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Human beta-mannosidosis is an autosomal recessive, lysosomal storage disease caused by a deficiency of the enzyme beta-mannosidase. Unlike the severe clinical manifestation of the disease in ruminants, in which it leads to neonatal death, the human disease phenotype is generally milder. In addition, the phenotypic manifestation among the reported cases of human beta-mannosidosis is variable, even among members of the same family. To understand the molecular basis of the human disease and the mechanisms for such clinical variability, we sequenced the entire coding region of the human beta-mannosidase gene using a combination of cDNA library screening, RT-PCR and 5' rapid amplification of cDNA ends (RACE). The composite cDNA is 3293 nt, consisting of an 87 nt 5'-untranslated region, 2640 nt coding region and 566 nt 3'-untranslated region. The gene was localized to human chromosome 4q22-25. Analysis of a multiple tissue northern blot demonstrated a single 3.7 kb transcript. Mutation analysis of a Czech gypsy family with two siblings differently affected with beta-mannosidosis demonstrated a homozygous A-->G transition 2 bp upstream of a splice acceptor site. The associated cryptic splice site activation and exon skipping caused by this mutation resulted in two abnormally spliced mutant mRNA species in both siblings.

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Previously, we showed that radial glia-like (RG) cells differentiated from embryonic stem (ES) cells after retinoic acid induction (Liour and Yu, 2003: Glia 42:109-117). In the present study, we demonstrate that the production of RG cells from ES cells is independent of the neural differentiation protocol used. These ES cell-derived RG (ES-RG) cells are similar in morphology to RG cells in vivo and express several characteristic RG cell markers. The processes of these ES-RG cells are organized into radial arrays similar to the RG scaffold in developing CNS. Expression of Pax6, along with other circumstantial data, suggests that at least some of these ES-RG cells are neural progenitors. The progression of neurogenesis into gliogenesis during the in vitro neural differentiation of ES cells recapitulates the in vivo developmental process. The identification of two cell surface markers, SSEA-1 and GM1, on both the native embryonic RG cells and ES-RG cells, may facilitate purification of radial glial cells for future studies and cell therapy. Overall, our study suggests that differentiation of radial glial cells is a common pathway during the neural differentiation of ES cells.

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