Temperature sensitive period for the M lineage defect Many of the cells that are affected in
lin-12 mutants require cell- cell interactions for the specification of their fates. The temperature sensitive periods (TSPs) for
lin-12 activity for the hermaphrodite cells Z1.aaa/Z4.ppp and P(3-8).p coincide with the times their fates are determined in wild-type, implying that
lin-12 acts or is synthesized at those times. The M lineage progeny M(d/v)(l/r)pa are also affected in
lin-12 mutant hermaphrodites (see Table 1). Unlike the other groups of cells affected by
lin-12 mutations, laser ablation experiments have not demonstrated cell interaction among M lineage progeny (C. Kenyon, J. Thomas, personal communication). During the course of studying non-null revertants of
lin-12(d) alleles, we identified an allele that is t.s. for the M lineage defect: at 20 C, 2/31 hermaphrodites have ventral coelomocytes (cc), whereas at 25 C, 17/25 hermaphrodites have ventral cc. To determine the TSP for
lin-12 activity in the M lineage, hermaphrodites grown at 20 C or at 25 C were staged according to the number of M cell progeny, shifted to the appropriate temperature, and subsequently scored for the presence of ventral cc. The data in Table 2 demonstrate the TSP for
lin-12 activity in the M lineage is when the lineally-homologous M. (d/v)(l/r)pa are born, suggesting that their fates are not determined before this time. The question of whether cell-cell interactions are important for the specification of their fates awaits genetic mosaic analysis, which is in progress. [See Figure 1] [See Figure 2]
lin-12(0) hermaphrodites are essentially sterile. Tim Schedl isolated
q269, a weakly fertile mutation, which we subsequently demonstrated is an allele of
lin-12. Tim observed that, in adult hermaphrodites, the proximal as well as the distal arms contained undifferentiated cells that are morphologically similar to germ cells: in the 'loop' region, the germ line differentiated into sperm and a few oocytes. Other recessive
lin-12 alleles, including an amber lin- 12(0) mutant, all show the same germ line phenotype. We thank Tim for sending us
q269 and for helping us identify the
lin-12(0) germ line phenotype.