Hox genes, arms and the man

The Role of Hox Genes in Female Reproductive Tract Development, Adult Function, and Fertility

HOX genes convey positional identity that leads to the proper partitioning and adult identity of the female reproductive track. Abnormalities in reproductive tract development can be caused by HOX gene mutations or altered HOX gene expression. Diethylstilbestrol (DES) and other endocrine disruptors cause Müllerian defects by changing HOX gene expression. HOX genes are also essential regulators of adult endometrial development. Regulated HOXA10 and HOXA11 expression is necessary for endometrial receptivity; decreased HOXA10 or HOXA11 expression leads to decreased implantation rates. Alternation of HOXA10 and HOXA11 expression has been identified as a mechanism of the decreased implantation associated with endometriosis, polycystic ovarian syndrome, leiomyoma, polyps, adenomyosis, and hydrosalpinx. Alteration of HOX gene expression causes both uterine developmental abnormalities and impaired adult endometrial development that prevent implantation and lead to female infertility.

THE EFFECTS OF 5-AZA-2'-DEOXYCYTIDINE (D-AZA) ON SONIC HEDGEHOG EXPRESSION IN MOUSE EMBRYONIC LIMB BUDS

5-Aza-2'-deoxycytidine (d-AZA) causes temporally-related defects in the mouse. At 1.0 mg/kg on gestational day (GD) 10, d-AZA causes hindlimb phocomelia. Sonic hedgehog (Shh) plays a significant role in the normal development of limbs in rodent species. Sonic hedgehog peptides, found in the posterior mesenchyme of limb buds, are involved in patterning functions and in the regulation of both anterior-posterior polarity and proximal-distal outgrowth of the limb. The objective of the present study was to analyze alterations in Shh expression subsequent to d-AZA exposure. Pregnant mice were treated with d-AZA via intraperitonlal injection on GD 10. Controls were untreated. The reverse transcription-polymerase chain reaction (RT-PCR), whole mount in situ hybridization (ISH), and whole mount immunohistochemistry (WMI) were used to analyze expression patterns of Shh . For RT-PCR, embryonic hindlimb buds (buds) were taken 0, 4, 8, 12, or 24 hr after exposure. Cyclophilin was used as the baseline monitor. RNA was transcribed to cDNA and used as template with Shh specific primers for amplification. Whole embryos were collected 12 and 24 hr posttreatment for ISH. An antisense primer specific for Shh was used in an oligo-based ISH protocol. Whole embryos were collected 36 and 48 hr posttreatment for WMI. The antibody corresponding to the amino terminal subunit of the Shh peptide was used. There was a treatment related up-regulation of Shh transcripts by 12 and 24 hr posttreatment. The protein response of up-regulation was detectable by 36 and 48 hr posttreatment. Our data suggest that 5-aza-2'-deoxycytidine-induced hindlimb defects may be associated with alterations in the level of Shh expression. This may be part of a cascade of signaling events involved in d-AZA-induced hindlimb defects. Work is ongoing to determine the relationship of other gene species that may cooperate with Shh in the induction of the hindlimb defects.

Identification of depot-specific human fat cell progenitors through distinct expression profiles and developmental gene patterns

Anatomically separate fat depots differ in size, function, and contribution to pathological states, such as the metabolic syndrome. We isolated preadipocytes from different human fat depots to determine whether the basis for this variation is partly attributable to differences in inherent properties of fat cell progenitors. We found that genome-wide expression profiles of primary preadipocytes cultured in parallel from abdominal subcutaneous, mesenteric, and omental fat depots were distinct. Interestingly, visceral fat was not homogeneous. Preadipocytes from one of the two main visceral depots, mesenteric fat, had an expression profile closer to that of subcutaneous than omental preadipocytes, the other main visceral depot. Expression of genes that regulate early development, including homeotic genes, differed extensively among undifferentiated preadipocytes isolated from different fat depots. These profiles were confirmed by real-time PCR analysis of preadipocytes from additional lean and obese male and female subjects. We made preadipocyte strains from single abdominal subcutaneous and omental preadipocytes by expressing telomerase. Depot-specific developmental gene expression profiles persisted for 40 population doublings in these strains. Thus, human fat cell progenitors from different regions are effectively distinct, consistent with different fat depots being separate mini-organs.

Teratogenic effects of nitroimidazopyridazine on the CNS in fetal Wistar (WU) rats

Teratogenic effects caused by a new nitroimidazopyridazine were examined in Wistar (WU) rats after repeated oral administration of 0, 2.5, 10, and 40 mg/kg, given on days 6-17 post coitum (p.c.) (Day of mating = Day 0) in a regular study on embryo-fetal development according to ICH S5A. At day 20 p.c., fetuses were removed and carefully examined under a dissecting microscope for external, visceral and skeletal malformations. The exposure to the high dose of the test compound during the organogenesis and early histogenesis periods of prenatal development induced prominent CNS malformations (exencephaly, neural tube defects (NTD)) associated with external malformations (hyperflexion of the forelimbs). To support the data from this study additional histological evaluation of the brains was performed with the following results: disorganization of the cerebral cortex associated with ectopic subcommissural organs. Additionally, an in vitro test (whole embryo culture, WEC) showed alterations of the developing neural tube after the incubation of rat embryos with the test compound on gestation days 9.5-11.5. Our data demonstrated that nitroimidazopyridazine caused NTDs and limb malformations during organogenesis. Based on these data the further development of the test compound was stopped.

Molecular Regulation of Müllerian Development by Hox Genes

HOX genes are a family of regulatory molecules that encode conserved transcription factors controlling aspects of morphogenesis and cell differentiation during normal embryonic development. All metazoans possess a common genetic system for embryonic patterning, and this system is also used in the reproductive tract. Hox genes are also expressed in the adult uterus. Hox genes are essential both for the development of mullerian tract in the embryonic period and adult function. Sex steroids regulate Hox gene expression during embryonic and endometrial development in the menstrual cycle. EMX2 and beta(3)-integrin acting downstream of Hoxa10 gene are likely involved in both these developmental processes. This article reviews the role and molecular regulation of Hox genes in reproductive tract development.

In vivo expression of the whole HOX gene network in human breast cancer

The HOX network contains 39 genes that act as transcriptional regulators and control crucial cellular functions during both embryonic development and adult life. Inside the network, this is achieved according to the rules of temporal and spatial co-linearity with 3' HOX genes acting on the anterior part of the body, central HOX genes on the thoracic part and lumbo-sacral HOX genes on the caudal region. We analysed HOX gene expression in normal breast tissue and in primary breast cancers by reverse-transcriptase-polymerase chain reaction (RT-PCR). 17 out of 39 HOX genes were expressed in the normal breast tissue. The expression of thoracic HOX genes tended to be similar in normal and neoplastic breast tissues suggesting that these genes are involved in breast organogenesis. In contrast, cervical and lumbo-sacral HOX gene expression was altered in the primary breast cancers with respect to normal breast tissue. This supports their involvement in breast cancer evolution and suggests they could be targets for future cancer therapies.

Altered hox gene expression and cellular pathogenesis of 5-aza-2'-deoxycytidine-induced murine hindlimb dysmorphogenesis

The DNA demethylating agent, 5-aza-2'-deoxycytidine (d-AZA), elicits temporally related morphological defects and altered gene expression in mouse hindlimbs. Segmental formation of limb regions (stylopod, zeugopod. and autopod) is partially dependent on Hox gene activation. The objective of this study was to understand the role of altered expression of key hox genes in the early pathogenesis of d-AZA-induced hindlimb defects in mice. Semiquantitative RT-PCR was used to analyze hox gene expression (Hox C-11 and Hox A and D homologs, paralogs 9-13). Untreated and treated fore and hindlimb buds were collected 12 and 24 hours after IP injection (1 mg/kg) of d-AZA at 9 am on gestational (GD) 10 and processed for RT-PCR. Additional pregnant mice were treated similarly and whole embryos collected 12 and 24 hours posttreatment and processed for histopathological analysis. No changes in hox gene expression were detected in the forelimb tissue. There was a 2-fold down-regulation of hoxA-11 and C-11 in the 12-hour hindlimb bud tissue. No changes in the HoxD series were detected in the hindlimb bud tissue. The 12- and 24-hour untreated mice exhibited some of the morphological features consistent with physiological apoptosis. Most tissues of the treated mice exhibited cellular changes consistent with cell death associated with the cytotoxicity of the compound. The data reported supports the hypothesis that altered gene expression and not cytotoxicity alone is associated with d-AZA-induced hindlimb dysmorphogenesis.

Congenital bone marrow failure syndromes associated with protean developmental defects and leukemia

Congenital bone marrow failure syndromes are associated with a number of congenital abnormalities affecting a wide range of organ systems. The underlying molecular abnormalities that cause these disorders affect normal embryonic development during the critical organogenesis phase (weeks 4 to 8). These syndromes predispose patients to leukemia and other malignancies, and these genetic disorders may represent the first hit of at least two hits necessary for malignant transformation. The molecular defects underlying these diseases are just beginning to be understood; mechanisms suggested by recent research include DNA repair (FA-A, FA-G); abnormalities of the ribosomes (DBA, DC); to disorders of electron transport (FA-C, Pearson's syndrome, Barth's syndrome). Understanding these molecular mechanisms provides the knowledge necessary to develop better therapy, possibly including gene therapy, offering for the first time the potential for curing the hematologic manifestations of these illnesses.

Compromised HOXA5 function can limit p53 expression in human breast tumours

Expression of the p53 gene protects cells against malignant transformation. Whereas control of p53 degradation has been a subject of intense scrutiny, little is known about the factors that regulate p53 synthesis. Here we show that p53 messenger RNA levels are low in a large proportion of breast tumours. Seeking potential regulators of p53 transcription, we found consensus HOX binding sites in the p53 promoterS. Transient transfection of Hox/HOXA5 activated the p53 promoter. Expression of HOXA5 in epithelial cancer cells expressing wild-type p53, but not in isogenic variants lacking the p53 gene, led to apoptotic cell death. Moreover, breast cancer cell lines and patient tumours display a coordinate loss of p53 and HOXA5 mRNA and protein expression. The HOXA5 promoter region was methylated in 16 out of 20 p53-negative breast tumour specimens. We conclude that loss of expression of p53 in human breast cancer may be primarily due to lack of expression of HOXA5.

Osteogenic induction in hereditary disorders of heterotopic ossification

The formation of heterotopic bone within soft connective tissue is a common feature of at least three distinct genetic disorders of osteogenesis in humans: fibrodysplasia ossificans progressiva; progressive osseous heteroplasia; and Albright hereditary osteodystrophy. The pathobiologic characteristics of osteogenic induction, the histopathologic features of osteogenesis, the anatomic distribution of heterotopic lesions, and the developmental patterns of disease progression differ among all three conditions. The molecular and cellular basis of redirecting a mature connective tissue phenotype to form bone is a remarkable biological phenomenon with enormous implications for the control of bone regeneration, fracture healing, and disorders of osteogenesis.

Vertebrate limb development and malformations

To understand limb abnormalities it is necessary to understand how the limb develops. The limb is the organ whose development is probably best understood. The limbs develop from small protrusions (the limb buds) that arise from the body wall of the embryo. Positioning and patterning the limb involves cellular interactions both between the ectoderm surrounding the limb bud and between the mesenchymal cells that form the core of the limb bud. As the limb grows out the cells acquire a positional value that relates to their position in the bud with respect to all three axes, proximo-distal, antero-posterior, and dorso-ventral. These positional values largely determine how the cells will develop such as what sort of cartilaginous elements they will form. The positional value of the cells is acquired in the progress zone at the tip of the growing bud. The time spent in the progress zone may determine the positional values along the proximo-distal axis, that is the formation of, for example the humerus, then the radius and ulna. Loss of the progress zone due to damage to the overlying apical ridge leads to truncations, and this progress zone model can also account for the effects of thalidomide. Position along the antero-posterior axis such as the character of the digits is by a signal from the polarizing region at the posterior margin of the limb and involves the signaling protein Sonic hedgehog. A signal from the dorsal ectoderm specifies the dorso-ventral axis. Hox genes that are transcription factors are expressed both along the body axis and in a complex pattern in the limb and may record positional value. Human mutations in these genes lead to limb abnormalities. Muscle cells have a separate origin from the cartilaginous cells and those that form connective tissue and tendons, and they migrate into the bud from the somites and are patterned by the connective tissue. Cell death separates the digits.

Fine mapping of the split-hand/split-foot locus (SHFM3) at 10q24: evidence for anticipation and segregation distortion

Split-hand/split-foot malformation (SHFM, ectrodactyly, or lobster-claw deformity) is a human limb malformation characterized by aberrant development of central digital rays with absence of fingers and toes, a deep median cleft, and fusion of remaining digits. SHFM is clinically heterogeneous, presenting both in an isolated form and in combination with additional abnormalities affecting the tibia and/or other organ systems, including the genitourinary, craniofacial, and ectodermal structures. Three SHFM disease loci have been genetically mapped to chromosomes 7q21 (SHFM1), Xq26 (SHFM2), and 10q24 (SHFM3). We mapped data from a large Turkish family with isolated SHFM to chromosome 10q24 and have narrowed the SHFM3 region from 9 cM to an approximately 2-cM critical interval between genetic markers D10S1147 and D10S1240. In several instances we found evidence for a more severe phenotype in offspring of a mildly affected parent, suggesting anticipation. Finally, data from this family, combined with those from six other pedigrees, mapped to 10q24, demonstrate biased transmission of SHFM3 alleles from affected fathers to offspring. The degree of this segregation distortion is obvious in male offspring and is possibly of the same magnitude for female offspring.

Complex camptopolydactyly: an unusual hand malformation

Different types of polydactylies and other hand malformations are commonly seen. Here, we describe a very unusual type of hand malformation characterised by campto-polydactyly with totally disorganised configuration of digits. The role of possible genes involved in development of hands and digits is discussed.

Role of the Bicoid-related homeodomain factor Pitx1 in specifying hindlimb morphogenesis and pituitary development

Pitx1 is a Bicoid-related homeodomain factor that exhibits preferential expression in the hindlimb, as well as expression in the developing anterior pituitary gland and first branchial arch. Here, we report that Pitx1 gene-deleted mice exhibit striking abnormalities in morphogenesis and growth of the hindlimb, resulting in a limb that exhibits structural changes in tibia and fibula as well as patterning alterations in patella and proximal tarsus, to more closely resemble the corresponding forelimb structures. Deletion of the Pitx1 locus results in decreased distal expression of the hindlimb-specific marker, the T-box factor, Tbx4. On the basis of similar expression patterns in chick, targeted misexpression of chick Pitx1 in the developing wing bud causes the resulting limb to assume altered digit number and morphogenesis, with Tbx4 induction. We hypothesize that Pitx1 serves to critically modulate morphogenesis, growth, and potential patterning of a specific hindlimb region, serving as a component of the morphological and growth distinctions in forelimb and hindlimb identity. Pitx1 gene-deleted mice also exhibit reciprocal abnormalities of two ventral and one dorsal anterior pituitary cell types, presumably on the basis of its synergistic functions with other transcription factors, and defects in the derivatives of the first branchial arch, including cleft palate, suggesting a proliferative defect in these organs analogous to that observed in the hindlimb.