Affiliation: | (1) Department of Reproductive Biology, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Vasco de Quiroga #15, Tlalpan, CP 14000, México D.F., México Tel. +1-525-573-1200 ext. 2423; Fax +1-525-655-9859 e-mail: vilchisuf@prodigy.net.mx, MX;(2) Medical Research Unit in Developmental Biology, Hospital de Pediatría, IMSS, México City, Mexico, MX |