Worm Breeder's Gazette 7(2): 43
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.
Mutations in several genes result in heterochronic development (see previous Newsletters), i.e., cause certain cells to adopt fates normally specific for other cells generated at different times in development. Heterochronic genes appear to participate in the specification or utilization of temporal information essential for the proper sequencing of developmental events. We have recently observed that two heterochronic genes may also be involved in the control of spatial and sexual information. The heterochronic mutant lin-28(n719) I displays precocious development of the lateral hypodermis: adult cuticle is formed at least one stage earlier than in wild type, and lateral hypodermal cell lineages skip the normal second stage ('S2') segment (Figs. A and B). In addition to displaying these and other heterochronic defects, n719 XX animals are partially transformed into males: V5.pa generates, in the L2, a normally male-specific ray, recognizable by lineage and morphology. (In wild-type, V5.pa generates a postdeirid). Thus, the developmental fate of V5.pa in n719 hermaphrodites is the same as that normally specific for V5.pppppa at a later stage of the same lineage in wild-type males (Fig. C). The mutant lin-14(n179) X at 25 C also displays precocious lateral hypodermal development (deletion of L1-specific cell divisions and precocious alae formation). The double mutant lin-28(n719); 79) displays enhanced precocious hypodermal cell lineages and alae formation (Fig. D). Furthermore, in the double mutant, any of the analogous blast cells V1-V5 can generate a lineage that apparently only V5 generates in the single mutant n719; e.g., in the animal represented in Fig. D, V1.pa as well as V5.pa generated a male ray. Thus, lin-28(n719); 79) results in a spatial (homoeotic) transformation in the fates of the lateral hypodermal blast cells. These observations indicate that certain heterochronic genes can influence not only the time at which a developmental event will occur, but also at what position in the animal and in what sex it will occur. The products of these genes may be elements of a system by which cells are provided with and/or interpret three kinds of developmental information. Alternatively, the spatial and sexual transformations of these mutants may be indirect results of their heterochronic development. For example, if the critical developmental period for positional determination (e.g., V1, not V5) or sexual determination (e. g., 'hermaphrodite' V5, not 'male' V5) is deleted, then this determination could not occur, and an alternative developmental fate may be expressed. [See Figure 1]