We are interested in how spermatids differentiate into activated spermatozoa capable of directional migration and fertilization of oocytes. Male sperm are stored in the seminal vesicle as immature spermatids and activate after transfer to a hermaphrodite. Prior to transfer, activation is inhibited by
swm-1, which encodes a protein with a secretion signal and two trypsin inhibitor-like domains. A suppression screen of
swm-1 identified
try-5, which encodes a trypsin-like serine protease. Whereas
swm-1 males contain prematurely activated sperm,
swm-1 try-5 males contain non-activated sperm. We propose a model in which
try-5 acts as the primary extracellular activating signal for male sperm. This pathway functions in parallel to a second pathway primarily used in hermaphrodites and defined by the
spe-8 group, a group of five genes (
spe-8,
spe-12,
spe-19,
spe-27, and
spe-29) necessary for self-sperm activation. Either pathway is sufficient for activation of male or hermaphrodite sperm. This model makes a number of predictions. First, TRY-5 should act extracellularly. This prediction is supported by the presence of a secretion signal on the putative TRY-5 protein and by
rrf-1 RNAi mosaic experiments, which show that
try-5 is functionally expressed in somatic tissue. Additionally,
try-5 does not suppress the Activated phenotype caused by mutations in
spe-6; SPE-6 is believed to act as an intracellular brake protein for activation, so a finding that
try-5 does not act downstream of
spe-6 is consistent with an extracellular function. A second prediction is that mating should rescue the defects caused by loss of either the male or hermaphrodite activation pathway. In the case of
spe-8 group hermaphrodites, which are self-sterile, sperm are trans-activated upon mating with a male. Likewise,
swm-1 try-5 males contain non-activated sperm, but are fertile when mated to hermaphrodites. A third prediction is that if both signals are lost, then both males and hermaphrodites should be sterile. Indeed, a
spe-27;
swm-1 try-5 strain is both hermaphrodite self-sterile (as expected due to the
spe-8 class
spe-27 mutation) and male-sterile. However, these hermaphrodites are capable of producing self-progeny when mated to wild-type males, indicating that the activation machinery is intact, and the defect is likely in signaling. We are currently testing a fourth prediction of this model:
try-5 should be required for trans-activation. This prediction thus far has been supported. Therefore, our results currently suggest that
try-5 acts as the male sperm activating signal and trans-activating factor.