Discovery of tMAC: a Drosophila testis-specific meiotic arrest complex paralogous to Myb–Muv B

Abstract

The Drosophila Myb-Muv B (MMB)/dREAM complex regulates gene expression and DNA replication site-specifically, but its activities in vivo have not been thoroughly explored. In ovarian amplification-stage follicle cell nuclei, the largest subunit, Mip130, is a negative regulator of replication, whereas another subunit, Myb, is a positive regulator. Here, we identified a mutation in mip40 and generated a mutation in mip120, two additional MMB subunits. Both mutants were viable, but mip120 mutants had many complex phenotypes including shortened longevity and severe eye defects. mip40 mutant females had severely reduced fertility, whereas mip120 mutant females were sterile, substantiating ovarian regulatory role(s) for MMB. Myb accumulation and binding to polytene chromosomes was dependent on the core factors of the MMB complex. In contrast to the documented mip130 mutant phenotypes, both mip40 and mip120 mutant males were sterile. We purified Mip40-containing complexes from testis nuclear extracts and identified tMAC, a new testis-specific meiotic arrest complex that contained Mip40, Caf1/p55, the Mip130 family member, Always early (Aly), and a Mip120 family member, Tombola (Tomb). Together, these data demonstrate that MMB serves diverse roles in different developmental pathways, and members of MMB can be found in alternative, noninteracting complexes in different cell types.[Keywords: Drosophila; Myb-Muv B; replication; spermatid differentiation; chorion amplification] Supplemental material is available at http://www.genesdev.org.

LINC, a Human Complex That is Related to pRB-Containing Complexes in Invertebrates Regulates the Expression of G2/M Genes

“…Remarkably, ��NC is related to three complexes that have been identified in Drosophila, (1) the Myb complex that functions in replication, 11 (2) the large E2F, RB and Myb containing complexes that repress developmental genes, 7,8 and (3) the testis specific tMAC complex. 25 Human ��NC is also similar to the recently identified DRM complex in C. elegans that is composed of a subset of synMuv class B gene products. 13 ��NC differs from the Myb-MuvB/dREAM and DRM complexes in invertebrates in that pocket proteins, E2F and B-MYB are not stable subunits of the core complex.…”

“…7,8 Tombola (Tomb), the second Drosophila CXC protein is a subunit of the recently identified testis specific tMAC complex. 25,26 Unlike the other CXC proteins, Tomb contains only one CXC domain (Fig. 1C).…”

Chromatin reader L(3)mbt requires the Myb–MuvB/DREAM transcriptional regulatory complex for chromosomal recruitment

“…These differences may underlie the phenotypical variations where loss of l(3)mbt function is more critical than that of any particular MMB/DREAM factor. What distinguishes the cis-acting vasa regulatory sequences from those at the piwi promoter is unclear, but partial MMB complexes are known to remain chromosome associated (41), and the distribution of such sites at each location along with the presence of other corepressive activities may be informative, as weak interactions of partial complexes with other targeting factors may be cooperative.…”

“…S7, Middle row), suggesting that neither Mip130 nor an intact MMB appears to be required for L(3)mbt recruitment. Moreover, Myb is almost completely lost from polytene chromosomes and tissue culture cells when mip130 is depleted (10,13,41), suggesting that it is not required for L(3)mbt recruitment. As Mip120 binding to chromatin is not lost in mip130-defective mutants (41), the data presented above support a more direct role for Mip120 in general L(3)mbt recruitment to the salivary gland chromosomes.…”

Transgenic expression of CBBP, a CXC domain protein, establishes paramutation in maize

“…CCP1 was shown to repress leghemoglobin gene expression; however, there is no report for its involvement in heritable silencing. The Drosophila CXC domain proteins Tombola and Mip120 have been found in chromatin-associated regulatory complexes (14)(15)(16).…”