lin-26 encodes a presumptive zinc-finger transcription factor that is expressed in hypodermal cells and neuron-associated support cells and that is required for these cells to execute their normal fates. In addition,
lin-26 is expressed in the somatic gonad precursor cells Z1 and Z4 and in a subset of their descendants including the AC, suggesting that
lin-26 might have a function in the somatic gonad. To reveal the potential function of
lin-26 in the somatic gonad, we have been able to generate promoter deletion derivatives that uncouple the essential
lin-26 expression in the ectoderm from its expression in the somatic gonad. A genomic fragment containing 4.6 kb of upstream regulatory sequence (pMLW006) rescues the
lin-26(
pk38mc15) embryonic lethality but leads to highly penetrant sterility. 93% (n=152) of the rescued animals have polyploid oocytes in the gonad arm or in the uterus. To start to identify the cause of the sterility we have used somatic gonad markers. There is no detectable
lin-26 expression in Z1 and Z4 in these mutants suggesting we removed sequences required for early
lin-26 expression in the somatic gonad.
ceh-18 antibody stains all 10 sheath nuclei in wild-type gonad arms but on average only 5.2 (n=22) in the mutant. MH27 antibody stains adherens junctions and is a marker for the spermatheca. As visualized by the MH27 antibody 15/40 sterile animals have an abnormal staining pattern in the spermatheca. The aberrant
ceh-18 and MH27 staining in gonads of the sterile mutants suggest that loss of
lin-26 expression affects the Z1 and Z4 lineage at the level of Z1.ap, Z1.paa, Z4.pa and Z4.app (these blast cells generate the entire sheath and most of the spermatheca and are called SS cells) or earlier. As oocyte arrest is under control of the four SS cells (ablation leads to polyploid oocytes; McCarter and Schedl, WBG,13#3, 42) the observed sterile phenotype could be a result of changes in the lineage of the four SS cells.
lag-2::lacZ can be used as a distal tip cell (dtc) marker. 14/43 gonad arms are missing in the mutant as was verified by the absence of
lag-2::lacZ staining. To narrow down the sequences required for early
lin-26 expression in the somatic gonad we generated smaller internal deletions within the
lin-26 promoter. Using this approach we have identified a 452 nt fragment situated approximately 6.5 kb upstream of the AUG which is required (but not sufficient) for correct
lin-26 expression in the somatic gonad. Sequence comparison between theC. elegans and C. briggsae
lin-26 promoter regions revealed that a region containing the 452 nt fragment is conserved between the two species and contains putative DNA binding sites (see abstract by Philippe Chanal and Michel Labouesse). Lineage analysis of somatic gonads in mutant animals is underway and progress in our analysis of the expression of different somatic gonad markers will be reported.