Figure 3.

Islet Expression in Ventral Motoneurons Represses a Sh-Mediated K⁺ Current

(A) The increase in I_Kfast observed in vMNs in the islet^−/− mutant is effectively blocked by the presence of 200 nM DTx in the bath saline indicative that the increased K⁺ current is Sh mediated. This conclusion is further supported by the observation that the effect of removing islet on I_Kfast requires the presence of Sh; no increase is seen in a Sh;islet double mutant.

(B) The presence of DTx significantly reduces I_Kfast in dMNs indicative that this neuron subgroup expresses an endogenous Sh-mediated K⁺ current. This is confirmed by a similar reduction in I_Kfast observed in a Sh null mutant (Sh^−/−). By contrast, I_Kfast is unaffected in WT vMNs either by exposure to DTx or loss of Sh. All recordings are done in the presence of Cd²⁺. Values shown are means ± SEM (n ≥ 8).

(C and D) In situ hybridization with Sh intron probes. Intron probes detect pre-mRNA at the site of transcription within the nucleus, but not fully processed mRNA in the cytoplasm. The black arrowheads (C) indicate staining for Sh transcript in dMN nuclei, labeled with anti-Eve. White arrowheads (D) indicate vMN nuclei, labeled with nuclear GFP, which do not express Sh. Early stage 17 embryos were analyzed. Scale bar is 5μm.