Worm Breeder's Gazette 12(2): 93 (January 1, 1992)

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.

Is there a gradient of lin-32 activity?

Connie Zhao, Scott W. Emmons

Department of Molecular Genetics, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461

The lin-32 gene functions in a switch between certain hypodermal and neuronal cell fates; mutation of the lin-32 gene causes the Q, postdeirid, and ray neuroblast cells to adopt hypodermal fates. As a result, lin-32 mutant males lack rays. mab-5 , mab-3 , lin-22 , pal-1 ,and egl-5 affect V rays; while mab-19 causes loss of T rays. lin-32 is unique among these genes in causing both V and T ray loss. Furthermore, lin-32 acts downstream of the control gene lin-22 (1). Therefore, lin-32 might function in the initiation of the ray sublineage program, while the other genes control lin-32 expression.

We observed that in tra-1 ( e1099 );Dp+ males (where Df is eT2 ,covering lin-32 )ray 1 was lost 50% of the time, indicating that the lin-32 locus is haplo-insufficient for generating ray 1. The strong allele of lin-32 , u282 ,behaves similarly, causing 40% ray 1 loss in tra-1 ( e1099 ); lin-32 ( u282 )/+heterozygous XX males. Therefore, u282 may be close to a null allele (although we know that it may not be a null since u282 /Dfhas never been seen and therefore is probably lethal). All three alleles of lin-32 show a graded extent of ray loss. Among V5 and V6 -derivedrays ( r1 - r6 ),anterior rays are lost more frequently than posterior rays. Thus, there is a gradient of ray loss from anterior to posterior. In the T-derived rays ( r7 - r9 ),this gradient is reversed. Statistical analysis revealed that the presence or absence of any ray is independent of the presence or absence of its neighbors. Furthermore, laser ablation has failed to demonstrate interactions between neighboring ray precursor cells. Thus, we propose that the probability that a ray precursor cell makes a ray depends solely on the lin-32 activity in that cell. A simple model is that lin-32 gene function in wild type increases from anterior to posterior among V rays, and the level of the gradient is lowered by the existing, presumably hypomorphic lin-32 alleles.

Since it has been shown that there is a gradient of mab-5 activity (2), we performed the following experiments to test if the gradient of mab-5 may establish the gradient of lin-32 .We constructed the mab-5 ( bx54 ); lin-32 ( e1926 )double mutant, and found that the double mutant had a much more severe ray loss phenotype than either single mutant. This synergistic effect suggests that mab-5 and lin-32 may function in the same pathway of ray development. Moreover, an extra copy of wild type mab-5 carried on the free duplication sDp3 increased the number of rays in lin-32 ( e1926 ); sDp3 males. We interpret this to mean that a higher level of mab-5 (+)product increases the level of lin-32 (+)activity in the hypomorphic background. Molecular characterization of lin-32 will demonstrate if there is a gradient of lin-32 protein or mRNA.

Literature Cited:

1. Zhao, C. and Emmon, S. W. (1991). WBG 11(4), 100.

2. Costa, M. et al (1988). Cell 55, 747-756.