The most common cause of primary autosomal recessive microcephaly (MCPH) appears to be mutations in the ASPM gene which is involved in the regulation of neurogenesis. The predicted gene product contains two putative N-terminal calponin-homology (CH) domains and a block of putative calmodulin-binding IQ domains common in actin binding cytoskeletal and signaling proteins. Previous studies in mouse suggest that ASPM is preferentially expressed in the developing brain. Our analyses reveal that ASPM is widely expressed in fetal and adult tissues and upregulated in malignant cells. Several alternatively spliced variants encoding putative ASPM isoforms with different numbers of IQ motifs were identified. The major ASPM transcript contains 81 IQ domains, most of which are organized into a higher order repeat (HOR) structure. Another prominent spliced form contains an in-frame deletion of exon 18 and encodes 14 IQ domains not organized into a HOR. This variant is conserved in mouse. Other spliced variants lacking both CH domains and a part of the IQ motifs were also detected, suggesting the existence of isoforms with potentially different functions. To elucidate the biochemical function of human ASPM, we developed peptide specific antibodies to the N- and C-termini of ASPM. In a western analysis of proteins from cultured human and mouse cells, the antibodies detected bands with mobilities corresponding to the predicted ASPM isoforms. Immunostaining of cultured human cells with antibodies revealed that ASPM is localized in the spindle poles during mitosis. This finding suggests that MCPH is the consequence of an impairment in mitotic spindle regulation in cortical progenitors due to mutations in ASPM.

, 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 mouse homologues of the breast cancer susceptibility genes, Brca1 and Brca2, are expressed in a cell cycle-dependent fashion in vitro and appear to be regulated by similar or overlapping pathways. Therefore, we compared the non isotopic in situ hybridization expression patterns of Brca1 and Brca2 mRNA in vivo in mitotic and meiotic cells during mouse embryogenesis, mammary gland development, and in adult tissues including testes, ovaries, and hormonally altered ovaries. Brca1 and Brca2 are expressed concordantly in proliferating cells of embryos, and the mammary gland undergoing morphogenesis and in most adult tissues. The expression pattern of Brca1 and Brca2 correlates with the localization of proliferating cell nuclear antigen, an indicator of proliferative activity. In the ovary, Brca1 and Brca2 exhibited a comparable hormone-independent pattern of expression in oocytes, granulosa cells and thecal cells of developing follicles. In the testes, Brca1 and Brca2 were expressed in mitotic spermatogonia and early meiotic prophase spermatocytes. Northern analyses of prepubertal mouse testes revealed that the time course of Brca2 expression was delayed in spermatogonia relative to Brca1. Thus, while Brca1 and Brca2 share concordant cell-speci®c patterns of expression in most proliferating tissues, these observations suggest that they may have distinct roles during meiosis.