Differential splicing of a single ZFX transcript results in five variants. Variants 1, 2 and 3 result in isoform I, variant 4 results in isoform II and variant 5 results in isoform III.

ZFX gene is a human X- chromosome gene that escapes X inactivation (Schneider-Gadicke et al.,1989a) and is composed of 10 exons, ranging in size from 57 to 6062 nt. Exons 1 to 5 in isoform 2 and exons 1 to 6 in isoform 1 comprise the 5 UTR and encodes N-terminal acidic domain. Exon 10 contains 3 UTR and AATAAA polyadenylation signal and encodes C-terminal zinc - finger domain for isoforms 1 and 2 (Schneider-Gadicke et al.,1989a).

Transcription initiation sites were not exactly identified, but there is same ORF with the first ATG codon at nucleotide 1 in cDNAs (Schneider-Gadicke et al.,1989b).

Pseudogenes were not exactly identified.

The ZFX isoform I, the longest isoform, contains 805 amino acids (130 kDa). Isoforms II (91 kDa) and III contain 576 and 432 amino acids, respectively. Isoform II binds to the AGGGCCCCA and AGGCCCCGA sequences located at HLA-A11 promoter (LHaridon et al.,1996) and in accompanying with isoform I could play a role as co-activators in HIV-1 LTR induction (Nikpour et al., 2012). Isoforms I and II contain three domains: acidic domain (transcription activation region), nuclear localization signal (NLS) and 13 zinc finger domains, that differ in the length of their N-terminal (acidic) domain resulting in qualitatively and quantitatively different regulatory properties (Schneider-Gadicke et al., 1989b).

ZFX gene escapes X inactivation in humans (Schneider-Gadicke et al., 1989a) and is expressed in a wide range of human tissues (Schneider-Gadicke et al.,1989b).

It was shown that ZFX isoform I is concentrated in the nucleus of glioma cell line, while ZFX isoform II is found in the cytoplasm (Zhu et al., 2013).

ZFX gene is differentially expressed in tissues and may have separate functions in gonadal and somatic tissues (Lau and Chan, 1989). It may play a role as a sex determination factor in mammals (Zhu et al., 2013). ZFX acts as a transcriptional regulator in self renewal and differentiation mechanisms in human embryonic and hematopoietic stem cells (Galan-Caridad et al., 2007; Harel et al., 2012). ZFX has an important role in cell cycle progression and cell growth control (Jiang et al., 2012b).

In mammals, ZFX gene is highly conserved (Ashworth et al., 1990; Lau and Chan, 1989; Palmer et al., 1990). Zinc finger protein X linked is one of the members of ZFY family comprised of three members: ZFX, ZFY and ZFA (Palmer et al., 1990).

A novel Xp22.11 deletion causing a syndrome of craniosynostosis and periventricular nodular heterotopias affecting all or part of three annotated genes, ZFX, PDK3, and PCYT1B has recently been reported in a male subject (van Kogelenberg et al., 2011). Furthermore, Zfx mutation results in small animal size and reduced germ cell number in male and female mice (Luoh et al., 1997). Moreover, molecular cytogenetic analysis of a male infant with severe mental retardation and autism shows that there is a duplication in Xp in this subject (Rao et al., 1994).