Published online 29 January 2011 Nucleic Acids Research, 2011, Vol. 39, No. 10 4109–4121 doi:10.1093/nar/gkq1315 Differential RNA-binding activity of the hnRNP G protein correlated with the sex genotype in the amphibian oocyte Rasha Kanhoush 1 , Danie` le Praseuth2, Caroline Perrin1, Dominique Chardard3, Joe¨ lle Vinh4 and May Penrad-Mobayed1,* 1Institut Jacques Monod, UMR 7592, CNRS and Universite´ Paris-Diderot, 2Museum National d’Histoire Naturelle, U 565, USM 503, UMR 5153, INSERM and CNRS, Paris, 3EA 3442 Aspects Cellulaires et Mole´ culaires de la Reproduction et du De´ veloppement, Nancy-Universite´ , Nancy and 4Ecole Supe´ rieure de Physique et de Chimie Industrielles de la Ville de Paris, CNRS/ESPCI ParisTech USR 3149, Paris, France Received November 5, 2010; Revised December 8, 2010; Accepted December 10, 2010 ABSTRACT A proteomic approach has enabled the identification of an orthologue of the splicing factor hnRNP G in the amphibians Xenopus tropicalis, Ambystoma mexicanum, Notophthalmus viridescens and Pleurodeles walt, which shows a specific RNA- binding affinity similar to that of the human hnRN G protein. Three isoforms of this protein with a dif- ferential binding affinity for a specific RNA probe were identified in the P. walt oocyte. In situ hybrid- ization to lampbrush chromosomes of P. waltl revealed the presence of a family of hnRNP G genes, which were mapped on the Z and W chromo- somes and one autosome. This indicates that the isoforms identified in this study are possibly encoded by a gene family linked to the evolution of sex chromosomes similarly to the hnRNP G/RBMX gene family in mammals. INTRODUCTION Heterogenous nuclear ribonucleoproteins (hnRNPs) are critical regulators of pre-mRNA processing in eukaryotic cells. Accumulating evidence shows that cellular control of mRNA biogenesis is dependent on these proteins even when they are in relatively low abundance in the nucleus. This is the case for the hnRNP G protein, which has emerged in the past few years as an important factor in the regulation of post-transcriptional processes. This protein has been implicated in the alternative splicing of several pre-mRNAs including transcripts of the aS- tropomyosin, dystrophin, survival motor neuron SMN2 and Tau genes in particular (1–3). In addition to its important functions in pre-mRNA splicing, hnRNP G has been shown to be involved in the tissue-speciﬁc regu- lation of the transcription of the SREBP-1c and GnRH1 genes (4,5). hnRNP G has been reported recently to act as a tumour suppressor in human head and neck cancer cells and a naturally occurring mutation has been identiﬁed in the RNA-binding domain of this protein in a tumour- derived cell line (6). hnRNP G is a well conserved protein in vertebrates and knockdown assays show that it is critically required for neural and muscle development in zebraﬁsh and Xenopus laevis embryos (7,8). In mammals the RBMX (RNA-binding motif, X chromosome) gene coding for hnRNP G is located on the X chromosome and has a paralogue on the Y chromo- some, the RBMY gene, which is important for normal sperm development (9,10). These two genes belong to the multigenic RBMX/RBMY family, which is linked to the evolution of sex chromosomes because it is presumed to have arisen from an ancient pair of genes on proto sex-chromosomes (11). A comparative sequence analysis of this family in different species suggests that the genes have evolved separately in different mammalian lineages (12). Accordingly, the RBMY gene has acquired a male- speciﬁc function and became ampliﬁed in multiple copies on the Y chromosome, while multiple processed copies of RBMX, referred to as RBMX-like (RBMXLs) genes are thought to have been retroposed on different chromo- somes. While RBMY is expressed in the testis only, hnRNP G is ubiquitously expressed. One of the retroposed autosomal copies, hnRNP G-T, gives rise to a protein, which is expressed predominantly in the testis and is important for male fertility in human and mouse (13–15). Only two other RBMXLs genes may be functional: RBMXL1 is expressed ubiquitously and RBMXL9 is expressed in the testis and brain but *To whom correspondence should be addressed. Tel: +33 1 57 27 81 18; Fax: +33 1 57 27 80 87; Email: penrad@ijm.univ-paris-diderot.fr The Author(s) 2011. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/2.5), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.