Homeobox gene HB24, a regulator of haematopoiesis, is a candidate for regulating differentiation of the extra-embryonic trophoblast cell lineage

Abstract

Expression of the human homeobox gene HB24 in the cytotrophoblast stem cellpopulation in rst-trimester human placenta was investigated.HB24expression was downregulated after cytotrophoblasthad differentiated into syncytiotrophoblast. Expression ofHB24 was also detected in rst-trimester invasiveextravillous cytotrophoblast cells. In term placenta,HB24 expression was detected in residual cytotrophoblastcells and in syncytiotrophoblast. Northern analysis revealed twoHB24 transcripts in rst-trimester placenta ofapproximately 2·5 kb and 5·3 kb. Ribonuclease protection assayswere used to conrm expression of HB24 in rst-trimesterand term placenta and also to provide evidence that HB24is downregulated in choriocarcinoma cell lines. In addition to being requiredfor differentiation of the haematopoietic cell lineage,HB24 may be required for differentiation of theextra-embryonic trophoblast cell lineage.