A mouse homeo box gene is expressed in spermatocytes and embryos

Expression of Rad51 and the histo-morphological evaluation of testis of the sterile male cattle-yak

Meiotic recombination is key to the repair of DNA double-strand break damage, provide a link between homologs for proper chromosome segregation as well as ensure genetic diversity in organisms. Defects in recombination often lead to sterility. The ubiquitously expressed Rad51 and the meiosis-specific DMC1 are two closely related recombinases that catalyze the key strand invasion and exchange step of meiotic recombination. This study cloned and sequenced the coding region of cattle-yak Rad51 and determined its mRNA and protein expression levels, evaluated its molecular and evolutionary relationship as well as evaluated the histo-morphological structure of testes in the yellow cattle, yak and the sterile cattle-yak hybrid. The Rad51 gene was amplified using PCR, cloned and sequenced using testicular cDNA from yak and cattle-yak. Real-time PCR was used to examine the expression levels of Rad51/DMC1 mRNA in the cattle, yak and cattle-yak testis while western blotting, immunofluorescence and immunohistochemistry were used to assess the protein expression and localization of Rad51/DMC1 protein in the testicular tissue sections. The results revealed that the mRNA and protein expression of Rad51 and DMC1 are extremely low in the male cattle-yak testis with a corresponding higher incidence of germ cell apoptosis. There was also thinning of the germinal epithelium possibly due to the depletion of the germ cells leading to the widening of the lumen area of the cattle-yak seminiferous tubule. Our findings provide support for the hypothesis that the low expression of Rad51 and DMC1 may contribute to the male hybrid sterility in the cattle-yak.

HOXC4 up-regulates NF-κB signaling and promotes the cell proliferation to drive development of human hematopoiesis, especially CD43+ cells

The hematopoietic function of HOXC4 has not been extensively investigated. Our research indicated that induction of HOXC4 in co-culture system from D10 significantly promoted productions of most hematopoietic progenitor cells. CD34−CD43+ cells could be clearly classified into CD34−CD43^low and CD34−CD43^high sub-populations at D14. The former cells had greater myelogenic potential, and their production was not significantly influenced by induction of HOXC4. By contrast, the latter cells had greater potential to differentiate into megakaryocytes and erythroid cells, and thus had properties of erythroid–megakaryocyte common progenitors, which abundance was increased by ∼2-fold when HOXC4 was induced from D10. For CD34−CD43^low, CD34+CD43+, and CD34−CD43^high sub-populations, CD43 level served as a natural index for the tendency to undergo hematopoiesis. Induction of HOXC4 from D10 caused more CD43+ cells sustain in S-phase with up-regulation of NF-κB signaling, which could be counteracted by inhibition of NF-κB signaling. These observations suggested that promotion of hematopoiesis by HOXC4 is closely related to NF-κB signaling and a change in cell-cycle status, which containing potential of clinical applications.

TOPAZ1, a germ cell specific factor, is essential for male meiotic progression

Topaz1 (Testis and Ovary-specific PAZ domain gene 1) is a germ cell specific gene highly conserved in vertebrates. The putative protein TOPAZ1 contains a PAZ domain, specifically found in PIWI, Argonaute and Zwille proteins. Consequently, Topaz1 is supposed to have a role during gametogenesis and may be involved in the piRNA pathway and contribute to silencing of transposable elements and maintenance of genome integrity. Here we report Topaz1 inactivation in mouse. Female fertility was not affected, but male sterility appeared exclusively in homozygous mutants in accordance with the high expression of Topaz1 in male germ cells. Pachytene Topaz1--deficient spermatocytes progress through meiosis without either derepression of retrotransposons or MSCI dysfunction, but become arrested before the post-meiotic round spermatid stage with extensive apoptosis. Consequently, an absence of spermatids and spermatozoa was observed in Topaz1(-/-) testis. Histological analysis also revealed that disturbances of spermatogenesis take place between post natal days 15 and 20, during the first wave of male meiosis and before the generation of haploid germ cells. Transcriptomic analysis at these two stages showed that TOPAZ1 influences the expression of one hundred transcripts, most of which are up-regulated in mutant testis at post natal day 20. Our results also showed that 10% of these transcripts are long non-coding RNA. This suggests that a highly regulated balance of lncRNAs seems to be essential during spermatogenesis for induction of appropriate male gamete production.

The low expression of Dmrt7 is associated with spermatogenic arrest in cattle-yak

Dmrt7 is a member of the DM domain family of genes. Dmrt7 deficiency is also a strong candidate as a cause for male cattle-yak infertility, as it is regarded as essential for male spermatogenesis, between the pachynema and diplonema stages. In our study, the coding region sequence of yak and cattle-yak Dmrt7 was cloned by molecular cloning techniques, and the sequence, conserved domains, functional sites, and secondary and tertiary structures of the Dmrt7-encoded protein were predicted and analyzed using bioinformatics methods. The coding region sequences of the Dmrt7 gene, encoding 370 amino acids, were consistent in yak and cattle-yak. The protein encoded by yak and cattle-yak Dmrt7 contains a DM domain. We detected Dmrt7 mRNA expression in testis, but not in any other tissue. Dmrt7 mRNA and protein expression was significantly higher in testis of cattle and yak than that in cattle-yak (p < 0.01). Histological analysis indicated that seminiferous tubules in male cattle-yak were highly vacuolated and contained primarily Sertoli cells and spermatogonia, while those of cattle and yak contained abundant primary spermatocytes. Male cattle-yak testis contained a significantly larger number of apoptotic cells than those in cattle and yak assessed by terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) analysis. The accumulation of SCP3-positive spermatocytes indicated the arrest of spermatogenesis at the pachynema stage in the cattle-yak. These results suggest low levels of Dmrt7 expression lead to male sterility in cattle-yak. The molecular function of Dmrt7 and the regulation of its expression warrant need to be examined in future studies.

RanBPM, a scaffolding protein for gametogenesis

RanBPM is a multimodular scaffold protein that interacts with a great variety of molecules including nuclear, cytoplasmic, and membrane proteins. By building multiprotein complexes, RanBPM is thought to regulate various signaling pathways, especially in the immune and nervous system. However, the diversity of these interactions does not facilitate the identification of its precise mechanism of action, and therefore the physiological role of RanBPM still remains unclear. Recently, RanBPM has been shown to be critical for the fertility of both genders in mouse. Although mechanistically it is still unclear how RanBPM affects gametogenesis, the data collected so far suggest that it is a key player in this process. Here, we examine the RanBPM sterility phenotype in the context of other genetic mutations affecting mouse gametogenesis to investigate whether this scaffold protein affects the function of other known proteins whose deficiency results in similar sterility phenotypes.

RanBPM is essential for mouse spermatogenesis and oogenesis

RanBPM is a recently identified scaffold protein that links and modulates interactions between cell surface receptors and their intracellular signaling pathways. RanBPM has been shown to interact with a variety of functionally unrelated proteins; however, its function remains unclear. Here, we show that RanBPM is essential for normal gonad development as both male and female RanBPM(-/-) mice are sterile. In the mutant testis there was a marked decrease in spermatogonia proliferation during postnatal development. Strikingly, the first wave of spermatogenesis was totally compromised, as seminiferous tubules of homozygous mutant animals were devoid of post-meiotic germ cells. We determined that spermatogenesis was arrested around the late pachytene-diplotene stages of prophase I; surprisingly, without any obvious defect in chromosome synapsis. Interestingly, RanBPM deletion led to a remarkably quick disappearance of all germ cell types at around one month of age, suggesting that spermatogonia stem cells are also affected by the mutation. Moreover, in chimeric mice generated with RanBPM(-/-) embryonic stem cells all mutant germ cells disappeared by 3 weeks of age suggesting that RanBPM is acting in a cell-autonomous way in germ cells. RanBPM homozygous mutant females displayed a premature ovarian failure due to a depletion of the germ cell pool at the end of prophase I, as in males. Taken together, our results highlight a crucial role for RanBPM in mammalian gametogenesis in both genders.

The molecular chaperone Hsp90α is required for meiotic progression of spermatocytes beyond pachytene in the mouse

The molecular chaperone Hsp90 has been found to be essential for viability in all tested eukaryotes, from the budding yeast to Drosophila. In mammals, two genes encode the two highly similar and functionally largely redundant isoforms Hsp90α and Hsp90β. Although they are co-expressed in most if not all cells, their relative levels vary between tissues and during development. Since mouse embryos lacking Hsp90β die at implantation, and despite the fact that Hsp90 inhibitors being tested as anti-cancer agents are relatively well tolerated, the organismic functions of Hsp90 in mammals remain largely unknown. We have generated mouse lines carrying gene trap insertions in the Hsp90α gene to investigate the global functions of this isoform. Surprisingly, mice without Hsp90α are apparently normal, with one major exception. Mutant male mice, whose Hsp90β levels are unchanged, are sterile because of a complete failure to produce sperm. While the development of the male reproductive system appears to be normal, spermatogenesis arrests specifically at the pachytene stage of meiosis I. Over time, the number of spermatocytes and the levels of the meiotic regulators and Hsp90 interactors Hsp70-2, NASP and Cdc2 are reduced. We speculate that Hsp90α may be required to maintain and to activate these regulators and/or to disassemble the synaptonemal complex that holds homologous chromosomes together. The link between fertility and Hsp90 is further supported by our finding that an Hsp90 inhibitor that can cross the blood-testis barrier can partially phenocopy the genetic defects.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 4: intercellular bridges, mitochondria, nuclear envelope, apoptosis, ubiquitination, membrane/voltage-gated channels, methylation/acetylation, and transcription factors

As germ cells divide and differentiate from spermatogonia to spermatozoa, they share a number of structural and functional features that are common to all generations of germ cells and these features are discussed herein. Germ cells are linked to one another by large intercellular bridges which serve to move molecules and even large organelles from the cytoplasm of one cell to another. Mitochondria take on different shapes and features and topographical arrangements to accommodate their specific needs during spermatogenesis. The nuclear envelope and pore complex also undergo extensive modifications concomitant with the development of germ cell generations. Apoptosis is an event that is normally triggered by germ cells and involves many proteins. It occurs to limit the germ cell pool and acts as a quality control mechanism. The ubiquitin pathway comprises enzymes that ubiquitinate as well as deubiquitinate target proteins and this pathway is present and functional in germ cells. Germ cells express many proteins involved in water balance and pH control as well as voltage-gated ion channel movement. In the nucleus, proteins undergo epigenetic modifications which include methylation, acetylation, and phosphorylation, with each of these modifications signaling changes in chromatin structure. Germ cells contain specialized transcription complexes that coordinate the differentiation program of spermatogenesis, and there are many male germ cell-specific differences in the components of this machinery. All of the above features of germ cells will be discussed along with the specific proteins/genes and abnormalities to fertility related to each topic.

Evolutionarily conserved mammalian adenine nucleotide translocase 4 is essential for spermatogenesis

The adenine nucleotide translocases (Ant) facilitate the transport of ADP and ATP by an antiport mechanism across the inner mitochondrial membrane, thus playing an essential role in cellular energy metabolism. We recently identified a novel member of the Ant family in mouse, Ant4, of which gene configuration as well as amino acid homology is well conserved among mammals. The conservation of Ant4 in mammals, along with the absence of Ant4 in nonmammalian species, suggests a unique and indispensable role for this ADP/ATP carrier in mammalian development. Of interest, in contrast to its paralog Ant2, which is encoded by the X chromosome and ubiquitously expressed in somatic cells, Ant4 is encoded by an autosome and selectively expressed in testicular germ cells. Immunohistochemical examination as well as RNA expression analysis using separated spermatogenic cell types revealed that Ant4 expression was particularly high in spermatocytes. When we generated Ant4-deficient mice by targeted disruption, a significant reduction in testicular size was observed without any other distinguishable abnormalities in the mice. Histological examination as well as stage-specific gene expression analysis in adult and neonatal testes revealed a severe reduction of spermatocytes accompanied by increased apoptosis. Subsequently, the Ant4-deficient male mice were infertile. Taken together, these data elucidated the indispensable role of Ant4 in murine spermatogenesis. Considering the unique conservation and chromosomal location of the Ant family genes in mammals, the Ant4 gene may have arisen in mammalian ancestors and been conserved in mammals to serve as the sole and essential mitochondrial ADP/ATP carrier during spermatogenesis where the sex chromosome-linked Ant2 gene is inactivated.

Mili, a mammalian member ofpiwifamily gene, is essential for spermatogenesis

The piwi family genes, which are defined by conserved PAZ and Piwi domains, play important roles in stem cell self-renewal, RNA silencing, and translational regulation in various organisms. To reveal the function of the mammalian homolog of piwi, we produced and analyzed mice with targeted mutations in the Mili gene, which is one of three mouse homologs of piwi. Spermatogenesis in the MILI-null mice was blocked completely at the early prophase of the first meiosis, from the zygotene to early pachytene, and the mice were sterile. However, primordial germ cell development and female germ cell production were not disturbed. Furthermore,MILI bound to MVH, which is an essential factor during the early spermatocyte stage. The similarities in the phenotypes of the MILI- and MVH-deficient mice and in the physical binding properties of MILI and MVH indicate a functional association of these proteins in post-transcriptional regulation. These data indicate that MILI is essential for the differentiation of spermatocytes.

Rosbin: a novel homeobox-like protein gene expressed exclusively in round spermatids

Mammalian spermiogenesis is a complex process occurring in a highly coordinated fashion within the seminiferous tubules. To elucidate the molecular mechanisms controlling haploid germ cell differentiation, we have isolated haploid germ cell- specific cDNA clones from a subtracted cDNA library of mouse testis. One of these cDNAs, Rosbin, is 3.2 kilobases (kb) long and has an open reading frame of 2385 nucleotides encoding a putative protein of 795 amino acid residues. A computer-mediated homology search revealed that it contained a domain similar to that of homeobox genes. Northern blot analysis revealed a 3.2-kb mRNA expressed exclusively in male germ cells. Transcription of the Rosbin gene was not observed in prepubertal testis but became detectable after Day 23. By Western blot analysis the protein encoded by this gene had a molecular mass of 89 kDa, expressing specifically in the testis and localized to the nucleus of stages IV-VIII haploid round spermatids, predominantly at stages VII-VIII of spermatogenesis. ROSBIN is associated with and is most likely phosphorylated by protein kinase A. We suggest that it plays an important role in transcriptional regulation in haploid germ cells.

Hypomorphic mutation in an essential cell-cycle kinase causes growth retardation and impaired spermatogenesis

Cdc7 kinase is essential for initiation of DNA replication. Cdc7(-/-) mouse embryonic stem (ES) cells are non-viable but their growth can be rescued by an ectopically expressed transgene (Cdc7(-/-)tg). Here we report that, despite the normal growth capability of Cdc7(-/-)tg ES cells, the mice with the identical genetic background exhibit growth retardation. Concomi tantly, Cdc7(-/-)tg embryonic fibroblasts (MEFs) display delayed S phase entry and slow S phase progression. Furthermore, spermatogenesis of Cdc7(-/-)tg mice is disrupted prior to pachytene stage of meiotic prophase I. The impairment in spermatogenesis correlates with the extremely low level of Cdc7 protein in testes, and is rescued by introducing an additional allele of transgene, which results in increase of Cdc7 expression. The increased level of Cdc7 also recovers the growth of Cdc7(-/-)tg MEFs and mice, indicating that the developmental abnormalities of Cdc7(-/-)tg mice are due to insufficiency of Cdc7 protein. Our results indicate the requirement of a critical level of a cell-cycle regulator for mouse development and provide genetic evidence that Cdc7 plays essential roles in meiotic processes in mammals.

Homeobox protein, Hmx3, in postnatally developing rat submandibular glands

Homeobox-containing (Hox) genes play important roles in development, particularly in the development of neurons and sensory organs, and in specification of body plan. The Hmx gene family is a new class of homeobox-containing genes defined by a conserved homeobox region and a characteristic pattern of expression in the central nervous system that is more rostral than that of the Hox genes. To date, three closely related members of the Hmx family, Hmx1, Hmx2, and Hmx3, have been described. All three Hmx genes are expressed in the craniofacial region of developing embryos. Here we show, for the first time, the expression of the transcription factor Hmx3 in postnatally developing salivary glands. Hmx3 protein is expressed in a cell type-specific manner in rat salivary glands. Hmx3 is present in both the nuclei and cytoplasm of specific groups of duct cells of the submandibular, parotid, and sublingual glands. Hmx3 expression increases during postnatal development of the submandibular gland. The duct cells show increasing concentrations of Hmx3 protein with progressive development of the submandibular gland. In contrast, the acinar cells of the three salivary glands do not exhibit detectable levels of Hmx3 protein.

Requirement of seminolipid in spermatogenesis revealed by UDP-galactose: Ceramide galactosyltransferase-deficient mice

Although seminolipid has long been suspected to play an essential role in spermatogenesis because of its uniquely abundant and temporally regulated expression in the spermatocytes, direct experimental evidence has been lacking. We have tested the hypothesis by examining the testis of the UDP-galactose:ceramide galactosyltransferase-deficient mouse, which is incapable of synthesizing seminolipid. Spermatogenesis in homozygous affected males is arrested at the late pachytene stage and the spermatogenic cells degenerate through the apoptotic process. This stage closely follows the phase of rapid seminolipid synthesis in the wild-type mouse. These observations not only provide the first experimental evidence that seminolipid is indeed essential for normal spermatogenesis but also support the broader concept that cell surface glycolipids are important in cellular differentiation and cell-to-cell interaction.

The mouse homolog of Drosophila Vasa is required for the development of male germ cells

Restricted expression of a mouse Vasa homolog gene (Mvh) expression is first detected in primordial germ cells (PGCs) after colonization of the genital ridges. Subsequently,Mvh is maintained until postmeiotic germ cells are formed. Here, we demonstrate that male mice homozygous for a targeted mutation of Mvh exhibit a reproductive deficiency. Male homozygotes produce no sperm in the testes, where premeiotic germ cells cease differentiation by the zygotene stage and undergo apoptotic death. In addition, the proliferation of PGCs that colonize homozygous male gonads is significantly hampered, and OCT-3/4 expression appears to be reduced. These results indicate that the loss ofMvh function causes a deficiency in the proliferation and differentiation of mouse male germ cells.

Interleukin 2 promoter/enhancer controlled expression of a synthetic cecropin-class lytic peptide in transgenic mice and subsequent resistance to Brucella abortus

The addition of an antimicrobial that can be synthesized by the mammalian immune system at the point of challenge may enhance disease resistance. A possible group of agents are cecropins, broad-spectrum antimicrobial peptides, which have been described and characterized. They are relatively non-toxic to normal cells from multicellular organisms but are toxic to a wide range of bacteria, protozoa and fungi, as well as infected and abnormal cells. Twenty-six lines of transgenic mice were produced by pronuclear injection of DNA consisting of the 5'-flanking region from -593 to +110 of the mouse interleukin 2 (IL-2) gene, Shiva 1a (a synthetic cecropinclass lytic peptide), and the SV40 polyadenylation/splice signal. A reverse-transcription PCR assay determined that two lines of transgenic mice were produced whose spleen-derived lymphocytes could be induced to transcribe and mature mRNA for Shiva 1a by exposure to 3.25 mg ml-1 of Con A. Two lines were challenged with an inoculation of 5 x 10(4) Brucella abortus strain 2308. After four weeks, there were significantly fewer B. abortus organisms in the spleens of transgenic mice than in non-transgenic control mice of the same strain (p < 0.05). Since the controlling regions of the IL-2 enhancer and the amino acid sequence of the signal peptide are highly conserved among several species, it is likely that this recombinant gene will function in other mammals.

Developmental profile of homeobox gene expression during 3T3-L1 adipogenesis

The homeobox family of proteins are transcription factors are known to be important during the differentiation of a variety of mammalian tissues, however, expression of the genes encoding homeobox proteins during adipogenesis or in adipose tissue has not been described. To investigate whether members of the homeobox gene family are expressed and regulated during adipocyte differentiation, RNA was isolated from 3T3-L1 preadipocyte cells during the hormonal induced differentiation of this cell line into adipocytes. A reverse transcriptase-polymerase chain reaction strategy using degenerate oligonucleotide primers complementary to the highly conserved homeodomain resulted in the identification of 10 different homeobox genes expressed during 3T3-L1 adipogenesis. One of the clones appears to be unique and 9 of the clones represented known members of the homeobox gene family. Examination of the relative mRNA levels encoding these proteins by ribonuclease protection assay during adipocyte differentiation revealed that 3 members, Hox a4, Hox a7, and Hox d4, are regulated as a function of adipocyte development. Further examination of RNA isolated from murine retroperitoneal adipose tissue revealed that these three regulated homeobox mRNAs are expressed in vivo. Combined, these results suggest that members of the homeobox gene family may serve an important role during the differentiation of adipocytes.

Arrest of spermatogenesis and defective breast development in mice lacking A-myb

The Myb gene family currently consists of three members, named A-, B- and c-myb. These genes encode nuclear proteins that bind DNA in a sequence-specific manner and function as regulators of transcription. In adult male mice, A-myb is expressed predominantly in male germ cells. In female mice, A-myb is expressed in breast ductal epithelium, mainly during pregnancy-induced ductal branching and alveolar development. We report here that mice homozygous for a germline mutation in A-myb develop to term but show defects in growth after birth and male infertility due to a block in spermatogenesis. Morphological examination of the testes of A-myb-/- males revealed that the germ cells enter meiotic prophase and arrest at pachytene. In adult homozygous null A-myb female mice, the breast epithelial compartment showed underdevelopment of breast tissue following pregnancy and the female mice were unable to nurse their newborn pups. These results demonstrate that A-myb plays a critical role in spermatogenesis and mammary gland development.

Homeobox genes and male reproductive development

PURPOSE

Homeobox genes encode transcription factors that dictate developmental events in philogenetically diverse organisms. In comparison to what is known about their role in embryogenesis, we know very little concerning homeobox gene function in neonates or adults. In this communication, we review studies that address the possible role of homeobox genes in male reproductive development, a system active in neonate and adult animals.

METHODS

Studies have shown that many homeobox genes are expressed in germ cells of the testis, while less is known about the identity of homeobox genes expressed in somatic cells of the testis or epididymis. Hox homeobox genes display a pattern of expression in testis that is dependent on their paralogous and orthologous position within the Hox gene chromosome clusters. Other homeobox genes are expressed in the male reproductive system, including many POU and Prd/Pax homeobox gene family members. More recently, it has been shown that the orphan homeobox gene, Pem, originally isolated by subtraction hybridization on the basis of its differential expression in tumor cell lines, is selectively expressed in reproductive tissue. Alternatively spliced Pem transcripts accumulate in testis and epididymis that differ from those expressed in tumors and placenta. Pem transcripts accumulate postnatally in the epididymis in a developmentally regulated manner.

CONCLUSIONS

The highly regulated pattern of expression exhibited by many homeobox genes in the male reproductive system suggests that homeobox transcription factors may dictate developmental events in this system. However, future studies are needed to determine the specific functional roles homeobox genes in male reproductive development and spermatogenesis.

Compound mutants for the paralogous hoxa-4, hoxb-4, and hoxd-4 genes show more complete homeotic transformations and a dose-dependent increase in the number of vertebrae transformed

The Hox gene products are transcription factors involved in specifying regional identity along the anteroposterior body axis. In the mouse, several single mutants for Hox genes show variably penetrant, partial homeotic transformations of vertebrae at their anterior limits of expression, suggesting that compound Hox mutants might show more complete transformations with greater penetrance than the single Hox mutants. Compound mutants for the paralogous group 3 genes, hoxa-3 and hoxd-3, show deletion of a cervical vertebrae, which is not readily interpretable in terms of an alteration in regional identity. Here, we report the skeletal phenotypes of compound mutants in the group 4 Hox genes, hoxa-4, hoxb-4, and hoxd-4. Mice mutant for each of these genes were intercrossed to generate the three possible double mutant combinations and the triple mutant. In contrast to the hoxa-3, hoxd-3 double mutants, group 4 Hox compound mutants displayed clear alterations in regional identity, including a nearly complete transformation of the second cervical vertebrae toward the morphology of the first cervical vertebra in one double mutant combination. In comparing the types of homeotic transformations observed, different double mutant combinations showed different degrees of synergism. These results suggest a certain degree of functional redundancy among paralogous genes in specifying regional identity. Furthermore, there was a remarkable dose-dependent increase in the number of vertebrae transformed to a first cervical vertebra identity, including the second through the fifth cervical vertebrae in the triple mutant. Thus, these genes are required in a larger anteroposterior domain than is revealed by the single mutant phenotypes alone, such that multiple mutations in these genes result in transformations of vertebrae that are not at their anterior limit of expression.

Structural abnormalities associated with congenital megacolon in transgenic mice that overexpress the Hoxa-4 gene

Congenital megacolon develops in transgenic mice that overexpress the homeobox-containing gene, Hoxa-4. The current study was done to identify abnormalities of the terminal colon that might account for the phenotype. The terminal bowel of transgenic mice was compared with that of control and lethal spotted (ls/ls) mice, a strain in which megacolon also develops. The terminal colon of the transgenic mice contained fewer ganglia than that of controls, but was hypoganglionic, rather than aganglionic like that of ls/ls mice. The neurons present in the adult transgenic colon were significantly increased in size and a subset of very large neurons (> 40 microns in maximum diameter) were observed. Electron microscopic studies of young adult transgenic mice revealed that the ganglia and nerves of the myenteric plexus had the ultrastructure of extraenteric peripheral nerve rather than that of the enteric nervous system (ENS). The myenteric ganglia in the transgenic animals contained Schwann cells associated with a basal lamina that enveloped axons completely and individually, instead of glia. Although collagen is excluded from the ganglia and thin nerve fibers of the normal ENS, a collagen-containing endoneurium surrounded each of the axon-Schwann cell units of the abnormal nerve fibers of the transgenic colon. Some of the neurons of the transgenic mice were located in these nerve bundles rather than in ganglia. There were also smooth muscle abnormalities in the terminal bowel of the transgenic mice. Wide gaps were present in the longitudinal muscle of the transgenic mice; these gaps contained ganglia that were in contact with the adventitia. These longitudinal smooth muscle cells were more irregular than those of controls and they contained fewer puncta adherens; moreover, a larger proportion of the volume of the cytoplasm of transgenic smooth muscle cells was occupied by organelles. Finally, an extensive thickening and reduplication of the basal lamina surrounding the smooth muscle cells of the muscularis mucosa was observed in the transgenic colon and resembled that found in ls/ls mice. These data suggest that both smooth muscle and the innervation of the terminal bowel of neonatal Hoxa-4 transgenic mice are structurally abnormal. Although some of the abnormalities seen in Hoxa-4 transgenic mice are similar to those which arise in ls/ls mice, the two conditions are not identical. In both animals, the data are consistent with the hypothesis that the defects arise as a result of a defective interaction between the precursors of enteric neurons and smooth muscle.

Protein product of the somatic-type transcript of the Hoxa-4 (Hox-1.4) gene binds to homeobox consensus binding sites in its promoter and intron

The murine Hoxa-4 gene encodes a protein with a homeodomain closely related to those produced by the Antennapedia-like class of Drosophila genes. Drosophila homeodomain proteins can function as transcription factors, binding to several specific DNA sequences. One sequence that is frequently encountered contains a core ATTA motif within a larger consensus sequence, such as CAATTAA. The in vitro synthesized protein product of Hoxa-4 was shown to bind to a subset of restriction fragments of the Hoxa-4 gene itself as determined by gel retardation experiments. Direct examination of the sequences of the fragments bound by Hoxa-4 protein revealed the presence of four regions containing the core ATTA motif. Two regions contained sequences of the CAATTAA class and were located approximately 1 kb upstream from the putative somatic Hoxa-4 promoter and within the intron. Two additional binding sites containing the consensus target sequence involved in autoregulation of Drosophila Deformed gene were identified: one immediately downstream of the putative embryonic transcription start site and one within the intron, respectively. Specific binding of the in vitro produced Hoxa-4 protein to oligonucleotides corresponding to these sequences was observed in gel retardation assays. The same results were obtained with Hoxa-4 protein produced in a Baculovirus expression system. Experiments using oligonucleotides containing base substitutions in positions 1, 3, 4, and 5 in the sequence CAATTAA showed severely reduced binding. The use of truncated mutant Hoxa-4 proteins in gel retardation assays and in transient co-transfection experiments revealed that the intact homeodomain was required for the binding. These results also suggested that the Hoxa-4 gene has the potential to auto-regulate its expression by interacting with the homeodomain binding sites present in the promoter as well as in the intron.

Pituitary hormone FSH directs the CREM functional switch during spermatogenesis

The CREM (cyclic AMP-responsive element modulator) gene encodes multiple regulators of the cAMP-transcriptional response by alternative splicing. A developmental switch in CREM expression occurs during spermatogenesis, whereby CREM function is converted from an antagonist to an activator (CREM tau; ref. 2) which accumulates to extremely high levels from the premeiotic spermatocyte stage onwards. To define the physiological mechanisms controlling the CREM developmental switch, we have hypophysectomized rats and observed the extinction of CREM tau expression in testis, thereby demonstrating a central role of the pituitary-hypothalamic axis. We then used the seasonal-dependent modulation of spermatogenesis in hamsters to dissect the hormonal programme controlling this developmental process. By this approach, combined with direct administration of pituitary-derived hormones, we have established that follicle-stimulating hormone (FSH) is responsible for the CREM switch. FSH appears to regulate CREM expression by alternative polyadenylation, which results in a dramatic enhancement of transcript stability.

Sequences 5′ of the homeobox of the Hox-1.4 gene direct tissue-specific expression of lacZ during mouse development

The murine homeobox-containing gene Hox-1.4 is expressed in restricted patterns during embryogenesis and in male germ cells. To begin identification of the cis-acting elements regulating this expression, transgenic mice were generated carrying a chimeric construct that contained approx. 4 kb of 5′ flanking sequence and approx. 1 kb of structural gene, fused in frame to the E. coli lacZ gene. This construct directed expression of the resulting Hox-1.4, beta-galactosidase fusion protein in a pattern that reproduced virtually the complete embryonic and adult sites of expression of the endogenous gene. Embryonic expression of the fusion protein was first detected in mesoderm at day 8.0 of gestation (E 8.0). Between gestational ages E 8.5 to E 12.5, beta-gal expression was observed in the somites, the lateral walls of the posterior myelencephalon, the dorsal region and ventral wall of the spinal cord, spinal ganglia and prevertebrae and their surrounding mesenchyme, between presumptive ribs, as well as in mesenchymal layers in the lung, kidney and portions of the gut. Expression was also noted in the pancreas and in the supporting cells and sheath around subsets of peripheral nerves, sites that had not been detected previously. Adult expression was observed in testes, specifically in meiotic and post-meiotic male germ cells. In contrast, transgenic mice carrying 5′ deletions of the construct which leave approx. 1.2 kb or approx. 2.0 kb of Hox-1.4 sequence 5′ to the embryonic promoter, did not exhibit beta-gal staining. These deletion experiments defined at least one cis-acting control element necessary for the expression of the Hox-1.4 gene to a 2 kb region located 2 to 4 kb 5′ of the embryonic transcription start site.

Expression of the Hox 2.2 homeobox gene in murine embryonic epidermis

The expression of the Hox 2.2 gene was studied in mouse fetal skin by in situ hybridization with an antisense RNA probe derived from the homeobox region of this gene. In contrast to the expression of Hox 2.2 in spinal cord, which is strongest in 11-day embryos, and is greatly diminished by day 14 and day 17, the signal for Hox 2.2 in skin could be not be detected in 11-day epidermis, was barely detectable on day 14, became strong on day 17, and decreased in new-born animals (day 19). RNase protection assays using Hox 2.2 homeobox-containing and 3' flanking region probes confirmed that the signals detected in 17-day fetal skin by in situ hybridization represent Hox 2.2 transcripts, and that the message is expressed throughout the day 15 to day 18 period during which the epidermis is undergoing terminal differentiation. RNase protection analysis also revealed two alternatively spliced forms of the Hox 2.2 mRNA are present throughout fetal skin development. Northern gel analysis of 17-day fetal skin using a Hox 2.2 homeobox-containing probe at high stringency showed two bands of 1.6 and 1.9 kb, respectively. The 1.9 kb band was greatly enhanced by hybridization at reduced stringency, suggesting the expression of additional homeobox genes with homology to Hox 2.2. These results suggest that the Hox 2.2 homeobox gene plays a role in epidermal development.

The ubiquitous transactivator Zfp-38 is upregulated during spermatogenesis with differential transcription

We describe the complete nucleotide sequence of a full length cDNA clone encoding a new mouse zinc finger protein gene, Zfp-38 and localize it on chromosome 5 by the interspecific backcross analysis. The N-terminal domain of the Zfp-38 protein (64 kDa) contains 358 amino acids and the C-terminal domain of 197 residues encodes 7 zinc fingers. We also present evidence that Zfp-38 is a strong transcriptional activator. The transactivation domain was localized in the non finger region and a fusion protein containing 112 amino acid residues from this region of the Zfp-38 and the DNA binding domain of the yeast Gal 4 protein, very efficiently transactivated the expression of a reporter CAT plasmid, harboring the Gal4 target site. By in situ hybridization and northern blotting technique, the Zfp-38 transcript can be detected at a highly elevated level during spermatogenesis. Its expression accompanies the progression from pachytene spermatocytes to round spermatids. The undifferentiated spermatogonia or the haploid elongated spermatid and the spermatozoa do not show any detectable level of the transcript. Interestingly, other tissues express low levels of a slightly shorter transcript with a different 5' end as determined by RNase protection. The presence of both a transcriptional activating domain and 7 DNA binding zinc fingers, coupled with the cell type(s) specific expression pattern, suggests that Zfp-38 has the potential to regulate transcription during spermatogenesis.

Expression of a mouse zinc finger protein gene in both spermatocytes and oocytes during meiosis

In order to identify genes regulating meiosis, a mouse spermatocyte cDNA library was screened for sequences encoding proteins with C2H2-type zinc finger motifs which are typically expressed by the Drosophila Krüppel gene. Three new cDNAs were isolated, and they were designated CTfin33, CTfin51, and CTfin92. Among them, CTfin51 was selected for further study. The deduced amino acid sequence revealed seven zinc finger motifs in its C-terminal region. Northern blot and in situ hybridization showed CTfin51 mRNA expression in spermatocytes after the pachytene stage and in early stage round spermatids of prepuberal and adult males. Immunocytochemical staining with an antiserum against beta-gal-CTfin51 fusion protein was localized within nuclei of spermatocytes and spermatids. Oocyte nuclei after the pachytene stage also were immunoreactive for CTfin51 protein. Immunoblots revealed a band at M(r) 75,000 in protein extracts from the testis and the ovary. These results suggest that the CTfin51 gene encodes a DNA-binding regulatory protein functionally associated with meiosis in both male and female gametogenesis.

Identification of 10 murine homeobox genes

In Drosophila a number of genes important in establishing segmentation patterns and in determining segment identities have been shown to carry the homeobox sequence. Over 30 murine homeobox genes have been cloned, many on the basis of sequence homology to Drosophila prototypes. Here we report the cloning and sequencing of 10 new and 6 previously known homeobox genes by screening a murine genomic library with a 768-fold degenerate oligonucleotide corresponding to the most conserved 8-amino acid motif in the recognition helix of the homeodomain. Eight of these new homeobox genes have been chromosomally mapped. Four genes do not belong to any of the known homeobox gene clusters but instead map to new locations on chromosome 1 (single gene) and chromosome 5 (three genes). Sequence comparisons indicate that two of these are very closely related and represent a distinct new category of homeobox genes. The remaining four mapped genes reside in previously established murine homeobox gene clusters. Specifically, two map to the cluster HOX-1 on chromosome 6 and one each to HOX-3 and HOX-4 on chromosome 15 and 2, respectively. The ratio of newly identified homeobox genes to the previously characterized murine homeobox genes suggests that there remain several uncharacterized homeobox genes in the murine genome.

Methylation patterns of testis-specific genes

The methylation patterns of genes expressed in the mouse male germ line have been examined. Int-1, Hox-2.1, and Prm-1, all of which contain 5' CpG islands, were found to be completely unmethylated at many sites in these domains, both in somatic tissues and in sperm DNA. Many other testis-specific genes have a similar structure and are probably also constitutively unmethylated. Pgk-2, a non-CpG-island gene, is similar to somatic tissue-specific genes in that it is highly methylated in nonexpressing cell types but undermethylated in pachytene spermatocytes and round spermatids, where it is actively transcribed. At later stages of spermatogenesis, however, the gene becomes remethylated and thus acquires the full modification pattern in sperm DNA. In all these cases, the sperm DNA that emerges from the testis does not contain any germ-line-specific unmethylated sites and thus carries the methylation pattern typical of that in somatic tissues.

Murine embryonic spinal cord and adult testis Hox-1.4 cDNAs are identical 3' to the homeo box

The Hox-1.4 murine homeo box containing gene is expressed in both embryonic spinal cord and adult testis where different sized Hox-1.4 transcripts are detected. In order to compare the sequences of these transcripts, Hox-1.4 cDNA clones were isolated from cDNA libraries prepared from mouse embryonic spinal cord and mouse adult testis. Sequence analysis showed these clones to be identical and extend from an internal EcoRI site at position 55 in the homeo box to a poly (A) stretch 20 nucleotides 3' to the polyadenylation signal. These data indicate that murine Hox-1.4 mRNAs expressed in embryonic spinal cord and adult testis are identical 3' to the homeo box and utilize the same polyadenylation signal.

The Wnt-1 (int-1) oncogene promoter and its mechanism of activation by insertion of proviral DNA of the mouse mammary tumor virus

Wnt-1 (int-1) is a cellular oncogene often activated by insertion of proviral DNA of the mouse mammary tumor virus. We have mapped the 5' end and the promoter area of the Wnt-1 gene by nuclease protection and primer extension assays. In differentiating P19 embryonal carcinoma cells, in which Wnt-1 is naturally expressed, two start sites of transcription were found, one preceded by two TATA boxes and one preceded by several GC boxes. In P19 cells, a 1-kilobase upstream sequence of Wnt-1 was able to confer differentiation-specific expression on a heterologous gene. We have investigated how Wnt-1 transcription was affected by mouse mammary tumor virus proviral integrations in various configurations near the promoters of the gene. One provirus has been inserted in the 5' nontranslated part of Wnt-1, in the same transcriptional orientation, and has functionally replaced the Wnt-1 promoters. Wnt-1 transcription in this tumor starts in the right long terminal repeat of the provirus, with considerable readthrough transcription from the left long terminal repeat. Another provirus has been inserted in the orientation opposite that of Wnt-1 into a GC box, disrupting the first Wnt-1 transcription start site but not the downstream start site. Most insertions have not structurally altered the Wnt-1 transcripts and have enhanced the activity of the normal two promoters.

Stage-specific expression of phosphoprotein p19 during spermatogenesis in the rat

The expression of phosphoprotein p19, a 19-kDa cytosolic substrate for cyclic adenosine monophosphate (cAMP)-dependent protein kinase, occurs abundantly in brain and testis and is developmentally regulated. In the present study we have identified the cell types of adult rat testis that contain p19. Using cryostat sections, which were first incubated with rabbit anti-p19 for immunohistochemistry followed by counterstaining with periodic acid-Schiff (PAS)-hematoxylin to reveal nuclear morphology, we demonstrate that immunoreactive p19 is detectable only in germ cells and is restricted to a limited stage of spermatogenesis. Expression first appears after the differentiating gametes have entered the prophase of meiosis, is abundant in spermatocytes until meiosis is completed, and declines to undetectable levels in maturing spermatids. We have ruled out immunocross-reactivity with SCG10, a 22-kDa protein that is closely related in structure to p19, by demonstrating, using Northern blot analysis, that RNA transcripts encoding SCG10 are not detectable in adult rat testis, whereas p19 is abundantly expressed. The transient expression of p19 during spermatogenesis suggests that the protein plays a role during male gamete differentiation.

The Wnt-1 (int-1) oncogene promoter and its mechanism of activation by insertion of proviral DNA of the mouse mammary tumor virus

Wnt-1 (int-1) is a cellular oncogene often activated by insertion of proviral DNA of the mouse mammary tumor virus. We have mapped the 5' end and the promoter area of the Wnt-1 gene by nuclease protection and primer extension assays. In differentiating P19 embryonal carcinoma cells, in which Wnt-1 is naturally expressed, two start sites of transcription were found, one preceded by two TATA boxes and one preceded by several GC boxes. In P19 cells, a 1-kilobase upstream sequence of Wnt-1 was able to confer differentiation-specific expression on a heterologous gene. We have investigated how Wnt-1 transcription was affected by mouse mammary tumor virus proviral integrations in various configurations near the promoters of the gene. One provirus has been inserted in the 5' nontranslated part of Wnt-1, in the same transcriptional orientation, and has functionally replaced the Wnt-1 promoters. Wnt-1 transcription in this tumor starts in the right long terminal repeat of the provirus, with considerable readthrough transcription from the left long terminal repeat. Another provirus has been inserted in the orientation opposite that of Wnt-1 into a GC box, disrupting the first Wnt-1 transcription start site but not the downstream start site. Most insertions have not structurally altered the Wnt-1 transcripts and have enhanced the activity of the normal two promoters.

Alternatively spliced Hox-1.7 transcripts encode different protein products

Two Hox-1.7 cDNAs, GPK5 and GPK6, were isolated from an adult guinea-pig kidney cDNA library by hybridization at low stringency using a Hox-1.7 cDNA probe, MH-1, cloned from mouse F9 teratocarcinoma cells. Sequence analysis of these two Hox-1.7 cDNAs showed that (a) GPK5 contains a putative initiation codon preceding an open reading frame which includes the homeo box, and may represent the complete protein coding region for the corresponding Hox-1.7 transcript; (b) the amino acids encoded by GPK6 and MH-1 are nearly identical (with two changes); (c) both adult guinea-pig kidney cDNA clones share identical homeo domains with the mouse Hox-1.7 cDNA; and (d) both adult guinea-pig kidney cDNA clones are identical in the homeo box region and in the 3' untranslated region but differ significantly starting from the 12th codon upstream from the homeo box. These data, supported by Southern blot analysis, indicate that a splice site is present 5' to the homeo box and that alternative splicing results in transcripts encoding different protein products.

A genomic clone of Zfy-1 from a YDOM mouse strain detects post-meiotic gene expression of Zfy in testes

In order to obtain a genomic clone of Zfy-1 from a Y chromosome of Mus musculus domesticus (YDOM) origin, we cloned size-fractionated SJL/J DNA in EMBL-4 and selected colonies which hybridized to pDP1007, a human zinc finger Y clone. The specificity of the clone in hybridizations to mouse and human DNA and partial sequencing confirmed that the clone (subcloned as pGZfy1D) was of Zfy-1 origin. Studies on the expression during testicular development of mRNAs hybridizing to the clone suggested that the gene is expressed post-meiotically.

Lineage-restricted expression of homeobox-containing genes in human hematopoietic cell lines

We investigated the role of homeobox-containing genes in human hematopoiesis because homeobox genes (i) control cell fate in the Drosophila embryo, (ii) are expressed in specific patterns in human embryos, and (iii) appear to function as transcription factors that control cell phenotype in other mammalian organs. Using four homeobox probes from the HOX2 locus and a previously undescribed homeobox cDNA (PL1), we screened mRNAs from 18 human leukemic cell lines representing erythroid, myeloid, and T- and B-cell lineages. Complex patterns of lineage-restricted expression are observed: some are restricted to a single lineage, while others are expressed in multiple lineages. No single homeobox gene is expressed in all types of hematopoietic cells, but each cell type exhibits homeobox gene expression. HOX2.2 and -2.3 homeobox-containing cDNAs were cloned from an erythroleukemia cell (HEL) cDNA library, while the homeobox cDNA PL1 was isolated from a monocytic cell (U-937) library. Differentiation of HEL and K-562 cells with various inducers results in modulation of specific homeobox transcripts. In addition, HOX2.2 is expressed in normal bone marrow cells. We have demonstrated (i) lineage-restricted expression of five homeobox genes in erythroid and monocytic cell lines; (ii) expression of additional homeobox genes in other cell lineages (HL-60 and lymphoid cells); (iii) expression of one homeobox gene in normal marrow cells; and (iv) modulation of expression during differentiation. These data suggest that these genes play a role in human hematopoietic development and lineage commitment.

Chromosome assignment of the murine Hox-4.1 gene

The murine homebox gene 4.1 was assigned to chromosome 2 by Southern analysis of somatic cell hybrids and by in situ hybridization. This assignment and the report of Featherstone et al. (M. S. Featherstone, A. Baron, S. J. Gaunt, M. G. Mattei, and D. Duboule, 1988, Proc. Natl. Acad. Sci. USA, 85, 4760-4764) indicate that a fourth group of homeobox genes is located on chromosome 2 in the mouse (in addition to the homeobox gene clusters on chromosomes 6, 11, and 15).

Expression of mouse protamine 1 genes in transgenic mice

Mouse protamine genes are expressed exclusively in spermatids. Mouse protamine 1 (mP1) transcriptional regulatory elements can target the expression of either marked mP1 transgenes or mP1 chimeric genes to spermatids in transgenic mice. Sequences between -40 and -465 bp relative to the transcription start site are required for expression in spermatids, whereas sequences 3' of the point of translation initiation are dispensable. mP1 transcriptional regulatory sequences were used to direct the expression of a toxic gene product to spermatids. The phenotypic consequences of toxin expression in spermatids are described.

Isolation and regional localization of the murine homeobox-containing gene Hox-3.3 to mouse chromosome region 15E

A murine homeobox-containing cDNA clone has been isolated from an adult spinal cord library. Using in situ hybridization and somatic cell genetics techniques, the newly isolated homeobox gene has been mapped to mouse chromosome region 15E. Because of its chromosomal location, we called this gene locus Hox-3.3. Nucleotide sequence analysis revealed that the Hox-3.3 gene represents the murine cognate of the human homeobox gene c8. The presumptive organization of the murine Hox-3 homeobox gene cluster is discussed.

The developmental expression pattern of a new murine homeo box gene: Hox-2.5

To examine the possible role of homeo box genes in murine development we have studied the structure and expression pattern of Hox-2.5, a newly isolated homeo box gene that maps to the left end of the mouse Hox-2 locus on chromosome 11. The sequence of the Hox-2.5 homeo box has been determined. It is highly homologous to Hox-1.7 and Hox-3.2, demonstrating extended conservation among three homeo box complexes in the mouse. Northern and in situ hybridization analyses of Hox-2.5 demonstrate a novel, regionally restricted pattern of expression in developing mesoderm and neurectoderm. We detect localized Hox-2.5 transcripts as early as 8.5 days postcoitum. The expression pattern of Hox-2.5 was analyzed over the next 3 days of ontogeny, as well as in later embryonic, newborn, and adult stages. Three-dimensional reconstruction of Hox-2.5 transcript localization within the central nervous system of early embryos clearly illustrates the neural expression domain. Although the Hox-2.5 expression pattern is regionally restricted during all of these stages of development, the pattern changes along the anteroposterior and dorsoventral axes of the CNS as the embryo undergoes complex morphogenetic movements and cytodifferentiation.

Early retinoic acid-induced F9 teratocarcinoma stem cell gene ERA-1: alternate splicing creates transcripts for a homeobox-containing protein and one lacking the homeobox

Retinoic acid (RA), the natural acidic derivative of vitamin A, can modulate the expression of specific genes and can induce some cell types, such as the murine F9 teratocarcinoma stem cell line, to differentiate in culture. As an initial step toward understanding the molecular mechanism(s) by which RA exerts these effects, we previously isolated cDNA clones for a gene, ERA-1, which has the characteristics of an early, direct target for RA. We demonstrated that RA causes a rapid, dose-dependent, and protein synthesis-independent expression of the ERA-1 gene (G. J. LaRosa and L. J. Gudas, Proc. Natl. Acad. Sci. USA 85:329-333, 1988). We now report the full-length cDNA sequence and the further characterization of this gene. The data indicate that the RA-induced 2.2- to 2.4-kilobase ERA-1 RNA species that we previously detected consists of two alternately spliced messages. One mRNA encodes a protein with a predicted mass of about 36 kilodaltons (kDa) that possesses the Hox 1.6 homeobox domain. The other mRNA encodes a truncated protein of about 15 kDa which is identical to the 36-kDa protein for 114 amino acids at the amino-terminal end but which lacks the homeobox amino acid sequence. The RA-associated increase in the ERA-1 mRNA level does not appear to be due to message stabilization, suggesting that the response is at the level of transcription. By Northern (RNA) blot analysis, the usual 2.2- to 2.4-kilobase mRNA species was also rapidly expressed in P19 teratocarcinoma cells during their differentiation to fibroblastic cells in response to RA and was detected in day 10.5 and day 13.5 mouse embryos. This result indicates that the expression of this gene is not limited to the endodermal differentiation of F9 cells.

Transgenic mice overexpressing the mouse homoeobox-containing gene Hox-1.4 exhibit abnormal gut development

The mouse homoeobox-containing genes exhibit temporally and spatially specific patterns of expression in embryonic and adult tissues and are thought to be important in regulation of development and cellular differentiation, perhaps by mechanisms analogous to homoeotic genes in Drosophila melanogaster. There has been no direct demonstration that expression of these mammalian genes can affect developmental processes, however. Hox-1.4, like other mouse homoeobox-containing genes, has been shown to be expressed in specific regions of the mid-gestation embryo, but is unique in that its highest level of expression in the adult animal is restricted to developing male germ cells. We have introduced a construct carrying the mouse Hox-1.4 gene into the germ line of mice to begin to identify the cis-acting elements required for proper expression and to assess the consequences of increasing Hox-1.4 gene expression. The construct was designed to produce normal Hox-1.4 protein from transcripts that are distinguishable from the products of the endogenous gene. The integrated transgene seemed to exhibit the appropriate tissue specificity of expression, but transcript levels were elevated in certain tissues, particularly the embryonic gut. This overexpression correlated with changes in the normal developmental program of the gut, resulting in an inherited abnormal phenotype known as megacolon.

Analysis of the chromosome complement in outbred mouse sperm fertilizing in vitro

The chromosome complements in a population of mouse sperm from random-bred ICR donors were analyzed at first-cleavage metaphase after in vitro fertilization (IVF) of oocytes from females of the same strain. The sperm were aged as donations occurred within an average of 31 days, either since last mating or at arrival at the animal facility in the case of virgin males. Of a total of 598 sperm complements studied from 22 sexually mature males aged 10-26 weeks old, there was one diploid complement (0.17%). The frequencies of hyperhaploidy and structural aberrations that were studied in 338 complements were 4.4% and 3.6%, respectively, giving an overall frequency of 8.0%. The hyperhaploid complements consisted of n + 1, n + 2, n + 3, and n + 7 counts, while the structural abnormalities were of the chromosome type and included large and small fragments and a possible translocation. This is the highest frequency of sperm chromosome abnormalities reported for mouse sperm obtained from males under physiological conditions and fertilized in vitro or in vivo. Sperm aging, strain, and/or technique differences are among the factors that may be responsible for this high frequency. Since the 8.0% frequency of hyperhaploidy and structural abnormalities is similar to the frequency reported for human sperm after IVF, the outbred murine in vitro fertilization system may be a useful model to study the origin of human sperm chromosome abnormalities.

Segregation products of male mice doubly heterozygous for the RB(6.16) and RB (16.17) translocations: influence of sperm karyotype on fertilizing competence under varying mating frequencies

The meiotic segregants of male mice heterozygous for Rb(6.16)24Lub and Rb(16.17)7Bnr were viewed, for the first time, at first cleavage metaphase. Chromosomes were analyzed after G-banding, C-banding, and karyotyping. To study sperm aging effects, chromosomes of 202 one-cell zygotes derived from males mating at intervals of approximately 3, 14, and 21 days were examined. At least 89.6% of sperm-derived complements were products of 2:2 segregation; at most, a possible 6.4% were 3:1 segregants. The six expected types of 2:2 segregants, both balanced and unbalanced, were equifrequent in the total zygote population derived from sperm of all ages. When the data were analyzed according to mating frequency, the 3-day sperm population considered most likely to be fresh showed a deficiency of the segregant nullisomic for chromosome 6 and disomic for chromosome 17, when compared with the reciprocal segregant (P less than 0.025) as well as to all other 2:2 segregants (P less than 0.05). However, these sperm fertilized in greater numbers (P less than 0.01) than their reciprocal segregant (disomic for 6 and nullisomic for 17) in the 14-day sperm population. While sperm with chromosomal abnormalities are capable of fertilization, the competence of segregants nullisomic for 6 and disomic for 17 apparently depends on the prior storage period in the male. Further, the results suggest that the effect of aneuploidy on sperm function is dependent on the specific chromosome(s) involved.