The AMP-activated protein kinase (AMPK) is a metabolic master switch that is activated under energy stress and acts to restore that balance. It is a heterotrimeric complex composed of an alpha catalytic subunit, and two regulatory subunits (beta and gamma). In C. elegans, the catalytic subunit is encoded by the
aak-1 and
aak-2 genes, which have 53% amino acid identity, and 68% similarity. Both genes are required and act additively, to inhibit germline stem cell (GSC) proliferation during dauer development. That functional equivalence between the two genes however does not hold true for other defects. For example, AAK-2 is largely responsible for promoting the animal's longevity and dauer survival. On the other hand, AAK-1 is specifically required for inducing oocyte and GSC quiescence in animals that lack sperm. As such, feminized
aak-1 mutants, but not feminized
aak-2 mutant adults, lay activated unfertilized oocytes, and have ongoing GSC proliferation. Here, we ask what is the basis for this
aak-1-specific requirement in homeostatic regulation of GSC proliferation. We first fluorescently tagged endogenous
aak-1 with mNG and compared its expression with that of tagged endogenous
aak-2 (a kind gift from Shaolin Li). We found that
aak-1 is weakly expressed in the gut and germline, and more strongly in the gonadal sheath cells. We then asked in which of these tissues
aak-1 was required for homeostatic GSC regulation. Our preliminary results suggest that AAK-1 functions in the gonadal sheath cells. Interestingly,
aak-2 is also expressed in the sheath cells, although at a lower level. As such, we consider two possible scenarios to explain the specific requirement for
aak-1. Either the two alpha subunits are functionally equivalent and the difference in expression levels in the sheath cells is what explains the respective mutant phenotypes. Alternatively, amino acid sequence divergences between the two subunits must translate into functional differences. To test this, we will overexpress
aak-2 in the gonadal sheath cells to verify whether that could compensate for
aak-1 function. In parallel, we will attempt to rescue
aak-1 null mutants with various AAK-1::AAK-2 chimeras to identify whether there are functional differences in their slightly divergent domains. Such analysis will help understanding the basis for the functional divergence among the catalytic subunits of AMPK. Keywords: Germline,
aak-1,
aak-2, AMPK, GSC