A meiotic chromosomal core consisting of cohesin complex proteins recruits DNA recombination proteins and promotes synapsis in the absence of an axial element in mammalian meiotic cells.

The behavior of meiotic chromosomes differs in several respects from that of their mitotic counterparts, resulting in the generation of genetically distinct haploid cells. This has been attributed in part to a meiosis-specific chromatin-associated protein structure, the synaptonemal complex. This complex consist of two parallel axial elements, each one associated with a pair of sister chromatids, and a transverse filament located between the synapsed homologous chromosomes. Recently, a different protein structure, the cohesin complex, was shown to be associated with meiotic chromosomes and to be required for chromosome segregation. To explore the functions of the two different protein structures, the synaptonemal complex and the cohesin complex, in mammalian male meiotic cells, we have analyzed how absence of the axial element affects early meiotic chromosome behavior. We find that the synaptonemal complex protein 3 (SCP3) is a main determinant of axial-element assembly and is required for attachment of this structure to meiotic chromosomes, whereas SCP2 helps shape the in vivo structure of the axial element. We also show that formation of a cohesin-containing chromosomal core in meiotic nuclei does not require SCP3 or SCP2. Our results also suggest that the cohesin core recruits recombination proteins and promotes synapsis between homologous chromosomes in the absence of an axial element. A model for early meiotic chromosome pairing and synapsis is proposed.

A visual intracellular classification strategy for uncharacterized human proteins.

The human cDNA and genomic sequencing projects will result in the identification and isolation of some 140,000 genes, the majority of which lack predicted functions and for which the cellular localizations are not known. The identification and characterization of protein components of specific cell structures and machineries are essential steps not only toward defining functions of genes but also toward understanding cell function and regulation. We describe here a new approach, termed PROLOC, which uses full-length cDNAs for systematic classification of novel proteins as a functional pointer. We have PCR-amplified 25 uncharacterized human genes and expressed the encoded proteins as GFP fusions in a human cell line. This pilot project has identified novel proteins associated with the nucleolus, mitochondria, the ER, the ER-Golgi-intermediate compartment (ERGIC), the GC, the plasma membrane, and cytoplasmic foci. This visual classification approach may be scaled up to handle a large number of novel genes and permit the generation of a global cellular protein localization map. Such information should be valuable for many aspects of functional genomics and cell biology.