Identification and Expression Analysis of Two Homologs from Xenopus laevis of the Tumorhead Putative Binding Protein, FBXO30

Abstract

Tumorhead (TH) is a maternal factor that regulates cell proliferation during early embryogenesis in Xenopus laevis. To understand how TH functions at the molecular level, we have been studying its relationship with the novel F‐Box containing protein FBXO30, found in a two‐hybrid screen for TH binding proteins. Using primers based on the sequence we obtained, along with primers based on the 5′ and 3′ UTRs of the Xenopus tropicalis FBXO3O mRNA, we obtained RT‐PCR products with total RNA samples from eggs and embryos at early developmental stages. Using this approach, we have uncovered the presence of two FBXO30 homolog genes in X. laevis, FBXO30‐A and FBXO30‐B. The predicted FBXO30‐A full length protein sequence is 91% and 63% identical to its counterparts from Xenopus tropicalis and Homo sapiens, respectively. These proteins contain very conserved Traf‐like zinc finger‐containing domains at their N‐terminus, and F‐Box domains at their C‐terminus, while the internal part of the proteins diverge extensively. By RT‐PCR, we have found that FBXO30‐A and FBXO30‐B are maternal factors as their messages are present in the unfertilized egg. The FBXO30‐A mRNA persists during the cleavage stages, but decreases after the mid‐blastula transition and is barely detected once gastrulation starts. Our studies show the presence of two homologs of FBXO30 in X. laevis that are maternally expressed, which could be key regulators of early development working with TH to promote cell proliferation.