Worm Breeder's Gazette 12(2): 64 (January 1, 1992)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Most elt-1 mRNA accumulation in adults is dependent upon the germ line

John Spieth, Kris Lea, Tom Blumenthal

Department of Biology, Indiana University, Bloomington, IN 47405

elt-1 is the worm homologue of the vertebrate transcription factor, GATA-1, which is responsible for activation of a number of erthyroid-specific genes including the globin genes. Previously we have shown that elt-1 mRNA accumulates to high levels in embryos. It is also present in larvae and adults but at a much lower level [Spieth et al. Mol. Cell Biol. 11, 4651 (1991)]. We wondered if the elt-1 RNA in embryos was maternal or zygotic. In order to begin to answer this question, we did Northern blots with RNA isolated from mutant worms containing only oocytes, fem-2 ( b245 )lf,or only sperm, fem-3 ( q20 )gf.We reasoned that if the elt-1 mRNA in adults was due to synthesis in embryos then the amount of elt-1 message would be low in both fem-2 lfand fem-3 gfadults. In contrast, if it was due to maternal transcription, then N2 and fem-2 lfadults should have relatively high levels and fem-3 gfadults relatively low levels. To our surprise, the elt-1 mRNA level was significantly higher in fem-3 gfadults than in N2 or fem-2 lfadults. Furthermore, elt-1 message was drastically reduced in glp-4 ( bn2 )adults, which have almost no germ cells. Taken together, these Northern results indicate that in adults elt-1 mRNA accumulation is dependent upon the presence of the germ line and either the female or male germ line is sufficient.

elt-1 mRNA is not restricted to the germ line however. In strains carrying an elt-1 /lacZfusion in extrachromosomal co-arrays with rol-6 ,ß-galactosidase staining is seen in a limited number of non-germ-line nuclei in embryos, larvae and adults. Typically between one and twenty nuclei/worm show ß-galactosidase activity. We have yet to identify the cells that stain in embryos, but staining is never seen in young embryos with fewer than about 50 nuclei. Although our fixations need to be improved to be certain of cell assignments, it is clear that in larvae and adults (males and hermaphrodites) nuclei of the six posterior intestinal cells often stain. We also sometimes see staining in what appear to be muscle and nerve cells (including axons). Staining is present in a few cells of the nerve ring and of the ventral cord (We thank Jeanne Harris for help in identifying cells). We find no staining of adult germ cells, a finding consistent with the failure of others studying known germ-line active promoters to detect the activity of introduced genes in the germ line. Nevertheless, elt-1 expression in adult somatic cells appears to be minor, based on the Northern results that show a drastic decrease in elt-1 mRNA in glp-4 worms; however, the possibility that the germ line is simply needed for induction of elt-1 in somatic cells has not been formally eliminated. The fact that we see equivalent levels of mRNA in N2 and fem-2 lfadults is consistent with the idea that the elt-1 mRNA present at high levels in embryos is primarily parental, since fem-2 lflacks embryonic transcription.

It seems likely that elt-1 is a transcription factor that acts on a number of genes throughout development . This is based on the variety of different cells that express the elt-1 /lacZfusion and the results of Shim et al. (next article) that show that elt-1 recognizes the sequence (A/T)GATA(A/G). This sequence is found in the vit promoters (called VPE2 ),as well as promoter regions of several other genes, including act-1 and -2, mlc-2 , col-1 ,-2 and -8, tra-2 , lin-14 a, elt-1 and the msp genes. In lin-14 a5' flanking DNA it is present multiple times in groups of 2 or 3, as it is in the elt-1 promoter itself. In the msp promoters it is found just once, immediately 5' of the TATA box. If elt-1 mRNA is truly present in the adult male germ line, then elt-1 protein is a good candidate to be an activator of the msp genes. The fact that the elt-1 gene is found adjacent to a cluster of msp genes and other sperm-specific genes on chromosome IV is intriguing.