Manipulating the genome to study reproduction. Mice with 'humanized' zonae pellucidae

Murine and human zona pellucida 3 derived from mouse eggs express identical O-glycans

Murine sperm initiate fertilization by binding to the outer covering of the egg known as the murine zona pellucida (mZP). This binding is thought to require the interaction of O-glycans linked to a specific mZP glycoprotein (mZP3) with egg-binding proteins coating the sperm plasma membrane. The precise molecular basis of this interaction remains to be resolved. In this study, we analyzed the O-glycosylation of the individual mZP glycoproteins by using ultrasensitive MS methods. We found that the majority of the O-glycans that are linked to mZP3 are core type 2 sequences terminated with sialic acid, lacNAc (Galbeta1-4GlcNAc), lacdiNAc (Gal-NAcbeta1-4GlcNAc), Galalpha1-3Gal, and NeuAcalpha2-3[GalNAcbeta1-4]Galbeta1-4 (Sda antigen). Many of these terminal sequences have been implicated previously in murine sperm-egg binding. Core type 1 O-glycans are also present and are generally unmodified, although some are terminated with sialic acid, beta-linked N-acetylhexosamine, or NeuAcalpha2-3[GalNAcbeta1-4]Galbeta1-4. Eggs expressing human ZP (huZP) glycoprotein huZP3, derived from transgenic mice, bind murine but not human sperm, implying that huZP3 acquires the same O-glycans as native mZP3. Sequencing of huZP3-associated O-glycans confirms that this implication is correct. The data obtained in this investigation may prove to be very useful for studies to determine the precise molecular basis of initial murine sperm-egg binding.

Use of human CD4 transgenic mice for studying immunogenicity of HIV-1 envelope protein gp120

HIV-1 envelope protein, gp120, is a major immunogenic protein of the AIDS virus. A specific feature of this protein is its interaction with the receptor protein, human CD4, an important component of the immune system. This interaction might affect the immunogenic properties of the gp 120 and modulate the immune response towards HIV. To test this hypothesis we used human CD4-transgenic mice for immunization with gp120. The dynamics of the immune response towards gp120, CD4 and other proteins was followed. The results show that the primary immune response to gp120 (two weeks) developed somewhat faster in CD4-transgenic mice versus non-transgenic mice. Both animals, however, ultimately mounted the same level of response over time. The primary immune response to gp120 when complexed with soluble CD4 before the immunization, developed similarly in both groups. The secondary immune response was earlier and markedly stronger in non-transgenic mice compared with the transgenic mice where a less efficient memory response to gp120 was observed. The ability of gp120 to directly interact with CD4+ helper lymphocytes appears to affect the humoral response towards this antigen. Moreover, these effects illustrate how viral modulation of these cells may in turn lead to potentially different states of immunological equilibrium.