We wish to understand the development and the functioning of the nervous system. The phenotype of the unique allele
e189 of
unc-32 suggests that one or two classes of motoneurones (VA and perhaps VB) are specifically affected: L1 are wild type and adults are ventral coilers. However serial reconstruction of the first repeat in the ventral nerve cord behind the RVG failed to show any wiring defect in the motor neurons (John White, Eileen Southgate and Nichol Thomson, pers. comm.). So the function of
unc-32 in the nervous system remains mysterious. There have been oral reports of failure to recover alleles of
unc-32. This may hide interesting genetic features. Therefore, we performed a standard EMS mutagenesis that gave 16% lethals and 6% visible mutants on the X chromosome, and looked for new alleles of
unc-32 and at the same time of
unc-116. Out of 11115 dpy- 17 mes tested for non complementation of unc- 116
(e2310)89), we found one new allele of
unc-116(
f121), which is a zygotic lethal presently under investigation, and three new alleles of
unc-32, among which two are zygotic lethals. The pattern of complementation is complex (see table). The dosage studies indicate that both
e189 and the new allele
f120 are hypomorphs: for instance
e189/e189/e189 is slightly less Unc than
e189/e189, and can be unambiguously recognized.
f121 and
f123 are non-complementing zygotic lethal alleles.
f123 could be the amorph. It has two zygotic effects, on embryonic viability and on coordination (as seen against uncoordinated alleles). In addition, when covered by the cosmid ZK637, which rescues
lin-9 ( Beitel and Horvitz, WBG 11.2, page 29) and
unc-32 (John Sulston, WBG 10.2
p97), both zygotic effects are removed, but a strict maternal effect early embryonic lethality is unmasked.
f121 fails to complement the lethality of
f123, but it complements almost fully the Unc phenotype of the Unc alleles. However, it cannot be a null allele of
unc-32: if it were, we should recover, by mutagenising
e189, around 1 in 3000 animals resembling
f121/e189, i.e. almost wild type, ratchety in reverse 'pseudo revertants'. But, out of 68000
e189 chromosomes mutagenised (18% lethals on X), only one semi-dominant suppressor of
e189,
f125, mapping on chromosome I, was recovered. We are trying to rescue the maternal effect by injection of cosmids overlapping ZK637 to the right and to segregate it away from the unc- 32 locus. We wish to study the suppressor and the cell autonomy of the zygotic lethality, by using qDp3 and
ncl-1, and also to get more alleles of
unc-32.[See Figure 1]