We have studied somatic cell hybrids between P3x63Ag8 mouse myeloma cells deficient in hypoxanthine phosphoribosyltransferase (EC 2.4.2.8) and either human peripheral lymphocytes or human lymphoblastoid or myeloma cells for the production of human immunoglobulin chains and for the expression of enzyme markers assigned to each of the different human chromosomes. Human chromosome 14 was the only human chromosome present in all independent hybrids producing mu, gamma, and alpha human heavy chains. In two of the independent hybrids that produced human heavy chains, human chromosome 14 was the only human chromosome present in the hybrid cells. Loss of human chromosome 14 from these hybrids resulted in the concomitant loss of their ability to produce human immunoglobulin heavy chains. In view of these results, we conclude that the genes for human immunoglobulin heavy chains are located on human chromosome 14 in immunoglobulin-producing human cells.

The wistar Institute ofAnatomy and Biology, PhiladelphiaLoss of human chromosomes from mouse X human hybridomas is not random. Human chromosomes 14, 5 and 22 are preferentially retained, while chromosomes 2 and 1 are preferentially lost. Interestingly, human chromosome 14, which carries the genes for human immunoglobulin heavy chains, appears to be retained by almost all the hybrid clones and subclones.

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Monoclonal antibodies against mouse testis‐specific phosphoglycerate kinase (PGK‐2) were produced in order to determine immunohistochemically the onset of PGK‐2 synthesis in the germinal epithelium of the mouse. PGK‐2 was detected in testis sections in spermatids as early as stage 12 and in spermatozoa, but not in earlier stages of spermatogenesis nor in any somatic cells of the testis. During ontogeny, PGK‐2 appears within the testis at day 30 post‐partum, concomitant with spermatids entering the maturation phase. All three allelic isozymes PGK‐2A, ‐2B, and ‐2C were detected equally by the monoclonal antibody in testis sections of several inbred mouse strains, each of which expresses a specific PGK‐2 variant. Moreover, the monoclonal antibody against mouse PGK‐2 reacted with heterologous sperm‐specific PGK from rat, rabbit, and bull and, therefore, may serve as a useful immunochemical marker for mammalian spermatogenesis.

Whole rat embryos cultured during the early stages of organogenesis were subjected to a panel of selected chemicals. Of seventeen known in vivo teratogens, seventeen also induced specific malformations in embryos grown in culture. Of ten chemicals which were reported to be negative in in vivo rat teratogenicity studies, eight also did not provoke dysmorphogenic effects in vitro. Of five additionally tested retinoids, all induced multiple malformations. However, concentrations used to induce these effects varied considerably, isotretinoin inducing malformations at 10(-5) M and arotinoid at 10(-11) M. The results indicate qualitatively as well as quantitatively a high predictability of this in vitro system and suggest that the postimplantation embryo culture system may also be useful in the prospective testing of new drugs and environmental chemicals.