271. Role of homeobox gene HLX expression in normal placental development

Abstract

In a screen for homeobox genes in the human placenta, we cloned and characterised HLX1 (also known as HB24) (1). Furthermore, we provided evidence that HLX1 may be a regulator of human placental develolpment (2). We have since shown that the mouse homologue of HLX1, called Hlx, is expressed in the murine placenta. In situ mRNA hybridisation studies and antibody localisation of Hlx revealed expression in the labyrinth layer (LL), secondary giant cells (GC) and in the spongiotrophoblast layer (STL) (3). The STL is required for structural support of the placenta. Targeted gene mutation of Hlx resulted in embryonic defects in the developing gut and the liver (4) but the effects on placental development were not investigated. Histological preparations of placental tissues collected from Days 10.5, 13.5 and 19.5 from Hlx mutant mice were investigated for morphological changes. Our preliminary observations reveal that by haematoxylin and eosin staining the STL of the mutant murine placenta is severely disrupted but the overlying GC layer appears to be unaffected. Endogenous alkaline phosphatase staining of the LL further confirmed that the highly vascularised LL where fetal- maternal exchange occurs, is disorganised and expands into the region normally occupied by the STL. These observations indicate that Hlx is essential for normal placental development.

(1) Quinn LM, Kalionis B. (1997) Gene 187, 55–61. (2) Quinn LM, Kalionis B. (1997) Repro. Dev. 9, 617–623. (3) Johnson B (1999) PhD Thesis, University of Adelaide. (4) Hentsch B, Harvey RP (1996) Gene Dev. 10, 70–79.