Müllerian inhibiting substance is anterogradely transported and does not attenuate avulsion-induced death of hypoglossal motor neurons

Abstract

Müllerian Inhibiting Substance (MIS, Anti-Müllerian hormone) is a gonadal hormone that contributes to the subtle sex-biases in the nervous system. Mature neurons of both sexes also produce MIS, suggesting that MIS may be a paracrine regulator of adult neural networks. We report here that murine hypoglossal motor neurons produce MIS and its receptors, MISRII and bone morphogenetic protein receptor 1A (BMPR1A, ALK3), but differentially transport them, with only MIS being detectable in axons. The production of MIS and its receptors were rapidly down regulated after axonal damage, which is a characteristic of genes involved in mature neuronal function. MIS is a survival factor for embryonic spinal motor neurons, but the rate of cell loss after hypoglossal nerve avulsion was normal in Mis(-/-) mice and was not attenuated by intraventricular administration of MIS. These observations suggest that MIS may be involved in anterograde rather than autocrine or retrograde regulation of neurons.

Fig. 1

MIS and its receptors are down regulated by avulsion (A–C). The levels of MIS (A), MISRII (B) and BMPR1A (C) protein were reduced in avulsed nuclei of male mice. The sections illustrate 3-day-post avulsion. day 0, 1 and 7 sections are illustrated in Fig. S3, together with measurements of the respective mRNA levels. The left avulsed hypoglossal nuclei are indicated with arrowheads, with arrows pointing to the right nucleus (arrows), which serves as an internal control. MIS protein was transported by motor neurons (D–G). Longitudinal sections (D–E) and cross sections (F and G) of ligated sciatic nerves (E–G) and hypoglossal nerves (D) from male mice were stained with anti-MIS (D–F) or control IgG (G) antibody. The MIS immunoreactivity was mainly observed at the proximal portion of the ligated nerves and trace level of MIS immunoreactivity at distal areas (see Fig. S4). The arrows point to the immunoreactivity of MIS in the axons. The scale bars=100 µm(D) and 25 µm(E–G). The rate and extent of neuronal loss after avulsion were not affected by MIS (H–I). The data is the ratio of the number of neurons in the avulsed nucleus, relative to the contralateral nucleus. (H) The time course of neuronal loss: Mis^+/+ males (dark blue circles); Mis^−/− males (light blue circles); Mis^+/+ females (deep pink triangles) and Mis^−/− females (light pink triangles). The four groups were not significantly different. (I) Infusion of rhMIS to the left ventricle of male mice did not alter the extent of neuronal loss after 15 days. The doses were designed to produce a concentration of MIS within the CSF of 5 ng/ml (0.8 ng/day), 50 ng/ml (8 ng/day) and 5 µg/ml (800 ng/day), based on a turnover rate of 160 µl/day (Johanson, et al., 2008).