Isolation of early immunoglobulin λ‐like gene transcripts in human fetal liver

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Abstract
In an attempt to identify early events of human Ig gene expression, we have screened a human fetal liver cDNA library (< 90 days of gestation) with Cμ‐, Cγ‐, Cχ‐, Cλ‐specific probes and we report the characterization of two clones, Fλ1 and Fλ8, that hybridized with a human Cλ gene. These two clones, which are only 85% homologous to the functional Cλ genes, were shown to be additional nonallelic members of the 14.1/16.1 Cλ‐like family. Using pulsed field gel electrophoresis these three Cλ‐like genes were shown to be present on a 200‐kb DNA fragment, defining a cluster distinct from that of the Cλ one. Fλ1 and Fλ8 contained an identical Cλ‐like region, and differed from each other by a splicing event which joins a Jλ‐like to the Cλ‐like exon in the Fλ1 clone in the absence of any rearrangement. Homologies observed between Fλ1 and the mouse λ5 gene suggest that this human clone may contain the exon 2 and 3 equivalents of λ5. Since λ5 is selectively expressed in pre‐B cells, our proposal is also supported by the early expression of this clone, together with the presence of full‐length μ and γ transcripts and the absence of functional Ig light chain transcripts. The presence of one nucleotide deletion in the C region of Fλ1 conferring it a pseudogene status, the actual λ5 equivalent might be either one of the 14.1 or 16.1 human Cλ‐like genes, the function of which is so far unknown.