Schedin P et al. (1991) Development "Autonomy and nonautonomy of sex determination in triploid intersex mosaics of C. elegans."

Schedin P, Wood WB, Hunter CP

[Development, 1991]

The primary sex-determining signal in Caenorhabditis elegans is the ratio of X chromosomes to sets of autosomes (X/A ratio), normally 1.0 in hermaphrodites (XX) and 0.5 in males (XO). XX triploids (X/A = 0.67) are males, but if these animals carry a partial duplication of the X chromosome such that X/A approximately equal to 0.7, they develop as intersexes that are sexually mosaic. We have analyzed these mosaics using Nomarski microscopy and in situ hybridization to obtain information on whether sex determination decisions can be made independently in different cells and tissues, and when these commitments are made. The observed patterns of male and female cells in individual animals indicate that sex determination decisions can be influenced by anterior-posterior position and that sex determination decisions can be made as late as the third larval stage of postembryonic development. Although these decisions clearly can be made independently in different lineages, they show substantial biases toward one sex or the other in individual animals. We interpret these results to suggest that sex determination in C. elegans is not entirely cell autonomous.

Schedin P et al. (1985) International C. elegans Meeting "intestinal mosaicism for expression of vitellogenin genes in C elegans intersexes."

Schedin P, Wood WB

[International C. elegans Meeting, 1985]

Schedin P et al. (1985) Worm Breeder's Gazette "mosaicism for expression of a single-copy vitellogenin gene in intestines of triploid intersexes."

Schedin P, Wood WB

[Worm Breeder's Gazette, 1985]

We showed previously that vitellogenin gene transcripts can be easily detected in intestinal cells of hermaphrodites but not males, by in situ hybridization to dissected intestines using a cloned vit-5 probe (from T. Blumenthal), which cross-hybridizes to four other members of a multigene family in addition to vit-5. Among triploid intersex animals (3A;2X plus a large X duplication), about twenty percent show mosaic intestines, with some cells that hybridize and some that do not. The patterns of positive and negative cells are nonrandom and inconsistent with a lineage-related mechanism of intestinal-cell sex determination based on patterns predicted from the known E lineage. Instead, all mosaics show eight to sixteen contiguous positive cells at the anterior end and negative cells throughout the remaining observable portion of the intestine, implying positional influences on the decision to express or not to express vitellogenin genes (Schedin and Wood, 1985 C. elegans Meeting Abstracts, p. 102). In some mosaic intestines the vit-5 hybridization level is not uniform in all positive cells, but shows a gradient of intensity, with anterior positive cells hybridizing more strongly than posterior positive cells. The variable hybridization could be due to more individual members of the vit-5 gene family being expressed anteriorly, or to variable levels of expression for one or more members of the family. Probes specific for individual family members are not available. Therefore, to ask whether a single vitellogenin gene could show variable expression, we analyzed intestines of intersexes using a single-gene vit-6 probe (from T. Blumenthal), which does not crosshybridize with the vit-5 gene family under our conditions. We found that vit-6 expression shows patterns similar to those seen for expression of the vit-5 gene family. Animals with mosaic intestines all show an anterior region of contiguous positive cells, and a posterior region of contiguous negative cells. The hybridization sometimes appears uniform over the positive cells and sometimes shows the same sort of anterior-posterior gradient of intensity seen with the vit-5 probe. We conclude that the level of expression of vit-6, a single-copy gene, can be variable in mosaic intestines. To determine whether the vit genes are coordinately regulated in intersex mosaics, we are currently doing double labelling experiments with a biotin-labelled vit-5 probe and a 35S-labelled vit- 6 probe.

Schedin P et al. (1986) Worm Breeder's Gazette "a maintenance function for her-1 in control of vitellogenin synthesis and oogenesis in XO adults."

Wood WB, Schedin P, Jonas Y

[Worm Breeder's Gazette, 1986]

Early expression of the her-l gene appears to be both necessary and sufficient to establish the male program of somatic development. Using the temperature-sensitive allele her-l(e1561), Hodgkin observed that a shift to restrictive temperature after embryogenesis has no significant effect on male tail or gonad morphology in the adult (JEEM 83, Supplement, 103-117, 1984). We have used the same allele to ask whether later her-l expression is required to maintain the male differentiated state in the intestine (no vitellogenin synthesis) and the germline (no oocyte production). To determine the temperature- sensitive period for her-l control of vitellogenin synthesis, her-l( e1561);him- 8(e1489) XO animals were raised to early adulthood at 16 C, and the resulting morphologically normal males were then shifted to 25 C. By about 36 hr after the shift, synthesis of the three vitellogenins yp88, yp115, and yp170 was detected by electrophoresis and silver staining of proteins from 45-animal samples on 6% polyacrylamide gels. The germline of these animals was also transformed; approximately 80% had oocytes present by 48 hr after the shift. Control animals left at 16 showed no production of vitellogenins or oocytes for several days, although 9-dayold animals were found to make vitellogenin and oocytes in reduced amounts compared to animals shifted to 25 C. In addition, him- 8(e1489) XO animals were never observed to make either vitellogenin or oocytes at any age whether reared continuously at 16 C or 25 C, or reared to early adulthood at 16 C and then shifted to 25 C. The difference between her-l(e1561);him-8(e1489) and him-8(e1489) XO animals at 16 suggests that the her-l(e1561) gene product is unstable even at the permissive temperature. The results of the temperature-shift experiments indicate that decisions regarding vitellogenin synthesis in the intestine and oocyte production in the germline are not made irreversibly based on the state of the her-l gene during embryogenesis, or even during larval development. Rather, her-l activity is required in adult XO animals to maintain the male differentiated states of these tissues.

Schedin P et al. (1987) Worm Breeder's Gazette "graded initiation of intestinal vitellogenin expression during larval development of N2 hermaphrodites."

Wood WB, Schedin P

[Worm Breeder's Gazette, 1987]

We showed previously by in situ hybridization with vit gene probes that the decision to express vitellogenin transcripts appears to be positionally influenced in intestinal cells of triploid intersex mosaic animals (3A;2X plus a large X duplication; Schedin and Wood, 1985, C. elegans Meeting Abstracts, p. 102; Schedin and Wood, 1985, Worm Breeder's Gazette 9:72.) All mosaics have a region of 8 to 12 contiguous positive cells at the anterior end, with the remaining observable portion of the intestine negative. In addition, about half the mosaics show a gradient of intensity, with more anterior positive cells hybridizing more strongly than more posterior positive cells. ( In diploid or triploid adult hermaphrodites, all 20 intestinal cells hybridize uniformly to the vit probes.) One possible explanation for these results would be that initiation of vitellogenin synthesis during larval development normally occurs in a gradient pattern, which is preserved in some triploid intersex adults. To test this possibility, a highly synchronous population of L1 larvae was prepared from N2 hermaphrodites and then assayed for vitellogenin (vit-5) transcripts by in situ hybridization at several larval stages. A gradient of transcription initiation was in fact observed, but surprisingly, with a polarity opposite to that described above. Autoradiographic grains were first seen over nuclei in the posterior portion of the intestine, shortly after condensation of the germ line nuclei undergoing spermatogenesis in the proximal arm of the gonad. Grains were then observed over the cytoplasm of the posterior intestinal cells with the more posterior cells hybridizing more strongly than the more anterior cells. At subsequent times, hybridization was observed more anteriorly. The most anterior cells, Int 1 and 2, were consistently the last to show hybridization. By the young adult stage, after the L4 molt but before initiation of oocyte production, the hybridization appeared uniform in all 20 intestinal cells. Therefore, the pattern of intestinal vitellogenin expression in the intersex animals is opposite to that found during larval development of normal diploid animals. These two results are not necessarily contradictory or even paradoxical. The first shows that intestinal cells can have positionally correlated differences in their final levels of vitellogenin expression in sexually ambiguous triploid intersexes; the second illustrates the kinetics of the normal hermaphrodite response. One of several possibilities, for example, would be that the normal hermaphrodite signal for vitellogenin expression is posteriorly initiated, causing posterior intestinal cells to respond first, whereas the ability of intestinal cells to respond is determined by the X/A ratio, which is somehow interpreted as being higher in the more anterior intestinal cells of triploid intersexes.

Schedin P et al. (1994) Dev Genet "Function of the her-1 gene is required for maintenance of male differentiation in adult tissues of C. elegans."

Wood WB, Schedin P, Jonas P

[Dev Genet, 1994]

Function of the sex-determining gene her-1 is required in XO embryos of C. elegans to specify male development. Using a temperature-sensitive mutant of her-1, we show that when XO males reared at a permissive temperature are shifted as adults to a nonpermissive temperature, they initiate vitellogenin synthesis in the intestine and oocyte production in the germline. A similar shift has no effect on her-1(+) males. We conclude that sexual differentiation of the intestine and germline is plastic, requiring her-1 expression throughout adulthood for maintenance of the male state.

Schedin P et al. (1987) International C. elegans Meeting "possible function of her-1 in maintaining differentiated states of the intestine and germ line in adult males."

Wood WB, Schedin P, Jonas P

[International C. elegans Meeting, 1987]

Z4.aappppp (5R) nucleus

nucleus of pedigree Z4.aap[p/r]p[p/r]p(5R)

Z4.aap[p/r]p[p/r]p

post-embryonic cell of pedigree Z4.aap[p/r]p[p/r]p

Z4.aapppp(5R) nucleus

nucleus of pedigree Z4.aap[p/r]p[p/r](5R)