Biology subjects

Jang, J. K.

Publications and source records attributed to Jang, J. K..

5 recordsLinked to original sources

bioRxiv2026

An interaction between HP1 and the Chromosomal Passenger Complex Initiates Acentrosomal Spindle Assembly in Drosophila oocytes

Chromosome segregation fidelity during meiosis is critical for genome integrity, with aneuploidy causing infertility, miscarriages, and congenital anomalies. In the oocytes of many species, spindle assembly occurs in the absence of centrosomes that normally function as microtubule-organizing centers at the poles. Such acentrosomal spindles are believed to pose significant challenges for accurate chromosome segregation compared to centrosomal organized spindles. Previous work in Drosophila has shown that the chromosomal passenger complex (CPC) is required for acentrosomal spindle assembly. We found that heterochromatin protein-1 (HP1) plays a critical role in regulating CPC localization and spindle assembly. Furthermore, HP1 moves to the microtubules, where it has roles in building a functional spindle and interacts with the CPC to regulate chromosome biorientation. These results indicate that spindle assembly is mediated by multiple interactions between the CPC, HP1, and the chromosomes, and provide insights into the mechanisms that restricts spindle assembly to the chromosomes in Drosophila oocytes.

cell biology↗

bioRxiv2025

Exploring the C(2)M Cohesin Complex: Structure, Dynamics, and Ability to Facilitate Assembly of the Synaptonemal Complex

There are two meiotic cohesin pathways that regulate synaptonemal complex (SC) assembly in Drosophila. We previously proposed that C(2)M, which is required for SC assembly, is the only meiosis-specific component of a complex that includes Stromalin (SA), Nipped-B, SMC1 and SMC3. This model also predicts that specific residues within the C-terminus and N-terminus of C(2)M should interact with SMC1 and SMC3 to form a ring structure that may regulate the ability of C(2)M to facilitate SC assembly. Through mutant analysis, our results show several residues known to interact with SMC1 or SMC3 are critical for SC formation, suggesting that C(2)M may require a ring structure to perform meiosis-specific functions such as the formation of SC. We also show that SA colocalizes with and depends on C(2)M. However, the dynamics of C(2)M differ from SA and the SMCs in a way that suggests C(2)M regulates the dynamics and chromosome loading of the other cohesin proteins SMC1 and SA. Consistent with this conclusion, our results suggest that C(2)M can promote chromosome localization of the other cohesin components, and can induce SC assembly when ectopically expressed in germline mitotic cells.

genetics↗

bioRxiv2024

Distinct checkpoint and homolog biorientation pathways regulate meiosis I in Drosophila oocytes

Mitosis and meiosis have two mechanisms for regulating the accuracy of chromosome segregation: error correction and the spindle assembly checkpoint (SAC). We have investigated the function of several checkpoint proteins in meiosis I of Drosophila oocytes. Evidence of a SAC response by several of these proteins is found upon depolymerization of microtubules by colchicine. However, unattached kinetochores or errors in biorientation of homologous chromosomes does not induce a SAC response. Furthermore, the metaphase I arrest does not depend on SAC genes, suggesting the APC is inhibited even if the SAC is silenced. Two SAC proteins, ROD of the ROD-ZW10-Zwilch (RZZ) complex and MPS1, are also required for the biorientation of homologous chromosomes during meiosis I, suggesting an error correction function. Both proteins aid in preventing or correcting erroneous attachments and depend on SPC105R for localization to the kinetochore. We have defined a region of SPC105R, amino acids 123-473, that is required for ROD localization and biorientation of homologous chromosomes at meiosis I. Surprisingly, ROD removal, or "streaming", is independent of the dynein adaptor Spindly and is not linked to the stabilization of end-on attachments. Instead, meiotic RZZ streaming appears to depend on cell cycle stage and may be regulated independently of kinetochore attachment or biorientation status. We also show that dynein adaptor Spindly is also required for biorientation at meiosis I, and surprisingly, the direction of RZZ streaming. Author SummaryThe Spindle Assembly Checkpoint (SAC) is known to delay cell cycle progression until chromosomes are properly attached to microtubules. Meiotic cells often have modified cell cycle phases, and natural arrest points such as metaphase I in Drosophila. We show that in Drosophila oocytes, the SAC is sensitive to loss of microtubules, but not sensitive to a variety of kinetochore attachment errors. Thus, the function of the SAC appears to be limited to monitoring oocyte spindle assembly, and not required for accurate chromosome segregation. However, two of the SAC genes, rod and Mps1, are required for the biorientation of homologous chromosomes during meiosis I, suggesting an error correction function. Rod is part of the RZZ complex and is notable for its property of streaming off the kinetochores. However, our results show that streaming off the kinetochore may not contribute to RZZ regulation of microtubule attachments, and only be associated with SAC function. Instead, the establishment of stable end-on attachments may occur while RZZ is still present at kinetochore. We suggest that RZZ interacts with multiple motors to promote bidirectional movement of kinetochores along microtubules, which allows chromosomes to find and attach to the correct pole.

genetics↗

bioRxiv2023

A Dynamic population of prophase CENP-C is required for meiotic chromosome segregation

The centromere is an epigenetic mark that is a loading site for the kinetochore during meiosis and mitosis. This mark is characterized by the H3 variant CENP-A, known as CID in Drosophila. In Drosophila, CENP-C is critical for maintaining CID at the centromeres and directly recruits outer kinetochore proteins after nuclear envelope break down. It is not known, however, if these two functions require the same CENP-C molecules. Furthermore, in Drosophila and many other metazoan oocytes, centromere maintenance and kinetochore assembly are separated by an extended prophase. Consistent with studies in mammals, CID is relatively stable and does not need to be expressed during prophase to remain at high levels in metaphase I of meiosis. Expression of CID during prophase can even be deleterious, causing ectopic localization to non-centromeric chromatin, abnormal meiosis and sterility. In contrast to CID, maintaining high levels of CENP-C requires expression during prophase. Confirming the importance of this loading, we found CENP-C prophase loading is required for multiple meiotic functions. In early meiotic prophase, CENP-C loading is required for sister centromere cohesion and centromere clustering. In late meiotic prophase, CENP-C loading is required to recruit kinetochore proteins. CENP-C is one of the few proteins identified in which expression during prophase is required for meiotic chromosome segregation. An implication of these results is that the failure to maintain recruitment of CENP-C during the extended prophase in oocytes would result in chromosome segregation errors in oocytes. Author SummaryMeiosis in oocytes of diverse organisms, including humans and Drosophila, is characterized by a long prophase pause and a cell cycle arrest in meiosis I or meiosis II. These pauses could be a challenge for centromeres, whose components are replenished during G1, and then must remain with the chromosomes until the meiotic divisions. We have investigated the stability, prophase dynamics and function of centromere protein CENP-C. We show that CENP-C expression and loading onto centromeres during prophase is required for multiple meiotic functions. In contrast, the expression of other centromere partners CID/CENP-A and CAL1 is not required during meiotic prophase. Furthermore, expression of CID during prophase can be deleterious and result in ectopic kinetochore formation. CENP-C loading in prophase is required for sister centromere cohesion and kinetochore assembly. Our results provide the first description of CENP-C dynamics during meiosis and show that prophase expression is required for oocyte spindle assembly and function. CENP-C is among a small number of proteins that are required for the meiotic divisions but are loaded prior to prometaphase. Failure to maintain these proteins during the long prophase of oocyte meiosis may contribute to the increased aneuploidy associated with advanced maternal age.

genetics↗

bioRxiv2020

Protein Phosphatase 2A-B56 maintains the meiotic spindle, kinetochore attachments and cohesion by antagonizing Aurora B Drosophila Oocytes

Meiosis in female oocytes lack centrosomes, the major microtubule-organizing center, which makes them especially vulnerable to aneuploidy. In the acentrosomal oocytes of Drosophila, meiotic spindle assembly depends on the chromosomal passenger complex (CPC). Aurora B is the catalytic component of the CPC while the remaining subunits regulate its localization. Using an inhibitor of Aurora B activity, Binucleine 2, we found that continuous Aurora B activity is required to maintain the oocyte spindle during meiosis I, and this activity is antagonized by phosphatases acting on spindle associated proteins such as kinesins. Protein Phosphatase 2A (PP2A) exists in two varieties, B55 and B56. While both antagonize Aurora B, B55 has only minor roles in meiosis I spindle function. The B56 subunit is encoded by two partially redundant paralogs in the Drosophila genome, wdb and wrd. Knocking down both paralogs showed that the B56 subunit is critical for maintaining sister chromatid cohesion, establishing end-on microtubule attachments, and the metaphase I arrest in oocytes. We found that WDB recruitment to the centromeres depends on BUBR1, MEI-S332, and kinetochore protein SPC105R. While BUBR1 has been shown previously to stabilize microtubule attachments in Drosophila oocytes, only SPC105R is required for cohesion maintenance during meiosis I. We propose that SPC105R promotes cohesion maintenance by recruiting two proteins that recruit PP2A, MEI-S332, and the Soronin homolog Dalmatian.

genetics↗