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CD3 zeta and eta chains are components of the T cell antigen receptor (TCR) complex and are transcribed from a common gene by alternative splicing. TCR complexes containing the zeta eta dimer have been thought to mediate different functions than complexes containing the zeta 2 dimer. To analyze the role of eta in the development and function of T cells, we generated eta‐deficient mice without affecting zeta by gene targeting in embryonic stem cells. Homozygous mutant embryos developed normally. Unexpectedly, however, these mice exhibited high mortality soon after birth for unknown reason(s). Analysis of surviving homozygous animals revealed that the development and function of T cells were normal in the absence of the eta chain. Recently, the zeta/eta locus was reported to encode a transcription factor, Oct‐1, on the opposite DNA strand. Our targeting strategy resulted in modulation of Oct‐1 transcription‐‐reduction of the authentic Oct‐1 mRNA and induction of aberrant transcripts. Although differences in tissue distribution and DNA binding capacity of Oct‐1 between wild‐type and eta‐deficient mice were not evident from in situ hybridization and gel shift analysis, the high mortality in the eta‐deficient strain may well be due to the disturbance of Oct‐1 transcription by the mutation in the zeta/eta locus. Such possible complexities have to be taken into account in the interpretation of gene targeting experiments.

Radioimmunoassays for rat FSH and LH have been studied taking advantage of rat FSH and LH radioimmunoassay kits supplied by the NIAMD. Separation of free and antibody bound labeled hormone was accomplished by the double antibody method with pre-precipitation technique. Although rat GH and prolactin did not react in the FSH assay, LH crossreacted slightly to a negligible extent. Hypophysectomized rat serum inhibited the reaction between labeled rat FSH and anti-rat FSH serum. To eliminate the nonspecific interference by serum, hypophysectomized rat serum was added to the diluent for reference preparations in the FSH assay. Rat GH and prolactin did not react in the LH assay. However, FSH crossreacted in the LH assay to a greater degree than LH in the FSH assay. This indicates that LH concentrations may be overestimated when samples with extraordinary large amounts of FSH are measured. Hypophysectomized rat serum did not influence the LH assay. The FSH activity of pituitary extracts determined by bioassay and that by radioimmunoassay agreed well. And there was also a good correlation between LH values obtained both by bioassay and by radioimmunoassay. Although a marked decrease in pituitary FSH and LH levels was found between proestrus and estrus, serum FSH and LH levels were elevated only slightly at 2:00 PM of the proestrus day. Serum and pituitary FSH and LH levels increased after ovariectomy.

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