1691 Introduction Tissue and cell type specific transcriptional activation is a fundamental feature of cellular differentiation that mediates many changes in cell behaviour and morphology during development. One of the most astonishing developmentally regulated changes in cell morphology occurs in the production of sperm. The cellular differentiation events that constitute spermiogenesis require many gene products used at no other time in development. The unique features of male gamete differentiation are reflected in a developmentally specific transcription programme that initiates in primary spermatocytes in preparation for spermiogenesis. In Drosophila spermatogenesis, transcription is essentially shut down as mature primary spermatocytes enter the meiotic divisions. Therefore, gene products required during differentiation are largely produced from transcripts expressed pre-meiotically (Olivieri and Olivieri, 1965; Schafer et al., 1995). A two-part genetic module, the meiotic arrest genes, is responsible for most of this transcriptional activation, and ensures that a large number of genes required for normal cellular morphogenesis are co-expressed in a cell type and developmental stage-specific manner (Lin et al., 1996; White- Cooper et al., 1998). Males mutant for any of the meiotic arrest genes [including always early (aly), cannonball (can), meiosis I arrest (mia), spermatocyte arrest (sa), cookie monster (comr), achintya/vismay (achi/vis) and no-hitter (nht)] are viable but sterile. Testes from flies mutant for any one of these genes contain morphologically normal spermatogenic cells up to mature primary spermatocytes. However, the mutant cells then arrest and fail to initiate either the meiotic divisions or spermatid differentiation (Ayyar et al., 2003; Jiang and White- Cooper, 2003; Lin et al., 1996). Although transcription of a number of broadly expressed genes (such as cyclin A) is normal in the mutant spermatocytes, transcription of many spermiogenesis genes (e.g. the mitochondrial fusion protein fzo) is very low or undetectable. The aly-class meiotic arrest genes (aly, comr, achi/vis) are likely to act in a pathway distinct from the can-class genes, because they are required for transcription of a wider range of target genes. In addition to a A robust developmentally regulated and cell type specific transcriptional programme is activated in primary spermatocytes in preparation for differentiation of the male gametes during spermatogenesis. Work in Drosophila is beginning to reveal the genetic networks that regulate this gene expression. The Drosophila aly-class meiotic arrest loci are essential for activation of transcription of many differentiation-specific genes, as well as several genes important for meiotic cell cycle progression, thus linking meiotic cell cycle progression to cellular differentiation during spermatogenesis. The three previously described aly-class proteins (aly, comr and achi/vis) form a complex and are associated with chromatin in primary spermatocytes. We identify, clone and characterize a new aly-class meiotic arrest gene, matotopetli (topi), which encodes a testis-specific Zn-finger protein that physically interacts with Comr. The topi mutant phenotype is most like achi/vis in that topi function is not required for the nuclear localization of Aly or Comr, but is required for their accumulation on chromatin. Most target genes in the transcriptional programme depend on both topi and achi/vis; however, a small subset of target genes are differentially sensitive to loss of topi or achi/vis, suggesting that these aly-class predicted DNA binding proteins can act independently in some contexts. Supplemental data available Key words: Spermatogenesis, Transcription, Chromatin, Meiosis, Differentiation. Summary Regulation of transcription of meiotic cell cycle and terminal differentiation genes by the testis-specific Zn-finger protein matotopetli Lucia Perezgasga 1, * ,‡ , JianQiao Jiang 2,‡ , Benjamin Bolival, Jr 1,‡ , Mark Hiller 1,† , Elizabeth Benson 2 , Margaret T. Fuller 1 and Helen White-Cooper 2,§ 1 Departments of Developmental Biology and Genetics, Stanford University School of Medicine, Beckman Center B300, 279 Campus Drive, Stanford, CA 94305-5329, USA 2 Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK *Present address: Departamento de Genética y Fisiología Molecular, Instituto de Biotecnología, UNAM, Avenida Universidad #2001 Col. Chamilpa Apdo. Postal 510-3, Cuernavaca, Mor. 62250 México † Present address: Department of Biological Sciences, Goucher College, 1021 Dulaney Valley Road, Baltimore, MD 21204-2794, USA ‡ These authors contributed equally to the work § Author for correspondence (e-mail: helen.white-cooper@zoo.ox.ac.uk) Accepted 11 December 2003 Development 131, 1691-1702 Published by The Company of Biologists 2004 doi:10.1242/dev.01032 Research article