This observation raised the possibility that UNC-18 functions in two separate sub-steps of the sperm-transfer process (both the initiation and the continuation of transfer), and that neuronal expression of unc-18 was responsible for the initiation of transfer, while the gonad expression may be necessary for continued transfer.
However, the b403 allele fails to complement sy671 for the initiation of transfer (0/16 animals initiated sperm transfer), and therefore it seems likely that the mutation in sy671 also alters vesicle release.
Slower progress than this crosses the alert line on the partograph, which may prompt initiation of the process of transfer to a facility with emergency obstetric capacity in preparation for intervention for prolonged labour.
Although these data also suggest it is specifically the B-type motor neurons in the ventral cord that are relevant for the initiation of sperm transfer, further experiments indicate that the male-specific CA ventral-cord motor neurons are stronger candidates (see below).
In a genetic screen, we isolated an allele of unc-18 defective for the initiation sub-step of sperm transfer (sy671), and we determined that the site of action for UNC-18 in the initiation of transfer was in the ventral-cord motor neurons, most likely the male-specific CA neurons.
By a series of transgenic site-of-action experiments, we found that motor neurons in the ventral nerve cord require UNC-18 for the initiation of sperm transfer, and that UNC-18 acts downstream or in parallel to the SPV sensory neurons in this process.
Although the sy671 mutants can be rescued for the initiation of sperm transfer using a transgene to drive neuronal expression of UNC-18 in a subset of ventral cord cholinergic neurons (most likely the CA neurons), these animals did not transfer as many sperm as wild type.
Also possible, and not ruled out by our experiments, is that the B-type motor neurons are responsible for the initiation of sperm transfer.
Relaxase proteins mediate the initiation of conjugal transfer of plasmid DNA.
High PCA Ca2+ transients occurred after insertion and decreased at the initiation of sperm transfer.
