukemias/lymphomas with immature phenotype, we found many discordances between phenotypes and genotypes, suggesting the stochastic nature of hematopoietic cell differentiation at the early stage. As for TcR β and γ chains, the rearrangement of γ chain gene is considered to occur slightly prior to that of β chain gene. However, we observed a mature T cell malignancy, adult T-cell leukemia, with rearranged β chain gene and germ line γ chain gene, showing the possible existence of another pathway of T cell differentiation.     

PATHOLOGY OF NEOPLASMS AND OTHER LESIONS INDUCED IN RATS WITH MOLONEY MURINE SARCOMA VIRUS

Moloney murine sarcoma virus (M-MSV) was injected directly into the fetuses of Sprague-Dawley rats during the late stage of gestation and into the neonates within 24 hours after birth. Ninety rats developed 188 neoplastic lesions during the 8-week period of observation. Nearly all of the neoplasms were of mesenchymal derivation. Sixty percent of these neoplasms revealed more complex histologic features than those previously reported for neoplasms induced in rodents with M-MSV and were designated "malignant mesenchymoma" which developed preferentially in the proximal parts of the extremities, distant from the inoculation site. Rhabdomyosarcoma and osteosarcoma which developed in a pure form at the various sites were the next most common tumor type. Osteosarcoma developing in a pure form and as a component of malignant mesenchymoma in the humerus and femur was comparable to that of juxtacortical osteosarcoma of man. The development of excessive bones were observed in the forelimb and/or hind leg, suggesting a type of skeletal malformation. The reaction to M-MSV merits attention as a model for the study of an osteosarcoma and malignant mesenchymoma as well as rhabdomyosarcoma and also for the study of viral teratogenesis in man, as "rubella syndrome".     

A patient with hypophosphatemic rickets and ossification of posterior longitudinal ligament caused by a novel homozygous mutation in ENPP1 gene

X-linked hypophosphatemic rickets/osteomalacia (XLH), autosomal dominant hypophosphatemic rickets/osteomalacia (ADHR) and autosomal recessive hypophosphatemic rickets/osteomalacia (ARHR1 or ARHR2) are hereditary fibroblast growth factor 23 (FGF23)-related hypophosphatemic rickets showing similar clinical features. We here show a patient with hypophosphatemic rickets and widespread ossification of posterior longitudinal ligament (OPLL). The proband is a 62-year-old female. Her parents are first cousins and showed no signs of rickets or osteomalacia. She showed hypophosphatemic rickets with elevated FGF23 level and had been clinically considered to be suffering from XLH. However, direct sequencing of all coding exons and exon–intron junctions of phosphate regulating gene with homologies to endopeptidases on the X chromosome (PHEX), FGF23 and dentin matrix protein 1 (DMP1) genes, responsible genes for XLH, ADHR and ARHR1, respectively, showed no mutation. A novel homozygous splice donor site mutation was found at the exon–intron junction of exon 21 of ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) gene responsible for ARHR2 (IVS21 + 1_3(GTA > CACC)). Subsequent analysis of mRNA revealed that this mutation caused skipping of exon 21 which created a premature stop codon in exon 22. These results indicate that genetic analysis is mandatory for the correct diagnosis of hereditary FGF23-related hypophosphatemic rickets. Because Enpp1 knockout mouse is a model of OPLL, this case also suggests that OPLL is associated with ARHR2.