Plants monosomic for chromosome 9 of Gossypium hirsutum, in addition to Haplo 9 plants, produce many kinds of aneuploid progenies consisting of monosomics, trisomics, multiple monosomics, and different monosomic-trisomic combinations. Cytological analysis of megasporagenesis was conducted to determine the stage and the mechanism that would account for the production of the different kinds of aneuploid progeny. Two new cytotypes involving chromosome 9 were isolated and identified as monotelodisome 9S (Telo 9S) and monoisodisome 9S (Iso 9S), both of which produce different kinds of aneuploids very similar to Haplo 9. Monotelodisomic 9L plants do not produce various kinds of aneuploid progeny like Haplo 9, Telo 9S and Iso 9S. These observations indicate that control of chromosome segregation is on the long arm of chromosome 9. There was no significant difference between Telo 9S and Iso 9S in the kinds and frequencies of aneuploids, but there was a significant difference between these two and Haplo 9. Haplo 9, Telo 9S and Iso 9S showed no significant difference in the chromosomes subtracted or added to the chromosome complement of their respective aneuploid progenies. Analysis of female gametogenesis in TM1 or control plants showed that premeiotic division occurred when bud size is 6.0 - 6.6mm; meiosis occurred when bud size is 6.3 - 7.2mm; the first mitotic division of the megaspore occurred when bud size is 6.9 - 7.8mm, and the second and third mitotic divisions of the megaspore occurred when bud size is 7.8 - 8.5mm. The premeiotic, meiotic, and post meiotic divisions were normal. Female gametogenesis was cytologically analyzed in Haplo 9 plants and it was observed that there was a higher frequency of gametophytes with fewer post meiotic divisions and that there was nonsynchrony of the post-meiotic divisions in a number of the developing female gametophytes. It is assumed that these irregularities are due to the absence of chromosome 9. It is concluded that the long arm of chromosome 9 has control over chromosome segregation, and that most likely nondisjunction occurs throughout female gametogenesis, but confined primarily to the three mitotic divisions following meiosis. Genetic tests showed that eight mutant genes were not located on chromosome 9. The aneuploids had lower seeds per boll than normal disomic plants.

No description available.

No description available.

Gametogenesis is a highly complex process that requires stringent control of gene expression, in which translational regulation plays an essential role. Deleted in Azoospermia-like (DAZL) belongs to the DAZ family of RNA-binding proteins, which are restricted to germ cells, and regulate mRNA translation. Importantly, loss of function of these proteins results in infertility in both males and females in a wide variety of organisms. A model for the mechanism by which DAZL stimulates translation has been proposed based on work in Xenopus laevis (X. laevis) oocytes. In this model, DAZL functions by recruiting the translation initiation factor poly(A)-binding protein (PABP) to the 3’ untranslated region (UTR) of messenger RNAs. Simultaneous binding of PABP to Dazl and factors at the 5’ end confers a “closed-loop” mRNA conformation, which promotes translation initiation. To examine whether DAZL plays a similar role in mammals, co-expression of Dazl and PABP family members was investigated in fetal and adult mouse gonads. In contrast to X. laevis, mammals encode four cytoplasmic PABPs which share a similar domain organisation: PABP1, tPABP, ePABP and PABP4, of which PABP1 and PABP4 appear to be expressed in a wide range of tissues. Immunohistochemistry revealed that Dazl, Pabp1 and Pabp4 are all expressed in primordial germ cells (PGCs) but these show different expression patterns following germ cell sex differentiation. In adult testes Dazl is expressed in spermatogonia and spermatocytes, coinciding with the peak of Pabp4 expression. In contrast, the peak of Pabp1 expression occurs later than that of Dazl, with these proteins only being co-expressed in late pachytene and secondary spermatocyte phases. In adult ovaries, Pabp1, Pabp4 and Dazl are all expressed in the oocytes of primordial and primary follicles. Since both PABP family members are co-expressed with Dazl, the ability of DAZL to interact with PABP1 and PABP4 was investigated in vitro and in vivo. Surprisingly, these studies showed that DAZL discriminates between different PABP family members, only interacting with PABP1, providing the first report of a PABP-specific protein partner. Several putative DAZL mutations have been identified in patients with impaired fertility. Two of these mutations, I37A and R115G, are located in the RNA recognition motif (RRM), a domain which is found in many RNA-binding proteins and mediates both RNA and protein interactions. Thus, the role of these mutations in the ability of DAZL to stimulate translation was investigated. To this end, a translational target of human DAZL (hDAZL) was sought. The 3’UTR of growth differentiation factor 9 (hGDF9) mRNA was found to confer regulation by hDAZL and thus the ability of mutant DAZLs to stimulate reporter mRNAs containing this 3’UTR was examined. This revealed that both mutations compromised the ability of hDAZL to stimulate hGDF9 translation, suggesting a causative effect. These results were further confirmed in assays in which hDAZL is artificially tethered to mRNAs. The ability of mutant hDAZLs to stimulate translation in this assay was compromised suggesting that loss of function is, at least in part, due to impaired protein-protein interactions rather than altered RNA-binding. This work provides insights into the molecular mechanism by which DAZL stimulates the translation of specific mRNAs during mammalian gametogenesis and provides evidence that this function may play an important physiological role in human reproduction.

<p>Gonadotropin Releasing Hormone (GnRH) is a hypothalmic decapeptide, which regulates mammalian gonadotropin secretions by binding to specific, high affinity receptors in the pituitary. Two forms of GnRH (GnRH I and GnRH II) are expressed in the brain of human and some primates. Even though primates have been used extensively in a variety of investigations in relation to the role of GnRH in reproduction, there is no evidence of any research to investigate the direct effect of GnRH on primate sperm.</p>

<p>Gonadotropin Releasing Hormone (GnRH) is a hypothalmic decapeptide, which regulates mammalian gonadotropin secretions by binding to specific, high affinity receptors in the pituitary. Two forms of GnRH (GnRH I and GnRH II) are expressed in the brain of human and some primates. Even though primates have been used extensively in a variety of investigations in relation to the role of GnRH in reproduction, there is no evidence of any research to investigate the direct effect of GnRH on primate sperm.</p>

Masters of Science / Gonadotropin Releasing Hormone (GnRH) is a hypothalmic decapeptide, which regulates mammalian gonadotropin secretions by binding to specific, high affinity receptors in the pituitary. Two forms of GnRH (GnRH I and GnRH II) are expressed in the brain of human and some primates. Even though primates have been used extensively in a variety of investigations in relation to the role of GnRH in reproduction, there is no evidence of any research to investigate the direct effect of GnRH on primate sperm. / South Africa

During the spring of 1955, while attending classes at the Pacific Marine Station, under the direction of Dr. Alden E. Nobel, Chairman of the Department of Zoology, College of the Pacific, Urechis caupo was introduced as a representative of the fauna of the mud flats of Tomales Bay. The unusual manner in which this animal lives would stimulate the curiosity of any student interested in biology, and especially those associated with marine life. The fact that the animal burrows its own home in a U-shaped tunnel and dwells there with three permanent commensals (Hesperonoë adventor, Skogsberg, a plynoid annelid; and 2 pinnotherid crabs, Scleroplax granulate, Rathburn, and Pinnixa franciscapa, Rathburn) is a unique characteristic. The goby fish, Clevelandia ios (Jordan and GIlbert), may also be considered a commensal, but it uses the burrow as a retreat rather than a permanent residence (Fisher, 1946). Studies on the early embryology of Urechis stimulated the writer to further study of the reproductive cycle. The puzzling descriptions and information pertaining to the immature gametes that are found in the coelomic fluid, coupled with the fact that no permanent gonad has been observed or indeed, that it may be wholly lacking, supplied a challenge that he could not ignore. The primary purpose of this investigation is to attempt to evaluate the reproductive cycle and to attempt to locate some type of germinal epithelium.

To determine the effects of different algal diets on freshwater mussels, tissues of Elliptio complanata were sampled for physiological, somatic, and gametogenic condition from August 1999 to May 2000. Treatments included mussels fed Scenedesmus quadricauda (S), Neochloris oleoabundans (N), a no feed treatment (NF), and a reference group of mussels from the Nottoway River (NR), Virginia. The levels of protein and glucose differed among treatments (p<0.0001), but glycogen and percentage tissue moisture did not (p>0.17). Production of ripe and developing gametes differed significantly among treatments (p=0.001), but stage of gamete development did not (p=0.70). Lipid levels and muscle fiber areas of treatment groups differed significantly (p<0.0001). Results of the feeding trial indicate that S. quadricauda is a suitable feed for E. complanata, but future experiments should identify algal species higher in carbohydrates for a mixed algal diet. To determine sex and stage of gametogenesis, tissue histological sections from gonads of Villosa iris and Utterbackia imbecillis were evaluated. Occurrences of oogenic, spermatogenic, and hermaphroditic tissues were summarized in frequency tables. Visceral sites from which similar tissues were collected from conspecific specimens were evaluated for gametogenic stage. Sex was accurately determined in the central, visceral portion V. iris and female regions of U. imbecillis; and spermatogenic tissue was consistent in the dorsal-anterior areas of U. imbecillis. These areas also provided accurate determination of gamete stage in specimens. Reproductive asynchrony was observed among males and females (p<0.02). Male regions of U. imbecillis showed gamete stage characterized by mature and developing spermatogenic tissue, while 2 groups of mussels were showed oogenic development characterized by mature oocytes and resorption of gametes. Male V. iris showed early gamete development without mature spermatozoa, and 2 groups of female V. iris showed mature and developing gametes and resorption of gametes. Protocols for biopsy tissue collection from selected visceral areas were developed for U. imbecillis and V. iris for sex determination and staging of gametogenesis. The application of this biopsy protocol should be considered population specific, and protocols appropriate for other populations and species should be developed with methods of this study. / Ph. D.

No description available.