Involvement of the EN-2 gene in normal and abnormal development of the human arcuate nucleus.

In this study, we wanted to evaluate whether the engrailed EN-2 gene, a homeobox gene with an essential role in the development of the rhombic lip derivatives in different species, is (1) expressed also in man in the differentiation process of the medullary arcuate nucleus (ArcN) and (2) involved in sudden unexplained perinatal and infant death, frequently related to developmental defects of the ArcN. We evaluated by means of the monoclonal antibody 4D9, exclusively recognizing engrailed-2 protein, the expression of the EN-2 gene in the ArcN on histological sections of the brainstems of 30 subjects aged from 17 gestational weeks to 10 postnatal months, who had died of known (17 cases) and unknown causes (13 cases). We observed in the greater number of the cases that the expression of the EN-2 gene is very high in the ArcN neurons from the 17th to the 22nd gestational week, then decreases up to the first days after birth and later disappears. Moreover, in eight of the 13 sudden deaths (61%), a hypoplasia of the ArcN was present. In almost all of these cases, EN-2 expression was negative. In conclusion, we support the role of the EN-2 gene in the normal neuronal development and in the anatomic organization of the human ArcN as well as the possible existence of EN-2 mutations related to hypoplasia of this nucleus.