Loss of heterozygosity (LOH) involving 3p occurs in many carcinomas but is complicated by the identification of four distinct homozygous deletion regions. One putative target, 3p14.2, contains the common fragile site, FRA3B, a hereditary renal carcinoma-associated 3;8 translocation and the candidate tumor suppressor gene, FHIT. Using a approximately 300 kb comsid/lambda contig, we identified homozygous deletions in cervix, breast, lung and colorectal carcinoma cell lines. The smallest deletion (CC19) was shown not to involve FHIT coding exons and no DNA sequence alterations were present in the transcript. We also detected discontinuous deletions as well as deletions in non-tumor DNAs, suggesting that FHIT is not a selective target. Further, we demonstrate that some reported FHIT aberrations represent normal splicing variation. DNA sequence analysis of 110 kb demonstrated that the region is high in A-T content, LINEs and MER repeats, whereas Alu elements are reduced. We note an intriguing similarity in repeat sequence composition between FRA3B and a 152 kb segment from the Fragile-X region. We also identified similarity between a FRA3B segment and a small polydispersed circular DNA. In contrast to the selective loss of a tumor suppressor gene, we propose an alternative hypothesis, that some putative targets including FRA3B may undergo loss as a consequence of genomic instability. This instability is not due to DNA mismatch repair deficiency, but may correlate in part with p53 inactivation.

, encoding cancer͞testis-specific antigens that are potential targets for cancer immunotherapy. These highly similar paralogous genes cluster on the X chromosome at Xq27. We isolated and sequenced primate genomic clones homologous to human SPANX. Analysis of these clones and search of the human genome sequence revealed an uncharacterized group of genes, SPANX-N, which are present in all primates as well as in mouse and rat. In humans, four SPANX-N genes comprise a series of tandem duplicates at Xq27; a fifth member of this subfamily is located at Xp11. Similarly to SPANX-A͞D, human SPANX-N genes are expressed in normal testis and some melanoma cell lines; testis-specific expression of SPANX is also conserved in mouse. Analysis of the taxonomic distribution of the long and short forms of the intron indicates that SPANX-N is the ancestral form, from which the SPANX-A͞D subfamily evolved in the common ancestor of the hominoid lineage. Strikingly, the coding sequences of the SPANX genes evolved much faster than the intron and the 5 untranslated region. There is a strong correlation between the rates of evolution of synonymous and nonsynonymous codon positions, both of which are accelerated 2-fold or more compared to the noncoding sequences. Thus, evolution of the SPANX family appears to have involved positive selection that affected not only the protein sequence but also the synonymous sites in the coding sequence. T he sperm protein associated with the nucleus on the X chromosome (SPANX) multigene family encodes proteins whose expression is restricted to the normal testis and certain tumors (1, 2). These postmeiotically transcribed genes comprise one of the few examples of haploid expression from X-linked genes (3). Antibodies against SPANX recognized spermatozoa craters and cytoplasmic droplets in ejaculated spermatozoa. Spermatozoa craters correspond to indentations on the nuclear surface and to vacuoles within the condensed chromatin in spermatozoa nuclei. Nuclear vacuoles are believed to be derived from the nucleolus of spermatocytes and spermatids (ref. 4 and references therein). The presence of these craters usually is linked to reduced fertility in mammals (5). However, the correlation between fertility and large nuclear craters in human spermatozoa remains controversial (6, 7).SPANX genes encode small proteins migrating as a broad band of 15-20 kDa under reducing electrophoresis conditions. In spermatozoa, SPANX proteins are found in the form of dimers or complexes with other proteins (1, 3). The SPANX cluster on chromosome X consists of five genes. These genes reside in the Xq26.3-Xq27.3 region, within Ϸ20 kb, highly similar tandem duplications. All SPANX genes consist of two exons separated by an Ϸ650-bp intron containing a solo retroviral LTR sequence (8). SPANX genes are divided into two groups, the SPANX-Aand -B-like subfamilies (8). Classification of SPANX genes is based on the presence of diagnostic amino acid substitutions.The SPANX-A-like subfamily consists of four members, SPANX-A1, -A2, -C, and -...

The role of mitochondria dynamics and its molecular regulators remains largely unknown during naïve-to-primed pluripotent cell interconversion. Here we report that mitochondrial MTCH2 is a regulator of mitochondrial fusion, essential for the naïve-to-primed interconversion of murine embryonic stem cells (ESCs). During this interconversion, wild-type ESCs elongate their mitochondria and slightly alter their glutamine utilization. In contrast, MTCH2−/− ESCs fail to elongate their mitochondria and to alter their metabolism, maintaining high levels of histone acetylation and expression of naïve pluripotency markers. Importantly, enforced mitochondria elongation by the pro-fusion protein Mitofusin (MFN) 2 or by a dominant negative form of the pro-fission protein dynamin-related protein (DRP) 1 is sufficient to drive the exit from naïve pluripotency of both MTCH2−/− and wild-type ESCs. Taken together, our data indicate that mitochondria elongation, governed by MTCH2, plays a critical role and constitutes an early driving force in the naïve-to-primed pluripotency interconversion of murine ESCs.