Worm Breeder's Gazette 13(1): 75 (October 1, 1993)
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.
lin-7 animals are vulvaless due to the expression of uninduced fates by P5 -7.pindicating that lin-7 is required for normal induction of the vulval precursor cells. We have begun a molecular analysis of lin-7 in order to better understand how lin-7 functions. We placed lin-7 between cosmids C37G2 and F26H11 ,a 200 Kb interval on the physical map by mapping RFLPs. Cosmids in this region did not rescue the lin-7 mutant phenotype in germline transformation experiments nor did they identify the location of lin-7 mutations by Southern blotting analysis. Fortunately, the lin-7 mutant phenotype was rescued by a YAC clone ( Y27H4 ;110 kb). We used recombination in yeast(l) to generate deletion derivatives of Y27H4 .This approach rapidly localized the region of lin-7 rescuing activity to 5 kb, and subsequent subcloning experiments narrowed this region to 3.5 kb. Analysis of the DNA sequence in this region indicates that it likely contains only one gene (R. Durbin, pers. comm.), suggesting that this gene is lin-7 .We will confirm that this gene is lin-7 by determining the sequence of lin-7 point mutations.
Iin-7 contains a GLGF domain, a domain that is approximately 100aa in length and has an unknown function. Surprisingly, this domain is also found in the lin-2 gene required for vulval induction (R. Hoskins, this issue). Iin-2 and lin-7 exhibit similar mutant phenotypes, and it is intriguing that they should encode proteins with similar domains. Several other signaling genes contain one or more GLGF domains, such as: the Drosophila disheveled (dsh) gene required for segment polarity by the wingless signaling pathway(2) and the Drosophila discs large gene required for growth control of imaginal discs.(3) In addition to signaling proteins, several proteins located in regions of cell-cell contact contain GLGF domains, such as a protein found in the post synaptic density of neuromuscular junctions ( PSD-95 )(4),a protein found in tight junctions (ZO-1)(5), and the human megakaryocyte protein tyrosine phosphatase.(6) It is not known whether PSD-95 or ZO-l are involved cell signaling. A common link among these GLGF domain proteins is their localization to the membrane or submembranous cytoskeleton. The localization of dsh, Lin-7 and Lin-2 remains to be determined. The GLGF domain may play a role in either the localization or the activation of these proteins.
What can this tell us about Lin-7 ?The virtually identical genetic behavior shared by the lin-7 and lin-2 genes raises the possibility that their gene products interact, possibly through their GLGF domains. The function of Lin-7 may be to insure the proper subcellular localization of Lin-2 ,as Lin-2 contains an enzymatic domain (a guanylate kinase) whereas Lin-7 does not. Alternatively, the finding that proteins localized to the submembranous cytoskeletonior to regions of cell-cell contact contain GLGF domains suggests that Lin-7 may be involved in specifying cell shape or polarity, and that lin-7 mutations may disrupt cell shape or polarity resulting in impaired cell signaling. Experiments to distinguish among these and other possibilities are in progress.