Cryptorchidism and homeotic transformations of spinal nerves and vertebrae in Hoxa-10 mutant mice

Role of endocytosis in cellular uptake of sex steroids

Androgens and estrogens are transported bound to the sex hormone binding globulin (SHBG). SHBG is believed to keep sex steroids inactive and to control the amount of free hormones that enter cells by passive diffusion. Contrary to the free hormone hypothesis, we demonstrate that megalin, an endocytic receptor in reproductive tissues, acts as a pathway for cellular uptake of biologically active androgens and estrogens bound to SHBG. In line with this function, lack of receptor expression in megalin knockout mice results in impaired descent of the testes into the scrotum in males and blockade of vagina opening in females. Both processes are critically dependent on sex-steroid signaling, and similar defects are seen in animals treated with androgen- or estrogen-receptor antagonists. Thus, our findings uncover the existence of endocytic pathways for protein bound androgens and estrogens and their crucial role in development of the reproductive organs.

Vertebral malformations induced by sodium salicylate correlate with shifts in expression domains of Hox genes

Several embryotoxic agents, which includes sodium salicylate, were reported to induce vertebral variations in the form of supernumerary ribs (SNR) when administered to pregnant rodents. Because the biological significance of SNR in toxicological studies is still a matter of debate, we investigated the molecular basis of this defect by analyzing the possible involvement of Hox genes, known to specify vertebrae identity. Sodium salicylate (300mg/kg) was administered to pregnant rats on gestational day 9 (GD 9). On GD 13, the expression of several Hox genes, selected according to the position of their anterior limit of expression, namely upstream (Hoxa9), at the level (Hoxa10) and downstream (Hoxd9) to the morphological alteration, were analyzed. Posterior shifts in the anterior limit of expression of Hoxa10 and Hoxd9 were observed following exposure to salicylate, which could explain an effect at the level of the axial skeleton. This finding suggests that the appearance of ectopic ribs can be attributed to an anterior transformation of lumbar vertebrae identity into thoracic vertebrae identity. Whether this transformation occurs with all compounds inducing SNR in rats remains to be determined.

Cryptorchidism: an indicator of testicular dysgenesis?

Cryptorchidism is a common ailment of new-born boys, affecting 1-9% of full term boys at birth. Cryptorchidism has been associated with an increased risk of testicular cancer and reduced fertility. Aetiology of cryptorchidism remains obscure in most cases. Familial occurrence suggests a heritable susceptibility to cryptorchidism; however, seasonal variation in the incidence of cryptorchidism suggests that environmental factors also contribute. Testicular descent is characterised by androgen-dependent regression of cranial suspensory ligament and androgen + insulin-like hormone 3 (Ins l3)-dependent gubernacular outgrowth. Even though hormonal defects are rarely detected in patients, both hypo-and hypergonadotropic hormonal patterns have been associated with cryptorchidism. Moreover, cryptorchid boys have significantly reduced serum androgen bioactivity at 3 months of age when normal boys have a strong surge of reproductive hormones. Defects in Ins l3 action cause cryptorchidism in male mice, and over-expression in female mice causes ovarian descent. Defects in leucine-rich repeat-containing G-protein-coupled receptor 8/G-protein-coupled receptor affecting testis descent (LGR8/GREAT), the receptor for Ins l3, manifest the same phenotype as Ins l3 knockout mutants. Even though mutations found in Ins l3 and LGR8/GREAT genes are not a common cause of cryptorchidism in patients, it remains to be resolved whether low Ins l3 levels during development are associated with cryptorchidism. Cryptorchidism may reflect foetal testicular dysgenesis that may later manifest as subfertility or testicular cancer.

Retinaldehyde dehydrogenase 2 and Hoxc8 are required in the murine brachial spinal cord for the specification of Lim1+ motoneurons and the correct distribution of Islet1+ motoneurons

Retinoic acid (RA) activity plays sequential roles during the development of the ventral spinal cord. Here, we have investigated the functions of local RA synthesis in the process of motoneuron specification and early differentiation using a conditional knockout strategy that ablates the function of the retinaldehyde dehydrogenase 2 (Raldh2) synthesizing enzyme essentially in brachial motoneurons, and later in mesenchymal cells at the base of the forelimb. Mutant (Raldh2L-/-) embryos display an early embryonic loss of a subset of Lim1+ brachial motoneurons, a mispositioning of Islet1+ neurons and inappropriate axonal projections of one of the nerves innervating extensor limb muscles, which lead to an adult forepaw neuromuscular defect. The molecular basis of the Raldh2L-/- phenotype relies in part on the deregulation of Hoxc8, which in turn regulates the RA receptor RARbeta. We further show that Hoxc8 mutant mice, which exhibit a similar congenital forepaw defect, display at embryonic stages molecular defects that phenocopy the Raldh2L-/- motoneuron abnormalities. Thus, interdependent RA signaling and Hox gene functions are required for the specification of brachial motoneurons in the mouse.

Evolution of the brain developmental plan: Insights from agnathans

In vertebrate evolution, the brain exhibits both conserved and unique morphological features in each animal group. Thus, the molecular program of nervous system development is expected to have experienced various changes through evolution. In this review, we discuss recent data from the agnathan lamprey (jawless vertebrate) together with available information from amphioxus and speculate the sequence of changes during chordate evolution that have been brought into the brain developmental plan to yield the current variety of the gnathostome (jawed vertebrate) brains.

Ectopic expression of Hoxd10 in thoracic spinal segments induces motoneurons with a lumbosacral molecular profile and axon projections to the limb

Hox genes encode anterior-posterior identity during central nervous system development. Few studies have examined Hox gene function at lumbosacral (LS) levels of the spinal cord, where there is extensive information on normal development. Hoxd10 is expressed at high levels in the embryonic LS cord but not the thoracic cord. To test the hypothesis that restricted expression of Hoxd10 contributes to the attainment of an LS identity, and specifically an LS motoneuron identity, Hoxd10 was ectopically expressed in thoracic segments in chick embryos by means of in ovo electroporation. Regional motoneuron identity was assessed after the normal period of motoneuron differentiation. Subsets of motoneurons in transfected thoracic segments developed a molecular profile normally shown by LS motoneurons, including Lim 1 and RALDH2 expression. In addition, motoneurons in posterior thoracic segments showed novel axon projections to two muscles in the anterodorsal limb, the sartorius and anterior iliotibialis muscles. At thoracic levels, we also found a decrease in motoneuron numbers and a reduction in gonad size. These last findings suggest that early and high levels of Hox expression impeded motoneuron development and neural-mesodermal interactions. Despite these adverse effects, our data indicate that Hoxd10 expression is sufficient to induce LS motoneuron identity and axon trajectories characteristic of motoneurons in the LS region.

Insulin-like 3 signalling in testicular descent

Undescended testis is one of the most common congenital defects in the newborn boys and the common cause of cryptorchidism. If left untreated, this condition is strongly associated with infertility and drastically increased risk of testicular cancer in adulthood. Testis position in developing males is defined by sexual dimorphic differentiation of two gonadal ligaments, gubernaculum and cranial suspensory ligament. Recent transgenic mouse studies identified testicular hormone insulin-like 3 (INSL3), and its receptor, GREAT/LGR8, as the critical regulators of the gubernacular differentiation. Mutation analysis of the two genes in patients with undescended testis revealed functionally deleterious mutations, which may be responsible for the abnormal phenotype in some of the patients.

Cryptorchidism: diagnosis, treatment, and long-term prognosis

Cryptorchidism is a common anomaly treated by every pediatric urologist. The etiology is multifactorial and includes hormonal and molecular factors. Diagnostic abilities may be enhanced by radiologic advances. Hormonal and surgical treatment modalities are discussed herein, as well as the identification and prevention of long-term sequelae.

Molecular and genetic regulation of testis descent and external genitalia development

Testicular descent as a prerequisite for the production of mature spermatozoa and normal external genitalia morphogenesis, and therefore facilitating copulation and internal fertilization, are essential developmental steps in reproduction of vertebrate species. Cryptorchidism, the failure of testis descent, and feminization of external genitalia in the male, usually in the form of hypospadias, in which the opening of the urethra occurs along the ventral aspect of the penis, are the most frequent pediatric complications. Thus, elucidating the molecular mechanisms involved in the regulation of testis descent and the formation of external genitalia merits a special focus. Natural and transgenic rodent models have demonstrated both morphogenic processes to be under the control of a plethora of genetic factors with complex time-, space-, and dose-restricted expression pattern. The review elucidates the molecular mechanisms involved in the regulation of testis descent and the formation of external genitalia and, wherever possible, assesses the differences between these rodent animal models and other mammalian species, including human.

Lack of LGR8 gene mutation in Finnish patients with a family history of cryptorchidism

Cryptorchidism is the most frequent congenital anomaly of the urogenital tract in the male. Although in Western countries 1-2% of males at the age of 3 months are diagnosed with this condition, its aetiology is still unknown. Animal models suggest a possible genetic basis for this disorder. Recently, the INSL3 (Leydig insulin-like peptide) gene and its cognate receptor, LGR8, were found to be important in testicular descent by regulating gubernacular development. Male mice null for either INSL3 or LGR8 genes exhibited bilateral cryptorchidism. Because earlier studies indicated that mutation of the INSL3 gene is not associated with the development of human cryptorchidism, this study analysed whether mutations in the LGR8 gene could be associated with this disorder. Sequencing of 18 exons of the LGR8 gene in 23 cryptorchid Finnish patients and a group of 33 control subjects allowed the identification of three nucleotide changes in exons 12 and 17, showing single base substitutions from A to G at positions 957, 993, and 1810 of LGR8. Among the three changes, only the 1810 A to G substitution is associated with an amino acid change from isoleucine to valine (Ile604Val) located in the fifth transmembrane domain of this seven-transmembrane receptor. This change was more frequent in a control group of normal fertile adult males and infant boys than in the group of cryptorchid males. The change is not associated with altered receptor signalling, thus suggesting the presence of a polymorphism unrelated to the cryptorchid phenotype. These data indicate that mutations involving the human LGR8 gene do not represent a frequent cause of cryptorchidism in the Finnish population.

Transgenic mice ectopically expressing HOXA5 in the dorsal spinal cord show structural defects of the cervical spinal cord along with sensory and motor defects of the forelimb

Mutation of murine Hoxa5 has shown that HOXA5 controls lung, gastrointestinal tract and vertebrae development. Hoxa5 is also expressed in the spinal cord, yet no central nervous system phenotype has been described in Hoxa5 knockouts. To identify the role of Hoxa5 in spinal cord development, we developed transgenic mice that express HOXA5 in the dorsal spinal cord in the brachial region. Using HOXA5-specific antibodies, we show this expression pattern is ectopic as the endogenous protein is expressed only in the ventral spinal cord at this anterio-posterior level. This transgenic line (Hoxa5SV2) also displays forelimb-specific motor and sensory defects. Hoxa5SV2 transgenic mice cannot support their body weight in a forelimb hang, and forelimb strength is decreased. However, Rotarod performance was not impaired in Hoxa5SV2 mice. Hoxa5SV2 mice also show a delayed forelimb response to noxious heat, although hindlimb response time was normal. Administration of an analgesic significantly reduced the hang test defect and decreased the transgene effect on forelimb strength, indicating that pain pathways may be affected. The morphology of transgenic cervical (but not lumbar) spinal cord is highly aberrant. Nissl staining indicates superficial laminae of the dorsal horn are severely disrupted. The distribution of cells and axons immunoreactive for substance P, neurokinin-B, and their primary receptors were aberrant only in transgenic cervical spinal cord. Further, we see increased levels of apoptosis in transgenic spinal cord at embryonic day 13.5. Our evidence suggests apoptosis due to HOXA5 misexpression is a major cause of loss of superficial lamina cells in Hoxa5SV2 mice.

Segmental development of reticulospinal and branchiomotor neurons in lamprey: insights into the evolution of the vertebrate hindbrain

During development, the vertebrate hindbrain is subdivided along its anteroposterior axis into a series of segmental bulges called rhombomeres. These segments in turn generate a repeated pattern of rhombomere-specific neurons, including reticular and branchiomotor neurons. In amphioxus(Cephalochordata), the sister group of the vertebrates, a bona fide segmented hindbrain is lacking, although the embryonic brain vesicle shows molecular anteroposterior regionalization. Therefore, evaluation of the segmental patterning of the central nervous system of agnathan embryos is relevant to our understanding of the origin of the developmental plan of the vertebrate hindbrain. To investigate the neuronal organization of the hindbrain of the Japanese lamprey, Lethenteron japonicum, we retrogradely labeled the reticulospinal and branchial motoneurons. By combining this analysis with a study of the expression patterns of genes identifying specific rhombomeric territories such as LjKrox20, LjPax6, LjEphC and LjHox3, we found that the reticular neurons in the lamprey hindbrain, including isthmic,bulbar and Mauthner cells, develop in conserved rhombomere-specific positions,similar to those in the zebrafish. By contrast, lamprey trigeminal and facial motor nuclei are not in register with rhombomere boundaries, unlike those of gnathostomes. The trigeminal-facial boundary corresponds to the rostral border of LjHox3 expression in the middle of rhombomere 4. Exogenous application of retinoic acid (RA) induced a rostral shift of both the LjHox3 expression domain and branchiomotor nuclei with no obvious repatterning of rhombomeric segmentation and reticular neurons. Therefore,whereas subtype variations of motoneuron identity along the anteroposterior axis may rely on Hox-dependent positional values, as in gnathostomes, such variations in the lamprey are not constrained by hindbrain segmentation. We hypothesize that the registering of hindbrain segmentation and neuronal patterning may have been acquired through successive and independent stepwise patterning changes during evolution.

HOXC and HOXD gene expression in human endometrium: lack of redundancy with HOXA paralogs

HOXA genes, essential regulators of differentiation in the embryo, are also essential for adult cyclic endometrial development and for endometrial receptivity. Mice deficient in Hoxa10 or Hoxa11 exhibit reduced fertility because of defects in implantation. We hypothesized that HOXC10, HOXC11, HOXD10, and HOXD11, paralogs of HOXA10 and HOXA11, might also be involved in endometrial development. Here, we showed that the expression of HOXC10, HOXC11, HOXD10, and HOXD11 was evident throughout the menstrual cycle in the endometrium by semiquantitative reverse transcription-polymerase chain reaction. In the secretory phase, expression of HOXC10, HOXC11, and HOXD11 decreased to 4% and HOXD10 decreased to 25% of the proliferative phase expression (P < 0.001, P < 0.001, P < 0.02, P < 0.01, respectively). In situ hybridization demonstrated expression of each of these HOX genes primarily in the stroma and confirmed the decreased expression in the secretory phase. HOXC10, HOXC11, HOXD10, and HOXD11 expression was not regulated by sex steroids in primary endometrial stromal cells or Ishikawa cells. The expression and regulation of HOXC and HOXD genes varies from that of HOXA10 and HOXA11. Whereas HOXA10 and HOXA11 are regulators of endometrial differentiation, HOXC and HOXD genes likely regulate endometrial proliferation. Paralogous HOX genes typically have a redundant function in development; a novel evolutionary divergence of paralogous Hox genes has resulted in HOXC and HOXD genes having distinct expression patterns, regulation, and likely also distinct functions from HOXA genes. A network of HOX genes may be involved in regulating multiple aspects of endometrial development, including both proliferation and differentiation.

Transabdominal testicular descent is disrupted in mice with deletion of insulinlike factor 3 receptor

BACKGROUND

Several factors are implicated in transabdominal testicular descent, including insulinlike factor 3 (INSL3) hormone and Müllerian-inhibiting substance (MIS). A transgene insertional mutation found on chromosome 5 in the mouse, known as crsp, causes deletion of a transmembrane G protein-coupled receptor gene, Great, which is highly expressed in the gubernaculum. The authors describe here a detailed analysis of the testicular descent and gubernacular development in crsp mice to determine the role of the Great gene in this process.

METHODS

Homozygous (crsp/crsp) mutant and wild-type heterozygous (crsp/+) mice were examined at birth (D 0) and at days 10 (D 10) and 30 (D 30) postnatally. Serial sagittal or coronal sections were analyzed for position of the gonads and cremaster sac development.

RESULTS

Transabdominal testicular descent was absent at D 0 in crsp/crsp homozygous mice with no swelling reaction in the gubernacula. By D 10 the cremaster sac was significantly thinner (P <.05) and contained less collagen in the mutants than in the wild-type controls. On D 30 the cremaster sacs of mutant males were similar in thickness to those in females.

CONCLUSIONS

Disruption of the Great gene causes failure of the transabdominal phase of descent, identical to that seen in the Insl3-deficient mutants, consistent with the recent data suggesting that Great gene encodes the Insl3 transmembrane receptor. No differences between D 30 mutant males and females were found in the gubernacula, suggesting that Insl3/Great signaling regulates gubernacular development.

Hoxa10 and Hoxd10 coordinately regulate lumbar motor neuron patterning

The paralogous Hox genes Hoxa10 and Hoxd10 are expressed in overlapping domains in the developing lumbar spinal cord and surrounding mesoderm. Independent inactivation of these two genes alters the trajectory of spinal nerves and decreases the complement of motor neurons present in the lumbar spinal cord, whereas dual inactivation of these two genes has been shown to alter peripheral nerve growth and development in the mouse hindlimb. We have examined the organization and distribution of lumbar motor neurons in the spinal cords of Hoxa10/Hoxd10 double mutant animals. Double mutant animals have decreased numbers of lumbar motor neurons in both the medial and lateral motor columns. The anteroposterior position of the lumbar motor column is shifted caudally in double mutant animals, and the distribution of motor neurons is altered across individual spinal segments. Distinctions between classes of motor neurons based on positional specificity appear disrupted in double mutants. Double mutants also demonstrate abnormal spinal cord vasculature and altered kidney placement and size. Our observations suggest that Hoxa10 and Hoxd10 activity is required to specify the position of the lumbar motor column and to provide segmental specification and identity for the lumbar motor neurons.

Update on cryptorchidism: endocrine, environmental and therapeutic aspects

Cryptorchidism is the most frequent developmental abnormality in boys, present in more than 1% of infants above three months of age. It is associated with an increased risk of infertility and testicular cancer. The etiological quest is often disappointing, except in bilateral cases or associated malformations. Recent focus is on genetic and environmental aspects. Animal models have revealed the role of genes encoding for proteins implicated in testicular migration (InsI3, Hoxa 10), but in humans results are less convincing. While some degree of endogenous hormonal abnormality is suspeeted in some patients, the endocrine disruptor hypothesis is also tested. It is unclear whether the incidence of cryptorchidism has really increased, or whether there is only a better screening for this condition. However, other male reproductive problems, such as subfertility, hypospadias and testicular cancer seem on the rise. This secular trend suggests the possible in utero impact of hormonally active environmental factors, such as pesticides with estrogenic or antiandrogenic effect, and is consistent with the increased risk of cryptorchidism observed in the sons of mothers exposed to diethylstilbestrol during pregnancy. From a therapeutic point of view, there is an agreement that the correction of cryptorchidism is needed, but there is controversy on the best medical and/or surgical approach and on the optimal timing. There is a recent trend in proposing early therapeutic intervention, before 1 yr of age, in the hope of improving fertility; however, there is no proof that such a strategy can reduce the risk of testicular cancer.

Duplication of the Hoxd11 gene causes alterations in the axial and appendicular skeleton of the mouse

The Hox genes encode a group of transcription factors essential for proper development of the mouse. Targeted mutation of the Hoxd11 gene causes reduced male fertility, vertebral transformation, carpal bone fusions, and reductions in digit length. A duplication of the Hoxd11 gene was created with the expectation that the consequences of restricted overexpression in the appropriate cells would provide further insight into the function of the Hoxd11 gene product. Genetic assays demonstrated that two tandem copies of Hoxd11 were functionally indistinguishable from the normal two copies of the gene on separate chromosomes with respect to formation of the axial and appendicular skeleton. Extra copies of Hoxd11 caused an increase in the lengths of some bones of the forelimb autopod and a decrease in the number of lumbar vertebrae. Further, analysis of the Hoxd11 duplication demonstrated that the Hoxd11 protein can perform some functions supplied by its paralogue Hoxa11. For example, the defects in forelimb bones are corrected when extra copies of Hoxd11 are present in the Hoxa11 homozygous mutant background. Thus, it appears that Hoxd11 can quantitatively compensate for the absence of Hoxa11 protein, and therefore Hoxa11 and Hoxd11 are functionally equivalent in the zeugopod. However, extra copies of Hoxd11 did not improve male or female fertility in Hoxa11 mutants. Interestingly, the insertion of an additional Hoxd11 locus into the HoxD complex does not appear to affect the expression patterns of the neighboring Hoxd10, -d12, or -d13 genes.

Embryonic myosin heavy chain and troponin T isoforms remain in the cremaster muscle of adult rat cryptorchidism induced with flutamide

We examined the immunolocalization of isoforms of muscle proteins, myosin and troponin, in the cremaster muscle of the undescended testis (cryptorchidism). In cryptorchid rats induced by a nonsteroidal androgen antagonist, flutamide, the cremaster muscle contained embryonic myosin and embryonic/cardiac troponin T in both immunofluorescence microscopy and Western blotting using antibodies against myosin and troponin T specific for embryonic, cardiac and fast skeletal muscles. However, in muscles other than the cremaster muscle, i. e., the masseter, pectoral and abdominal muscles, embryonic isoforms of these proteins were undetectable by immunohistochemistry with these antibodies, even in the muscles from cryptorchid rats. Our results showing that high levels of embryonic isoforms of muscle proteins were specifically present in the cremaster muscle of cryptorchid rats induced by flutamide suggest that flutamide treatment of pregnant rats might affect genes controlling the development of the lumbar region of the fetus body resulting in the presence of embryonic protein isoforms in the cremaster muscles which are closely associated with undescended testes.

Gestational and lactational exposure of male mice to diethylstilbestrol causes long-term effects on the testis, sperm fertilizing ability in vitro, and testicular gene expression

The objective of the study was to determine the long-term effects of gestational and lactational exposure to diethylstilbestrol (DES; 0, 0.1, 1, and 10 microg/kg maternal body weight) on mouse testicular growth, epididymal sperm count, in vitro fertilizing ability, and testicular gene expression using cDNA microarrays and real-time PCR in mice on postnatal day (PND) 21, 105, and 315. In the high dose group there was a persistent decrease in the number of Sertoli cells, and sperm count was decreased on PND315 (P < 0.05). Sperm motion was unaffected; however, the in vitro fertilizing ability of epididymal sperm was decreased in the high dose group on both PND105 (P < 0.001) and PND315 (P < 0.05). Early and latent alterations in the expression of genes involved in estrogen signaling (estrogen receptor alpha), steroidogenesis (steroidogenic factor 1, 17alpha-hydroxylase/C17,20-lyase, P450 side chain cleavage, steroidogenic acute regulatory protein, and scavenger receptor class B1), lysosomal function (LGP85 and prosaposin), and regulation of testicular development (testicular receptor 2, inhibin/activin beta C, and Hoxa10) were confirmed by real-time PCR. The results demonstrate that early exposure to DES causes long-term adverse effects on testicular development and sperm function, and these effects are associated with changes in testicular gene expression, even long after the cessation of DES exposure.

Cryptorchidism: seasonal variations in Greece do not support the theory of light

To examine seasonal trends of cryptorchidism in Greece, 583 males with true isolated cryptorchidism were analyzed. All 208 912 live-born boys born during the same period were used as a comparison group. Seasonality by month of birth was evaluated using both Edwards' model with adjusted frequencies and exact theta(i), and Walter-Elwood method with exact theta(i). Both tests resulted in consistent findings. The incidence of cryptorchid births in Greece follows a documented cyclic pattern of simple harmonic type with spring being the season of statistical predominance (peak in March with a second, almost equivalent, peak in May). In contrast, in autumn the incidence of cryptorchid births was considerably lower (trough in September). Given the fact that no significant differences in daylight length are found among seasons in Greece, the detection of a significant seasonal variation suggests that factors other than light are involved in the pathogenesis of cryptorchidism. Low environmental temperature is proposed as a causative factor negatively influencing the maternal hCG profiles and the inguinoscrotal phase of testicular descent. This is further supported by: (i) the similarity of our results to those reported by other European countries of different longitude and geographical width and (ii) our data showing significantly smaller maternal hCG profiles at the 26th week of gestation during winter compared with summer.

Absence of mutations in the HoxA10, HoxA11 and HoxD11 nucleotide coding sequences in thrombocytopenia with absent radius syndrome

Recent studies have suggested the HoxA10, HoxA11 and HoxD11 homeobox genes as candidate loci for the thrombocytopenia with absent radius (TAR) syndrome. For example, targeted disruptions of these Hox genes result in abnormal development of the mouse radius, while overexpression of HoxA10 stimulates mouse megakaryocyte (MK) development in vitro. To examine the expression of Hox genes in human MK cells, we utilized reverse transcription polymerase chain reaction with degenerate oligonucleotides to study megakaryocytic cell lines (MEG-01, DAMI), and primary human MK purified from adult and cord blood. Using this approach, 13 out of 40 clones isolated from cell lines, 10 out of 21 from cord MK, and 11 out of 21 from adult MK were identified as HoxA10, while HoxA11 and HoxD11 sequences were not detected. The normal genomic sequences for the human HoxA10, -A11, and -D11 genes were then determined and sequenced in 10 unrelated individuals with TAR syndrome. In all patients the derived amino acid sequence for the three Hox genes was identical to normal controls. Southern blotting did not reveal genomic rearrangements or deletions at these loci, and in two patients intact HoxA10 transcripts were detected by amplification in myeloid cells. Although these studies cannot completely exclude the possibility that the TAR syndrome results from non-coding mutations that affect the level of Hox gene expression in megakaryocytes, mutations in the coding sequence of the Hox genes known to affect radial development are not a common cause of TAR syndrome.

Hoxd10 induction and regionalization in the developing lumbosacral spinal cord

We have used Hoxd10 expression as a primary marker of the lumbosacral region to examine the early programming of regional characteristics within the posterior spinal cord of the chick embryo. Hoxd10 is uniquely expressed at a high level in the lumbosacral cord, from the earliest stages of motor column formation through stages of motoneuron axon outgrowth. To define the time period when this gene pattern is determined, we assessed Hoxd10 expression after transposition of lumbosacral and thoracic segments at early neural tube stages. We present evidence that there is an early prepattern for Hoxd10 expression in the lumbosacral neural tube; a prepattern that is established at or before stages of neural tube closure. Cells within more posterior lumbosacral segments have a greater ability to develop high level Hoxd10 expression than the most anterior lumbosacral segments or thoracic segments. During subsequent neural tube stages, this prepattern is amplified and stabilized by environmental signals such that all lumbosacral segments acquire the ability to develop high levels of Hoxd10, independent of their axial environment. Results from experiments in which posterior neural segments and/or paraxial mesoderm segments were placed at different axial levels suggest that signals setting Hoxd10 expression form a decreasing posterior-to-anterior gradient. Our experiments do not, however, implicate adjacent paraxial mesoderm as the only source of graded signals. We suggest, instead, that signals from more posterior embryonic regions influence Hoxd10 expression after the early establishment of a regional prepattern. Concurrent analyses of patterns of LIM proteins and motor column organization after experimental surgeries suggest that the programming of these characteristics follows similar rules.

The paralogous Hox genes Hoxa10 and Hoxd10 interact to pattern the mouse hindlimb peripheral nervous system and skeleton

The most 5' mouse Hoxa and Hoxd genes, which occupy positions 9-13 and which are related to the Drosophila AbdB gene, are all active in patterning developing limbs. Inactivation of individual genes produces alterations in skeletal elements of both forelimb and hindlimb; inactivation of some of these genes also alters hindlimb innervation. Simultaneous inactivation of paralogous or nonparalogous Hoxa and Hoxd genes produces more widespread alterations, suggesting that combinatorial interactions between these genes are required for proper limb patterning. We have examined the effects of simultaneous inactivation of Hoxa10 and Hoxd10 on mouse hindlimb skeletal and nervous system development. These paralogous genes are expressed at lumbar and sacral levels of the developing neural tube and surrounding axial mesoderm as well as in developing forelimb and hindlimb buds. Double-mutant animals demonstrated impaired locomotor behavior and altered development of posterior vertebrae and hindlimb skeletal elements. Alterations in hindlimb innervation were also observed, including truncations and deletions of the tibial and peroneal nerves. Animals carrying fewer mutant alleles show similar, but less extreme phenotypes. These observations suggest that Hoxa10 and Hoxd10 coordinately regulate skeletal development and innervation of the hindlimb.

Establishing sexual dimorphism: conservation amidst diversity?

The molecular mechanisms that control sexual dimorphism are very different in distantly related animals. Did sex determination arise several times with different regulatory mechanisms, or is it an ancient process with little surviving evidence of ancestral genes? The recent identification of related sexual regulators in different phyla indicates that some aspects of sexual regulation might be ancient. Studies of sex-determining mechanisms are beginning to reveal how sexual dimorphism arises and evolves.

A transgenic insertion causing cryptorchidism in mice

A distinctive feature of gonadal maturation in mammals is the movement to an extraabdominal location. Testicular descent is a complex, multistage process whereby the embryonic gonads migrate from their initial abdominal position to the scrotum. Failure in this process results in cryptorchidism, a frequent congenital birth defect in humans. We report here a new mouse transgenic insertional mutation, cryptorchidism with white spotting (crsp). Males homozygous for crsp exhibit a high intraabdominal position of the testes, associated with complete sterility. Heterozygous males have a wild-type phenotype, and homozygous females are fertile. Surgically descended testes in crsp/crsp males show normal spermatogenesis. Using FISH and genetic analyses, the transgenic insert causing the crsp mutation has been mapped to the distal part of mouse chromosome 5. Transgene integration resulted in a 550-kb deletion located upstream of the Brca2 gene. A candidate gene encoding a novel G protein-coupled receptor (Great) with an expression pattern suggesting involvement in testicular descent has been identified.

Hormones in male sexual development

Classical embryology has provided a clear view of the timing and hormonal cues that govern sexual differentiation. Molecular biology has added important details to this picture. The cloning of SRY, MIS, and INSL3 provide insight into the molecular signals that provide important cues at the cellular level. Continued understanding of these pathways may provide the necessary information to one day reverse defects of sexual differentiation.

Insulin-like 3/relaxin-like factor gene mutations are associated with cryptorchidism

Cryptorchidism is a common anomaly of male sexual differentiation. Two phases of testicular descent are recognized, transabdominal and inguinoscrotal. With evidence that androgens and Müllerian inhibitory hormone were not completely responsible for testicular descent, the existence of a third testicular hormone mediating testicular descent was postulated. Insulin-like 3 (INSL3) [also known as relaxin-like factor (RLF) and Leydig insulin-like protein (LEY I-L)] is a member of the insulin/relaxin hormone superfamily that is highly expressed in Leydig cells. The phenotype of transgenic mice with targeted deletion of the Insl3 gene was bilateral cryptorchidism with morphological evidence of abnormal gubernacular development. With this implicit evidence that Insl3 mediates testicular descent in mice, we performed mutation detection analysis of the coding regions of the 2 exon INSL3 gene in genomic DNA samples obtained from 145 formerly cryptorchid patients and 36 adult male controls. Single-strand conformational polymorphism analysis was used for the mutation detection studies. Two mutations, R49X and P69L, and several polymorphisms were identified. Both mutations were located in the connecting peptide region of the protein. The frequency of INSL3/RLF gene mutations as a cause of cryptorchidism is low, because only 2 of 145 (1.4%) formerly cryptorchid patients were found to have mutations.

Characterization of Hoxa-10/Hoxa-11 transheterozygotes reveals functional redundancy and regulatory interactions

Hox genes show related sequences and overlapping expression domains that often reflect functional redundancy as well as a common evolutionary origin. To accurately define their functions, it has become necessary to compare phenotypes of mice with single and multiple Hox gene mutations. Here, we focus on two Abd-B-type genes, Hoxa-10 and Hoxa-11, which are coexpressed in developing vertebrae, limbs, and reproductive tracts. To assess possible functional redundancy between these two genes, Hoxa-10/Hoxa-11 transheterozygotes were produced by genetic intercrosses and analyzed. This compound mutation resulted in synergistic defects in transheterozygous limbs and reproductive tracts, but not in vertebrae. In the forelimb, distal radial/ulnar thickening and pisiform/triangular carpal fusion were observed in 35 and 21% of transheterozygotes, respectively, but were effectively absent in Hoxa-10 and Hoxa-11 +/- forelimbs. In the hindlimb, distal tibial/fibular thickening and loss of tibial/fibular fusion were observed in >80% of transheterozygotes but in no Hoxa-10 or Hoxa-11 +/- hindlimbs, and all transheterozygotes displayed reduced medial patellar sesamoids, compared to modest incidences in Hoxa-10 and Hoxa-11 +/- mutants. Furthermore, while the reproductive tracts of Hoxa-10 and Hoxa-11 single heterozygous mutants of both sexes were primarily unaffected, male transheterozygotes displayed cryptorchidism and abnormal tortuosity of the ductus deferens, and female transheterozygotes exhibited abnormal uterotubal junctions and narrowing of the uterus. In addition we observed that the targeted mutations of Hoxa-10 and Hoxa-11 each affected the expression of the other gene in the developing prevertebra and reproductive tracts. These results provide a measure of the functional redundancy of Hoxa-10 and Hoxa-11 and a deeper understanding of the phenotypes resulting in the single mutants and help elucidate the regulatory interactions between these two genes.

A common polymorphism in the human relaxin-like factor (RLF) gene: no relationship with cryptorchidism

The incidence of impaired testicular descent (cryptorchidism) is high; 1-2% of boys at the age of 3 mo are diagnosed for this condition in western countries. Recent data on mice with targeted disruption of the Insl3/relaxin-like factor (RLF) gene proposed that this factor plays a role in testicular descent in fetal life. Male RLF-/- mice exhibit bilateral cryptorchidism due to developmental abnormalities of the gubernaculum, associated with abnormal spermatogenesis and infertility. In the present study, we have sequenced the promoter region and both exons of the RLF gene in a cohort of 30 boys, seven of whom presented with a possible familial form of cryptorchidism and 23 with sporadic cryptorchidism. One of the nucleotide substitutions detected, G to A at position 178, predicted amino acid change. The mutation was localized to the C-peptide region, resulting in an alanine to threonine change and therefore classified as a conservative mutation. Four of the 30 cases analyzed were homozygous (13%), and 15 were heterozygous for the mutation (50%). However, the same mutation was also found in a control group of 89 men; 10% of them were homozygous, and 39% were heterozygous. Our results indicate that mutations in the RLF gene are not a common reason for cryptorchidism and that the common G178A polymorphism has no apparent relationship with this condition.

Targeted disruption of Hoxd9 and Hoxd10 alters locomotor behavior, vertebral identity, and peripheral nervous system development

The five most 5' HoxD genes, which are related to the Drosophila Abd-B gene, play an important role in patterning axial and appendicular skeletal elements and the nervous system of developing vertebrate embryos. Three of these genes, Hoxd11, Hoxd12, and Hoxd13, act synergistically to pattern the hindlimb autopod. In this study, we examine the combined effects of two additional 5' HoxD genes, Hoxd9 and Hoxd10. Both of these genes are expressed posteriorly in overlapping domains in the developing neural tube and axial mesoderm as well as in developing limbs. Locomotor behavior in animals carrying a double mutation in these two genes was altered; these alterations included changes in gait, mobility, and adduction. Morphological analysis showed alterations in axial and appendicular skeletal structure, hindlimb peripheral nerve organization and projection, and distal hindlimb musculature. These morphological alterations are likely to provide the substrate for the observed alterations in locomotor behavior. The alterations observed in double-mutant mice are distinct from the phenotypes observed in mice carrying single mutations in either gene, but exhibit most of the features of both individual phenotypes. This suggests that the combined activity of two adjacent Hox genes provides more patterning information than activity of each gene alone. These observations support the idea that adjacent Hox genes with overlapping expression patterns may interact functionally to provide patterning information to the same regions of developing mouse embryos.

Targeted inactivation of Hoxb8 affects survival of a spinal ganglion and causes aberrant limb reflexes

Hoxb8 mutant mice were generated by inserting the lacZ coding sequence in frame with the first exon of Hoxb8. These mice express a fusion protein with a functional beta-galactosidase activity instead of Hoxb8. Mutant embryos were analyzed for anatomical changes. The results indicate that Hoxb8 is not an indispensable regulator of A-P patterning in the forelimb, unlike suggested by our Hoxb8 gain of function experiments (Charité J, DeGraaff W, Shen S, Deschamps J. Cell 1994;78:589-601). The null mutant phenotypic traits include degeneration of the second spinal ganglion (C2), an abnormality opposite to the alteration in the gain of function transgenic mice. Subtle changes in the thoracic part of the vertebral column were observed as well. Adult homozygous mutants exhibit an abnormal clasping reflex of the limbs.

Differential expression of Hoxa-2 protein along the dorsal-ventral axis of the developing and adult mouse spinal cord

We have used synthetic oligopeptides derived from the coding sequence of the murine Hoxa-2 protein to produce polyclonal antibodies that specifically recognize the Hoxa-2 recombinant protein. Immunohistochemical studies reveal a distinct pattern of spatial and temporal expression of Hoxa-2 protein within the mouse spinal cord which is concomitant with the cytoarchitectural changes occurring in the developing cord. Hoxa-2 protein is predominantly detected in the nuclei of cells in the ventral mantle region of 10-day-old mouse embryos. Islet-1, a marker for motor neurons was also shown to be co-localized with Hoxa-2 in nuclei of cells in this region. As development progresses from 10-days to 14-days of gestation, Hoxa-2 protein expression gradually extends to the dorsal regions of the mantle layer. The Hoxa-2 protein expression pattern changes at 16-days of embryonic development with strong expression visible throughout the dorsal mantle layer. In 18-day-old and adult mouse spinal cords, Hoxa-2 protein was expressed predominantly by cells of the dorsal horn and only by a few cells of the ventral horn. Double labeling studies with an antibody against glial fibrillary acidic protein (GFAP, an astrocyte-specific intermediate filament protein) showed that within the adult spinal cord, astrocytes rarely expressed the Hoxa-2 protein. However, Hoxa-2 and GFAP double-labeled astrocytes were found in the neopallial cultures, although not all astrocytes expressed Hoxa-2. Hoxa-2 expressing oligodendrocyte progenitor cells were also identified after double-labeling with O4 and Hoxa-2 antibodies; although cells in this lineage that have begun to develop a more extensive array of cytoplasmic processes were less likely to be Hoxa-2 positive. The early pattern of Hoxa-2 protein expression across transverse sections of the neural tube is temporally and spatially modified as each major class of neuron is generated. This congruence in the expression of the Hoxa-2 protein and the generation of neurons in the cord suggests that the Hoxa-2 protein may contribute to dorsal-ventral patterning and/or to the specification of neuronal phenotype. Dev Dyn 1999;216:201-217.

Gene expression in the epididymis

The epididymis is a tubular organ exhibiting vectorial functions of sperm concentration, maturation, transport, and storage. The molecular basis for these functions is poorly understood. However, it has become increasingly clear that regional differences along the length of the duct play a role in epididymal physiology and that region-specific gene expression is involved in the formation of these differences. Although not an overtly segmented organ, the epididymis consists of a series of highly coiled "zones," separated by connective tissue septulae and distinct by cell morphology and their pattern of gene expression. Thus, it constitutes an interesting mammalian model to study how pattern formation is achieved by differential gene activity. A large number of epididymis-expressed genes have been cloned and analyzed at the molecular level, most of them have been characterized by a distinct temporal and spatial expression pattern within the organ. Only recently have theories been developed about how and when during ontogenesis this pattern formation takes place and what its significance might be. This review summarizes the current knowledge on regionalized gene expression in the epididymis and presents hypotheses concerning its ontogenetic origin and regulation in the adult.

Evidence that Hoxa expression domains are evolutionarily transposed in spinal ganglia, and are established by forward spreading in paraxial mesoderm

Transposition of anatomical structures along the anteroposterior axis has been a commonly used mechanism for changing body proportions during the course of evolutionary time. Earlier work (Gaunt, S.J., 1994. Conservation in the Hox code during morphological evolution. Int. J. Dev. Biol. 38, 549-552; Burke, A.C., Nelson, C.E., Morgan, B.A., Tabin, C., 1995. Hox genes and the evolution of vertebrate axial morphology. Development 121, 333-346) showed how transposition in mesodermal derivatives (vertebrae) could be attributed to transposition in the expression of Hox genes along the axial series of somites. We now show how transposition in the segmental arrangement of the spinal nerves can also be correlated with shifts in the expression domains of Hox genes. Specifically, we show how the expression domains of Hoxa-7, a-9 and a-10 in spinal ganglia correspond similarly in both mouse and chick with the positions of the brachial and lumbosacral plexuses, and that this is true even though the brachial plexus of chick is shifted posteriorly, relative to mouse, by seven segmental units. In spite of these marked species differences in the boundaries of Hoxa-7 expression, cis regulatory elements located up to 5 kb upstream of the chick Hoxa-7 gene showed much functional and structural conservation with those described in the mouse (Puschel, A.W., Balling, R., Gruss, P., 1991. Separate elements cause lineage restriction and specify boundaries of Hox-1.1 expression. Development 112, 279-287; Knittel, T., Kessel, M., Kim, M.H., Gruss, P., 1995. A conserved enhancer of the human and murine Hoxa-7 gene specifies the anterior boundary of expression during embryonal development. Development 121, 1077-1088). We also show that chick Hoxa-7 and a-10 expression domains spread forward into regions of somites that are initially negative for the expression of these genes. We discuss this as evidence that Hox expression in paraxial mesoderm spreads forward, as earlier found for neurectoderm and lateral plate mesoderm, in a process that occurs independently of cell movement.

Absence of microdeletions in the Y chromosome in patients with a history of cryptorchidism and azoospermia or oligospermia

OBJECTIVE

To determine if cryptorchidism is associated with microdeletions of interval 6 of the Y chromosome, we evaluated this locus in men with a history of cryptorchidism with and without azoospermia or oligospermia and in a control group.

DESIGN

Clinical study.

SETTING

Academic research environment.

PATIENT(S)

Men in whom surgical treatment of cryptorchidism had been performed in childhood and healthy control male subjects.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Genotyping of interval 6 of the Y chromosome.

RESULT(S)

Analysis of semen obtained from men treated for cryptorchidism in childhood showed azoospermia or oligospermia in 14 of 38 (37%) men. No microdeletions were identified with polymerase chain reaction amplification of 17 distinct sequence tagged sites located on the long arm of the Y chromosome and the sex determining region on Y (SRY) gene.

CONCLUSION(S)

Microdeletions of interval 6 of the Y chromosome were not detected in either the formerly cryptorchid or in the healthy subjects. Although we cannot exclude the possibility of point mutations, we conclude that cryptorchidism or cryptorchidism associated with azoospermia or oligospermia is not due to microdeletions involving interval 6 of the Y chromosome.

Hoxa-10 deficient male mice exhibit abnormal development of the accessory sex organs

The role of mammalian Hox genes in regulating segmental patterning of axial structures and the limb is well established. A similar role in development of soft tissue organ systems has recently been suggested by observations linking several 5' members of the HoxA and HoxD clusters to segmentation events and morphogenesis in the gastrointestinal and genitourinary systems. We have specifically examined the role of Hoxa-10 in development of the male accessory sex organs by characterizing expression of Hoxa-10 in the developing male reproductive tract and correlating expression to morphologic abnormalities in knockout mice deficient for Hoxa-10 function. We report that Hoxa-10 expression in the Wolffian duct and urogenital sinus is regionally restricted and temporally regulated. The domain of expression is defined anteriorly by the caudal epididymis and extends posteriorly to the prostatic anlagen of the urogenital sinus. Expression was maximal at E18 and down-regulated postnatally, well before accessory sex organ morphogenesis is completed. Expression in the prostatic anlagen of the urogenital sinus cultured in vitro does not depend upon the presence of testosterone. Loss of Hoxa-10 function is associated with diminished stromal clefting of the seminal vesicles and decreased size and branching of the coagulating gland. The ductal architecture of the coagulating gland was altered in approximately 30% of mutants examined and suggests a partial posterior morphologic transformation of the coagulating gland. We interpret these data to indicate that Hoxa-10 is expressed in a region specific manner during late gestation and into the perinatal period and that Hoxa-10 is required for normal accessory sex organ development.

Genetic analysis of a conserved sequence in the HoxD complex: regulatory redundancy or limitations of the transgenic approach?

Extensive sequencing in the HoxD complex of several vertebrate species has revealed a set of conserved DNA sequences interspersed between neighboring Hox genes. Their high degree of conservation strongly suggested that they are used for regulatory purposes, a hypothesis that was largely confirmed by using "classical transgenesis" or in vivo mutagenesis through the embryonic stem (ES) cell technology. Here, we show that this is not always the case. We report that the deletion of a conserved regulatory sequence located in the HoxD complex gives different results, depending on the transgenic approach that was used. In "conventional" transgenesis, this sequence was necessary for proper expression in a subdomain of the developing limb. However, a deletion of this sequence in complexo did not confirm this effect, thereby creating an important discrepancy between the classical transgenic and the ES cell-based, targeted mutagenesis. This unexpected observation may show the limitations of the former technology. Alternatively, it could illustrate a redundancy in regulatory circuits and, thus, justify the combination of parallel strategies.

Abdominal B (AbdB) Hoxa genes: regulation in adult uterus by estrogen and progesterone and repression in müllerian duct by the synthetic estrogen diethylstilbestrol (DES)

Mice deficient for the Abdominal B (AbdB) Hox gene Hoxa-10 exhibit reduced fertility due to defects in implantation. During the peri-implantation period Hoxa-10 is sequentially expressed in the uterine epithelium and stroma. These observations, combined with the stringent regulation of uterine implantation by ovarian steroids, prompted us to test whether estrogen and progesterone directly regulate the expression of Hoxa-10 and other AbdB Hoxa genes. Here we show that Hoxa-10 expression in the adult uterus is strongly activated by progesterone. This activation is blocked by the progesterone receptor antagonist RU486 and is independent of new protein synthesis. In addition, Hoxa-10 expression is repressed by estrogen in a protein synthesis-independent manner. Analysis of adjacent AbdB Hoxa genes reveals that Hoxa-9 and a-11 are also activated in a colinear fashion by progesterone but differentially regulated by estrogen. These results suggest that the regulation of AbdB Hox gene expression in the adult uterus by ovarian steroids is a property related to position within the cluster, mediated by the direct action of estrogen and progesterone receptors upon these genes. We next examined whether the embryonic expression of Hoxa10 is regulable by hormonal factors. Previous work has demonstrated that perinatal administration of the synthetic estrogen diethylstilbestrol (DES) to mice and humans produces uterine, cervical, and oviductal malformations. Certain of these phenotypes resemble those in Hoxa-10 knockout mice, suggesting that Hoxa-10 gene expression might be repressed by DES during reproductive tract morphogenesis. Exposure of the developing female reproductive tract to DES, either in vivo or in organ culture, represses the expression of Hoxa-10 in the Müllerian duct. Thus, these data not only establish a direct link between ovarian steroids and AbdB Hoxa gene expression in the adult uterus, but also provide a potential mechanism for the teratogenic effects of DES on the developing reproductive tract.

Limb development: molecular dysmorphology is at hand!

We present a review of limb development integrating current molecular information and selected genetic disorders to illustrate the advances made in this field over the last few years. With this knowledge, clinical geneticists can now begin to consider molecular mechanisms and pathways when investigating patients with limb malformation syndromes.

Hox group 3 paralogs regulate the development and migration of the thymus, thyroid, and parathyroid glands

The thymus, thyroid, and parathyroid glands in vertebrates develop from the pharyngeal region, with contributions both from pharyngeal endoderm and from neural crest cells in the pharyngeal arches. Hoxa3 mutant homozygotes have defects in the development of all three organs. Roles for the Hoxa3 paralogs, Hoxb3 and Hoxd3, were investigated by examining various mutant combinations. The thyroid defects seen in Hoxa3 single mutants are exacerbated in double mutants with either of its paralogs, although none of the double-mutant combinations resulted in thyroid agenesis. The results indicate that the primary role of these genes in thyroid development is their effect on the development and migration of the ultimobranchial bodies, which contribute the parafollicular or C-cells to the thyroid. Hoxb3, Hoxd3 double mutants show no obvious defects in the thymus or parathyroids. However, the removal of one functional copy of Hoxa3 from the Hoxb3, Hoxd3 double mutants (Hoxa3 +/-, Hoxb3-/-, Hoxd3-/-) results in the failure of the thymus and parathyroid glands to migrate to their normal positions in the throat. Very little is known about the molecular mechanisms used to mediate the movement of tissues during development. These results indicate that Hoxa3, Hoxb3, and Hoxd3 have highly overlapping functions in mediating the migration of pharyngeal organ primordia. In addition, Hoxa3 has a unique function with respect to its paralogs in thymus, parathyroid, and thyroid development. This unique function may be conferred by the expression of Hoxa3, but not Hoxb3 nor Hoxd3, in the pharyngeal pouch endoderm.

Regulation of sexual dimorphism in mammals

Sexual dimorphism in humans has been the subject of wonder for centuries. In 355 BC, Aristotle postulated that sexual dimorphism arose from differences in the heat of semen at the time of copulation. In his scheme, hot semen generated males, whereas cold semen made females (Jacquart, D., and C. Thomasset. Sexuality and Medicine in the Middle Ages, 1988). In medieval times, there was great controversy about the existence of a female pope, who may have in fact had an intersex phenotype (New, M. I., and E. S. Kitzinger. J. Clin. Endocrinol. Metab. 76: 3-13, 1993.). Recent years have seen a resurgence of interest in mechanisms controlling sexual differentiation in mammals. Sex differentiation relies on establishment of chromosomal sex at fertilization, followed by the differentiation of gonads, and ultimately the establishment of phenotypic sex in its final form at puberty. Each event in sex determination depends on the preceding event, and normally, chromosomal, gonadal, and somatic sex all agree. There are, however, instances where chromosomal, gonadal, or somatic sex do not agree, and sexual differentiation is ambiguous, with male and female characteristics combined in a single individual. In humans, well-characterized patients are 46, XY women who have the syndrome of pure gonadal dysgenesis, and a subset of true hermaphrodites are phenotypic men with a 46, XX karyotype. Analysis of such individuals has permitted identification of some of the molecules involved in sex determination, including SRY (sex-determining region Y gene), which is a Y chromosomal gene fulfilling the genetic and conceptual requirements of a testis-determining factor. The purpose of this review is to summarize the molecular basis for syndromes of sexual ambiguity seen in human patients and to identify areas where further research is needed. Understanding how sex-specific gene activity is orchestrated may provide insight into the molecular basis of other cell fate decisions during development which, in turn, may lead to an understanding of aberrant cell fate decisions made in patients with birth defects and during neoplastic change.

Targeted disruption of Hoxd-10 affects mouse hindlimb development

Targeted disruption of the Hoxd-10 gene, a 5′ member of the mouse HoxD linkage group, produces mice with hindlimb-specific defects in gait and adduction. To determine the underlying causes of this locomotor defect, mutant mice were examined for skeletal, muscular and neural abnormalities. Mutant mice exhibit alterations in the vertebral column and in the bones of the hindlimb. Sacral vertebrae beginning at the level of S2 exhibit homeotic transformations to adopt the morphology of the next most anterior vertebra. In the hindlimb, there is an anterior shift in the position of the patella, an occasional production of an anterior sesamoid bone, and an outward rotation of the lower part of the leg, all of which contribute to the defects in locomotion. No major alterations in hindlimb musculature were observed, but defects in the nervous system were evident. There was a decrease in the number of spinal segments projecting nerve fibers through the sacral plexus to innervate the musculature of the hindlimb. Deletion of a hindlimb nerve was seen in some animals, and a shift was evident in the position of the lumbar lateral motor column. These observations suggest a role for the Hoxd-10 gene in establishing regional identity within the spinal cord and imply that patterning of the spinal cord may have intrinsic components and is not completely imposed by the surrounding mesoderm.

Homeobox genes in embryogenesis and pathogenesis

The homeobox, a 60-amino acid-encoding DNA sequence, originally discovered in the genome of the fruit fly Drosophila, was subsequently identified throughout the three kingdoms of multicellular organisms. Homeobox-containing genes encode DNA-binding proteins that regulate gene expression and control various aspects of morphogenesis and cell differentiation. In particular, the Hox family of clustered homeobox genes plays a fundamental role in the morphogenesis of the vertebrate embryo, providing cells with regional information along the main body axis. The nonclustered or divergent homeobox genes include a large number of genes scattered throughout the genome that, nevertheless, can be organized in distinct families based on their homologies and functional similarities. This review will provide the reader with a brief overview on some recent studies aimed at understanding the functional role of homeobox genes in normal mammalian development as well as their involvement in congenital malformations and oncogenesis.

Male accessory sex organ morphogenesis is altered by loss of function of Hoxd-13

The role of the Hox gene Hoxd-13 in postnatal morphogenesis of the male accessory sex organs was examined by correlating the distribution and temporal regulation of expression in the accessory sex organs of postnatal mice with morphologic abnormalities of Hoxd-13-deficient transgenic mice. Previous studies of Hoxd-13 expression in the perinatal period have shown a broad domain of expression in the lower genitourinary tract, with expression in both mesenchyme and epithelium; focal expression was also noted in the epithelium of the nascent ducts of the developing prostate. Quantitative RT-PCR studies of Hoxd-13 expression in the 5 day mouse confirm widespread expression in the accessory sex organs developing from both the Wolffian duct and the urogenital sinus. Expression is down-regulated with age, and a detailed time course of expression in the developing prostate shows that the level of Hoxd-13 expression correlates with morphogenetic activity in the development of the prostate ductal system. Transgenic Hoxd-13-deficient mice display multiple abnormalities in the male accessory sex organs. The most severe abnormalities were observed in organs exhibiting ductal branching during postnatal development and included diminished mesenchymal folding in the seminal vesicles, decreased size and diminished ductal branching in the ventral and dorsal prostate, and agenesis of the bulbourethral gland. We conclude that Hoxd-13 expression in the postnatal period correlates with a period of intense morphogenetic activity in accessory sex organ development and that the function of Hoxd-13 is evidenced by morphologic abnormalities in accessory sex organs of the Hoxd-13-deficient mutant.