Worm Breeder's Gazette 13(3): 59 (June 1, 1994)

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.

mab-5 Expression Repeatedly Switches ON and OFF in the V5 Lineage

S. Salser, C. Kenyon

Figure 1

UCSF, San Francisco, CA. 94143

The homeotic cluster gene mab-5 is required for V5 & V6 to generate sensory rays in the male. In the absence of mab-5 they instead generate adult seam cells (that make alae) as do V1 -V4.The V5 cell is unique in that it lies on the border: it gives rise to a single ray precursor, a single alae producing cell, and also the postdeirid. We wondered if careful regulation of mab-5 expression within the branches of the V5 lineage is required to generate the proper pattern of cell fates. It turns out that it is.

First, what is the expression pattern? By antibody staining mab-5 is OFF in V5 ,first switches ON in V5 .pp,switches OFF again in V5 .ppp,and finally switches ON in V5 .pppp- the branch of V5 which produces the sensory ray. In contrast, mab-5 is expressed throughout the V6 lineage. This is exactly the type of expression pattern we might have predicted based on the distribution of sensory rays.

Is this OFF/ON/OFF/ON regulation functionally important? The answer appears to be yes. Using a heat-shock- mab-5 fusion construct to express mab-5 ,we find that pulses of expression in L3 (time point 3 shown below) lead to the production of an extra V5 ray in the place of the V5 alae. Expression in L2 (time window 2) is necessary to promote the mab-5 dependent L3 doubling division of V5 (in a mab-5 (-)background). Finally, expression in late L1 (time window 1) interferes with postdeirid formation, leading to a symmetric L2 division pattern similar to that of the other V cells. Expression later in L3 does not influence the pattern of ray production, but instead appears to influence ray identity, causing apparent ray 6 to ray 4 transformations (these have not been carefully analyzed).

Figure 1